Convert Origin of Species to Noise

gistfile1.txt

library(readr)
library(stringr)
oos <- read_csv("Documents/oos.txt", col_names = FALSE)

flatoos <- str_flatten(oos$X1, " ")

splitflatoos <- strsplit(flatoos, " ")

nchar(splitflatoos[[1]][1])

len_oos <- c()

# change len_oos[i]== to desired n \in Z>0 for words of length n

for(i in 1:length(splitflatoos[[1]])){
  #print(i)
  
  len_oos[i] <- nchar(splitflatoos[[1]][i])
  
  if(len_oos[i]==17){
    print(splitflatoos[[1]][i])
  }
  
}

len_oos <- (len_oos[which(len_oos!=0)])

hist(len_oos, col="red", xlab="Number of Characters in a Word", main="", breaks=18)


plot(c(0, 18), c(0, 18), type= "n", xlab = "", ylab = "")
rect(1, 17, 2, 18, col=length_1112, border=NA)

length_12 <- "#000EFF"
length_34 <- "#0086FF"
length_56 <- "#00FFFF"
length_78 <- "#15FF7F" 
length_910 <- "#2BFF00"  
length_1112 <- "#95F900" 
length_1314 <- "#FFF300"  
length_1516 <- "#FF7900"
length_1718 <- "#FF0000"



#produces rows decreasing alpha proportional to length of word

for(i in 0:17){
  for(j in 1:((17^2)/17)){
    rect(i%%19, (18-j), (1+i)%%19, (19-j), col=rgb(1, 0, 0, 1-(0.95*((i%%19)/18))), border=NA)
  }
}

plotmax <- 200 #438 is max

plot(c(0, plotmax), c(0, plotmax), type= "n", xlab = "", ylab = "") 

for(i in 0:(plotmax-1)){
  for(j in 1:plotmax){
    #print(j+(i*plotmax)) #This is an index from the 1th word to the 100th word. 
    #print(len_oos[j+((i-1)*10)]) this works
    if(len_oos[j+(i*plotmax)] == 1 || len_oos[j+(i*plotmax)] == 2 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_12, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 3 || len_oos[j+(i*plotmax)] == 4 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_34, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 5 || len_oos[j+(i*plotmax)] == 6 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_56, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 7 || len_oos[j+(i*plotmax)] == 8 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_78, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 9 || len_oos[j+(i*plotmax)] == 10 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_910, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 11 || len_oos[j+(i*plotmax)] == 12 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1112, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 13 || len_oos[j+(i*plotmax)] == 14 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1314, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 15 || len_oos[j+(i*plotmax)] == 16 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1516, border=NA)
    } else {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1718, border=NA)
    }
  }
}

### Brownian Document ###


#check <- c()

sample_me <- c(-1, 1)

start_length <- 0

plotmax <- 200

plot(c(0, plotmax), c(0, plotmax), type= "n", xlab = "", ylab = "") 

for(i in 0:(plotmax-1)){
  for(j in 1:plotmax){
    
    start_length <- start_length + sample(sample_me)[1]
    
    if(start_length >= 18){
      start_length <- 18
    }
    if(start_length <= 1){
      start_length <- 1
    }
    
    #check[j+(i*plotmax)] <- start_length
    
    if(start_length == 1 || start_length == 2) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_12, border=NA)
    } else if(start_length == 3 || start_length == 4 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_34, border=NA)
    } else if(start_length == 5 || start_length == 6 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_56, border=NA)
    } else if(start_length == 7 || start_length == 8 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_78, border=NA)
    } else if(start_length == 9 || start_length == 10 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_910, border=NA)
    } else if(start_length == 11 || start_length == 12 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1112, border=NA)
    } else if(start_length == 13 || start_length == 14 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1314, border=NA)
    } else if(start_length == 15 || start_length == 16 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1516, border=NA)
    } else {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1718, border=NA)
    }
  }
}




### White Document ###


sample_me_white <- c(1:18)

plotmax <- 200

plot(c(0, plotmax), c(0, plotmax), type= "n", xlab = "", ylab = "") 

for(i in 0:(plotmax-1)){
  for(j in 1:plotmax){
    white_value <- sample(sample_me_white)[1]
    #print(j+(i*plotmax)) #This is an index from the 1th word to the 100th word. 
    #print(len_oos[j+((i-1)*10)]) this works
    if(white_value == 1 || white_value == 2) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_12, border=NA)
    } else if(white_value == 3 || white_value == 4 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_34, border=NA)
    } else if(white_value == 5 || white_value == 6 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_56, border=NA)
    } else if(white_value == 7 || white_value == 8 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_78, border=NA)
    } else if(white_value == 9 || white_value == 10 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_910, border=NA)
    } else if(white_value == 11 || white_value == 12 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1112, border=NA)
    } else if(white_value == 13 || white_value == 14 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1314, border=NA)
    } else if(white_value == 15 || white_value == 16 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1516, border=NA)
    } else {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1718, border=NA)
    }
  }
}

lookat <- hist(len_oos, breaks=18, col="red", main="", xlab="Word Length")
lookat$counts
lookat$breaks


### True Pink* NOPE###

plotsampler <- c()

index_boi <- 17

for(i in 1:18){
  plotsampler <- c(plotsampler, rep(i, 2^index_boi))
  print(2^index_boi)
  index_boi <- index_boi - 1
}


plotmax <- 100

plot(c(0, plotmax), c(0, plotmax), type= "n", xlab = "", ylab = "") 

for(i in 0:(plotmax-1)){
  for(j in 1:plotmax){
    pink_value <- sample(plotsampler)[1]
    #print(j+(i*plotmax)) #This is an index from the 1th word to the 100th word. 
    #print(len_oos[j+((i-1)*10)]) this works
    if(pink_value == 1 || pink_value == 2) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_12, border=NA)
    } else if(pink_value == 3 || pink_value == 4 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_34, border=NA)
    } else if(pink_value == 5 || pink_value == 6 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_56, border=NA)
    } else if(pink_value == 7 || pink_value == 8 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_78, border=NA)
    } else if(pink_value == 9 || pink_value == 10 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_910, border=NA)
    } else if(pink_value == 11 || pink_value == 12 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1112, border=NA)
    } else if(pink_value == 13 || pink_value == 14 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1314, border=NA)
    } else if(pink_value == 15 || pink_value == 16 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1516, border=NA)
    } else {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1718, border=NA)
    }
  }
}

### Drawing a plot, square by square OR line by line ### 


## Brownian has an interesting mode, so a good starting place ##

library(magick)

sample_me <- c(-1, 1)

start_length <- 0

plotmax <- 100

frame <- 0

plot(c(0, plotmax), c(0, plotmax), type= "n", xlab = "", ylab = "", axes=FALSE) 

for(i in 0:(plotmax-1)){
  for(j in 1:plotmax){
    
    start_length <- start_length + sample(sample_me)[1]
    
    if(start_length >= 18){
      start_length <- 18
    }
    if(start_length <= 1){
      start_length <- 1
    }
    
    #check[j+(i*plotmax)] <- start_length
    
    
    if(start_length == 1 || start_length == 2) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_12, border=NA)
    } else if(start_length == 3 || start_length == 4 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_34, border=NA)
    } else if(start_length == 5 || start_length == 6 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_56, border=NA)
    } else if(start_length == 7 || start_length == 8 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_78, border=NA)
    } else if(start_length == 9 || start_length == 10 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_910, border=NA)
    } else if(start_length == 11 || start_length == 12 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1112, border=NA)
    } else if(start_length == 13 || start_length == 14 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1314, border=NA)
    } else if(start_length == 15 || start_length == 16 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1516, border=NA)
    } else {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1718, border=NA)
    }
    
    if(frame%%15==14){
      p <- recordPlot()
      
      if(frame <10){
        name <- paste('00000', frame, '.png', sep = '')
      }
      if(frame <100 && frame >=10){
        name <- paste('0000', frame, '.png', sep = '')
      }
      if(frame <1000 && frame >=100){
        name <- paste('000', frame, '.png', sep = '')
      }
      if(frame <10000 && frame >=1000){
        name <- paste('00', frame, '.png', sep = '')
      }
      if(frame >=10000){
        name <- paste('0', frame, '.png', sep = '')
      } 
      
      png(name, width=400, height=600)
      
      replayPlot(p) 
      
      dev.off()
    } 
    
    frame <- frame + 1
  }
}

# library(magick)
# my_command <- 'convert *.png -delay 0.2 -loop 1 brown.gif'
# system(my_command)
setwd("~/GIF Holder")
files <- list.files(path="~/GIF Holder", pattern=".png",all.files=T, full.names=F, no.. = T)
list_of_images = lapply(files, image_read)



image_list <- c()

for (i in 1:length(list_of_images)){
  image_list[i] <- list_of_images[i]
}

animation <- image_animate(image_scale(image_join(image_list), "400x600"), fps = 100, dispose = "previous")
image_write(animation, "brownian.gif")

### Switch to OOS ###

library(magick)

plotmax <- 100

frame <- 0

plot(c(0, plotmax), c(0, plotmax), type= "n", xlab = "", ylab = "", axes=FALSE) 

for(i in 0:(plotmax-1)){
  for(j in 1:plotmax){
    #print(j+(i*plotmax)) #This is an index from the 1th word to the 100th word. 
    #print(len_oos[j+((i-1)*10)]) this works
    if(len_oos[j+(i*plotmax)] == 1 || len_oos[j+(i*plotmax)] == 2 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_12, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 3 || len_oos[j+(i*plotmax)] == 4 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_34, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 5 || len_oos[j+(i*plotmax)] == 6 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_56, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 7 || len_oos[j+(i*plotmax)] == 8 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_78, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 9 || len_oos[j+(i*plotmax)] == 10 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_910, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 11 || len_oos[j+(i*plotmax)] == 12 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1112, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 13 || len_oos[j+(i*plotmax)] == 14 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1314, border=NA)
    } else if(len_oos[j+(i*plotmax)] == 15 || len_oos[j+(i*plotmax)] == 16 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1516, border=NA)
    } else {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1718, border=NA)
    }
    
    if(frame%%15==14){
      p <- recordPlot()
      
      if(frame <10){
        name <- paste('00000', frame, '.png', sep = '')
      }
      if(frame <100 && frame >=10){
        name <- paste('0000', frame, '.png', sep = '')
      }
      if(frame <1000 && frame >=100){
        name <- paste('000', frame, '.png', sep = '')
      }
      if(frame <10000 && frame >=1000){
        name <- paste('00', frame, '.png', sep = '')
      }
      if(frame >=10000){
        name <- paste('0', frame, '.png', sep = '')
      } 
      
      png(name, width=400, height=600)
      
      replayPlot(p) 
      
      dev.off()
    } 
    
    frame <- frame + 1
    
    
    
  }
}





# library(magick)
# my_command <- 'convert *.png -delay 0.2 -loop 1 brown.gif'
# system(my_command)
setwd("~/GIF Holder")
files <- list.files(path="~/GIF Holder", pattern=".png",all.files=T, full.names=F, no.. = T)
list_of_images = lapply(files, image_read)



image_list <- c()

for (i in 1:length(list_of_images)){
  image_list[i] <- list_of_images[i]
}

animation <- image_animate(image_scale(image_join(image_list), "400x600"), fps = 100, dispose = "previous")
image_write(animation, "oos.gif")

### Switch to White ###

library(magick)

sample_me_white <- c(1:18)

plotmax <- 100

frame <- 0

plot(c(0, plotmax), c(0, plotmax), type= "n", xlab = "", ylab = "", axes=FALSE) 

for(i in 0:(plotmax-1)){
  for(j in 1:plotmax){
    white_value <- sample(sample_me_white)[1]
    #print(j+(i*plotmax)) #This is an index from the 1th word to the 100th word. 
    #print(len_oos[j+((i-1)*10)]) this works
    if(white_value == 1 || white_value == 2) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_12, border=NA)
    } else if(white_value == 3 || white_value == 4 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_34, border=NA)
    } else if(white_value == 5 || white_value == 6 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_56, border=NA)
    } else if(white_value == 7 || white_value == 8 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_78, border=NA)
    } else if(white_value == 9 || white_value == 10 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_910, border=NA)
    } else if(white_value == 11 || white_value == 12 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1112, border=NA)
    } else if(white_value == 13 || white_value == 14 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1314, border=NA)
    } else if(white_value == 15 || white_value == 16 ) {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1516, border=NA)
    } else {
      rect(j-1, (plotmax-1)-i, j, (plotmax)-i, col=length_1718, border=NA)
    }
    
    if(frame%%15==14){
      p <- recordPlot()
      
      if(frame <10){
        name <- paste('00000', frame, '.png', sep = '')
      }
      if(frame <100 && frame >=10){
        name <- paste('0000', frame, '.png', sep = '')
      }
      if(frame <1000 && frame >=100){
        name <- paste('000', frame, '.png', sep = '')
      }
      if(frame <10000 && frame >=1000){
        name <- paste('00', frame, '.png', sep = '')
      }
      if(frame >=10000){
        name <- paste('0', frame, '.png', sep = '')
      } 
      
      png(name, width=400, height=600)
      
      replayPlot(p) 
      
      dev.off()
    } 
    
    frame <- frame + 1
    
  }
}




# library(magick)
# my_command <- 'convert *.png -delay 0.2 -loop 1 brown.gif'
# system(my_command)
setwd("~/GIF Holder")
files <- list.files(path="~/GIF Holder", pattern=".png",all.files=T, full.names=F, no.. = T)
list_of_images = lapply(files, image_read)



image_list <- c()

for (i in 1:length(list_of_images)){
  image_list[i] <- list_of_images[i]
}

animation <- image_animate(image_scale(image_join(image_list), "400x600"), fps = 100, dispose = "previous")
image_write(animation, "white.gif")

oos.txt

INTRODUCTION

When on board HMS Beagle as naturalist I was much struck with
certain facts in the distribution of the organic beings inhabiting South
America and in the geological relations of the present to the past
inhabitants of that continent These facts as will be seen in the
latter chapters of this volume seemed to throw some light on the origin
of species that mystery of mysteries as it has been called by one
of our greatest philosophers On my return home it occurred to me
in 1837 that something might perhaps be made out on this question by
patiently accumulating and reflecting on all sorts of facts which could
possibly have any bearing on it After five years work I allowed myself
to speculate on the subject and drew up some short notes these I
enlarged in 1844 into a sketch of the conclusions which then seemed to
me probable from that period to the present day I have steadily pursued
the same object I hope that I may be excused for entering on these
personal details as I give them to show that I have not been hasty in
coming to a decision

My work is now 1859 nearly finished but as it will take me many more
years to complete it and as my health is far from strong I have been
urged to publish this abstract I have more especially been induced to
do this as Mr Wallace who is now studying the natural history of
the Malay Archipelago has arrived at almost exactly the same general
conclusions that I have on the origin of species In 1858 he sent me a
memoir on this subject with a request that I would forward it to Sir
Charles Lyell who sent it to the Linnean Society and it is published
in the third volume of the Journal of that Society Sir C Lyell and Dr
Hooker who both knew of my work the latter having read my sketch
of 1844 honoured me by thinking it advisable to publish with Mr
Wallaces excellent memoir some brief extracts from my manuscripts

This abstract which I now publish must necessarily be imperfect I
cannot here give references and authorities for my several statements
and I must trust to the reader reposing some confidence in my accuracy
No doubt errors may have crept in though I hope I have always been
cautious in trusting to good authorities alone I can here give only
the general conclusions at which I have arrived with a few facts in
illustration but which I hope in most cases will suffice No one can
feel more sensible than I do of the necessity of hereafter publishing in
detail all the facts with references on which my conclusions have been
grounded and I hope in a future work to do this For I am well aware
that scarcely a single point is discussed in this volume on which facts
cannot be adduced often apparently leading to conclusions directly
opposite to those at which I have arrived A fair result can be obtained
only by fully stating and balancing the facts and arguments on both
sides of each question and this is here impossible

I much regret that want of space prevents my having the satisfaction of
acknowledging the generous assistance which I have received from very
many naturalists some of them personally unknown to me I cannot
however let this opportunity pass without expressing my deep
obligations to Dr Hooker who for the last fifteen years has aided me
in every possible way by his large stores of knowledge and his excellent
judgment

In considering the origin of species it is quite conceivable that a
naturalist reflecting on the mutual affinities of organic beings
on their embryological relations their geographical distribution
geological succession and other such facts might come to the
conclusion that species had not been independently created but had
descended like varieties from other species Nevertheless such a
conclusion even if well founded would be unsatisfactory until it
could be shown how the innumerable species inhabiting this world
have been modified so as to acquire that perfection of structure
and coadaptation which justly excites our admiration Naturalists
continually refer to external conditions such as climate food etc
as the only possible cause of variation In one limited sense as
we shall hereafter see this may be true but it is preposterous to
attribute to mere external conditions the structure for instance
of the woodpecker with its feet tail beak and tongue so admirably
adapted to catch insects under the bark of trees In the case of the
mistletoe which draws its nourishment from certain trees which has
seeds that must be transported by certain birds and which has flowers
with separate sexes absolutely requiring the agency of certain insects
to bring pollen from one flower to the other it is equally preposterous
to account for the structure of this parasite with its relations to
several distinct organic beings by the effects of external conditions
or of habit or of the volition of the plant itself

It is therefore of the highest importance to gain a clear insight into
the means of modification and coadaptation At the commencement of
my observations it seemed to me probable that a careful study of
domesticated animals and of cultivated plants would offer the best
chance of making out this obscure problem Nor have I been disappointed
in this and in all other perplexing cases I have invariably found that
our knowledge imperfect though it be of variation under domestication
afforded the best and safest clue I may venture to express my
conviction of the high value of such studies although they have been
very commonly neglected by naturalists

From these considerations I shall devote the first chapter of this
abstract to variation under domestication We shall thus see that a
large amount of hereditary modification is at least possible and what
is equally or more important we shall see how great is the power of man
in accumulating by his selection successive slight variations I will
then pass on to the variability of species in a state of nature but
I shall unfortunately be compelled to treat this subject far too
briefly as it can be treated properly only by giving long catalogues of
facts We shall however be enabled to discuss what circumstances
are most favourable to variation In the next chapter the struggle
for existence among all organic beings throughout the world which
inevitably follows from the high geometrical ratio of their increase
will be considered This is the doctrine of Malthus applied to the
whole animal and vegetable kingdoms As many more individuals of each
species are born than can possibly survive and as consequently there
is a frequently recurring struggle for existence it follows that any
being if it vary however slightly in any manner profitable to itself
under the complex and sometimes varying conditions of life will have
a better chance of surviving and thus be NATURALLY SELECTED From
the strong principle of inheritance any selected variety will tend to
propagate its new and modified form

This fundamental subject of natural selection will be treated at
some length in the fourth chapter and we shall then see how natural
selection almost inevitably causes much extinction of the less improved
forms of life and leads to what I have called divergence of character
In the next chapter I shall discuss the complex and little known laws
of variation In the five succeeding chapters the most apparent and
gravest difficulties in accepting the theory will be given namely
first the difficulties of transitions or how a simple being or a
simple organ can be changed and perfected into a highly developed
being or into an elaborately constructed organ secondly the subject of
instinct or the mental powers of animals thirdly hybridism or the
infertility of species and the fertility of varieties when intercrossed
and fourthly the imperfection of the geological record In the next
chapter I shall consider the geological succession of organic beings
throughout time in the twelfth and thirteenth their geographical
distribution throughout space in the fourteenth their classification
or mutual affinities both when mature and in an embryonic condition In
the last chapter I shall give a brief recapitulation of the whole work
and a few concluding remarks

No one ought to feel surprise at much remaining as yet unexplained in
regard to the origin of species and varieties if he make due allowance
for our profound ignorance in regard to the mutual relations of the
many beings which live around us Who can explain why one species ranges
widely and is very numerous and why another allied species has a narrow
range and is rare Yet these relations are of the highest importance
for they determine the present welfare and as I believe the future
success and modification of every inhabitant of this world Still less
do we know of the mutual relations of the innumerable inhabitants of the
world during the many past geological epochs in its history Although
much remains obscure and will long remain obscure I can entertain no
doubt after the most deliberate study and dispassionate judgment of
which I am capable that the view which most naturalists until recently
entertained and which I formerly entertained namely that each species
has been independently created is erroneous I am fully convinced that
species are not immutable but that those belonging to what are called
the same genera are lineal descendants of some other and generally
extinct species in the same manner as the acknowledged varieties of
any one species are the descendants of that species Furthermore I am
convinced that natural selection has been the most important but not
the exclusive means of modification




CHAPTER I VARIATION UNDER DOMESTICATION

 Causes of Variability Effects of Habit and the use and disuse of
 Parts Correlated Variation Inheritance Character of Domestic
 Varieties Difficulty of distinguishing between Varieties and
 Species Origin of Domestic Varieties from one or more Species Domestic
 Pigeons their Differences and Origin Principles of Selection
 anciently followed their Effects Methodical and Unconscious
 Selection Unknown Origin of our Domestic Productions Circumstances
 favourable to Mans power of Selection


CAUSES OF VARIABILITY

When we compare the individuals of the same variety or subvariety of
our older cultivated plants and animals one of the first points which
strikes us is that they generally differ more from each other than do
the individuals of any one species or variety in a state of nature And
if we reflect on the vast diversity of the plants and animals which have
been cultivated and which have varied during all ages under the most
different climates and treatment we are driven to conclude that this
great variability is due to our domestic productions having been raised
under conditions of life not so uniform as and somewhat different from
those to which the parent species had been exposed under nature There
is also some probability in the view propounded by Andrew Knight that
this variability may be partly connected with excess of food It seems
clear that organic beings must be exposed during several generations to
new conditions to cause any great amount of variation and that when
the organisation has once begun to vary it generally continues varying
for many generations No case is on record of a variable organism
ceasing to vary under cultivation Our oldest cultivated plants such
as wheat still yield new varieties our oldest domesticated animals are
still capable of rapid improvement or modification

As far as I am able to judge after long attending to the subject the
conditions of life appear to act in two ways directly on the whole
organisation or on certain parts alone and in directly by affecting the
reproductive system With respect to the direct action we must bear in
mind that in every case as Professor Weismann has lately insisted
and as I have incidently shown in my work on Variation under
Domestication there are two factors namely the nature of the
organism and the nature of the conditions The former seems to be much
the more important for nearly similar variations sometimes arise under
as far as we can judge dissimilar conditions and on the other hand
dissimilar variations arise under conditions which appear to be
nearly uniform The effects on the offspring are either definite or in
definite They may be considered as definite when all or nearly all the
offspring of individuals exposed to certain conditions during several
generations are modified in the same manner It is extremely difficult
to come to any conclusion in regard to the extent of the changes which
have been thus definitely induced There can however be little doubt
about many slight changes such as size from the amount of food
colour from the nature of the food thickness of the skin and hair from
climate etc Each of the endless variations which we see in the plumage
of our fowls must have had some efficient cause and if the same cause
were to act uniformly during a long series of generations on many
individuals all probably would be modified in the same manner Such
facts as the complex and extraordinary out growths which variably
follow from the insertion of a minute drop of poison by a gallproducing
insect shows us what singular modifications might result in the case of
plants from a chemical change in the nature of the sap

In definite variability is a much more common result of changed
conditions than definite variability and has probably played a more
important part in the formation of our domestic races We see in
definite variability in the endless slight peculiarities which
distinguish the individuals of the same species and which cannot be
accounted for by inheritance from either parent or from some more remote
ancestor Even stronglymarked differences occasionally appear in the
young of the same litter and in seedlings from the same seedcapsule
At long intervals of time out of millions of individuals reared in the
same country and fed on nearly the same food deviations of structure so
strongly pronounced as to deserve to be called monstrosities arise but
monstrosities cannot be separated by any distinct line from slighter
variations All such changes of structure whether extremely slight or
strongly marked which appear among many individuals living together
may be considered as the in definite effects of the conditions of life
on each individual organism in nearly the same manner as the chill
effects different men in an in definite manner according to their
state of body or constitution causing coughs or colds rheumatism or
inflammation of various organs

With respect to what I have called the in direct action of changed
conditions namely through the reproductive system of being affected
we may infer that variability is thus induced partly from the fact of
this system being extremely sensitive to any change in the conditions
and partly from the similarity as Kolreuter and others have remarked
between the variability which follows from the crossing of distinct
species and that which may be observed with plants and animals when
reared under new or unnatural conditions Many facts clearly show how
eminently susceptible the reproductive system is to very slight changes
in the surrounding conditions Nothing is more easy than to tame an
animal and few things more difficult than to get it to breed freely
under confinement even when the male and female unite How many animals
there are which will not breed though kept in an almost free state in
their native country  This is generally but erroneously attributed to
vitiated instincts Many cultivated plants display the utmost vigour
and yet rarely or never seed  In some few cases it has been discovered
that a very trifling change such as a little more or less water at some
particular period of growth will determine whether or not a plant will
produce seeds I cannot here give the details which I have collected and
elsewhere published on this curious subject but to show how singular
the laws are which determine the reproduction of animals under
confinement I may mention that carnivorous animals even from the
tropics breed in this country pretty freely under confinement with
the exception of the plantigrades or bear family which seldom produce
young whereas carnivorous birds with the rarest exception hardly
ever lay fertile eggs Many exotic plants have pollen utterly worthless
in the same condition as in the most sterile hybrids When on the one
hand we see domesticated animals and plants though often weak and
sickly breeding freely under confinement and when on the other hand
we see individuals though taken young from a state of nature perfectly
tamed longlived and healthy of which I could give numerous
instances yet having their reproductive system so seriously affected
by unperceived causes as to fail to act we need not be surprised at
this system when it does act under confinement acting irregularly
and producing offspring somewhat unlike their parents I may add that
as some organisms breed freely under the most unnatural conditions for
instance rabbits and ferrets kept in hutches showing that their
reproductive organs are not easily affected so will some animals
and plants withstand domestication or cultivation and vary very
slightly perhaps hardly more than in a state of nature

Some naturalists have maintained that all variations are connected with
the act of sexual reproduction but this is certainly an error for I
have given in another work a long list of sporting plants as they are
called by gardeners that is of plants which have suddenly produced a
single bud with a new and sometimes widely different character from that
of the other buds on the same plant These bud variations as they may
be named can be propagated by grafts offsets etc and sometimes
by seed They occur rarely under nature but are far from rare under
culture As a single bud out of many thousands produced year after year
on the same tree under uniform conditions has been known suddenly to
assume a new character and as buds on distinct trees growing
under different conditions have sometimes yielded nearly the same
variety for instance buds on peachtrees producing nectarines and
buds on common roses producing mossroses we clearly see that the
nature of the conditions is of subordinate importance in comparison
with the nature of the organism in determining each particular form of
variation perhaps of not more importance than the nature of the spark
by which a mass of combustible matter is ignited has in determining the
nature of the flames

EFFECTS OF HABIT AND OF THE USE OR DISUSE OF PARTS CORRELATED
VARIATION INHERITANCE

Changed habits produce an inherited effect as in the period of the
flowering of plants when transported from one climate to another With
animals the increased use or disuse of parts has had a more marked
influence thus I find in the domestic duck that the bones of the wing
weigh less and the bones of the leg more in proportion to the whole
skeleton than do the same bones in the wild duck and this change may
be safely attributed to the domestic duck flying much less and walking
more than its wild parents The great and inherited development of the
udders in cows and goats in countries where they are habitually milked
in comparison with these organs in other countries is probably another
instance of the effects of use Not one of our domestic animals can be
named which has not in some country drooping ears and the view which
has been suggested that the drooping is due to disuse of the muscles of
the ear from the animals being seldom much alarmed seems probable

Many laws regulate variation some few of which can be dimly seen and
will hereafter be briefly discussed I will here only allude to what may
be called correlated variation Important changes in the embryo or larva
will probably entail changes in the mature animal In monstrosities
the correlations between quite distinct parts are very curious and many
instances are given in Isidore Geoffroy St Hilaires great work on this
subject Breeders believe that long limbs are almost always accompanied
by an elongated head Some instances of correlation are quite whimsical
thus cats which are entirely white and have blue eyes are generally
deaf but it has been lately stated by Mr Tait that this is confined to
the males Colour and constitutional peculiarities go together of which
many remarkable cases could be given among animals and plants From
facts collected by Heusinger it appears that white sheep and pigs
are injured by certain plants while darkcoloured individuals escape
Professor Wyman has recently communicated to me a good illustration of
this fact on asking some farmers in Virginia how it was that all their
pigs were black they informed him that the pigs ate the paintroot
Lachnanthes which coloured their bones pink and which caused
the hoofs of all but the black varieties to drop off and one of the
crackers ie Virginia squatters added we select the black members
of a litter for raising as they alone have a good chance of living
Hairless dogs have imperfect teeth longhaired and coarsehaired
animals are apt to have as is asserted long or many horns pigeons
with feathered feet have skin between their outer toes pigeons with
short beaks have small feet and those with long beaks large feet Hence
if man goes on selecting and thus augmenting any peculiarity he will
almost certainly modify unintentionally other parts of the structure
owing to the mysterious laws of correlation

The results of the various unknown or but dimly understood laws of
variation are infinitely complex and diversified It is well worth while
carefully to study the several treatises on some of our old cultivated
plants as on the hyacinth potato even the dahlia etc and it
is really surprising to note the endless points of structure and
constitution in which the varieties and subvarieties differ slightly
from each other The whole organisation seems to have become plastic
and departs in a slight degree from that of the parental type

Any variation which is not inherited is unimportant for us But the
number and diversity of inheritable deviations of structure both
those of slight and those of considerable physiological importance
are endless Dr Prosper Lucas treatise in two large volumes is the
fullest and the best on this subject No breeder doubts how strong is
the tendency to inheritance that like produces like is his fundamental
belief doubts have been thrown on this principle only by theoretical
writers When any deviation of structure often appears and we see it
in the father and child we cannot tell whether it may not be due to the
same cause having acted on both but when among individuals apparently
exposed to the same conditions any very rare deviation due to some
extraordinary combination of circumstances appears in the parent say
once among several million individuals and it reappears in the
child the mere doctrine of chances almost compels us to attribute
its reappearance to inheritance Every one must have heard of cases of
albinism prickly skin hairy bodies etc appearing in several members
of the same family If strange and rare deviations of structure are
truly inherited less strange and commoner deviations may be freely
admitted to be inheritable Perhaps the correct way of viewing the whole
subject would be to look at the inheritance of every character whatever
as the rule and noninheritance as the anomaly

The laws governing inheritance are for the most part unknown no one
can say why the same peculiarity in different individuals of the same
species or in different species is sometimes inherited and sometimes
not so why the child often reverts in certain characteristics to its
grandfather or grandmother or more remote ancestor why a peculiarity is
often transmitted from one sex to both sexes or to one sex alone
more commonly but not exclusively to the like sex It is a fact of
some importance to us that peculiarities appearing in the males of our
domestic breeds are often transmitted either exclusively or in a much
greater degree to the males alone A much more important rule which I
think may be trusted is that at whatever period of life a peculiarity
first appears it tends to reappear in the offspring at a corresponding
age though sometimes earlier In many cases this could not be
otherwise thus the inherited peculiarities in the horns of cattle could
appear only in the offspring when nearly mature peculiarities in the
silkworm are known to appear at the corresponding caterpillar or cocoon
stage But hereditary diseases and some other facts make me believe
that the rule has a wider extension and that when there is no apparent
reason why a peculiarity should appear at any particular age yet that
it does tend to appear in the offspring at the same period at which it
first appeared in the parent I believe this rule to be of the highest
importance in explaining the laws of embryology These remarks are of
course confined to the first APPEARANCE of the peculiarity and not
to the primary cause which may have acted on the ovules or on the male
element in nearly the same manner as the increased length of the horns
in the offspring from a shorthorned cow by a longhorned bull though
appearing late in life is clearly due to the male element

Having alluded to the subject of reversion I may here refer to
a statement often made by naturalists namely that our domestic
varieties when run wild gradually but invariably revert in character
to their aboriginal stocks Hence it has been argued that no deductions
can be drawn from domestic races to species in a state of nature I
have in vain endeavoured to discover on what decisive facts the above
statement has so often and so boldly been made There would be great
difficulty in proving its truth we may safely conclude that very many
of the most strongly marked domestic varieties could not possibly live
in a wild state In many cases we do not know what the aboriginal stock
was and so could not tell whether or not nearly perfect reversion
had ensued It would be necessary in order to prevent the effects of
intercrossing that only a single variety should be turned loose in
its new home Nevertheless as our varieties certainly do occasionally
revert in some of their characters to ancestral forms it seems to me
not improbable that if we could succeed in naturalising or were to
cultivate during many generations the several races for instance
of the cabbage in very poor soil in which case however some
effect would have to be attributed to the DEFINITE action of the poor
soil that they would to a large extent or even wholly revert to the
wild aboriginal stock Whether or not the experiment would succeed is
not of great importance for our line of argument for by the experiment
itself the conditions of life are changed If it could be shown that our
domestic varieties manifested a strong tendency to reversion that is
to lose their acquired characters while kept under the same conditions
and while kept in a considerable body so that free intercrossing might
check by blending together any slight deviations in their structure
in such case I grant that we could deduce nothing from domestic
varieties in regard to species But there is not a shadow of evidence
in favour of this view to assert that we could not breed our cart
and racehorses long and shorthorned cattle and poultry of various
breeds and esculent vegetables for an unlimited number of generations
would be opposed to all experience

CHARACTER OF DOMESTIC VARIETIES DIFFICULTY OF DISTINGUISHING BETWEEN
VARIETIES AND SPECIES ORIGIN OF DOMESTIC VARIETIES FROM ONE OR MORE
SPECIES

When we look to the hereditary varieties or races of our domestic
animals and plants and compare them with closely allied species we
generally perceive in each domestic race as already remarked less
uniformity of character than in true species Domestic races often
have a somewhat monstrous character by which I mean that although
differing from each other and from other species of the same genus in
several trifling respects they often differ in an extreme degree in
some one part both when compared one with another and more especially
when compared with the species under nature to which they are nearest
allied With these exceptions and with that of the perfect fertility of
varieties when crossed a subject hereafter to be discussed domestic
races of the same species differ from each other in the same manner as
do the closely allied species of the same genus in a state of nature
but the differences in most cases are less in degree This must be
admitted as true for the domestic races of many animals and plants have
been ranked by some competent judges as the descendants of aboriginally
distinct species and by other competent judges as mere varieties
If any well marked distinction existed between a domestic race and a
species this source of doubt would not so perpetually recur It has
often been stated that domestic races do not differ from each other in
characters of generic value It can be shown that this statement is not
correct but naturalists differ much in determining what characters are
of generic value all such valuations being at present empirical When
it is explained how genera originate under nature it will be seen that
we have no right to expect often to find a generic amount of difference
in our domesticated races

In attempting to estimate the amount of structural difference between
allied domestic races we are soon involved in doubt from not knowing
whether they are descended from one or several parent species This
point if it could be cleared up would be interesting if for
instance it could be shown that the greyhound bloodhound terrier
spaniel and bulldog which we all know propagate their kind truly were
the offspring of any single species then such facts would have great
weight in making us doubt about the immutability of the many closely
allied natural species for instance of the many foxes inhabiting the
different quarters of the world I do not believe as we shall presently
see that the whole amount of difference between the several breeds of
the dog has been produced under domestication I believe that a small
part of the difference is due to their being descended from distinct
species In the case of strongly marked races of some other domesticated
species there is presumptive or even strong evidence that all are
descended from a single wild stock

It has often been assumed that man has chosen for domestication animals
and plants having an extraordinary inherent tendency to vary and
likewise to withstand diverse climates I do not dispute that these
capacities have added largely to the value of most of our domesticated
productions but how could a savage possibly know when he first tamed
an animal whether it would vary in succeeding generations and whether
it would endure other climates Has the little variability of the ass
and goose or the small power of endurance of warmth by the reindeer
or of cold by the common camel prevented their domestication I
cannot doubt that if other animals and plants equal in number to our
domesticated productions and belonging to equally diverse classes and
countries were taken from a state of nature and could be made to breed
for an equal number of generations under domestication they would on
an average vary as largely as the parent species of our existing
domesticated productions have varied

In the case of most of our anciently domesticated animals and plants
it is not possible to come to any definite conclusion whether they are
descended from one or several wild species The argument mainly relied
on by those who believe in the multiple origin of our domestic animals
is that we find in the most ancient times on the monuments of Egypt
and in the lakehabitations of Switzerland much diversity in the
breeds and that some of these ancient breeds closely resemble or are
even identical with those still existing But this only throws far
backward the history of civilisation and shows that animals were
domesticated at a much earlier period than has hitherto been supposed
The lakeinhabitants of Switzerland cultivated several kinds of wheat
and barley the pea the poppy for oil and flax and they possessed
several domesticated animals They also carried on commerce with other
nations All this clearly shows as Heer has remarked that they had at
this early age progressed considerably in civilisation and this again
implies a long continued previous period of less advanced civilisation
during which the domesticated animals kept by different tribes in
different districts might have varied and given rise to distinct races
Since the discovery of flint tools in the superficial formations of many
parts of the world all geologists believe that barbarian men existed at
an enormously remote period and we know that at the present day there
is hardly a tribe so barbarous as not to have domesticated at least the
dog

The origin of most of our domestic animals will probably forever remain
vague But I may here state that looking to the domestic dogs of the
whole world I have after a laborious collection of all known facts
come to the conclusion that several wild species of Canidae have been
tamed and that their blood in some cases mingled together flows in
the veins of our domestic breeds In regard to sheep and goats I can
form no decided opinion From facts communicated to me by Mr Blyth
on the habits voice constitution and structure of the humped Indian
cattle it is almost certain that they are descended from a different
aboriginal stock from our European cattle and some competent judges
believe that these latter have had two or three wild progenitors
whether or not these deserve to be called species This conclusion as
well as that of the specific distinction between the humped and common
cattle may indeed be looked upon as established by the admirable
researches of Professor Rutimeyer With respect to horses from reasons
which I cannot here give I am doubtfully inclined to believe in
opposition to several authors that all the races belong to the same
species Having kept nearly all the English breeds of the fowl alive
having bred and crossed them and examined their skeletons it appears
to me almost certain that all are the descendants of the wild Indian
fowl Gallus bankiva and this is the conclusion of Mr Blyth and
of others who have studied this bird in India In regard to ducks and
rabbits some breeds of which differ much from each other the evidence
is clear that they are all descended from the common duck and wild
rabbit

The doctrine of the origin of our several domestic races from several
aboriginal stocks has been carried to an absurd extreme by some
authors They believe that every race which breeds true let the
distinctive characters be ever so slight has had its wild prototype
At this rate there must have existed at least a score of species of wild
cattle as many sheep and several goats in Europe alone and several
even within Great Britain One author believes that there formerly
existed eleven wild species of sheep peculiar to Great Britain  When we
bear in mind that Britain has now not one peculiar mammal and France
but few distinct from those of Germany and so with Hungary Spain
etc but that each of these kingdoms possesses several peculiar breeds
of cattle sheep etc we must admit that many domestic breeds must
have originated in Europe for whence otherwise could they have been
derived So it is in India Even in the case of the breeds of the
domestic dog throughout the world which I admit are descended from
several wild species it cannot be doubted that there has been an
immense amount of inherited variation for who will believe that animals
closely resembling the Italian greyhound the bloodhound the bulldog
pugdog or Blenheim spaniel etc so unlike all wild Canidae ever
existed in a state of nature It has often been loosely said that all
our races of dogs have been produced by the crossing of a few
aboriginal species but by crossing we can only get forms in some degree
intermediate between their parents and if we account for our several
domestic races by this process we must admit the former existence of
the most extreme forms as the Italian greyhound bloodhound bulldog
etc in the wild state Moreover the possibility of making distinct
races by crossing has been greatly exaggerated Many cases are on record
showing that a race may be modified by occasional crosses if aided
by the careful selection of the individuals which present the desired
character but to obtain a race intermediate between two quite distinct
races would be very difficult Sir J Sebright expressly experimented
with this object and failed The offspring from the first cross between
two pure breeds is tolerably and sometimes as I have found with
pigeons quite uniform in character and every thing seems simple
enough but when these mongrels are crossed one with another for several
generations hardly two of them are alike and then the difficulty of
the task becomes manifest

BREEDS OF THE DOMESTIC PIGEON THEIR DIFFERENCES AND ORIGIN

Believing that it is always best to study some special group I have
after deliberation taken up domestic pigeons I have kept every breed
which I could purchase or obtain and have been most kindly favoured
with skins from several quarters of the world more especially by the
Hon W Elliot from India and by the Hon C Murray from Persia Many
treatises in different languages have been published on pigeons and
some of them are very important as being of considerable antiquity I
have associated with several eminent fanciers and have been permitted
to join two of the London Pigeon Clubs The diversity of the breeds is
something astonishing Compare the English carrier and the shortfaced
tumbler and see the wonderful difference in their beaks entailing
corresponding differences in their skulls The carrier more especially
the male bird is also remarkable from the wonderful development of the
carunculated skin about the head and this is accompanied by greatly
elongated eyelids very large external orifices to the nostrils and a
wide gape of mouth The shortfaced tumbler has a beak in outline almost
like that of a finch and the common tumbler has the singular inherited
habit of flying at a great height in a compact flock and tumbling in
the air head over heels The runt is a bird of great size with long
massive beak and large feet some of the subbreeds of runts have very
long necks others very long wings and tails others singularly short
tails The barb is allied to the carrier but instead of a long beak
has a very short and broad one The pouter has a much elongated body
wings and legs and its enormously developed crop which it glories in
inflating may well excite astonishment and even laughter The turbit
has a short and conical beak with a line of reversed feathers down the
breast and it has the habit of continually expanding slightly the
upper part of the oesophagus The Jacobin has the feathers so much
reversed along the back of the neck that they form a hood and it
has proportionally to its size elongated wing and tail feathers The
trumpeter and laugher as their names express utter a very different
coo from the other breeds The fantail has thirty or even forty
tailfeathers instead of twelve or fourteen the normal number in all
the members of the great pigeon family these feathers are kept expanded
and are carried so erect that in good birds the head and tail touch the
oilgland is quite aborted Several other less distinct breeds might be
specified

In the skeletons of the several breeds the development of the bones of
the face in length and breadth and curvature differs enormously The
shape as well as the breadth and length of the ramus of the lower jaw
varies in a highly remarkable manner The caudal and sacral vertebrae
vary in number as does the number of the ribs together with their
relative breadth and the presence of processes The size and shape of
the apertures in the sternum are highly variable so is the degree
of divergence and relative size of the two arms of the furcula The
proportional width of the gape of mouth the proportional length of the
eyelids of the orifice of the nostrils of the tongue not always in
strict correlation with the length of beak the size of the crop and
of the upper part of the oesophagus the development and abortion of
the oilgland the number of the primary wing and caudal feathers the
relative length of the wing and tail to each other and to the body
the relative length of the leg and foot the number of scutellae on
the toes the development of skin between the toes are all points of
structure which are variable The period at which the perfect plumage is
acquired varies as does the state of the down with which the nestling
birds are clothed when hatched The shape and size of the eggs vary The
manner of flight and in some breeds the voice and disposition differ
remarkably Lastly in certain breeds the males and females have come
to differ in a slight degree from each other

Altogether at least a score of pigeons might be chosen which if shown
to an ornithologist and he were told that they were wild birds would
certainly be ranked by him as welldefined species Moreover I do not
believe that any ornithologist would in this case place the English
carrier the shortfaced tumbler the runt the barb pouter and
fantail in the same genus more especially as in each of these breeds
several trulyinherited subbreeds or species as he would call them
could be shown him

Great as are the differences between the breeds of the pigeon I am
fully convinced that the common opinion of naturalists is correct
namely that all are descended from the rockpigeon Columba livia
including under this term several geographical races or subspecies
which differ from each other in the most trifling respects As several
of the reasons which have led me to this belief are in some degree
applicable in other cases I will here briefly give them If the several
breeds are not varieties and have not proceeded from the rockpigeon
they must have descended from at least seven or eight aboriginal stocks
for it is impossible to make the present domestic breeds by the crossing
of any lesser number how for instance could a pouter be produced
by crossing two breeds unless one of the parentstocks possessed the
characteristic enormous crop The supposed aboriginal stocks must all
have been rockpigeons that is they did not breed or willingly perch
on trees But besides C livia with its geographical subspecies only
two or three other species of rockpigeons are known and these have
not any of the characters of the domestic breeds Hence the supposed
aboriginal stocks must either still exist in the countries where they
were originally domesticated and yet be unknown to ornithologists and
this considering their size habits and remarkable characters seems
improbable or they must have become extinct in the wild state But
birds breeding on precipices and good flyers are unlikely to be
exterminated and the common rockpigeon which has the same habits with
the domestic breeds has not been exterminated even on several of the
smaller British islets or on the shores of the Mediterranean Hence the
supposed extermination of so many species having similar habits with
the rockpigeon seems a very rash assumption Moreover the several
abovenamed domesticated breeds have been transported to all parts of
the world and therefore some of them must have been carried back
again into their native country but not one has become wild or feral
though the dovecotpigeon which is the rockpigeon in a very slightly
altered state has become feral in several places Again all recent
experience shows that it is difficult to get wild animals to breed
freely under domestication yet on the hypothesis of the multiple origin
of our pigeons it must be assumed that at least seven or eight species
were so thoroughly domesticated in ancient times by halfcivilized man
as to be quite prolific under confinement

An argument of great weight and applicable in several other cases is
that the abovespecified breeds though agreeing generally with the wild
rockpigeon in constitution habits voice colouring and in most parts
of their structure yet are certainly highly abnormal in other parts we
may look in vain through the whole great family of Columbidae for a beak
like that of the English carrier or that of the shortfaced tumbler or
barb for reversed feathers like those of the Jacobin for a crop like
that of the pouter for tailfeathers like those of the fantail Hence
it must be assumed not only that halfcivilized man succeeded in
thoroughly domesticating several species but that he intentionally or
by chance picked out extraordinarily abnormal species and further that
these very species have since all become extinct or unknown So many
strange contingencies are improbable in the highest degree

Some facts in regard to the colouring of pigeons well deserve
consideration The rockpigeon is of a slatyblue with white loins
but the Indian subspecies C intermedia of Strickland has this
part bluish The tail has a terminal dark bar with the outer feathers
externally edged at the base with white The wings have two black bars
Some semidomestic breeds and some truly wild breeds have besides the
two black bars the wings chequered with black These several marks do
not occur together in any other species of the whole family Now in
every one of the domestic breeds taking thoroughly wellbred birds all
the above marks even to the white edging of the outer tailfeathers
sometimes concur perfectly developed Moreover when birds belonging to
two or more distinct breeds are crossed none of which are blue or have
any of the abovespecified marks the mongrel offspring are very apt
suddenly to acquire these characters To give one instance out of
several which I have observed I crossed some white fantails which
breed very true with some black barbs and it so happens that blue
varieties of barbs are so rare that I never heard of an instance in
England and the mongrels were black brown and mottled I also crossed
a barb with a spot which is a white bird with a red tail and red spot
on the forehead and which notoriously breeds very true the mongrels
were dusky and mottled I then crossed one of the mongrel barbfantails
with a mongrel barbspot and they produced a bird of as beautiful a
blue colour with the white loins double black wingbar and barred and
whiteedged tailfeathers as any wild rockpigeon  We can understand
these facts on the wellknown principle of reversion to ancestral
characters if all the domestic breeds are descended from the
rockpigeon But if we deny this we must make one of the two following
highly improbable suppositions Either first that all the several
imagined aboriginal stocks were coloured and marked like the
rockpigeon although no other existing species is thus coloured and
marked so that in each separate breed there might be a tendency to
revert to the very same colours and markings Or secondly that each
breed even the purest has within a dozen or at most within a score
of generations been crossed by the rockpigeon I say within a dozen
or twenty generations for no instance is known of crossed descendants
reverting to an ancestor of foreign blood removed by a greater number
of generations In a breed which has been crossed only once the tendency
to revert to any character derived from such a cross will naturally
become less and less as in each succeeding generation there will be
less of the foreign blood but when there has been no cross and there
is a tendency in the breed to revert to a character which was lost
during some former generation this tendency for all that we can see to
the contrary may be transmitted undiminished for an indefinite
number of generations These two distinct cases of reversion are often
confounded together by those who have written on inheritance

Lastly the hybrids or mongrels from between all the breeds of the
pigeon are perfectly fertile as I can state from my own observations
purposely made on the most distinct breeds Now hardly any cases
have been ascertained with certainty of hybrids from two quite distinct
species of animals being perfectly fertile Some authors believe
that longcontinued domestication eliminates this strong tendency to
sterility in species From the history of the dog and of some other
domestic animals this conclusion is probably quite correct if applied
to species closely related to each other But to extend it so far as to
suppose that species aboriginally as distinct as carriers tumblers
pouters and fantails now are should yield offspring perfectly fertile
inter se seems to me rash in the extreme

From these several reasons namely the improbability of man having
formerly made seven or eight supposed species of pigeons to breed freely
under domestication these supposed species being quite unknown in a
wild state and their not having become anywhere feral these species
presenting certain very abnormal characters as compared with all other
Columbidae though so like the rockpigeon in most other respects the
occasional reappearance of the blue colour and various black marks in
all the breeds both when kept pure and when crossed and lastly the
mongrel offspring being perfectly fertile from these several reasons
taken together we may safely conclude that all our domestic breeds are
descended from the rockpigeon or Columba livia with its geographical
subspecies

In favour of this view I may add firstly that the wild C livia has
been found capable of domestication in Europe and in India and that it
agrees in habits and in a great number of points of structure with all
the domestic breeds Secondly that although an English carrier or a
shortfaced tumbler differs immensely in certain characters from the
rockpigeon yet that by comparing the several subbreeds of these two
races more especially those brought from distant countries we can
make between them and the rockpigeon an almost perfect series so
we can in some other cases but not with all the breeds Thirdly
those characters which are mainly distinctive of each breed are in each
eminently variable for instance the wattle and length of beak of
the carrier the shortness of that of the tumbler and the number of
tailfeathers in the fantail and the explanation of this fact will be
obvious when we treat of selection Fourthly pigeons have been watched
and tended with the utmost care and loved by many people They have
been domesticated for thousands of years in several quarters of the
world the earliest known record of pigeons is in the fifth Aegyptian
dynasty about 3000 BC as was pointed out to me by Professor Lepsius
but Mr Birch informs me that pigeons are given in a bill of fare in
the previous dynasty In the time of the Romans as we hear from Pliny
immense prices were given for pigeons nay they are come to this pass
that they can reckon up their pedigree and race Pigeons were much
valued by Akber Khan in India about the year 1600 never less than
20000 pigeons were taken with the court The monarchs of Iran and
Turan sent him some very rare birds and continues the courtly
historian His Majesty by crossing the breeds which method was never
practised before has improved them astonishingly About this same
period the Dutch were as eager about pigeons as were the old Romans The
paramount importance of these considerations in explaining the immense
amount of variation which pigeons have undergone will likewise be
obvious when we treat of selection We shall then also see how it is
that the several breeds so often have a somewhat monstrous character
It is also a most favourable circumstance for the production of distinct
breeds that male and female pigeons can be easily mated for life and
thus different breeds can be kept together in the same aviary

I have discussed the probable origin of domestic pigeons at some
yet quite insufficient length because when I first kept pigeons and
watched the several kinds well knowing how truly they breed I
felt fully as much difficulty in believing that since they had been
domesticated they had all proceeded from a common parent as any
naturalist could in coming to a similar conclusion in regard to the
many species of finches or other groups of birds in nature One
circumstance has struck me much namely that nearly all the breeders of
the various domestic animals and the cultivators of plants with whom
I have conversed or whose treatises I have read are firmly convinced
that the several breeds to which each has attended are descended
from so many aboriginally distinct species Ask as I have asked a
celebrated raiser of Hereford cattle whether his cattle might not have
descended from Longhorns or both from a common parentstock and he
will laugh you to scorn I have never met a pigeon or poultry or duck
or rabbit fancier who was not fully convinced that each main breed was
descended from a distinct species Van Mons in his treatise on pears
and apples shows how utterly he disbelieves that the several sorts
for instance a Ribstonpippin or Codlinapple could ever have proceeded
from the seeds of the same tree Innumerable other examples could be
given The explanation I think is simple from longcontinued study
they are strongly impressed with the differences between the several
races and though they well know that each race varies slightly for
they win their prizes by selecting such slight differences yet they
ignore all general arguments and refuse to sum up in their minds slight
differences accumulated during many successive generations May not
those naturalists who knowing far less of the laws of inheritance than
does the breeder and knowing no more than he does of the intermediate
links in the long lines of descent yet admit that many of our domestic
races are descended from the same parents may they not learn a lesson
of caution when they deride the idea of species in a state of nature
being lineal descendants of other species

PRINCIPLES OF SELECTION ANCIENTLY FOLLOWED AND THEIR EFFECTS

Let us now briefly consider the steps by which domestic races have been
produced either from one or from several allied species Some effect
may be attributed to the direct and definite action of the external
conditions of life and some to habit but he would be a bold man who
would account by such agencies for the differences between a dray and
racehorse a greyhound and bloodhound a carrier and tumbler pigeon
One of the most remarkable features in our domesticated races is that we
see in them adaptation not indeed to the animals or plants own good
but to mans use or fancy Some variations useful to him have probably
arisen suddenly or by one step many botanists for instance believe
that the fullers teasel with its hooks which can not be rivalled by
any mechanical contrivance is only a variety of the wild Dipsacus and
this amount of change may have suddenly arisen in a seedling So it has
probably been with the turnspit dog and this is known to have been
the case with the ancon sheep But when we compare the drayhorse and
racehorse the dromedary and camel the various breeds of sheep fitted
either for cultivated land or mountain pasture with the wool of one
breed good for one purpose and that of another breed for another
purpose when we compare the many breeds of dogs each good for man
in different ways when we compare the gamecock so pertinacious in
battle with other breeds so little quarrelsome with everlasting
layers which never desire to sit and with the bantam so small and
elegant when we compare the host of agricultural culinary orchard
and flowergarden races of plants most useful to man at different
seasons and for different purposes or so beautiful in his eyes we
must I think look further than to mere variability We can not suppose
that all the breeds were suddenly produced as perfect and as useful as
we now see them indeed in many cases we know that this has not been
their history The key is mans power of accumulative selection nature
gives successive variations man adds them up in certain directions
useful to him In this sense he may be said to have made for himself
useful breeds

The great power of this principle of selection is not hypothetical
It is certain that several of our eminent breeders have even within a
single lifetime modified to a large extent their breeds of cattle
and sheep In order fully to realise what they have done it is almost
necessary to read several of the many treatises devoted to this subject
and to inspect the animals Breeders habitually speak of an animals
organisation as something plastic which they can model almost as they
please If I had space I could quote numerous passages to this effect
from highly competent authorities Youatt who was probably better
acquainted with the works of agriculturalists than almost any other
individual and who was himself a very good judge of animals speaks of
the principle of selection as that which enables the agriculturist not
only to modify the character of his flock but to change it altogether
It is the magicians wand by means of which he may summon into life
whatever form and mould he pleases Lord Somerville speaking of
what breeders have done for sheep says It would seem as if they had
chalked out upon a wall a form perfect in itself and then had given it
existence In Saxony the importance of the principle of selection in
regard to merino sheep is so fully recognised that men follow it as a
trade the sheep are placed on a table and are studied like a picture
by a connoisseur this is done three times at intervals of months and
the sheep are each time marked and classed so that the very best may
ultimately be selected for breeding

What English breeders have actually effected is proved by the enormous
prices given for animals with a good pedigree and these have been
exported to almost every quarter of the world The improvement is by no
means generally due to crossing different breeds all the best breeders
are strongly opposed to this practice except sometimes among closely
allied subbreeds And when a cross has been made the closest selection
is far more indispensable even than in ordinary cases If selection
consisted merely in separating some very distinct variety and breeding
from it the principle would be so obvious as hardly to be worth
notice but its importance consists in the great effect produced by
the accumulation in one direction during successive generations of
differences absolutely inappreciable by an uneducated eye differences
which I for one have vainly attempted to appreciate Not one man in
a thousand has accuracy of eye and judgment sufficient to become an
eminent breeder If gifted with these qualities and he studies his
subject for years and devotes his lifetime to it with indomitable
perseverance he will succeed and may make great improvements if he
wants any of these qualities he will assuredly fail Few would readily
believe in the natural capacity and years of practice requisite to
become even a skilful pigeonfancier

The same principles are followed by horticulturists but the variations
are here often more abrupt No one supposes that our choicest
productions have been produced by a single variation from the aboriginal
stock We have proofs that this is not so in several cases in which
exact records have been kept thus to give a very trifling instance
the steadily increasing size of the common gooseberry may be quoted
We see an astonishing improvement in many florists flowers when the
flowers of the present day are compared with drawings made only
twenty or thirty years ago When a race of plants is once pretty well
established the seedraisers do not pick out the best plants but
merely go over their seedbeds and pull up the rogues as they call
the plants that deviate from the proper standard With animals this kind
of selection is in fact likewise followed for hardly any one is so
careless as to breed from his worst animals

In regard to plants there is another means of observing the accumulated
effects of selection namely by comparing the diversity of flowers in
the different varieties of the same species in the flowergarden the
diversity of leaves pods or tubers or whatever part is valued in the
kitchengarden in comparison with the flowers of the same varieties
and the diversity of fruit of the same species in the orchard in
comparison with the leaves and flowers of the same set of varieties See
how different the leaves of the cabbage are and how extremely alike the
flowers how unlike the flowers of the heartsease are and how alike the
leaves how much the fruit of the different kinds of gooseberries differ
in size colour shape and hairiness and yet the flowers present very
slight differences It is not that the varieties which differ largely
in some one point do not differ at all in other points this is hardly
ever I speak after careful observation perhaps never the case The
law of correlated variation the importance of which should never be
overlooked will ensure some differences but as a general rule it
cannot be doubted that the continued selection of slight variations
either in the leaves the flowers or the fruit will produce races
differing from each other chiefly in these characters

It may be objected that the principle of selection has been reduced to
methodical practice for scarcely more than threequarters of a century
it has certainly been more attended to of late years and many treatises
have been published on the subject and the result has been in a
corresponding degree rapid and important But it is very far from
true that the principle is a modern discovery I could give several
references to works of high antiquity in which the full importance of
the principle is acknowledged In rude and barbarous periods of English
history choice animals were often imported and laws were passed to
prevent their exportation the destruction of horses under a certain
size was ordered and this may be compared to the roguing of plants
by nurserymen The principle of selection I find distinctly given in an
ancient Chinese encyclopaedia Explicit rules are laid down by some of
the Roman classical writers From passages in Genesis it is clear that
the colour of domestic animals was at that early period attended to
Savages now sometimes cross their dogs with wild canine animals to
improve the breed and they formerly did so as is attested by passages
in Pliny The savages in South Africa match their draught cattle by
colour as do some of the Esquimaux their teams of dogs Livingstone
states that good domestic breeds are highly valued by the negroes in the
interior of Africa who have not associated with Europeans Some of these
facts do not show actual selection but they show that the breeding of
domestic animals was carefully attended to in ancient times and is now
attended to by the lowest savages It would indeed have been a strange
fact had attention not been paid to breeding for the inheritance of
good and bad qualities is so obvious

UNCONSCIOUS SELECTION

At the present time eminent breeders try by methodical selection with
a distinct object in view to make a new strain or subbreed superior
to anything of the kind in the country But for our purpose a form of
selection which may be called unconscious and which results from every
one trying to possess and breed from the best individual animals is
more important Thus a man who intends keeping pointers naturally tries
to get as good dogs as he can and afterwards breeds from his own best
dogs but he has no wish or expectation of permanently altering the
breed Nevertheless we may infer that this process continued during
centuries would improve and modify any breed in the same way as
Bakewell Collins etc by this very same process only carried on more
methodically did greatly modify even during their lifetimes the forms
and qualities of their cattle Slow and insensible changes of this kind
could never be recognised unless actual measurements or careful drawings
of the breeds in question have been made long ago which may serve for
comparison In some cases however unchanged or but little changed
individuals of the same breed exist in less civilised districts where
the breed has been less improved There is reason to believe that King
Charles spaniel has been unconsciously modified to a large extent
since the time of that monarch Some highly competent authorities are
convinced that the setter is directly derived from the spaniel and
has probably been slowly altered from it It is known that the English
pointer has been greatly changed within the last century and in this
case the change has it is believed been chiefly effected by crosses
with the foxhound but what concerns us is that the change has been
effected unconsciously and gradually and yet so effectually that
though the old Spanish pointer certainly came from Spain Mr Borrow
has not seen as I am informed by him any native dog in Spain like our
pointer

By a similar process of selection and by careful training English
racehorses have come to surpass in fleetness and size the parent Arabs
so that the latter by the regulations for the Goodwood Races are
favoured in the weights which they carry Lord Spencer and others have
shown how the cattle of England have increased in weight and in early
maturity compared with the stock formerly kept in this country By
comparing the accounts given in various old treatises of the former
and present state of carrier and tumbler pigeons in Britain India
and Persia we can trace the stages through which they have insensibly
passed and come to differ so greatly from the rockpigeon

Youatt gives an excellent illustration of the effects of a course of
selection which may be considered as unconscious in so far that the
breeders could never have expected or even wished to produce the
result which ensued namely the production of the distinct strains The
two flocks of Leicester sheep kept by Mr Buckley and Mr Burgess as
Mr Youatt remarks Have been purely bred from the original stock
of Mr Bakewell for upwards of fifty years There is not a suspicion
existing in the mind of any one at all acquainted with the subject that
the owner of either of them has deviated in any one instance from the
pure blood of Mr Bakewells flock and yet the difference between the
sheep possessed by these two gentlemen is so great that they have the
appearance of being quite different varieties

If there exist savages so barbarous as never to think of the inherited
character of the offspring of their domestic animals yet any one animal
particularly useful to them for any special purpose would be carefully
preserved during famines and other accidents to which savages are
so liable and such choice animals would thus generally leave more
offspring than the inferior ones so that in this case there would be a
kind of unconscious selection going on We see the value set on animals
even by the barbarians of Tierra del Fuego by their killing and
devouring their old women in times of dearth as of less value than
their dogs

In plants the same gradual process of improvement through the occasional
preservation of the best individuals whether or not sufficiently
distinct to be ranked at their first appearance as distinct varieties
and whether or not two or more species or races have become blended
together by crossing may plainly be recognised in the increased size
and beauty which we now see in the varieties of the heartsease rose
pelargonium dahlia and other plants when compared with the older
varieties or with their parentstocks No one would ever expect to get
a firstrate heartsease or dahlia from the seed of a wild plant No one
would expect to raise a firstrate melting pear from the seed of a wild
pear though he might succeed from a poor seedling growing wild if it
had come from a gardenstock The pear though cultivated in classical
times appears from Plinys description to have been a fruit of very
inferior quality I have seen great surprise expressed in horticultural
works at the wonderful skill of gardeners in having produced such
splendid results from such poor materials but the art has been simple
and as far as the final result is concerned has been followed almost
unconsciously It has consisted in always cultivating the best known
variety sowing its seeds and when a slightly better variety chanced
to appear selecting it and so onwards But the gardeners of the
classical period who cultivated the best pears which they could
procure never thought what splendid fruit we should eat though we
owe our excellent fruit in some small degree to their having naturally
chosen and preserved the best varieties they could anywhere find

A large amount of change thus slowly and unconsciously accumulated
explains as I believe the wellknown fact that in a number of cases
we cannot recognise and therefore do not know the wild parentstocks
of the plants which have been longest cultivated in our flower and
kitchen gardens If it has taken centuries or thousands of years to
improve or modify most of our plants up to their present standard of
usefulness to man we can understand how it is that neither Australia
the Cape of Good Hope nor any other region inhabited by quite
uncivilised man has afforded us a single plant worth culture It is
not that these countries so rich in species do not by a strange chance
possess the aboriginal stocks of any useful plants but that the native
plants have not been improved by continued selection up to a standard
of perfection comparable with that acquired by the plants in countries
anciently civilised

In regard to the domestic animals kept by uncivilised man it should
not be overlooked that they almost always have to struggle for their
own food at least during certain seasons And in two countries very
differently circumstanced individuals of the same species having
slightly different constitutions or structure would often succeed
better in the one country than in the other and thus by a process of
natural selection as will hereafter be more fully explained two
subbreeds might be formed This perhaps partly explains why the
varieties kept by savages as has been remarked by some authors
have more of the character of true species than the varieties kept in
civilised countries

On the view here given of the important part which selection by man has
played it becomes at once obvious how it is that our domestic races
show adaptation in their structure or in their habits to mans wants
or fancies We can I think further understand the frequently abnormal
character of our domestic races and likewise their differences being so
great in external characters and relatively so slight in internal parts
or organs Man can hardly select or only with much difficulty any
deviation of structure excepting such as is externally visible and
indeed he rarely cares for what is internal He can never act by
selection excepting on variations which are first given to him in some
slight degree by nature No man would ever try to make a fantail till he
saw a pigeon with a tail developed in some slight degree in an unusual
manner or a pouter till he saw a pigeon with a crop of somewhat unusual
size and the more abnormal or unusual any character was when it first
appeared the more likely it would be to catch his attention But to use
such an expression as trying to make a fantail is I have no doubt in
most cases utterly incorrect The man who first selected a pigeon
with a slightly larger tail never dreamed what the descendants of
that pigeon would become through longcontinued partly unconscious and
partly methodical selection Perhaps the parent bird of all fantails
had only fourteen tailfeathers somewhat expanded like the present Java
fantail or like individuals of other and distinct breeds in which as
many as seventeen tailfeathers have been counted Perhaps the first
pouterpigeon did not inflate its crop much more than the turbit now
does the upper part of its oesophagus a habit which is disregarded by
all fanciers as it is not one of the points of the breed

Nor let it be thought that some great deviation of structure would
be necessary to catch the fanciers eye he perceives extremely small
differences and it is in human nature to value any novelty however
slight in ones own possession Nor must the value which would formerly
have been set on any slight differences in the individuals of the same
species be judged of by the value which is now set on them after
several breeds have fairly been established It is known that with
pigeons many slight variations now occasionally appear but these are
rejected as faults or deviations from the standard of perfection in
each breed The common goose has not given rise to any marked varieties
hence the Toulouse and the common breed which differ only in colour
that most fleeting of characters have lately been exhibited as distinct
at our poultryshows

These views appear to explain what has sometimes been noticed namely
that we know hardly anything about the origin or history of any of our
domestic breeds But in fact a breed like a dialect of a language
can hardly be said to have a distinct origin A man preserves and breeds
from an individual with some slight deviation of structure or takes
more care than usual in matching his best animals and thus improves
them and the improved animals slowly spread in the immediate
neighbourhood But they will as yet hardly have a distinct name
and from being only slightly valued their history will have been
disregarded When further improved by the same slow and gradual process
they will spread more widely and will be recognised as something
distinct and valuable and will then probably first receive a provincial
name In semicivilised countries with little free communication the
spreading of a new subbreed will be a slow process As soon as the
points of value are once acknowledged the principle as I have called
it of unconscious selection will always tend perhaps more at one
period than at another as the breed rises or falls in fashion perhaps
more in one district than in another according to the state of
civilisation of the inhabitants slowly to add to the characteristic
features of the breed whatever they may be But the chance will be
infinitely small of any record having been preserved of such slow
varying and insensible changes

CIRCUMSTANCES FAVOURABLE TO MANS POWER OF SELECTION

I will now say a few words on the circumstances favourable or the
reverse to mans power of selection A high degree of variability is
obviously favourable as freely giving the materials for selection to
work on not that mere individual differences are not amply sufficient
with extreme care to allow of the accumulation of a large amount
of modification in almost any desired direction But as variations
manifestly useful or pleasing to man appear only occasionally the
chance of their appearance will be much increased by a large number of
individuals being kept Hence number is of the highest importance for
success On this principle Marshall formerly remarked with respect
to the sheep of part of Yorkshire As they generally belong to poor
people and are mostly IN SMALL LOTS they never can be improved On
the other hand nurserymen from keeping large stocks of the same plant
are generally far more successful than amateurs in raising new and
valuable varieties A large number of individuals of an animal or
plant can be reared only where the conditions for its propagation are
favourable When the individuals are scanty all will be allowed to
breed whatever their quality may be and this will effectually prevent
selection But probably the most important element is that the animal or
plant should be so highly valued by man that the closest attention is
paid to even the slightest deviations in its qualities or structure
Unless such attention be paid nothing can be effected I have seen it
gravely remarked that it was most fortunate that the strawberry began
to vary just when gardeners began to attend to this plant No doubt the
strawberry had always varied since it was cultivated but the slight
varieties had been neglected As soon however as gardeners picked out
individual plants with slightly larger earlier or better fruit and
raised seedlings from them and again picked out the best seedlings and
bred from them then with some aid by crossing distinct species
those many admirable varieties of the strawberry were raised which have
appeared during the last halfcentury

With animals facility in preventing crosses is an important element
in the formation of new races at least in a country which is already
stocked with other races In this respect enclosure of the land plays a
part Wandering savages or the inhabitants of open plains rarely possess
more than one breed of the same species Pigeons can be mated for life
and this is a great convenience to the fancier for thus many races may
be improved and kept true though mingled in the same aviary and this
circumstance must have largely favoured the formation of new breeds
Pigeons I may add can be propagated in great numbers and at a very
quick rate and inferior birds may be freely rejected as when killed
they serve for food On the other hand cats from their nocturnal
rambling habits can not be easily matched and although so much valued
by women and children we rarely see a distinct breed long kept up such
breeds as we do sometimes see are almost always imported from some other
country Although I do not doubt that some domestic animals vary less
than others yet the rarity or absence of distinct breeds of the cat
the donkey peacock goose etc may be attributed in main part
to selection not having been brought into play in cats from the
difficulty in pairing them in donkeys from only a few being kept by
poor people and little attention paid to their breeding for recently
in certain parts of Spain and of the United States this animal has been
surprisingly modified and improved by careful selection in peacocks
from not being very easily reared and a large stock not kept in geese
from being valuable only for two purposes food and feathers and more
especially from no pleasure having been felt in the display of distinct
breeds but the goose under the conditions to which it is exposed when
domesticated seems to have a singularly inflexible organisation though
it has varied to a slight extent as I have elsewhere described

Some authors have maintained that the amount of variation in our
domestic productions is soon reached and can never afterward be
exceeded It would be somewhat rash to assert that the limit has been
attained in any one case for almost all our animals and plants have
been greatly improved in many ways within a recent period and this
implies variation It would be equally rash to assert that characters
now increased to their utmost limit could not after remaining fixed
for many centuries again vary under new conditions of life No doubt
as Mr Wallace has remarked with much truth a limit will be at last
reached For instance there must be a limit to the fleetness of any
terrestrial animal as this will be determined by the friction to
be overcome the weight of the body to be carried and the power of
contraction in the muscular fibres But what concerns us is that the
domestic varieties of the same species differ from each other in almost
every character which man has attended to and selected more than do
the distinct species of the same genera Isidore Geoffroy St Hilaire
has proved this in regard to size and so it is with colour and
probably with the length of hair With respect to fleetness which
depends on many bodily characters Eclipse was far fleeter and
a drayhorse is comparably stronger than any two natural species
belonging to the same genus So with plants the seeds of the different
varieties of the bean or maize probably differ more in size than do the
seeds of the distinct species in any one genus in the same two families
The same remark holds good in regard to the fruit of the several
varieties of the plum and still more strongly with the melon as well
as in many other analogous cases

To sum up on the origin of our domestic races of animals and plants
Changed conditions of life are of the highest importance in causing
variability both by acting directly on the organisation and
indirectly by affecting the reproductive system It is not probable
that variability is an inherent and necessary contingent under all
circumstances The greater or less force of inheritance and reversion
determine whether variations shall endure Variability is governed
by many unknown laws of which correlated growth is probably the most
important Something but how much we do not know may be attributed to
the definite action of the conditions of life Some perhaps a great
effect may be attributed to the increased use or disuse of parts The
final result is thus rendered infinitely complex In some cases the
intercrossing of aboriginally distinct species appears to have played
an important part in the origin of our breeds When several breeds have
once been formed in any country their occasional intercrossing with
the aid of selection has no doubt largely aided in the formation
of new subbreeds but the importance of crossing has been much
exaggerated both in regard to animals and to those plants which are
propagated by seed With plants which are temporarily propagated by
cuttings buds etc the importance of crossing is immense for the
cultivator may here disregard the extreme variability both of hybrids
and of mongrels and the sterility of hybrids but plants not propagated
by seed are of little importance to us for their endurance is only
temporary Over all these causes of change the accumulative action of
selection whether applied methodically and quickly or unconsciously
and slowly but more efficiently seems to have been the predominant
power




CHAPTER II VARIATION UNDER NATURE

 Variability Individual differences Doubtful species Wide ranging
 much diffused and common species vary most Species of the larger
 genera in each country vary more frequently than the species of the
 smaller genera Many of the species of the larger genera resemble
 varieties in being very closely but unequally related to each other
 and in having restricted ranges


Before applying the principles arrived at in the last chapter to organic
beings in a state of nature we must briefly discuss whether these
latter are subject to any variation To treat this subject properly a
long catalogue of dry facts ought to be given but these I shall reserve
for a future work Nor shall I here discuss the various definitions
which have been given of the term species No one definition has
satisfied all naturalists yet every naturalist knows vaguely what
he means when he speaks of a species Generally the term includes the
unknown element of a distinct act of creation The term variety is
almost equally difficult to define but here community of descent is
almost universally implied though it can rarely be proved We have also
what are called monstrosities but they graduate into varieties By a
monstrosity I presume is meant some considerable deviation of structure
generally injurious or not useful to the species Some authors use
the term variation in a technical sense as implying a modification
directly due to the physical conditions of life and variations in
this sense are supposed not to be inherited but who can say that the
dwarfed condition of shells in the brackish waters of the Baltic or
dwarfed plants on Alpine summits or the thicker fur of an animal from
far northwards would not in some cases be inherited for at least a few
generations And in this case I presume that the form would be called a
variety

It may be doubted whether sudden and considerable deviations of
structure such as we occasionally see in our domestic productions more
especially with plants are ever permanently propagated in a state
of nature Almost every part of every organic being is so beautifully
related to its complex conditions of life that it seems as improbable
that any part should have been suddenly produced perfect as that a
complex machine should have been invented by man in a perfect state
Under domestication monstrosities sometimes occur which resemble normal
structures in widely different animals Thus pigs have occasionally been
born with a sort of proboscis and if any wild species of the same genus
had naturally possessed a proboscis it might have been argued that this
had appeared as a monstrosity but I have as yet failed to find after
diligent search cases of monstrosities resembling normal structures in
nearly allied forms and these alone bear on the question If monstrous
forms of this kind ever do appear in a state of nature and are capable
of reproduction which is not always the case as they occur rarely
and singly their preservation would depend on unusually favourable
circumstances They would also during the first and succeeding
generations cross with the ordinary form and thus their abnormal
character would almost inevitably be lost But I shall have to return
in a future chapter to the preservation and perpetuation of single or
occasional variations

INDIVIDUAL DIFFERENCES

The many slight differences which appear in the offspring from the
same parents or which it may be presumed have thus arisen from being
observed in the individuals of the same species inhabiting the same
confined locality may be called individual differences No one supposes
that all the individuals of the same species are cast in the same actual
mould These individual differences are of the highest importance for
us for they are often inherited as must be familiar to every one
and they thus afford materials for natural selection to act on and
accumulate in the same manner as man accumulates in any given direction
individual differences in his domesticated productions These individual
differences generally affect what naturalists consider unimportant
parts but I could show by a long catalogue of facts that parts
which must be called important whether viewed under a physiological or
classificatory point of view sometimes vary in the individuals of the
same species I am convinced that the most experienced naturalist
would be surprised at the number of the cases of variability even in
important parts of structure which he could collect on good authority
as I have collected during a course of years It should be remembered
that systematists are far from being pleased at finding variability
in important characters and that there are not many men who will
laboriously examine internal and important organs and compare them in
many specimens of the same species It would never have been expected
that the branching of the main nerves close to the great central
ganglion of an insect would have been variable in the same species
it might have been thought that changes of this nature could have been
effected only by slow degrees yet Sir J Lubbock has shown a degree of
variability in these main nerves in Coccus which may almost be compared
to the irregular branching of the stem of a tree This philosophical
naturalist I may add has also shown that the muscles in the larvae
of certain insects are far from uniform Authors sometimes argue in a
circle when they state that important organs never vary for these
same authors practically rank those parts as important as some few
naturalists have honestly confessed which do not vary and under
this point of view no instance will ever be found of an important part
varying but under any other point of view many instances assuredly can
be given

There is one point connected with individual differences which is
extremely perplexing I refer to those genera which have been called
protean or polymorphic in which species present an inordinate
amount of variation With respect to many of these forms hardly two
naturalists agree whether to rank them as species or as varieties We
may instance Rubus Rosa and Hieracium among plants several genera of
insects and of Brachiopod shells In most polymorphic genera some
of the species have fixed and definite characters Genera which
are polymorphic in one country seem to be with a few exceptions
polymorphic in other countries and likewise judging from Brachiopod
shells at former periods of time These facts are very perplexing for
they seem to show that this kind of variability is independent of the
conditions of life I am inclined to suspect that we see at least in
some of these polymorphic genera variations which are of no service or
disservice to the species and which consequently have not been seized
on and rendered definite by natural selection as hereafter to be
explained

Individuals of the same species often present as is known to every one
great differences of structure independently of variation as in the
two sexes of various animals in the two or three castes of sterile
females or workers among insects and in the immature and larval states
of many of the lower animals There are also cases of dimorphism and
trimorphism both with animals and plants Thus Mr Wallace who has
lately called attention to the subject has shown that the females of
certain species of butterflies in the Malayan Archipelago regularly
appear under two or even three conspicuously distinct forms not
connected by intermediate varieties Fritz Muller has described
analogous but more extraordinary cases with the males of certain
Brazilian Crustaceans thus the male of a Tanais regularly occurs
under two distinct forms one of these has strong and differently shaped
pincers and the other has antennae much more abundantly furnished with
smellinghairs Although in most of these cases the two or three forms
both with animals and plants are not now connected by intermediate
gradations it is possible that they were once thus connected Mr
Wallace for instance describes a certain butterfly which presents in
the same island a great range of varieties connected by intermediate
links and the extreme links of the chain closely resemble the two forms
of an allied dimorphic species inhabiting another part of the Malay
Archipelago Thus also with ants the several workercastes are
generally quite distinct but in some cases as we shall hereafter see
the castes are connected together by finely graduated varieties So it
is as I have myself observed with some dimorphic plants It certainly
at first appears a highly remarkable fact that the same female butterfly
should have the power of producing at the same time three distinct
female forms and a male and that an hermaphrodite plant should produce
from the same seedcapsule three distinct hermaphrodite forms bearing
three different kinds of females and three or even six different kinds
of males Nevertheless these cases are only exaggerations of the common
fact that the female produces offspring of two sexes which sometimes
differ from each other in a wonderful manner

DOUBTFUL SPECIES

The forms which possess in some considerable degree the character of
species but which are so closely similar to other forms or are so
closely linked to them by intermediate gradations that naturalists do
not like to rank them as distinct species are in several respects the
most important for us We have every reason to believe that many of
these doubtful and closely allied forms have permanently retained their
characters for a long time for as long as far as we know as have good
and true species Practically when a naturalist can unite by means of
intermediate links any two forms he treats the one as a variety of the
other ranking the most common but sometimes the one first described
as the species and the other as the variety But cases of great
difficulty which I will not here enumerate sometimes arise in deciding
whether or not to rank one form as a variety of another even when
they are closely connected by intermediate links nor will the commonly
assumed hybrid nature of the intermediate forms always remove the
difficulty In very many cases however one form is ranked as a variety
of another not because the intermediate links have actually been found
but because analogy leads the observer to suppose either that they do
now somewhere exist or may formerly have existed and here a wide door
for the entry of doubt and conjecture is opened

Hence in determining whether a form should be ranked as a species or
a variety the opinion of naturalists having sound judgment and wide
experience seems the only guide to follow We must however in many
cases decide by a majority of naturalists for few wellmarked and
wellknown varieties can be named which have not been ranked as species
by at least some competent judges

That varieties of this doubtful nature are far from uncommon cannot be
disputed Compare the several floras of Great Britain of France or
of the United States drawn up by different botanists and see what
a surprising number of forms have been ranked by one botanist as good
species and by another as mere varieties Mr HC Watson to whom I
lie under deep obligation for assistance of all kinds has marked for
me 182 British plants which are generally considered as varieties but
which have all been ranked by botanists as species and in making this
list he has omitted many trifling varieties but which nevertheless have
been ranked by some botanists as species and he has entirely omitted
several highly polymorphic genera Under genera including the most
polymorphic forms Mr Babington gives 251 species whereas Mr Bentham
gives only 112 a difference of 139 doubtful forms  Among animals which
unite for each birth and which are highly locomotive doubtful forms
ranked by one zoologist as a species and by another as a variety can
rarely be found within the same country but are common in separated
areas How many of the birds and insects in North America and Europe
which differ very slightly from each other have been ranked by one
eminent naturalist as undoubted species and by another as varieties
or as they are often called geographical races  Mr Wallace in
several valuable papers on the various animals especially on the
Lepidoptera inhabiting the islands of the great Malayan Archipelago
shows that they may be classed under four heads namely as variable
forms as local forms as geographical races or subspecies and as true
representative species The first or variable forms vary much within the
limits of the same island The local forms are moderately constant and
distinct in each separate island but when all from the several islands
are compared together the differences are seen to be so slight and
graduated that it is impossible to define or describe them though
at the same time the extreme forms are sufficiently distinct The
geographical races or subspecies are local forms completely fixed and
isolated but as they do not differ from each other by strongly marked
and important characters There is no possible test but individual
opinion to determine which of them shall be considered as species and
which as varieties Lastly representative species fill the same
place in the natural economy of each island as do the local forms and
subspecies but as they are distinguished from each other by a greater
amount of difference than that between the local forms and subspecies
they are almost universally ranked by naturalists as true species
Nevertheless no certain criterion can possibly be given by which
variable forms local forms sub species and representative species can
be recognised

Many years ago when comparing and seeing others compare the birds
from the closely neighbouring islands of the Galapagos Archipelago
one with another and with those from the American mainland I was
much struck how entirely vague and arbitrary is the distinction between
species and varieties On the islets of the little Madeira group there
are many insects which are characterized as varieties in Mr Wollastons
admirable work but which would certainly be ranked as distinct species
by many entomologists Even Ireland has a few animals now generally
regarded as varieties but which have been ranked as species by some
zoologists Several experienced ornithologists consider our British red
grouse as only a strongly marked race of a Norwegian species whereas
the greater number rank it as an undoubted species peculiar to Great
Britain A wide distance between the homes of two doubtful forms leads
many naturalists to rank them as distinct species but what distance it
has been well asked will suffice if that between America and Europe
is ample will that between Europe and the Azores or Madeira or the
Canaries or between the several islets of these small archipelagos be
sufficient

Mr BD Walsh a distinguished entomologist of the United States has
described what he calls Phytophagic varieties and Phytophagic species
Most vegetablefeeding insects live on one kind of plant or on one
group of plants some feed indiscriminately on many kinds but do not
in consequence vary In several cases however insects found living on
different plants have been observed by Mr Walsh to present in their
larval or mature state or in both states slight though constant
differences in colour size or in the nature of their secretions
In some instances the males alone in other instances both males and
females have been observed thus to differ in a slight degree When the
differences are rather more strongly marked and when both sexes and
all ages are affected the forms are ranked by all entomologists as good
species But no observer can determine for another even if he can do so
for himself which of these Phytophagic forms ought to be called species
and which varieties Mr Walsh ranks the forms which it may be supposed
would freely intercross as varieties and those which appear to have
lost this power as species As the differences depend on the insects
having long fed on distinct plants it cannot be expected that
intermediate links connecting the several forms should now be found
The naturalist thus loses his best guide in determining whether to rank
doubtful forms as varieties or species This likewise necessarily occurs
with closely allied organisms which inhabit distinct continents or
islands When on the other hand an animal or plant ranges over the
same continent or inhabits many islands in the same archipelago and
presents different forms in the different areas there is always a
good chance that intermediate forms will be discovered which will link
together the extreme states and these are then degraded to the rank of
varieties

Some few naturalists maintain that animals never present varieties but
then these same naturalists rank the slightest difference as of specific
value and when the same identical form is met with in two distant
countries or in two geological formations they believe that two
distinct species are hidden under the same dress The term species thus
comes to be a mere useless abstraction implying and assuming a separate
act of creation It is certain that many forms considered by highly
competent judges to be varieties resemble species so completely in
character that they have been thus ranked by other highly competent
judges But to discuss whether they ought to be called species or
varieties before any definition of these terms has been generally
accepted is vainly to beat the air

Many of the cases of strongly marked varieties or doubtful species well
deserve consideration for several interesting lines of argument from
geographical distribution analogical variation hybridism etc have
been brought to bear in the attempt to determine their rank but space
does not here permit me to discuss them Close investigation in many
cases will no doubt bring naturalists to agree how to rank doubtful
forms Yet it must be confessed that it is in the best known countries
that we find the greatest number of them I have been struck with the
fact that if any animal or plant in a state of nature be highly useful
to man or from any cause closely attracts his attention varieties of
it will almost universally be found recorded These varieties moreover
will often be ranked by some authors as species Look at the common oak
how closely it has been studied yet a German author makes more than a
dozen species out of forms which are almost universally considered
by other botanists to be varieties and in this country the highest
botanical authorities and practical men can be quoted to show that the
sessile and pedunculated oaks are either good and distinct species or
mere varieties

I may here allude to a remarkable memoir lately published by A de
Candolle on the oaks of the whole world No one ever had more ample
materials for the discrimination of the species or could have worked on
them with more zeal and sagacity He first gives in detail all the many
points of structure which vary in the several species and estimates
numerically the relative frequency of the variations He specifies above
a dozen characters which may be found varying even on the same branch
sometimes according to age or development sometimes without any
assignable reason Such characters are not of course of specific value
but they are as Asa Gray has remarked in commenting on this memoir
such as generally enter into specific definitions De Candolle then goes
on to say that he gives the rank of species to the forms that differ by
characters never varying on the same tree and never found connected
by intermediate states After this discussion the result of so much
labour he emphatically remarks They are mistaken who repeat that the
greater part of our species are clearly limited and that the doubtful
species are in a feeble minority This seemed to be true so long as
a genus was imperfectly known and its species were founded upon a few
specimens that is to say were provisional Just as we come to know
them better intermediate forms flow in and doubts as to specific
limits augment He also adds that it is the best known species which
present the greatest number of spontaneous varieties and subvarieties
Thus Quercus robur has twentyeight varieties all of which excepting
six are clustered round three subspecies namely Q pedunculata
sessiliflora and pubescens The forms which connect these three
subspecies are comparatively rare and as Asa Gray again remarks if
these connecting forms which are now rare were to become totally extinct
the three subspecies would hold exactly the same relation to each other
as do the four or five provisionally admitted species which closely
surround the typical Quercus robur Finally De Candolle admits that
out of the 300 species which will be enumerated in his Prodromus
as belonging to the oak family at least twothirds are provisional
species that is are not known strictly to fulfil the definition above
given of a true species It should be added that De Candolle no longer
believes that species are immutable creations but concludes that the
derivative theory is the most natural one and the most accordant with
the known facts in palaeontology geographical botany and zoology of
anatomical structure and classification

When a young naturalist commences the study of a group of organisms
quite unknown to him he is at first much perplexed in determining what
differences to consider as specific and what as varietal for he knows
nothing of the amount and kind of variation to which the group is
subject and this shows at least how very generally there is some
variation But if he confine his attention to one class within one
country he will soon make up his mind how to rank most of the doubtful
forms His general tendency will be to make many species for he will
become impressed just like the pigeon or poultry fancier before alluded
to with the amount of difference in the forms which he is continually
studying and he has little general knowledge of analogical variation
in other groups and in other countries by which to correct his first
impressions As he extends the range of his observations he will meet
with more cases of difficulty for he will encounter a greater number of
closelyallied forms But if his observations be widely extended he
will in the end generally be able to make up his own mind but he will
succeed in this at the expense of admitting much variation and the
truth of this admission will often be disputed by other naturalists
When he comes to study allied forms brought from countries not now
continuous in which case he cannot hope to find intermediate links
he will be compelled to trust almost entirely to analogy and his
difficulties will rise to a climax

Certainly no clear line of demarcation has as yet been drawn between
species and subspecies that is the forms which in the opinion of some
naturalists come very near to but do not quite arrive at the rank of
species or again between subspecies and wellmarked varieties or
between lesser varieties and individual differences These differences
blend into each other by an insensible series and a series impresses
the mind with the idea of an actual passage

Hence I look at individual differences though of small interest to the
systematist as of the highest importance for us as being the first
step towards such slight varieties as are barely thought worth recording
in works on natural history And I look at varieties which are in any
degree more distinct and permanent as steps toward more strongly marked
and permanent varieties and at the latter as leading to subspecies
and then to species The passage from one stage of difference to another
may in many cases be the simple result of the nature of the organism
and of the different physical conditions to which it has long been
exposed but with respect to the more important and adaptive characters
the passage from one stage of difference to another may be safely
attributed to the cumulative action of natural selection hereafter
to be explained and to the effects of the increased use or disuse
of parts A wellmarked variety may therefore be called an incipient
species but whether this belief is justifiable must be judged by the
weight of the various facts and considerations to be given throughout
this work

It need not be supposed that all varieties or incipient species attain
the rank of species They may become extinct or they may endure as
varieties for very long periods as has been shown to be the case by Mr
Wollaston with the varieties of certain fossil landshells in Madeira
and with plants by Gaston de Saporta If a variety were to flourish so
as to exceed in numbers the parent species it would then rank as the
species and the species as the variety or it might come to supplant
and exterminate the parent species or both might coexist and both
rank as independent species But we shall hereafter return to this
subject

From these remarks it will be seen that I look at the term species
as one arbitrarily given for the sake of convenience to a set
of individuals closely resembling each other and that it does not
essentially differ from the term variety which is given to less
distinct and more fluctuating forms The term variety again
in comparison with mere individual differences is also applied
arbitrarily for convenience sake

WIDERANGING MUCH DIFFUSED AND COMMON SPECIES VARY MOST

Guided by theoretical considerations I thought that some interesting
results might be obtained in regard to the nature and relations of the
species which vary most by tabulating all the varieties in several
wellworked floras At first this seemed a simple task but Mr HC
Watson to whom I am much indebted for valuable advice and assistance
on this subject soon convinced me that there were many difficulties as
did subsequently Dr Hooker even in stronger terms I shall reserve for
a future work the discussion of these difficulties and the tables of
the proportional numbers of the varying species Dr Hooker permits me
to add that after having carefully read my manuscript and examined
the tables he thinks that the following statements are fairly well
established The whole subject however treated as it necessarily here
is with much brevity is rather perplexing and allusions cannot be
avoided to the struggle for existence divergence of character and
other questions hereafter to be discussed

Alphonse de Candolle and others have shown that plants which have
very wide ranges generally present varieties and this might have been
expected as they are exposed to diverse physical conditions and as
they come into competition which as we shall hereafter see is a far
more important circumstance with different sets of organic beings But
my tables further show that in any limited country the species which
are the most common that is abound most in individuals and the species
which are most widely diffused within their own country and this is a
different consideration from wide range and to a certain extent from
commonness oftenest give rise to varieties sufficiently wellmarked to
have been recorded in botanical works Hence it is the most flourishing
or as they may be called the dominant species those which range
widely are the most diffused in their own country and are the most
numerous in individuals which oftenest produce wellmarked varieties
or as I consider them incipient species And this perhaps might have
been anticipated for as varieties in order to become in any degree
permanent necessarily have to struggle with the other inhabitants of
the country the species which are already dominant will be the most
likely to yield offspring which though in some slight degree modified
still inherit those advantages that enabled their parents to become
dominant over their compatriots In these remarks on predominence it
should be understood that reference is made only to the forms which come
into competition with each other and more especially to the members
of the same genus or class having nearly similar habits of life With
respect to the number of individuals or commonness of species the
comparison of course relates only to the members of the same group One
of the higher plants may be said to be dominant if it be more numerous
in individuals and more widely diffused than the other plants of the
same country which live under nearly the same conditions A plant of
this kind is not the less dominant because some conferva inhabiting
the water or some parasitic fungus is infinitely more numerous in
individuals and more widely diffused But if the conferva or parasitic
fungus exceeds its allies in the above respects it will then be
dominant within its own class

SPECIES OF THE LARGER GENERA IN EACH COUNTRY VARY MORE FREQUENTLY THAN
THE SPECIES OF THE SMALLER GENERA

If the plants inhabiting a country as described in any Flora be divided
into two equal masses all those in the larger genera ie those
including many species being placed on one side and all those in the
smaller genera on the other side the former will be found to include a
somewhat larger number of the very common and much diffused or dominant
species This might have been anticipated for the mere fact of many
species of the same genus inhabiting any country shows that there
is something in the organic or inorganic conditions of that country
favourable to the genus and consequently we might have expected to
have found in the larger genera or those including many species a
larger proportional number of dominant species But so many causes tend
to obscure this result that I am surprised that my tables show even a
small majority on the side of the larger genera I will here allude
to only two causes of obscurity Fresh water and saltloving plants
generally have very wide ranges and are much diffused but this seems to
be connected with the nature of the stations inhabited by them and has
little or no relation to the size of the genera to which the species
belong Again plants low in the scale of organisation are generally
much more widely diffused than plants higher in the scale and here
again there is no close relation to the size of the genera The cause of
lowlyorganised plants ranging widely will be discussed in our chapter
on Geographical Distribution

From looking at species as only strongly marked and welldefined
varieties I was led to anticipate that the species of the larger genera
in each country would oftener present varieties than the species of the
smaller genera for wherever many closely related species ie species
of the same genus have been formed many varieties or incipient species
ought as a general rule to be now forming Where many large trees
grow we expect to find saplings Where many species of a genus have
been formed through variation circumstances have been favourable
for variation and hence we might expect that the circumstances would
generally still be favourable to variation On the other hand if we
look at each species as a special act of creation there is no apparent
reason why more varieties should occur in a group having many species
than in one having few

To test the truth of this anticipation I have arranged the plants of
twelve countries and the coleopterous insects of two districts into
two nearly equal masses the species of the larger genera on one side
and those of the smaller genera on the other side and it has invariably
proved to be the case that a larger proportion of the species on the
side of the larger genera presented varieties than on the side of the
smaller genera Moreover the species of the large genera which present
any varieties invariably present a larger average number of varieties
than do the species of the small genera Both these results follow when
another division is made and when all the least genera with from only
one to four species are altogether excluded from the tables These
facts are of plain signification on the view that species are only
strongly marked and permanent varieties for wherever many species of
the same genus have been formed or where if we may use the expression
the manufactory of species has been active we ought generally to find
the manufactory still in action more especially as we have every reason
to believe the process of manufacturing new species to be a slow one
And this certainly holds true if varieties be looked at as incipient
species for my tables clearly show as a general rule that wherever
many species of a genus have been formed the species of that genus
present a number of varieties that is of incipient species beyond the
average It is not that all large genera are now varying much and are
thus increasing in the number of their species or that no small genera
are now varying and increasing for if this had been so it would have
been fatal to my theory inasmuch as geology plainly tells us that small
genera have in the lapse of time often increased greatly in size
and that large genera have often come to their maxima declined and
disappeared All that we want to show is that where many species of a
genus have been formed on an average many are still forming and this
certainly holds good

MANY OF THE SPECIES INCLUDED WITHIN THE LARGER GENERA RESEMBLE VARIETIES
IN BEING VERY CLOSELY BUT UNEQUALLY RELATED TO EACH OTHER AND IN
HAVING RESTRICTED RANGES

There are other relations between the species of large genera and their
recorded varieties which deserve notice We have seen that there is no
infallible criterion by which to distinguish species and wellmarked
varieties and when intermediate links have not been found between
doubtful forms naturalists are compelled to come to a determination by
the amount of difference between them judging by analogy whether or not
the amount suffices to raise one or both to the rank of species Hence
the amount of difference is one very important criterion in settling
whether two forms should be ranked as species or varieties Now Fries
has remarked in regard to plants and Westwood in regard to insects
that in large genera the amount of difference between the species is
often exceedingly small I have endeavoured to test this numerically by
averages and as far as my imperfect results go they confirm the view
I have also consulted some sagacious and experienced observers
and after deliberation they concur in this view In this respect
therefore the species of the larger genera resemble varieties more
than do the species of the smaller genera Or the case may be put in
another way and it may be said that in the larger genera in which a
number of varieties or incipient species greater than the average are
now manufacturing many of the species already manufactured still to a
certain extent resemble varieties for they differ from each other by a
less than the usual amount of difference

Moreover the species of the larger genera are related to each other in
the same manner as the varieties of any one species are related to
each other No naturalist pretends that all the species of a genus are
equally distinct from each other they may generally be divided into
subgenera or sections or lesser groups As Fries has well remarked
little groups of species are generally clustered like satellites around
other species And what are varieties but groups of forms unequally
related to each other and clustered round certain forms that is round
their parentspecies Undoubtedly there is one most important point of
difference between varieties and species namely that the amount of
difference between varieties when compared with each other or with
their parentspecies is much less than that between the species of the
same genus But when we come to discuss the principle as I call it of
divergence of character we shall see how this may be explained and
how the lesser differences between varieties tend to increase into the
greater differences between species

There is one other point which is worth notice Varieties generally have
much restricted ranges This statement is indeed scarcely more than a
truism for if a variety were found to have a wider range than that of
its supposed parentspecies their denominations would be reversed
But there is reason to believe that the species which are very closely
allied to other species and in so far resemble varieties often have
much restricted ranges For instance Mr HC Watson has marked for me
in the wellsifted London catalogue of Plants 4th edition sixtythree
plants which are therein ranked as species but which he considers as
so closely allied to other species as to be of doubtful value these
sixtythree reputed species range on an average over 69 of the
provinces into which Mr Watson has divided Great Britain Now in this
same catalogue fiftythree acknowledged varieties are recorded and
these range over 77 provinces whereas the species to which these
varieties belong range over 143 provinces So that the acknowledged
varieties have very nearly the same restricted average range as have
the closely allied forms marked for me by Mr Watson as doubtful
species but which are almost universally ranked by British botanists as
good and true species

SUMMARY

Finally varieties cannot be distinguished from species except first
by the discovery of intermediate linking forms and secondly by a
certain indefinite amount of difference between them for two forms
if differing very little are generally ranked as varieties
notwithstanding that they cannot be closely connected but the amount
of difference considered necessary to give to any two forms the rank of
species cannot be defined In genera having more than the average number
of species in any country the species of these genera have more than
the average number of varieties In large genera the species are apt to
be closely but unequally allied together forming little clusters round
other species Species very closely allied to other species apparently
have restricted ranges In all these respects the species of large
genera present a strong analogy with varieties And we can clearly
understand these analogies if species once existed as varieties and
thus originated whereas these analogies are utterly inexplicable if
species are independent creations

We have also seen that it is the most flourishing or dominant species
of the larger genera within each class which on an average yield the
greatest number of varieties and varieties as we shall hereafter see
tend to become converted into new and distinct species Thus the larger
genera tend to become larger and throughout nature the forms of life
which are now dominant tend to become still more dominant by leaving
many modified and dominant descendants But by steps hereafter to be
explained the larger genera also tend to break up into smaller genera
And thus the forms of life throughout the universe become divided into
groups subordinate to groups




CHAPTER III STRUGGLE FOR EXISTENCE

 Its bearing on natural selection The term used in a wide
 sense Geometrical ratio of increase Rapid increase of naturalised
 animals and plants Nature of the checks to increase Competition
 universal Effects of climate Protection from the number of
 individuals Complex relations of all animals and plants throughout
 nature Struggle for life most severe between individuals and varieties
 of the same species often severe between species of the same genus The
 relation of organism to organism the most important of all relations

Before entering on the subject of this chapter I must make a few
preliminary remarks to show how the struggle for existence bears on
natural selection It has been seen in the last chapter that
among organic beings in a state of nature there is some individual
variability indeed I am not aware that this has ever been disputed
It is immaterial for us whether a multitude of doubtful forms be called
species or subspecies or varieties what rank for instance the two or
three hundred doubtful forms of British plants are entitled to hold
if the existence of any wellmarked varieties be admitted But the
mere existence of individual variability and of some few wellmarked
varieties though necessary as the foundation for the work helps us but
little in understanding how species arise in nature How have all those
exquisite adaptations of one part of the organisation to another part
and to the conditions of life and of one organic being to another being
been perfected We see these beautiful coadaptations most plainly in
the woodpecker and the mistletoe and only a little less plainly in the
humblest parasite which clings to the hairs of a quadruped or feathers
of a bird in the structure of the beetle which dives through the water
in the plumed seed which is wafted by the gentlest breeze in short we
see beautiful adaptations everywhere and in every part of the organic
world

Again it may be asked how is it that varieties which I have called
incipient species become ultimately converted into good and distinct
species which in most cases obviously differ from each other far
more than do the varieties of the same species How do those groups
of species which constitute what are called distinct genera and which
differ from each other more than do the species of the same genus
arise All these results as we shall more fully see in the next
chapter follow from the struggle for life Owing to this struggle
variations however slight and from whatever cause proceeding if they
be in any degree profitable to the individuals of a species in their
infinitely complex relations to other organic beings and to their
physical conditions of life will tend to the preservation of such
individuals and will generally be inherited by the offspring The
offspring also will thus have a better chance of surviving for of
the many individuals of any species which are periodically born but a
small number can survive I have called this principle by which
each slight variation if useful is preserved by the term natural
selection in order to mark its relation to mans power of selection
But the expression often used by Mr Herbert Spencer of the Survival of
the Fittest is more accurate and is sometimes equally convenient We
have seen that man by selection can certainly produce great results and
can adapt organic beings to his own uses through the accumulation of
slight but useful variations given to him by the hand of Nature But
Natural Selection we shall hereafter see is a power incessantly ready
for action and is as immeasurably superior to mans feeble efforts as
the works of Nature are to those of Art

We will now discuss in a little more detail the struggle for existence
In my future work this subject will be treated as it well deserves
at greater length The elder De Candolle and Lyell have largely and
philosophically shown that all organic beings are exposed to severe
competition In regard to plants no one has treated this subject with
more spirit and ability than W Herbert Dean of Manchester evidently
the result of his great horticultural knowledge Nothing is easier than
to admit in words the truth of the universal struggle for life or
more difficult at least I found it so than constantly to bear this
conclusion in mind Yet unless it be thoroughly engrained in the mind
the whole economy of nature with every fact on distribution rarity
abundance extinction and variation will be dimly seen or quite
misunderstood We behold the face of nature bright with gladness we
often see superabundance of food we do not see or we forget that the
birds which are idly singing round us mostly live on insects or seeds
and are thus constantly destroying life or we forget how largely these
songsters or their eggs or their nestlings are destroyed by birds and
beasts of prey we do not always bear in mind that though food may be
now superabundant it is not so at all seasons of each recurring year

THE TERM STRUGGLE FOR EXISTENCE USED IN A LARGE SENSE

I should premise that I use this term in a large and metaphorical sense
including dependence of one being on another and including which is
more important not only the life of the individual but success in
leaving progeny Two canine animals in a time of dearth may be truly
said to struggle with each other which shall get food and live But a
plant on the edge of a desert is said to struggle for life against the
drought though more properly it should be said to be dependent on the
moisture A plant which annually produces a thousand seeds of which
only one of an average comes to maturity may be more truly said to
struggle with the plants of the same and other kinds which already
clothe the ground The mistletoe is dependent on the apple and a few
other trees but can only in a farfetched sense be said to struggle
with these trees for if too many of these parasites grow on the same
tree it languishes and dies But several seedling mistletoes growing
close together on the same branch may more truly be said to struggle
with each other As the mistletoe is disseminated by birds its
existence depends on them and it may metaphorically be said to struggle
with other fruitbearing plants in tempting the birds to devour and
thus disseminate its seeds In these several senses which pass into
each other I use for convenience sake the general term of Struggle for
Existence

GEOMETRICAL RATIO OF INCREASE

A struggle for existence inevitably follows from the high rate at which
all organic beings tend to increase Every being which during its
natural lifetime produces several eggs or seeds must suffer destruction
during some period of its life and during some season or occasional
year otherwise on the principle of geometrical increase its numbers
would quickly become so inordinately great that no country could support
the product Hence as more individuals are produced than can possibly
survive there must in every case be a struggle for existence either
one individual with another of the same species or with the individuals
of distinct species or with the physical conditions of life It is the
doctrine of Malthus applied with manifold force to the whole animal and
vegetable kingdoms for in this case there can be no artificial increase
of food and no prudential restraint from marriage Although some
species may be now increasing more or less rapidly in numbers all
cannot do so for the world would not hold them

There is no exception to the rule that every organic being naturally
increases at so high a rate that if not destroyed the earth would
soon be covered by the progeny of a single pair Even slowbreeding
man has doubled in twentyfive years and at this rate in less than
a thousand years there would literally not be standing room for his
progeny Linnaeus has calculated that if an annual plant produced only
two seeds and there is no plant so unproductive as this and their
seedlings next year produced two and so on then in twenty years there
would be a million plants The elephant is reckoned the slowest breeder
of all known animals and I have taken some pains to estimate its
probable minimum rate of natural increase it will be safest to assume
that it begins breeding when thirty years old and goes on breeding
till ninety years old bringing forth six young in the interval and
surviving till one hundred years old if this be so after a period of
from 740 to 750 years there would be nearly nineteen million elephants
alive descended from the first pair

But we have better evidence on this subject than mere theoretical
calculations namely the numerous recorded cases of the astonishingly
rapid increase of various animals in a state of nature when
circumstances have been favourable to them during two or three following
seasons Still more striking is the evidence from our domestic animals
of many kinds which have run wild in several parts of the world if the
statements of the rate of increase of slowbreeding cattle and horses
in South America and latterly in Australia had not been well
authenticated they would have been incredible So it is with plants
cases could be given of introduced plants which have become common
throughout whole islands in a period of less than ten years Several of
the plants such as the cardoon and a tall thistle which are now the
commonest over the wide plains of La Plata clothing square leagues
of surface almost to the exclusion of every other plant have been
introduced from Europe and there are plants which now range in India
as I hear from Dr Falconer from Cape Comorin to the Himalaya which
have been imported from America since its discovery In such cases and
endless others could be given no one supposes that the fertility of
the animals or plants has been suddenly and temporarily increased in any
sensible degree The obvious explanation is that the conditions of life
have been highly favourable and that there has consequently been less
destruction of the old and young and that nearly all the young have been
enabled to breed Their geometrical ratio of increase the result
of which never fails to be surprising simply explains their
extraordinarily rapid increase and wide diffusion in their new homes

In a state of nature almost every fullgrown plant annually produces
seed and among animals there are very few which do not annually pair
Hence we may confidently assert that all plants and animals are tending
to increase at a geometrical ratio that all would rapidly stock every
station in which they could any how exist and that this geometrical
tendency to increase must be checked by destruction at some period of
life Our familiarity with the larger domestic animals tends I think
to mislead us we see no great destruction falling on them and we do
not keep in mind that thousands are annually slaughtered for food
and that in a state of nature an equal number would have somehow to be
disposed of

The only difference between organisms which annually produce eggs or
seeds by the thousand and those which produce extremely few is
that the slow breeders would require a few more years to people under
favourable conditions a whole district let it be ever so large The
condor lays a couple of eggs and the ostrich a score and yet in the
same country the condor may be the more numerous of the two The Fulmar
petrel lays but one egg yet it is believed to be the most numerous bird
in the world One fly deposits hundreds of eggs and another like the
hippobosca a single one But this difference does not determine how
many individuals of the two species can be supported in a district A
large number of eggs is of some importance to those species which depend
on a fluctuating amount of food for it allows them rapidly to increase
in number But the real importance of a large number of eggs or seeds is
to make up for much destruction at some period of life and this period
in the great majority of cases is an early one If an animal can in any
way protect its own eggs or young a small number may be produced and
yet the average stock be fully kept up but if many eggs or young are
destroyed many must be produced or the species will become extinct It
would suffice to keep up the full number of a tree which lived on an
average for a thousand years if a single seed were produced once in a
thousand years supposing that this seed were never destroyed and could
be ensured to germinate in a fitting place so that in all cases the
average number of any animal or plant depends only indirectly on the
number of its eggs or seeds

In looking at Nature it is most necessary to keep the foregoing
considerations always in mind never to forget that every single organic
being may be said to be striving to the utmost to increase in numbers
that each lives by a struggle at some period of its life that heavy
destruction inevitably falls either on the young or old during each
generation or at recurrent intervals Lighten any check mitigate the
destruction ever so little and the number of the species will almost
instantaneously increase to any amount

NATURE OF THE CHECKS TO INCREASE

The causes which check the natural tendency of each species to increase
are most obscure Look at the most vigorous species by as much as it
swarms in numbers by so much will it tend to increase still further We
know not exactly what the checks are even in a single instance Nor will
this surprise any one who reflects how ignorant we are on this head
even in regard to mankind although so incomparably better known than
any other animal This subject of the checks to increase has been ably
treated by several authors and I hope in a future work to discuss it at
considerable length more especially in regard to the feral animals of
South America Here I will make only a few remarks just to recall to
the readers mind some of the chief points Eggs or very young animals
seem generally to suffer most but this is not invariably the case With
plants there is a vast destruction of seeds but from some observations
which I have made it appears that the seedlings suffer most from
germinating in ground already thickly stocked with other plants
Seedlings also are destroyed in vast numbers by various enemies for
instance on a piece of ground three feet long and two wide dug and
cleared and where there could be no choking from other plants I marked
all the seedlings of our native weeds as they came up and out of 357
no less than 295 were destroyed chiefly by slugs and insects If turf
which has long been mown and the case would be the same with turf
closely browsed by quadrupeds be let to grow the more vigorous plants
gradually kill the less vigorous though fully grown plants thus out of
twenty species grown on a little plot of mown turf three feet by four
nine species perished from the other species being allowed to grow up
freely

The amount of food for each species of course gives the extreme limit
to which each can increase but very frequently it is not the obtaining
food but the serving as prey to other animals which determines the
average number of a species Thus there seems to be little doubt that
the stock of partridges grouse and hares on any large estate depends
chiefly on the destruction of vermin If not one head of game were shot
during the next twenty years in England and at the same time if no
vermin were destroyed there would in all probability be less game
than at present although hundreds of thousands of game animals are now
annually shot On the other hand in some cases as with the elephant
none are destroyed by beasts of prey for even the tiger in India most
rarely dares to attack a young elephant protected by its dam

Climate plays an important part in determining the average numbers of
a species and periodical seasons of extreme cold or drought seem to be
the most effective of all checks I estimated chiefly from the greatly
reduced numbers of nests in the spring that the winter of 18545
destroyed fourfifths of the birds in my own grounds and this is
a tremendous destruction when we remember that ten per cent is an
extraordinarily severe mortality from epidemics with man The action of
climate seems at first sight to be quite independent of the struggle for
existence but in so far as climate chiefly acts in reducing food it
brings on the most severe struggle between the individuals whether of
the same or of distinct species which subsist on the same kind of food
Even when climate for instance extreme cold acts directly it will
be the least vigorous individuals or those which have got least food
through the advancing winter which will suffer the most When we travel
from south to north or from a damp region to a dry we invariably
see some species gradually getting rarer and rarer and finally
disappearing and the change of climate being conspicuous we are
tempted to attribute the whole effect to its direct action But this is
a false view we forget that each species even where it most abounds
is constantly suffering enormous destruction at some period of its life
from enemies or from competitors for the same place and food and if
these enemies or competitors be in the least degree favoured by any
slight change of climate they will increase in numbers and as each
area is already fully stocked with inhabitants the other species must
decrease When we travel southward and see a species decreasing in
numbers we may feel sure that the cause lies quite as much in other
species being favoured as in this one being hurt So it is when we
travel northward but in a somewhat lesser degree for the number of
species of all kinds and therefore of competitors decreases northward
hence in going northward or in ascending a mountain we far oftener
meet with stunted forms due to the DIRECTLY injurious action of
climate than we do in proceeding southward or in descending a mountain
When we reach the Arctic regions or snowcapped summits or absolute
deserts the struggle for life is almost exclusively with the elements

That climate acts in main part indirectly by favouring other species we
clearly see in the prodigious number of plants which in our gardens can
perfectly well endure our climate but which never become naturalised
for they cannot compete with our native plants nor resist destruction by
our native animals

When a species owing to highly favourable circumstances increases
inordinately in numbers in a small tract epidemics at least this
seems generally to occur with our game animals often ensue and here
we have a limiting check independent of the struggle for life But even
some of these socalled epidemics appear to be due to parasitic worms
which have from some cause possibly in part through facility of
diffusion among the crowded animals been disproportionally favoured
and here comes in a sort of struggle between the parasite and its prey

On the other hand in many cases a large stock of individuals of the
same species relatively to the numbers of its enemies is absolutely
necessary for its preservation Thus we can easily raise plenty of
corn and rapeseed etc in our fields because the seeds are in great
excess compared with the number of birds which feed on them nor can
the birds though having a superabundance of food at this one season
increase in number proportionally to the supply of seed as their
numbers are checked during the winter but any one who has tried knows
how troublesome it is to get seed from a few wheat or other such plants
in a garden I have in this case lost every single seed This view of
the necessity of a large stock of the same species for its preservation
explains I believe some singular facts in nature such as that of very
rare plants being sometimes extremely abundant in the few spots where
they do exist and that of some social plants being social that is
abounding in individuals even on the extreme verge of their range For
in such cases we may believe that a plant could exist only where
the conditions of its life were so favourable that many could exist
together and thus save the species from utter destruction I should
add that the good effects of intercrossing and the ill effects of close
interbreeding no doubt come into play in many of these cases but I
will not here enlarge on this subject

COMPLEX RELATIONS OF ALL ANIMALS AND PLANTS TO EACH OTHER IN THE
STRUGGLE FOR EXISTENCE

Many cases are on record showing how complex and unexpected are the
checks and relations between organic beings which have to struggle
together in the same country I will give only a single instance which
though a simple one interested me In Staffordshire on the estate of
a relation where I had ample means of investigation there was a large
and extremely barren heath which had never been touched by the hand
of man but several hundred acres of exactly the same nature had been
enclosed twentyfive years previously and planted with Scotch fir The
change in the native vegetation of the planted part of the heath was
most remarkable more than is generally seen in passing from one quite
different soil to another not only the proportional numbers of the
heathplants were wholly changed but twelve species of plants not
counting grasses and carices flourished in the plantations which could
not be found on the heath The effect on the insects must have been
still greater for six insectivorous birds were very common in the
plantations which were not to be seen on the heath and the heath was
frequented by two or three distinct insectivorous birds Here we see how
potent has been the effect of the introduction of a single tree nothing
whatever else having been done with the exception of the land having
been enclosed so that cattle could not enter But how important an
element enclosure is I plainly saw near Farnham in Surrey Here
there are extensive heaths with a few clumps of old Scotch firs on
the distant hilltops within the last ten years large spaces have been
enclosed and selfsown firs are now springing up in multitudes so
close together that all cannot live When I ascertained that these young
trees had not been sown or planted I was so much surprised at their
numbers that I went to several points of view whence I could examine
hundreds of acres of the unenclosed heath and literally I could not
see a single Scotch fir except the old planted clumps But on looking
closely between the stems of the heath I found a multitude of seedlings
and little trees which had been perpetually browsed down by the cattle
In one square yard at a point some hundred yards distant from one of
the old clumps I counted thirtytwo little trees and one of them with
twentysix rings of growth had during many years tried to raise its
head above the stems of the heath and had failed No wonder that as
soon as the land was enclosed it became thickly clothed with vigorously
growing young firs Yet the heath was so extremely barren and so
extensive that no one would ever have imagined that cattle would have so
closely and effectually searched it for food

Here we see that cattle absolutely determine the existence of the Scotch
fir but in several parts of the world insects determine the existence
of cattle Perhaps Paraguay offers the most curious instance of this
for here neither cattle nor horses nor dogs have ever run wild though
they swarm southward and northward in a feral state and Azara and
Rengger have shown that this is caused by the greater number in Paraguay
of a certain fly which lays its eggs in the navels of these animals
when first born The increase of these flies numerous as they are
must be habitually checked by some means probably by other parasitic
insects Hence if certain insectivorous birds were to decrease in
Paraguay the parasitic insects would probably increase and this would
lessen the number of the navelfrequenting flies then cattle and horses
would become feral and this would certainly greatly alter as indeed
I have observed in parts of South America the vegetation this again
would largely affect the insects and this as we have just seen
in Staffordshire the insectivorous birds and so onwards in
everincreasing circles of complexity Not that under nature the
relations will ever be as simple as this Battle within battle must be
continually recurring with varying success and yet in the longrun the
forces are so nicely balanced that the face of nature remains for long
periods of time uniform though assuredly the merest trifle would give
the victory to one organic being over another Nevertheless so profound
is our ignorance and so high our presumption that we marvel when we
hear of the extinction of an organic being and as we do not see the
cause we invoke cataclysms to desolate the world or invent laws on the
duration of the forms of life 

I am tempted to give one more instance showing how plants and animals
remote in the scale of nature are bound together by a web of complex
relations I shall hereafter have occasion to show that the exotic
Lobelia fulgens is never visited in my garden by insects and
consequently from its peculiar structure never sets a seed Nearly
all our orchidaceous plants absolutely require the visits of insects
to remove their pollenmasses and thus to fertilise them I find
from experiments that humblebees are almost indispensable to the
fertilisation of the heartsease Viola tricolor for other bees do
not visit this flower I have also found that the visits of bees are
necessary for the fertilisation of some kinds of clover for instance
twenty heads of Dutch clover Trifolium repens yielded 2290 seeds but
twenty other heads protected from bees produced not one Again 100
heads of red clover T pratense produced 2700 seeds but the same
number of protected heads produced not a single seed Humble bees alone
visit red clover as other bees cannot reach the nectar It has been
suggested that moths may fertilise the clovers but I doubt whether they
could do so in the case of the red clover from their weight not being
sufficient to depress the wing petals Hence we may infer as highly
probable that if the whole genus of humblebees became extinct or very
rare in England the heartsease and red clover would become very rare
or wholly disappear The number of humblebees in any district depends
in a great measure upon the number of fieldmice which destroy their
combs and nests and Colonel Newman who has long attended to the habits
of humblebees believes that more than twothirds of them are
thus destroyed all over England Now the number of mice is largely
dependent as every one knows on the number of cats and Colonel
Newman says Near villages and small towns I have found the nests
of humblebees more numerous than elsewhere which I attribute to the
number of cats that destroy the mice Hence it is quite credible that
the presence of a feline animal in large numbers in a district might
determine through the intervention first of mice and then of bees the
frequency of certain flowers in that district 

In the case of every species many different checks acting at different
periods of life and during different seasons or years probably come
into play some one check or some few being generally the most potent
but all will concur in determining the average number or even
the existence of the species In some cases it can be shown that
widelydifferent checks act on the same species in different districts
When we look at the plants and bushes clothing an entangled bank we
are tempted to attribute their proportional numbers and kinds to what we
call chance But how false a view is this  Every one has heard that when
an American forest is cut down a very different vegetation springs
up but it has been observed that ancient Indian ruins in the Southern
United States which must formerly have been cleared of trees now
display the same beautiful diversity and proportion of kinds as in the
surrounding virgin forests What a struggle must have gone on during
long centuries between the several kinds of trees each annually
scattering its seeds by the thousand what war between insect and
insect between insects snails and other animals with birds and beasts
of prey all striving to increase all feeding on each other or on the
trees their seeds and seedlings or on the other plants which first
clothed the ground and thus checked the growth of the trees Throw up
a handful of feathers and all fall to the ground according to definite
laws but how simple is the problem where each shall fall compared to
that of the action and reaction of the innumerable plants and animals
which have determined in the course of centuries the proportional
numbers and kinds of trees now growing on the old Indian ruins 

The dependency of one organic being on another as of a parasite on its
prey lies generally between beings remote in the scale of nature This
is likewise sometimes the case with those which may strictly be said to
struggle with each other for existence as in the case of locusts and
grassfeeding quadrupeds But the struggle will almost invariably
be most severe between the individuals of the same species for they
frequent the same districts require the same food and are exposed
to the same dangers In the case of varieties of the same species the
struggle will generally be almost equally severe and we sometimes see
the contest soon decided for instance if several varieties of wheat be
sown together and the mixed seed be resown some of the varieties which
best suit the soil or climate or are naturally the most fertile will
beat the others and so yield more seed and will consequently in a few
years supplant the other varieties To keep up a mixed stock of even
such extremely close varieties as the variously coloured sweetpeas
they must be each year harvested separately and the seed then mixed
in due proportion otherwise the weaker kinds will steadily decrease in
number and disappear So again with the varieties of sheep it has
been asserted that certain mountainvarieties will starve out other
mountainvarieties so that they cannot be kept together The same
result has followed from keeping together different varieties of the
medicinal leech It may even be doubted whether the varieties of any
of our domestic plants or animals have so exactly the same strength
habits and constitution that the original proportions of a mixed
stock crossing being prevented could be kept up for halfadozen
generations if they were allowed to struggle together in the same
manner as beings in a state of nature and if the seed or young were not
annually preserved in due proportion

STRUGGLE FOR LIFE MOST SEVERE BETWEEN INDIVIDUALS AND VARIETIES OF THE
SAME SPECIES

As the species of the same genus usually have though by no means
invariably much similarity in habits and constitution and always in
structure the struggle will generally be more severe between them if
they come into competition with each other than between the species of
distinct genera We see this in the recent extension over parts of the
United States of one species of swallow having caused the decrease of
another species The recent increase of the misselthrush in parts of
Scotland has caused the decrease of the songthrush How frequently we
hear of one species of rat taking the place of another species under
the most different climates  In Russia the small Asiatic cockroach
has everywhere driven before it its great congener In Australia the
imported hivebee is rapidly exterminating the small stingless native
bee One species of charlock has been known to supplant another species
and so in other cases We can dimly see why the competition should be
most severe between allied forms which fill nearly the same place in
the economy of nature but probably in no one case could we precisely
say why one species has been victorious over another in the great battle
of life

A corollary of the highest importance may be deduced from the foregoing
remarks namely that the structure of every organic being is related
in the most essential yet often hidden manner to that of all other
organic beings with which it comes into competition for food or
residence or from which it has to escape or on which it preys This
is obvious in the structure of the teeth and talons of the tiger and in
that of the legs and claws of the parasite which clings to the hair on
the tigers body But in the beautifully plumed seed of the dandelion
and in the flattened and fringed legs of the waterbeetle the relation
seems at first confined to the elements of air and water Yet the
advantage of the plumed seeds no doubt stands in the closest relation
to the land being already thickly clothed with other plants so that the
seeds may be widely distributed and fall on unoccupied ground In the
waterbeetle the structure of its legs so well adapted for diving
allows it to compete with other aquatic insects to hunt for its own
prey and to escape serving as prey to other animals

The store of nutriment laid up within the seeds of many plants seems at
first sight to have no sort of relation to other plants But from the
strong growth of young plants produced from such seeds as peas and
beans when sown in the midst of long grass it may be suspected that
the chief use of the nutriment in the seed is to favour the growth of
the seedlings whilst struggling with other plants growing vigorously
all around

Look at a plant in the midst of its range  Why does it not double or
quadruple its numbers We know that it can perfectly well withstand a
little more heat or cold dampness or dryness for elsewhere it ranges
into slightly hotter or colder damper or drier districts In this case
we can clearly see that if we wish in imagination to give the plant the
power of increasing in numbers we should have to give it some advantage
over its competitors or over the animals which prey on it On the
confines of its geographical range a change of constitution with
respect to climate would clearly be an advantage to our plant but we
have reason to believe that only a few plants or animals range so far
that they are destroyed exclusively by the rigour of the climate Not
until we reach the extreme confines of life in the Arctic regions or on
the borders of an utter desert will competition cease The land may be
extremely cold or dry yet there will be competition between some few
species or between the individuals of the same species for the warmest
or dampest spots

Hence we can see that when a plant or animal is placed in a new country
among new competitors the conditions of its life will generally be
changed in an essential manner although the climate may be exactly the
same as in its former home If its average numbers are to increase in
its new home we should have to modify it in a different way to what we
should have had to do in its native country for we should have to give
it some advantage over a different set of competitors or enemies

It is good thus to try in imagination to give any one species an
advantage over another Probably in no single instance should we know
what to do This ought to convince us of our ignorance on the mutual
relations of all organic beings a conviction as necessary as it is
difficult to acquire All that we can do is to keep steadily in mind
that each organic being is striving to increase in a geometrical ratio
that each at some period of its life during some season of the year
during each generation or at intervals has to struggle for life and
to suffer great destruction When we reflect on this struggle we may
console ourselves with the full belief that the war of nature is not
incessant that no fear is felt that death is generally prompt and
that the vigorous the healthy and the happy survive and multiply




CHAPTER IV NATURAL SELECTION OR THE SURVIVAL OF THE FITTEST

 Natural Selection its power compared with mans selection its power
 on characters of trifling importance its power at all ages and on
 both sexes Sexual Selection On the generality of intercrosses
 between individuals of the same species Circumstances favourable and
 unfavourable to the results of Natural Selection namely intercrossing
 isolation number of individuals Slow action Extinction caused by
 Natural Selection Divergence of Character related to the diversity of
 inhabitants of any small area and to naturalisation Action of Natural
 Selection through Divergence of Character and Extinction on the
 descendants from a common parent Explains the Grouping of all organic
 beings Advance in organisation Low forms preserved Convergence of
 character Indefinite multiplication of species Summary


How will the struggle for existence briefly discussed in the last
chapter act in regard to variation Can the principle of selection
which we have seen is so potent in the hands of man apply under nature
I think we shall see that it can act most efficiently Let the endless
number of slight variations and individual differences occurring in our
domestic productions and in a lesser degree in those under nature be
borne in mind as well as the strength of the hereditary tendency Under
domestication it may truly be said that the whole organisation becomes
in some degree plastic But the variability which we almost universally
meet with in our domestic productions is not directly produced as
Hooker and Asa Gray have well remarked by man he can neither originate
varieties nor prevent their occurrence he can only preserve and
accumulate such as do occur Unintentionally he exposes organic beings
to new and changing conditions of life and variability ensues but
similar changes of conditions might and do occur under nature Let it
also be borne in mind how infinitely complex and closefitting are
the mutual relations of all organic beings to each other and to their
physical conditions of life and consequently what infinitely varied
diversities of structure might be of use to each being under changing
conditions of life Can it then be thought improbable seeing that
variations useful to man have undoubtedly occurred that other
variations useful in some way to each being in the great and complex
battle of life should occur in the course of many successive
generations If such do occur can we doubt remembering that many more
individuals are born than can possibly survive that individuals having
any advantage however slight over others would have the best chance
of surviving and procreating their kind On the other hand we may feel
sure that any variation in the least degree injurious would be rigidly
destroyed This preservation of favourable individual differences and
variations and the destruction of those which are injurious I have
called Natural Selection or the Survival of the Fittest Variations
neither useful nor injurious would not be affected by natural selection
and would be left either a fluctuating element as perhaps we see in
certain polymorphic species or would ultimately become fixed owing to
the nature of the organism and the nature of the conditions

Several writers have misapprehended or objected to the term Natural
Selection Some have even imagined that natural selection induces
variability whereas it implies only the preservation of such variations
as arise and are beneficial to the being under its conditions of life
No one objects to agriculturists speaking of the potent effects of mans
selection and in this case the individual differences given by nature
which man for some object selects must of necessity first occur Others
have objected that the term selection implies conscious choice in the
animals which become modified and it has even been urged that as
plants have no volition natural selection is not applicable to them 
In the literal sense of the word no doubt natural selection is a
false term but who ever objected to chemists speaking of the elective
affinities of the various elements and yet an acid cannot strictly be
said to elect the base with which it in preference combines It has been
said that I speak of natural selection as an active power or Deity but
who objects to an author speaking of the attraction of gravity as ruling
the movements of the planets Every one knows what is meant and is
implied by such metaphorical expressions and they are almost necessary
for brevity So again it is difficult to avoid personifying the word
Nature but I mean by nature only the aggregate action and product of
many natural laws and by laws the sequence of events as ascertained
by us With a little familiarity such superficial objections will be
forgotten

We shall best understand the probable course of natural selection by
taking the case of a country undergoing some slight physical change for
instance of climate The proportional numbers of its inhabitants will
almost immediately undergo a change and some species will probably
become extinct We may conclude from what we have seen of the intimate
and complex manner in which the inhabitants of each country are
bound together that any change in the numerical proportions of the
inhabitants independently of the change of climate itself would
seriously affect the others If the country were open on its borders
new forms would certainly immigrate and this would likewise seriously
disturb the relations of some of the former inhabitants Let it be
remembered how powerful the influence of a single introduced tree or
mammal has been shown to be But in the case of an island or of a
country partly surrounded by barriers into which new and better adapted
forms could not freely enter we should then have places in the economy
of nature which would assuredly be better filled up if some of the
original inhabitants were in some manner modified for had the area
been open to immigration these same places would have been seized on
by intruders In such cases slight modifications which in any way
favoured the individuals of any species by better adapting them to
their altered conditions would tend to be preserved and natural
selection would have free scope for the work of improvement

We have good reason to believe as shown in the first chapter
that changes in the conditions of life give a tendency to increased
variability and in the foregoing cases the conditions the changed and
this would manifestly be favourable to natural selection by affording
a better chance of the occurrence of profitable variations Unless such
occur natural selection can do nothing Under the term of variations
it must never be forgotten that mere individual differences are
included As man can produce a great result with his domestic animals
and plants by adding up in any given direction individual differences
so could natural selection but far more easily from having incomparably
longer time for action Nor do I believe that any great physical change
as of climate or any unusual degree of isolation to check immigration
is necessary in order that new and unoccupied places should be left
for natural selection to fill up by improving some of the varying
inhabitants For as all the inhabitants of each country are struggling
together with nicely balanced forces extremely slight modifications in
the structure or habits of one species would often give it an advantage
over others and still further modifications of the same kind would
often still further increase the advantage as long as the species
continued under the same conditions of life and profited by similar
means of subsistence and defence No country can be named in which all
the native inhabitants are now so perfectly adapted to each other and to
the physical conditions under which they live that none of them could
be still better adapted or improved for in all countries the natives
have been so far conquered by naturalised productions that they have
allowed some foreigners to take firm possession of the land And as
foreigners have thus in every country beaten some of the natives we
may safely conclude that the natives might have been modified with
advantage so as to have better resisted the intruders

As man can produce and certainly has produced a great result by his
methodical and unconscious means of selection what may not natural
selection effect Man can act only on external and visible characters
Nature if I may be allowed to personify the natural preservation or
survival of the fittest cares nothing for appearances except in so far
as they are useful to any being She can act on every internal organ
on every shade of constitutional difference on the whole machinery of
life Man selects only for his own good Nature only for that of the
being which she tends Every selected character is fully exercised by
her as is implied by the fact of their selection Man keeps the natives
of many climates in the same country He seldom exercises each selected
character in some peculiar and fitting manner he feeds a long and a
shortbeaked pigeon on the same food he does not exercise a longbacked
or longlegged quadruped in any peculiar manner he exposes sheep
with long and short wool to the same climate does not allow the most
vigorous males to struggle for the females he does not rigidly destroy
all inferior animals but protects during each varying season as far as
lies in his power all his productions He often begins his selection
by some halfmonstrous form or at least by some modification prominent
enough to catch the eye or to be plainly useful to him Under nature
the slightest differences of structure or constitution may well turn the
nicelybalanced scale in the struggle for life and so be preserved
How fleeting are the wishes and efforts of man  How short his time
and consequently how poor will be his results compared with those
accumulated by Nature during whole geological periods  Can we wonder
then that Natures productions should be far truer in character than
mans productions that they should be infinitely better adapted to the
most complex conditions of life and should plainly bear the stamp of
far higher workmanship

It may metaphorically be said that natural selection is daily and hourly
scrutinising throughout the world the slightest variations rejecting
those that are bad preserving and adding up all that are good silently
and insensibly working WHENEVER AND WHEREVER OPPORTUNITY OFFERS at
the improvement of each organic being in relation to its organic and
inorganic conditions of life We see nothing of these slow changes in
progress until the hand of time has marked the long lapse of ages and
then so imperfect is our view into longpast geological ages that we see
only that the forms of life are now different from what they formerly
were

In order that any great amount of modification should be effected in a
species a variety when once formed must again perhaps after a long
interval of time vary or present individual differences of the same
favourable nature as before and these must again be preserved and so
onward step by step Seeing that individual differences of the
same kind perpetually recur this can hardly be considered as an
unwarrantable assumption But whether it is true we can judge only
by seeing how far the hypothesis accords with and explains the general
phenomena of nature On the other hand the ordinary belief that the
amount of possible variation is a strictly limited quantity is likewise
a simple assumption

Although natural selection can act only through and for the good of each
being yet characters and structures which we are apt to consider as of
very trifling importance may thus be acted on When we see leafeating
insects green and barkfeeders mottledgrey the alpine ptarmigan white
in winter the redgrouse the colour of heather we must believe that
these tints are of service to these birds and insects in preserving them
from danger Grouse if not destroyed at some period of their lives
would increase in countless numbers they are known to suffer largely
from birds of prey and hawks are guided by eyesight to their prey so
much so that on parts of the continent persons are warned not to keep
white pigeons as being the most liable to destruction Hence natural
selection might be effective in giving the proper colour to each kind
of grouse and in keeping that colour when once acquired true and
constant Nor ought we to think that the occasional destruction of an
animal of any particular colour would produce little effect we should
remember how essential it is in a flock of white sheep to destroy a lamb
with the faintest trace of black We have seen how the colour of hogs
which feed on the paintroot in Virginia determines whether they
shall live or die In plants the down on the fruit and the colour of
the flesh are considered by botanists as characters of the most trifling
importance yet we hear from an excellent horticulturist Downing
that in the United States smoothskinned fruits suffer far more from a
beetle a Curculio than those with down that purple plums suffer far
more from a certain disease than yellow plums whereas another disease
attacks yellowfleshed peaches far more than those with other coloured
flesh If with all the aids of art these slight differences make a
great difference in cultivating the several varieties assuredly in a
state of nature where the trees would have to struggle with other trees
and with a host of enemies such differences would effectually settle
which variety whether a smooth or downy a yellow or a purplefleshed
fruit should succeed

In looking at many small points of difference between species which
as far as our ignorance permits us to judge seem quite unimportant we
must not forget that climate food etc have no doubt produced some
direct effect It is also necessary to bear in mind that owing to
the law of correlation when one part varies and the variations are
accumulated through natural selection other modifications often of the
most unexpected nature will ensue

As we see that those variations which under domestication appear at
any particular period of life tend to reappear in the offspring at the
same period for instance in the shape size and flavour of the seeds
of the many varieties of our culinary and agricultural plants in the
caterpillar and cocoon stages of the varieties of the silkworm in the
eggs of poultry and in the colour of the down of their chickens in the
horns of our sheep and cattle when nearly adult so in a state of nature
natural selection will be enabled to act on and modify organic beings at
any age by the accumulation of variations profitable at that age and
by their inheritance at a corresponding age If it profit a plant to
have its seeds more and more widely disseminated by the wind I can see
no greater difficulty in this being effected through natural selection
than in the cottonplanter increasing and improving by selection the
down in the pods on his cottontrees Natural selection may modify
and adapt the larva of an insect to a score of contingencies wholly
different from those which concern the mature insect and these
modifications may affect through correlation the structure of the
adult So conversely modifications in the adult may affect the
structure of the larva but in all cases natural selection will ensure
that they shall not be injurious for if they were so the species would
become extinct

Natural selection will modify the structure of the young in relation to
the parent and of the parent in relation to the young In social animals
it will adapt the structure of each individual for the benefit of the
whole community if the community profits by the selected change What
natural selection cannot do is to modify the structure of one species
without giving it any advantage for the good of another species
and though statements to this effect may be found in works of natural
history I cannot find one case which will bear investigation A
structure used only once in an animals life if of high importance to
it might be modified to any extent by natural selection for instance
the great jaws possessed by certain insects used exclusively for
opening the cocoon or the hard tip to the beak of unhatched birds
used for breaking the eggs It has been asserted that of the best
shortbeaked tumblerpigeons a greater number perish in the egg than are
able to get out of it so that fanciers assist in the act of hatching
Now if nature had to make the beak of a fullgrown pigeon very short
for the birds own advantage the process of modification would be very
slow and there would be simultaneously the most rigorous selection
of all the young birds within the egg which had the most powerful and
hardest beaks for all with weak beaks would inevitably perish or more
delicate and more easily broken shells might be selected the thickness
of the shell being known to vary like every other structure

It may be well here to remark that with all beings there must be much
fortuitous destruction which can have little or no influence on the
course of natural selection For instance a vast number of eggs or
seeds are annually devoured and these could be modified through natural
selection only if they varied in some manner which protected them from
their enemies Yet many of these eggs or seeds would perhaps if not
destroyed have yielded individuals better adapted to their conditions
of life than any of those which happened to survive So again a vast
number of mature animals and plants whether or not they be the best
adapted to their conditions must be annually destroyed by accidental
causes which would not be in the least degree mitigated by certain
changes of structure or constitution which would in other ways be
beneficial to the species But let the destruction of the adults be ever
so heavy if the number which can exist in any district be not wholly
kept down by such causes or again let the destruction of eggs or
seeds be so great that only a hundredth or a thousandth part are
developed yet of those which do survive the best adapted individuals
supposing that there is any variability in a favourable direction
will tend to propagate their kind in larger numbers than the less
well adapted If the numbers be wholly kept down by the causes just
indicated as will often have been the case natural selection will
be powerless in certain beneficial directions but this is no valid
objection to its efficiency at other times and in other ways for we
are far from having any reason to suppose that many species ever undergo
modification and improvement at the same time in the same area

SEXUAL SELECTION

Inasmuch as peculiarities often appear under domestication in one sex
and become hereditarily attached to that sex so no doubt it will be
under nature Thus it is rendered possible for the two sexes to be
modified through natural selection in relation to different habits
of life as is sometimes the case or for one sex to be modified in
relation to the other sex as commonly occurs This leads me to say a
few words on what I have called sexual selection This form of selection
depends not on a struggle for existence in relation to other organic
beings or to external conditions but on a struggle between the
individuals of one sex generally the males for the possession of the
other sex The result is not death to the unsuccessful competitor but
few or no offspring Sexual selection is therefore less rigorous than
natural selection Generally the most vigorous males those which are
best fitted for their places in nature will leave most progeny But in
many cases victory depends not so much on general vigour but on having
special weapons confined to the male sex A hornless stag or spurless
cock would have a poor chance of leaving numerous offspring Sexual
selection by always allowing the victor to breed might surely give
indomitable courage length of spur and strength to the wing to
strike in the spurred leg in nearly the same manner as does the brutal
cockfighter by the careful selection of his best cocks How low in the
scale of nature the law of battle descends I know not male alligators
have been described as fighting bellowing and whirling round like
Indians in a wardance for the possession of the females male salmons
have been observed fighting all day long male stagbeetles sometimes
bear wounds from the huge mandibles of other males the males of certain
hymenopterous insects have been frequently seen by that inimitable
observer M Fabre fighting for a particular female who sits by an
apparently unconcerned beholder of the struggle and then retires
with the conqueror The war is perhaps severest between the males
of polygamous animals and these seem oftenest provided with special
weapons The males of carnivorous animals are already well armed though
to them and to others special means of defence may be given through
means of sexual selection as the mane of the lion and the hooked jaw
to the male salmon for the shield may be as important for victory as
the sword or spear

Among birds the contest is often of a more peaceful character All
those who have attended to the subject believe that there is the
severest rivalry between the males of many species to attract by
singing the females The rockthrush of Guiana birds of paradise
and some others congregate and successive males display with the most
elaborate care and show off in the best manner their gorgeous plumage
they likewise perform strange antics before the females which standing
by as spectators at last choose the most attractive partner Those who
have closely attended to birds in confinement well know that they
often take individual preferences and dislikes thus Sir R Heron has
described how a pied peacock was eminently attractive to all his hen
birds I cannot here enter on the necessary details but if man can in a
short time give beauty and an elegant carriage to his bantams according
to his standard of beauty I can see no good reason to doubt that female
birds by selecting during thousands of generations the most melodious
or beautiful males according to their standard of beauty might produce
a marked effect Some wellknown laws with respect to the plumage of
male and female birds in comparison with the plumage of the young can
partly be explained through the action of sexual selection on variations
occurring at different ages and transmitted to the males alone or to
both sexes at corresponding ages but I have not space here to enter on
this subject

Thus it is as I believe that when the males and females of any animal
have the same general habits of life but differ in structure colour
or ornament such differences have been mainly caused by sexual
selection that is by individual males having had in successive
generations some slight advantage over other males in their weapons
means of defence or charms which they have transmitted to their
male offspring alone Yet I would not wish to attribute all sexual
differences to this agency for we see in our domestic animals
peculiarities arising and becoming attached to the male sex which
apparently have not been augmented through selection by man The tuft of
hair on the breast of the wild turkeycock cannot be of any use and it
is doubtful whether it can be ornamental in the eyes of the female bird
indeed had the tuft appeared under domestication it would have been
called a monstrosity

ILLUSTRATIONS OF THE ACTION OF NATURAL SELECTION OR THE SURVIVAL OF THE
FITTEST

In order to make it clear how as I believe natural selection acts I
must beg permission to give one or two imaginary illustrations Let us
take the case of a wolf which preys on various animals securing some
by craft some by strength and some by fleetness and let us suppose
that the fleetest prey a deer for instance had from any change in
the country increased in numbers or that other prey had decreased
in numbers during that season of the year when the wolf was hardest
pressed for food Under such circumstances the swiftest and slimmest
wolves have the best chance of surviving and so be preserved or
selected provided always that they retained strength to master their
prey at this or some other period of the year when they were compelled
to prey on other animals I can see no more reason to doubt that
this would be the result than that man should be able to improve the
fleetness of his greyhounds by careful and methodical selection or by
that kind of unconscious selection which follows from each man trying to
keep the best dogs without any thought of modifying the breed I may
add that according to Mr Pierce there are two varieties of the wolf
inhabiting the Catskill Mountains in the United States one with a
light greyhoundlike form which pursues deer and the other more bulky
with shorter legs which more frequently attacks the shepherds flocks

Even without any change in the proportional numbers of the animals on
which our wolf preyed a cub might be born with an innate tendency to
pursue certain kinds of prey Nor can this be thought very improbable
for we often observe great differences in the natural tendencies of our
domestic animals one cat for instance taking to catch rats another
mice one cat according to Mr St John bringing home winged game
another hares or rabbits and another hunting on marshy ground and
almost nightly catching woodcocks or snipes The tendency to catch rats
rather than mice is known to be inherited Now if any slight innate
change of habit or of structure benefited an individual wolf it would
have the best chance of surviving and of leaving offspring Some of its
young would probably inherit the same habits or structure and by the
repetition of this process a new variety might be formed which would
either supplant or coexist with the parentform of wolf Or again
the wolves inhabiting a mountainous district and those frequenting the
lowlands would naturally be forced to hunt different prey and from the
continued preservation of the individuals best fitted for the two sites
two varieties might slowly be formed These varieties would cross and
blend where they met but to this subject of intercrossing we shall soon
have to return I may add that according to Mr Pierce there are two
varieties of the wolf inhabiting the Catskill Mountains in the United
States one with a light greyhoundlike form which pursues deer and
the other more bulky with shorter legs which more frequently attacks
the shepherds flocks

It should be observed that in the above illustration I speak of the
slimmest individual wolves and not of any single strongly marked
variation having been preserved In former editions of this work I
sometimes spoke as if this latter alternative had frequently occurred
I saw the great importance of individual differences and this led me
fully to discuss the results of unconscious selection by man
which depends on the preservation of all the more or less valuable
individuals and on the destruction of the worst I saw also that
the preservation in a state of nature of any occasional deviation of
structure such as a monstrosity would be a rare event and that if at
first preserved it would generally be lost by subsequent intercrossing
with ordinary individuals Nevertheless until reading an able and
valuable article in the North British Review 1867 I did not
appreciate how rarely single variations whether slight or strongly
marked could be perpetuated The author takes the case of a pair of
animals producing during their lifetime two hundred offspring of
which from various causes of destruction only two on an average
survive to procreate their kind This is rather an extreme estimate
for most of the higher animals but by no means so for many of the lower
organisms He then shows that if a single individual were born which
varied in some manner giving it twice as good a chance of life as that
of the other individuals yet the chances would be strongly against its
survival Supposing it to survive and to breed and that half its young
inherited the favourable variation still as the Reviewer goes onto
show the young would have only a slightly better chance of surviving
and breeding and this chance would go on decreasing in the succeeding
generations The justice of these remarks cannot I think be disputed
If for instance a bird of some kind could procure its food more easily
by having its beak curved and if one were born with its beak strongly
curved and which consequently flourished nevertheless there would be
a very poor chance of this one individual perpetuating its kind to the
exclusion of the common form but there can hardly be a doubt judging
by what we see taking place under domestication that this result would
follow from the preservation during many generations of a large number
of individuals with more or less strongly curved beaks and from the
destruction of a still larger number with the straightest beaks

It should not however be overlooked that certain rather strongly
marked variations which no one would rank as mere individual
differences frequently recur owing to a similar organisation being
similarly acted on of which fact numerous instances could be given with
our domestic productions In such cases if the varying individual did
not actually transmit to its offspring its newlyacquired character it
would undoubtedly transmit to them as long as the existing conditions
remained the same a still stronger tendency to vary in the same manner
There can also be little doubt that the tendency to vary in the same
manner has often been so strong that all the individuals of the same
species have been similarly modified without the aid of any form of
selection Or only a third fifth or tenth part of the individuals may
have been thus affected of which fact several instances could be given
Thus Graba estimates that about onefifth of the guillemots in the Faroe
Islands consist of a variety so well marked that it was formerly ranked
as a distinct species under the name of Uria lacrymans In cases of this
kind if the variation were of a beneficial nature the original form
would soon be supplanted by the modified form through the survival of
the fittest

To the effects of intercrossing in eliminating variations of all kinds
I shall have to recur but it may be here remarked that most animals and
plants keep to their proper homes and do not needlessly wander about
we see this even with migratory birds which almost always return to the
same spot Consequently each newlyformed variety would generally be at
first local as seems to be the common rule with varieties in a state
of nature so that similarly modified individuals would soon exist in a
small body together and would often breed together If the new variety
were successful in its battle for life it would slowly spread from
a central district competing with and conquering the unchanged
individuals on the margins of an everincreasing circle

It may be worth while to give another and more complex illustration of
the action of natural selection Certain plants excrete sweet juice
apparently for the sake of eliminating something injurious from the sap
this is effected for instance by glands at the base of the stipules in
some Leguminosae and at the backs of the leaves of the common laurel
This juice though small in quantity is greedily sought by insects but
their visits do not in any way benefit the plant Now let us suppose
that the juice or nectar was excreted from the inside of the flowers of
a certain number of plants of any species Insects in seeking the nectar
would get dusted with pollen and would often transport it from one
flower to another The flowers of two distinct individuals of the same
species would thus get crossed and the act of crossing as can be fully
proved gives rise to vigorous seedlings which consequently would have
the best chance of flourishing and surviving The plants which produced
flowers with the largest glands or nectaries excreting most nectar
would oftenest be visited by insects and would oftenest be crossed and
so in the longrun would gain the upper hand and form a local variety
The flowers also which had their stamens and pistils placed in
relation to the size and habits of the particular insect which visited
them so as to favour in any degree the transportal of the pollen would
likewise be favoured We might have taken the case of insects visiting
flowers for the sake of collecting pollen instead of nectar and as
pollen is formed for the sole purpose of fertilisation its destruction
appears to be a simple loss to the plant yet if a little pollen
were carried at first occasionally and then habitually by the
pollendevouring insects from flower to flower and a cross thus
effected although ninetenths of the pollen were destroyed it
might still be a great gain to the plant to be thus robbed and the
individuals which produced more and more pollen and had larger anthers
would be selected

When our plant by the above process long continued had been rendered
highly attractive to insects they would unintentionally on their part
regularly carry pollen from flower to flower and that they do this
effectually I could easily show by many striking facts I will give only
one as likewise illustrating one step in the separation of the sexes of
plants Some hollytrees bear only male flowers which have four stamens
producing a rather small quantity of pollen and a rudimentary pistil
other hollytrees bear only female flowers these have a fullsized
pistil and four stamens with shrivelled anthers in which not a grain
of pollen can be detected Having found a female tree exactly sixty
yards from a male tree I put the stigmas of twenty flowers taken from
different branches under the microscope and on all without exception
there were a few pollengrains and on some a profusion As the wind had
set for several days from the female to the male tree the pollen could
not thus have been carried The weather had been cold and boisterous and
therefore not favourable to bees nevertheless every female flower which
I examined had been effectually fertilised by the bees which had flown
from tree to tree in search of nectar But to return to our imaginary
case as soon as the plant had been rendered so highly attractive to
insects that pollen was regularly carried from flower to flower another
process might commence No naturalist doubts the advantage of what has
been called the physiological division of labour hence we may believe
that it would be advantageous to a plant to produce stamens alone in one
flower or on one whole plant and pistils alone in another flower or on
another plant In plants under culture and placed under new conditions
of life sometimes the male organs and sometimes the female organs
become more or less impotent now if we suppose this to occur in ever
so slight a degree under nature then as pollen is already carried
regularly from flower to flower and as a more complete separation of
the sexes of our plant would be advantageous on the principle of
the division of labour individuals with this tendency more and more
increased would be continually favoured or selected until at last a
complete separation of the sexes might be effected It would take up
too much space to show the various steps through dimorphism and other
means by which the separation of the sexes in plants of various kinds
is apparently now in progress but I may add that some of the species
of holly in North America are according to Asa Gray in an exactly
intermediate condition or as he expresses it are more or less
dioeciously polygamous

Let us now turn to the nectarfeeding insects we may suppose the
plant of which we have been slowly increasing the nectar by continued
selection to be a common plant and that certain insects depended in
main part on its nectar for food I could give many facts showing how
anxious bees are to save time for instance their habit of cutting
holes and sucking the nectar at the bases of certain flowers which with
a very little more trouble they can enter by the mouth Bearing such
facts in mind it may be believed that under certain circumstances
individual differences in the curvature or length of the proboscis
etc too slight to be appreciated by us might profit a bee or other
insect so that certain individuals would be able to obtain their
food more quickly than others and thus the communities to which they
belonged would flourish and throw off many swarms inheriting the same
peculiarities The tubes of the corolla of the common red or incarnate
clovers Trifolium pratense and incarnatum do not on a hasty glance
appear to differ in length yet the hivebee can easily suck the nectar
out of the incarnate clover but not out of the common red clover which
is visited by humblebees alone so that whole fields of the red clover
offer in vain an abundant supply of precious nectar to the hivebee
That this nectar is much liked by the hivebee is certain for I have
repeatedly seen but only in the autumn many hivebees sucking the
flowers through holes bitten in the base of the tube by humble bees
The difference in the length of the corolla in the two kinds of clover
which determines the visits of the hivebee must be very trifling for
I have been assured that when red clover has been mown the flowers of
the second crop are somewhat smaller and that these are visited by many
hivebees I do not know whether this statement is accurate nor whether
another published statement can be trusted namely that the Ligurian
bee which is generally considered a mere variety of the common
hivebee and which freely crosses with it is able to reach and suck
the nectar of the red clover Thus in a country where this kind of
clover abounded it might be a great advantage to the hivebee to have a
slightly longer or differently constructed proboscis On the other hand
as the fertility of this clover absolutely depends on bees visiting the
flowers if humblebees were to become rare in any country it might be
a great advantage to the plant to have a shorter or more deeply divided
corolla so that the hivebees should be enabled to suck its flowers
Thus I can understand how a flower and a bee might slowly become either
simultaneously or one after the other modified and adapted to each
other in the most perfect manner by the continued preservation of all
the individuals which presented slight deviations of structure mutually
favourable to each other

I am well aware that this doctrine of natural selection exemplified in
the above imaginary instances is open to the same objections which
were first urged against Sir Charles Lyells noble views on the modern
changes of the earth as illustrative of geology but we now seldom
hear the agencies which we see still at work spoken of as trifling and
insignificant when used in explaining the excavation of the deepest
valleys or the formation of long lines of inland cliffs Natural
selection acts only by the preservation and accumulation of small
inherited modifications each profitable to the preserved being and
as modern geology has almost banished such views as the excavation of a
great valley by a single diluvial wave so will natural selection banish
the belief of the continued creation of new organic beings or of any
great and sudden modification in their structure

ON THE INTERCROSSING OF INDIVIDUALS

I must here introduce a short digression In the case of animals
and plants with separated sexes it is of course obvious that two
individuals must always with the exception of the curious and not well
understood cases of parthenogenesis unite for each birth but in the
case of hermaphrodites this is far from obvious Nevertheless there is
reason to believe that with all hermaphrodites two individuals either
occasionally or habitually concur for the reproduction of their kind
This view was long ago doubtfully suggested by Sprengel Knight and
Kolreuter We shall presently see its importance but I must here treat
the subject with extreme brevity though I have the materials prepared
for an ample discussion All vertebrate animals all insects and some
other large groups of animals pair for each birth Modern research
has much diminished the number of supposed hermaphrodites and of real
hermaphrodites a large number pair that is two individuals regularly
unite for reproduction which is all that concerns us But still there
are many hermaphrodite animals which certainly do not habitually pair
and a vast majority of plants are hermaphrodites What reason it may be
asked is there for supposing in these cases that two individuals ever
concur in reproduction As it is impossible here to enter on details I
must trust to some general considerations alone

In the first place I have collected so large a body of facts and made
so many experiments showing in accordance with the almost universal
belief of breeders that with animals and plants a cross between
different varieties or between individuals of the same variety but of
another strain gives vigour and fertility to the offspring and on the
other hand that CLOSE interbreeding diminishes vigour and fertility
that these facts alone incline me to believe that it is a general law
of nature that no organic being fertilises itself for a perpetuity
of generations but that a cross with another individual is
occasionally perhaps at long intervals of time indispensable

On the belief that this is a law of nature we can I think understand
several large classes of facts such as the following which on any
other view are inexplicable Every hybridizer knows how unfavourable
exposure to wet is to the fertilisation of a flower yet what a
multitude of flowers have their anthers and stigmas fully exposed to the
weather  If an occasional cross be indispensable notwithstanding that
the plants own anthers and pistil stand so near each other as almost
to ensure selffertilisation the fullest freedom for the entrance of
pollen from another individual will explain the above state of exposure
of the organs Many flowers on the other hand have their organs of
fructification closely enclosed as in the great papilionaceous or
peafamily but these almost invariably present beautiful and curious
adaptations in relation to the visits of insects So necessary are the
visits of bees to many papilionaceous flowers that their fertility is
greatly diminished if these visits be prevented Now it is scarcely
possible for insects to fly from flower to flower and not to carry
pollen from one to the other to the great good of the plant
Insects act like a camelhair pencil and it is sufficient to ensure
fertilisation just to touch with the same brush the anthers of one
flower and then the stigma of another but it must not be supposed that
bees would thus produce a multitude of hybrids between distinct species
for if a plants own pollen and that from another species are placed
on the same stigma the former is so prepotent that it invariably and
completely destroys as has been shown by Gartner the influence of the
foreign pollen

When the stamens of a flower suddenly spring towards the pistil or
slowly move one after the other towards it the contrivance seems
adapted solely to ensure selffertilisation and no doubt it is useful
for this end but the agency of insects is often required to cause the
stamens to spring forward as Kolreuter has shown to be the case with
the barberry and in this very genus which seems to have a special
contrivance for selffertilisation it is well known that if
closelyallied forms or varieties are planted near each other it is
hardly possible to raise pure seedlings so largely do they naturally
cross In numerous other cases far from selffertilisation being
favoured there are special contrivances which effectually prevent the
stigma receiving pollen from its own flower as I could show from the
works of Sprengel and others as well as from my own observations for
instance in Lobelia fulgens there is a really beautiful and elaborate
contrivance by which all the infinitely numerous pollengranules are
swept out of the conjoined anthers of each flower before the stigma of
that individual flower is ready to receive them and as this flower is
never visited at least in my garden by insects it never sets a seed
though by placing pollen from one flower on the stigma of another I
raise plenty of seedlings Another species of Lobelia which is visited
by bees seeds freely in my garden In very many other cases though
there is no special mechanical contrivance to prevent the stigma
receiving pollen from the same flower yet as Sprengel and more
recently Hildebrand and others have shown and as I can confirm either
the anthers burst before the stigma is ready for fertilisation or the
stigma is ready before the pollen of that flower is ready so that
these sonamed dichogamous plants have in fact separated sexes and
must habitually be crossed So it is with the reciprocally dimorphic and
trimorphic plants previously alluded to How strange are these facts 
How strange that the pollen and stigmatic surface of the same flower
though placed so close together as if for the very purpose of
selffertilisation should be in so many cases mutually useless to each
other  How simply are these facts explained on the view of an occasional
cross with a distinct individual being advantageous or indispensable 

If several varieties of the cabbage radish onion and of some other
plants be allowed to seed near each other a large majority of the
seedlings thus raised turn out as I found mongrels for instance I
raised 233 seedling cabbages from some plants of different varieties
growing near each other and of these only 78 were true to their kind
and some even of these were not perfectly true Yet the pistil of each
cabbageflower is surrounded not only by its own six stamens but by
those of the many other flowers on the same plant and the pollen of
each flower readily gets on its stigma without insect agency for I
have found that plants carefully protected from insects produce the
full number of pods How then comes it that such a vast number of the
seedlings are mongrelized It must arise from the pollen of a distinct
VARIETY having a prepotent effect over the flowers own pollen and
that this is part of the general law of good being derived from the
intercrossing of distinct individuals of the same species When distinct
SPECIES are crossed the case is reversed for a plants own pollen
is always prepotent over foreign pollen but to this subject we shall
return in a future chapter

In the case of a large tree covered with innumerable flowers it may be
objected that pollen could seldom be carried from tree to tree and at
most only from flower to flower on the same tree and flowers on the
same tree can be considered as distinct individuals only in a limited
sense I believe this objection to be valid but that nature has largely
provided against it by giving to trees a strong tendency to bear flowers
with separated sexes When the sexes are separated although the male
and female flowers may be produced on the same tree pollen must be
regularly carried from flower to flower and this will give a better
chance of pollen being occasionally carried from tree to tree That
trees belonging to all orders have their sexes more often separated than
other plants I find to be the case in this country and at my request
Dr Hooker tabulated the trees of New Zealand and Dr Asa Gray those
of the United States and the result was as I anticipated On the
other hand Dr Hooker informs me that the rule does not hold good in
Australia but if most of the Australian trees are dichogamous the same
result would follow as if they bore flowers with separated sexes I have
made these few remarks on trees simply to call attention to the subject

Turning for a brief space to animals various terrestrial species are
hermaphrodites such as the landmollusca and earthworms but these
all pair As yet I have not found a single terrestrial animal which
can fertilise itself This remarkable fact which offers so strong a
contrast with terrestrial plants is intelligible on the view of an
occasional cross being indispensable for owing to the nature of the
fertilising element there are no means analogous to the action of
insects and of the wind with plants by which an occasional cross could
be effected with terrestrial animals without the concurrence of two
individuals Of aquatic animals there are many selffertilising
hermaphrodites but here the currents of water offer an obvious means
for an occasional cross As in the case of flowers I have as yet
failed after consultation with one of the highest authorities namely
Professor Huxley to discover a single hermaphrodite animal with the
organs of reproduction so perfectly enclosed that access from without
and the occasional influence of a distinct individual can be shown to
be physically impossible Cirripedes long appeared to me to present
under this point of view a case of great difficulty but I have been
enabled by a fortunate chance to prove that two individuals though
both are selffertilising hermaphrodites do sometimes cross

It must have struck most naturalists as a strange anomaly that both
with animals and plants some species of the same family and even of
the same genus though agreeing closely with each other in their whole
organisation are hermaphrodites and some unisexual But if in fact
all hermaphrodites do occasionally intercross the difference between
them and unisexual species is as far as function is concerned very
small

From these several considerations and from the many special facts which
I have collected but which I am unable here to give it appears that
with animals and plants an occasional intercross between distinct
individuals is a very general if not universal law of nature

CIRCUMSTANCES FAVOURABLE FOR THE PRODUCTION OF NEW FORMS THROUGH NATURAL
SELECTION

This is an extremely intricate subject A great amount of variability
under which term individual differences are always included will
evidently be favourable A large number of individuals by giving a
better chance within any given period for the appearance of profitable
variations will compensate for a lesser amount of variability in each
individual and is I believe a highly important element of success
Though nature grants long periods of time for the work of natural
selection she does not grant an indefinite period for as all organic
beings are striving to seize on each place in the economy of nature if
any one species does not become modified and improved in a corresponding
degree with its competitors it will be exterminated Unless favourable
variations be inherited by some at least of the offspring nothing can
be effected by natural selection The tendency to reversion may often
check or prevent the work but as this tendency has not prevented man
from forming by selection numerous domestic races why should it prevail
against natural selection

In the case of methodical selection a breeder selects for some definite
object and if the individuals be allowed freely to intercross his work
will completely fail But when many men without intending to alter
the breed have a nearly common standard of perfection and all try to
procure and breed from the best animals improvement surely but slowly
follows from this unconscious process of selection notwithstanding that
there is no separation of selected individuals Thus it will be under
nature for within a confined area with some place in the natural
polity not perfectly occupied all the individuals varying in the right
direction though in different degrees will tend to be preserved
But if the area be large its several districts will almost certainly
present different conditions of life and then if the same species
undergoes modification in different districts the newly formed
varieties will intercross on the confines of each But we shall see in
the sixth chapter that intermediate varieties inhabiting intermediate
districts will in the long run generally be supplanted by one of the
adjoining varieties Intercrossing will chiefly affect those animals
which unite for each birth and wander much and which do not breed at a
very quick rate Hence with animals of this nature for instance birds
varieties will generally be confined to separated countries and this
I find to be the case With hermaphrodite organisms which cross only
occasionally and likewise with animals which unite for each birth but
which wander little and can increase at a rapid rate a new and improved
variety might be quickly formed on any one spot and might there
maintain itself in a body and afterward spread so that the individuals
of the new variety would chiefly cross together On this principle
nurserymen always prefer saving seed from a large body of plants as the
chance of intercrossing is thus lessened

Even with animals which unite for each birth and which do not propagate
rapidly we must not assume that free intercrossing would always
eliminate the effects of natural selection for I can bring forward
a considerable body of facts showing that within the same area two
varieties of the same animal may long remain distinct from haunting
different stations from breeding at slightly different seasons or from
the individuals of each variety preferring to pair together

Intercrossing plays a very important part in nature by keeping the
individuals of the same species or of the same variety true and
uniform in character It will obviously thus act far more efficiently
with those animals which unite for each birth but as already stated
we have reason to believe that occasional intercrosses take place with
all animals and plants Even if these take place only at long intervals
of time the young thus produced will gain so much in vigour and
fertility over the offspring from longcontinued selffertilisation
that they will have a better chance of surviving and propagating their
kind and thus in the long run the influence of crosses even at rare
intervals will be great With respect to organic beings extremely low
in the scale which do not propagate sexually nor conjugate and which
cannot possibly intercross uniformity of character can be retained by
them under the same conditions of life only through the principle
of inheritance and through natural selection which will destroy any
individuals departing from the proper type If the conditions of life
change and the form undergoes modification uniformity of character
can be given to the modified offspring solely by natural selection
preserving similar favourable variations

Isolation also is an important element in the modification of species
through natural selection In a confined or isolated area if not very
large the organic and inorganic conditions of life will generally be
almost uniform so that natural selection will tend to modify all
the varying individuals of the same species in the same manner
Intercrossing with the inhabitants of the surrounding districts
will also be thus prevented Moritz Wagner has lately published an
interesting essay on this subject and has shown that the service
rendered by isolation in preventing crosses between newlyformed
varieties is probably greater even than I supposed But from reasons
already assigned I can by no means agree with this naturalist that
migration and isolation are necessary elements for the formation of new
species The importance of isolation is likewise great in preventing
after any physical change in the conditions such as of climate
elevation of the land etc the immigration of better adapted
organisms and thus new places in the natural economy of the district
will be left open to be filled up by the modification of the old
inhabitants Lastly isolation will give time for a new variety to be
improved at a slow rate and this may sometimes be of much importance
If however an isolated area be very small either from being
surrounded by barriers or from having very peculiar physical
conditions the total number of the inhabitants will be small and this
will retard the production of new species through natural selection by
decreasing the chances of favourable variations arising

The mere lapse of time by itself does nothing either for or against
natural selection I state this because it has been erroneously asserted
that the element of time has been assumed by me to play an allimportant
part in modifying species as if all the forms of life were necessarily
undergoing change through some innate law Lapse of time is only so far
important and its importance in this respect is great that it gives
a better chance of beneficial variations arising and of their being
selected accumulated and fixed It likewise tends to increase the
direct action of the physical conditions of life in relation to the
constitution of each organism

If we turn to nature to test the truth of these remarks and look at any
small isolated area such as an oceanic island although the number of
the species inhabiting it is small as we shall see in our chapter on
Geographical Distribution yet of these species a very large proportion
are endemic that is have been produced there and nowhere else in the
world Hence an oceanic island at first sight seems to have been highly
favourable for the production of new species But we may thus deceive
ourselves for to ascertain whether a small isolated area or a large
open area like a continent has been most favourable for the production
of new organic forms we ought to make the comparison within equal
times and this we are incapable of doing

Although isolation is of great importance in the production of new
species on the whole I am inclined to believe that largeness of area
is still more important especially for the production of species which
shall prove capable of enduring for a long period and of spreading
widely Throughout a great and open area not only will there be a
better chance of favourable variations arising from the large number of
individuals of the same species there supported but the conditions of
life are much more complex from the large number of already existing
species and if some of these many species become modified and improved
others will have to be improved in a corresponding degree or they
will be exterminated Each new form also as soon as it has been much
improved will be able to spread over the open and continuous area and
will thus come into competition with many other forms Moreover great
areas though now continuous will often owing to former oscillations
of level have existed in a broken condition so that the good effects
of isolation will generally to a certain extent have concurred
Finally I conclude that although small isolated areas have been in
some respects highly favourable for the production of new species yet
that the course of modification will generally have been more rapid on
large areas and what is more important that the new forms produced on
large areas which already have been victorious over many competitors
will be those that will spread most widely and will give rise to the
greatest number of new varieties and species They will thus play a more
important part in the changing history of the organic world

In accordance with this view we can perhaps understand some
facts which will be again alluded to in our chapter on Geographical
Distribution for instance the fact of the productions of the
smaller continent of Australia now yielding before those of the larger
EuropaeoAsiatic area Thus also it is that continental productions
have everywhere become so largely naturalised on islands On a small
island the race for life will have been less severe and there will
have been less modification and less extermination Hence we can
understand how it is that the flora of Madeira according to Oswald
Heer resembles to a certain extent the extinct tertiary flora of
Europe All fresh water basins taken together make a small area
compared with that of the sea or of the land Consequently the
competition between fresh water productions will have been less severe
than elsewhere new forms will have been more slowly produced and old
forms more slowly exterminated And it is in fresh water basins that
we find seven genera of Ganoid fishes remnants of a once preponderant
order and in fresh water we find some of the most anomalous forms now
known in the world as the Ornithorhynchus and Lepidosiren which like
fossils connect to a certain extent orders at present widely separated
in the natural scale These anomalous forms may be called living
fossils they have endured to the present day from having inhabited
a confined area and from having been exposed to less varied and
therefore less severe competition

To sum up as far as the extreme intricacy of the subject permits the
circumstances favourable and unfavourable for the production of new
species through natural selection I conclude that for terrestrial
productions a large continental area which has undergone many
oscillations of level will have been the most favourable for the
production of many new forms of life fitted to endure for a long
time and to spread widely While the area existed as a continent the
inhabitants will have been numerous in individuals and kinds and will
have been subjected to severe competition When converted by subsidence
into large separate islands there will still have existed many
individuals of the same species on each island intercrossing on the
confines of the range of each new species will have been checked after
physical changes of any kind immigration will have been prevented so
that new places in the polity of each island will have had to be filled
up by the modification of the old inhabitants and time will have been
allowed for the varieties in each to become well modified and perfected
When by renewed elevation the islands were reconverted into a
continental area there will again have been very severe competition
the most favoured or improved varieties will have been enabled to
spread there will have been much extinction of the less improved forms
and the relative proportional numbers of the various inhabitants of the
reunited continent will again have been changed and again there will
have been a fair field for natural selection to improve still further
the inhabitants and thus to produce new species

That natural selection generally act with extreme slowness I fully
admit It can act only when there are places in the natural polity of a
district which can be better occupied by the modification of some of its
existing inhabitants The occurrence of such places will often depend
on physical changes which generally take place very slowly and on the
immigration of better adapted forms being prevented As some few of
the old inhabitants become modified the mutual relations of others will
often be disturbed and this will create new places ready to be filled
up by better adapted forms but all this will take place very slowly
Although all the individuals of the same species differ in some slight
degree from each other it would often be long before differences of
the right nature in various parts of the organisation might occur The
result would often be greatly retarded by free intercrossing Many will
exclaim that these several causes are amply sufficient to neutralise the
power of natural selection I do not believe so But I do believe that
natural selection will generally act very slowly only at long intervals
of time and only on a few of the inhabitants of the same region I
further believe that these slow intermittent results accord well with
what geology tells us of the rate and manner at which the inhabitants of
the world have changed

Slow though the process of selection may be if feeble man can do much
by artificial selection I can see no limit to the amount of change
to the beauty and complexity of the coadaptations between all organic
beings one with another and with their physical conditions of life
which may have been effected in the long course of time through natures
power of selection that is by the survival of the fittest

EXTINCTION CAUSED BY NATURAL SELECTION

This subject will be more fully discussed in our chapter on Geology but
it must here be alluded to from being intimately connected with natural
selection Natural selection acts solely through the preservation of
variations in some way advantageous which consequently endure Owing to
the high geometrical rate of increase of all organic beings each area
is already fully stocked with inhabitants and it follows from this
that as the favoured forms increase in number so generally will the
less favoured decrease and become rare Rarity as geology tells us
is the precursor to extinction We can see that any form which
is represented by few individuals will run a good chance of utter
extinction during great fluctuations in the nature or the seasons or
from a temporary increase in the number of its enemies But we may go
further than this for as new forms are produced unless we admit that
specific forms can go on indefinitely increasing in number many old
forms must become extinct That the number of specific forms has not
indefinitely increased geology plainly tells us and we shall presently
attempt to show why it is that the number of species throughout the
world has not become immeasurably great

We have seen that the species which are most numerous in individuals
have the best chance of producing favourable variations within any given
period We have evidence of this in the facts stated in the second
chapter showing that it is the common and diffused or dominant species
which offer the greatest number of recorded varieties Hence rare
species will be less quickly modified or improved within any given
period they will consequently be beaten in the race for life by the
modified and improved descendants of the commoner species

From these several considerations I think it inevitably follows
that as new species in the course of time are formed through natural
selection others will become rarer and rarer and finally extinct
The forms which stand in closest competition with those undergoing
modification and improvement will naturally suffer most And we have
seen in the chapter on the Struggle for Existence that it is the most
closelyallied forms varieties of the same species and species of
the same genus or related genera which from having nearly the same
structure constitution and habits generally come into the severest
competition with each other Consequently each new variety or species
during the progress of its formation will generally press hardest
on its nearest kindred and tend to exterminate them We see the same
process of extermination among our domesticated productions through
the selection of improved forms by man Many curious instances could be
given showing how quickly new breeds of cattle sheep and other animals
and varieties of flowers take the place of older and inferior kinds In
Yorkshire it is historically known that the ancient black cattle were
displaced by the longhorns and that these were swept away by the
shorthorns I quote the words of an agricultural writer as if by
some murderous pestilence

DIVERGENCE OF CHARACTER

The principle which I have designated by this term is of high
importance and explains as I believe several important facts In
the first place varieties even stronglymarked ones though having
somewhat of the character of species as is shown by the hopeless doubts
in many cases how to rank them yet certainly differ far less from each
other than do good and distinct species Nevertheless according to my
view varieties are species in the process of formation or are as
I have called them incipient species How then does the lesser
difference between varieties become augmented into the greater
difference between species That this does habitually happen we must
infer from most of the innumerable species throughout nature presenting
wellmarked differences whereas varieties the supposed prototypes and
parents of future wellmarked species present slight and illdefined
differences Mere chance as we may call it might cause one variety
to differ in some character from its parents and the offspring of this
variety again to differ from its parent in the very same character and
in a greater degree but this alone would never account for so habitual
and large a degree of difference as that between the species of the same
genus

As has always been my practice I have sought light on this head from
our domestic productions We shall here find something analogous It
will be admitted that the production of races so different as shorthorn
and Hereford cattle race and cart horses the several breeds of
pigeons etc could never have been effected by the mere chance
accumulation of similar variations during many successive generations
In practice a fancier is for instance struck by a pigeon having a
slightly shorter beak another fancier is struck by a pigeon having a
rather longer beak and on the acknowledged principle that fanciers do
not and will not admire a medium standard but like extremes they
both go on as has actually occurred with the subbreeds of the
tumblerpigeon choosing and breeding from birds with longer and longer
beaks or with shorter and shorter beaks Again we may suppose that at
an early period of history the men of one nation or district required
swifter horses while those of another required stronger and bulkier
horses The early differences would be very slight but in the course
of time from the continued selection of swifter horses in the one case
and of stronger ones in the other the differences would become greater
and would be noted as forming two subbreeds Ultimately after the
lapse of centuries these subbreeds would become converted into two
wellestablished and distinct breeds As the differences became greater
the inferior animals with intermediate characters being neither very
swift nor very strong would not have been used for breeding and will
thus have tended to disappear Here then we see in mans productions
the action of what may be called the principle of divergence causing
differences at first barely appreciable steadily to increase and
the breeds to diverge in character both from each other and from their
common parent

But how it may be asked can any analogous principle apply in nature
I believe it can and does apply most efficiently though it was a long
time before I saw how from the simple circumstance that the more
diversified the descendants from any one species become in structure
constitution and habits by so much will they be better enabled to
seize on many and widely diversified places in the polity of nature and
so be enabled to increase in numbers

We can clearly discern this in the case of animals with simple habits
Take the case of a carnivorous quadruped of which the number that can
be supported in any country has long ago arrived at its full average
If its natural power of increase be allowed to act it can succeed in
increasing the country not undergoing any change in conditions only by
its varying descendants seizing on places at present occupied by other
animals some of them for instance being enabled to feed on new kinds
of prey either dead or alive some inhabiting new stations climbing
trees frequenting water and some perhaps becoming less carnivorous
The more diversified in habits and structure the descendants of our
carnivorous animals become the more places they will be enabled to
occupy What applies to one animal will apply throughout all time to
all animals that is if they vary for otherwise natural selection can
effect nothing So it will be with plants It has been experimentally
proved that if a plot of ground be sown with one species of grass
and a similar plot be sown with several distinct genera of grasses
a greater number of plants and a greater weight of dry herbage can be
raised in the latter than in the former case The same has been found
to hold good when one variety and several mixed varieties of wheat have
been sown on equal spaces of ground Hence if any one species of grass
were to go on varying and the varieties were continually selected which
differed from each other in the same manner though in a very slight
degree as do the distinct species and genera of grasses a greater
number of individual plants of this species including its modified
descendants would succeed in living on the same piece of ground And
we know that each species and each variety of grass is annually sowing
almost countless seeds and is thus striving as it may be said to
the utmost to increase in number Consequently in the course of many
thousand generations the most distinct varieties of any one species
of grass would have the best chance of succeeding and of increasing
in numbers and thus of supplanting the less distinct varieties and
varieties when rendered very distinct from each other take the rank of
species

The truth of the principle that the greatest amount of life can be
supported by great diversification of structure is seen under many
natural circumstances In an extremely small area especially if freely
open to immigration and where the contest between individual and
individual must be very severe we always find great diversity in its
inhabitants For instance I found that a piece of turf three feet by
four in size which had been exposed for many years to exactly the same
conditions supported twenty species of plants and these belonged to
eighteen genera and to eight orders which shows how much these plants
differed from each other So it is with the plants and insects on small
and uniform islets also in small ponds of fresh water Farmers find
that they can raise more food by a rotation of plants belonging to the
most different orders nature follows what may be called a simultaneous
rotation Most of the animals and plants which live close round any
small piece of ground could live on it supposing its nature not to be
in any way peculiar and may be said to be striving to the utmost
to live there but it is seen that where they come into the closest
competition the advantages of diversification of structure with the
accompanying differences of habit and constitution determine that the
inhabitants which thus jostle each other most closely shall as a
general rule belong to what we call different genera and orders

The same principle is seen in the naturalisation of plants through mans
agency in foreign lands It might have been expected that the plants
which would succeed in becoming naturalised in any land would generally
have been closely allied to the indigenes for these are commonly looked
at as specially created and adapted for their own country It might
also perhaps have been expected that naturalised plants would have
belonged to a few groups more especially adapted to certain stations in
their new homes But the case is very different and Alph de Candolle
has well remarked in his great and admirable work that floras gain by
naturalisation proportionally with the number of the native genera and
species far more in new genera than in new species To give a single
instance in the last edition of Dr Asa Grays Manual of the Flora of
the Northern United States 260 naturalised plants are enumerated and
these belong to 162 genera We thus see that these naturalised plants
are of a highly diversified nature They differ moreover to a large
extent from the indigenes for out of the 162 naturalised genera
no less than 100 genera are not there indigenous and thus a large
proportional addition is made to the genera now living in the United
States

By considering the nature of the plants or animals which have in any
country struggled successfully with the indigenes and have there become
naturalised we may gain some crude idea in what manner some of the
natives would have had to be modified in order to gain an advantage over
their compatriots and we may at least infer that diversification of
structure amounting to new generic differences would be profitable to
them

The advantage of diversification of structure in the inhabitants of the
same region is in fact the same as that of the physiological division
of labour in the organs of the same individual body a subject so well
elucidated by Milne Edwards No physiologist doubts that a stomach by
being adapted to digest vegetable matter alone or flesh alone draws
most nutriment from these substances So in the general economy of
any land the more widely and perfectly the animals and plants are
diversified for different habits of life so will a greater number of
individuals be capable of there supporting themselves A set of animals
with their organisation but little diversified could hardly compete
with a set more perfectly diversified in structure It may be doubted
for instance whether the Australian marsupials which are divided into
groups differing but little from each other and feebly representing as
Mr Waterhouse and others have remarked our carnivorous ruminant and
rodent mammals could successfully compete with these welldeveloped
orders In the Australian mammals we see the process of diversification
in an early and incomplete stage of development

THE PROBABLE EFFECTS OF THE ACTION OF NATURAL SELECTION THROUGH
DIVERGENCE OF CHARACTER AND EXTINCTION ON THE DESCENDANTS OF A COMMON
ANCESTOR

After the foregoing discussion which has been much compressed we may
assume that the modified descendants of any one species will succeed so
much the better as they become more diversified in structure and are
thus enabled to encroach on places occupied by other beings Now let
us see how this principle of benefit being derived from divergence of
character combined with the principles of natural selection and of
extinction tends to act

The accompanying diagram will aid us in understanding this rather
perplexing subject Let A to L represent the species of a genus large
in its own country these species are supposed to resemble each other
in unequal degrees as is so generally the case in nature and as is
represented in the diagram by the letters standing at unequal distances
I have said a large genus because as we saw in the second chapter on
an average more species vary in large genera than in small genera and
the varying species of the large genera present a greater number of
varieties We have also seen that the species which are the commonest
and most widelydiffused vary more than do the rare and restricted
species Let A be a common widelydiffused and varying species
belonging to a genus large in its own country The branching and
diverging dotted lines of unequal lengths proceeding from A may
represent its varying offspring The variations are supposed to be
extremely slight but of the most diversified nature they are not
supposed all to appear simultaneously but often after long intervals of
time nor are they all supposed to endure for equal periods Only
those variations which are in some way profitable will be preserved or
naturally selected And here the importance of the principle of benefit
derived from divergence of character comes in for this will generally
lead to the most different or divergent variations represented by
the outer dotted lines being preserved and accumulated by natural
selection When a dotted line reaches one of the horizontal lines
and is there marked by a small numbered letter a sufficient amount of
variation is supposed to have been accumulated to form it into a fairly
wellmarked variety such as would be thought worthy of record in a
systematic work

The intervals between the horizontal lines in the diagram may represent
each a thousand or more generations After a thousand generations
species A is supposed to have produced two fairly wellmarked
varieties namely a1 and m1 These two varieties will generally still
be exposed to the same conditions which made their parents variable and
the tendency to variability is in itself hereditary consequently they
will likewise tend to vary and commonly in nearly the same manner as
did their parents Moreover these two varieties being only slightly
modified forms will tend to inherit those advantages which made their
parent A more numerous than most of the other inhabitants of the same
country they will also partake of those more general advantages which
made the genus to which the parentspecies belonged a large genus
in its own country And all these circumstances are favourable to the
production of new varieties

If then these two varieties be variable the most divergent of
their variations will generally be preserved during the next thousand
generations And after this interval variety a1 is supposed in the
diagram to have produced variety a2 which will owing to the principle
of divergence differ more from A than did variety a1 Variety m1 is
supposed to have produced two varieties namely m2 and s2 differing
from each other and more considerably from their common parent A We
may continue the process by similar steps for any length of time some
of the varieties after each thousand generations producing only
a single variety but in a more and more modified condition some
producing two or three varieties and some failing to produce any Thus
the varieties or modified descendants of the common parent A will
generally go on increasing in number and diverging in character In the
diagram the process is represented up to the tenthousandth generation
and under a condensed and simplified form up to the fourteenthousandth
generation

But I must here remark that I do not suppose that the process ever goes
on so regularly as is represented in the diagram though in itself made
somewhat irregular nor that it goes on continuously it is far more
probable that each form remains for long periods unaltered and then
again undergoes modification Nor do I suppose that the most divergent
varieties are invariably preserved a medium form may often long endure
and may or may not produce more than one modified descendant for
natural selection will always act according to the nature of the places
which are either unoccupied or not perfectly occupied by other beings
and this will depend on infinitely complex relations But as a general
rule the more diversified in structure the descendants from any one
species can be rendered the more places they will be enabled to seize
on and the more their modified progeny will increase In our diagram
the line of succession is broken at regular intervals by small numbered
letters marking the successive forms which have become sufficiently
distinct to be recorded as varieties But these breaks are imaginary
and might have been inserted anywhere after intervals long enough to
allow the accumulation of a considerable amount of divergent variation

As all the modified descendants from a common and widelydiffused
species belonging to a large genus will tend to partake of the
same advantages which made their parent successful in life they will
generally go on multiplying in number as well as diverging in character
this is represented in the diagram by the several divergent branches
proceeding from A The modified offspring from the later and more
highly improved branches in the lines of descent will it is probable
often take the place of and so destroy the earlier and less improved
branches this is represented in the diagram by some of the lower
branches not reaching to the upper horizontal lines In some cases no
doubt the process of modification will be confined to a single line of
descent and the number of modified descendants will not be increased
although the amount of divergent modification may have been augmented
This case would be represented in the diagram if all the lines
proceeding from A were removed excepting that from a1 to a10 In the
same way the English racehorse and English pointer have apparently
both gone on slowly diverging in character from their original stocks
without either having given off any fresh branches or races

After ten thousand generations species A is supposed to have produced
three forms a10 f10 and m10 which from having diverged in character
during the successive generations will have come to differ largely but
perhaps unequally from each other and from their common parent If we
suppose the amount of change between each horizontal line in our diagram
to be excessively small these three forms may still be only wellmarked
varieties but we have only to suppose the steps in the process of
modification to be more numerous or greater in amount to convert these
three forms into doubtful or at least into welldefined species
thus the diagram illustrates the steps by which the small differences
distinguishing varieties are increased into the larger differences
distinguishing species By continuing the same process for a greater
number of generations as shown in the diagram in a condensed and
simplified manner we get eight species marked by the letters between
a14 and m14 all descended from A Thus as I believe species are
multiplied and genera are formed

In a large genus it is probable that more than one species would vary
In the diagram I have assumed that a second species I has produced by
analogous steps after ten thousand generations either two wellmarked
varieties w10 and z10 or two species according to the amount of
change supposed to be represented between the horizontal lines After
fourteen thousand generations six new species marked by the letters
n14 to z14 are supposed to have been produced In any genus the
species which are already very different in character from each
other will generally tend to produce the greatest number of modified
descendants for these will have the best chance of seizing on new and
widely different places in the polity of nature hence in the diagram I
have chosen the extreme species A and the nearly extreme species I
as those which have largely varied and have given rise to new varieties
and species The other nine species marked by capital letters of our
original genus may for long but unequal periods continue to transmit
unaltered descendants and this is shown in the diagram by the dotted
lines unequally prolonged upwards

But during the process of modification represented in the diagram
another of our principles namely that of extinction will have played
an important part As in each fully stocked country natural selection
necessarily acts by the selected form having some advantage in the
struggle for life over other forms there will be a constant tendency in
the improved descendants of any one species to supplant and exterminate
in each stage of descent their predecessors and their original
progenitor For it should be remembered that the competition will
generally be most severe between those forms which are most nearly
related to each other in habits constitution and structure Hence all
the intermediate forms between the earlier and later states that is
between the less and more improved states of a the same species as well
as the original parentspecies itself will generally tend to become
extinct So it probably will be with many whole collateral lines of
descent which will be conquered by later and improved lines If
however the modified offspring of a species get into some distinct
country or become quickly adapted to some quite new station in which
offspring and progenitor do not come into competition both may continue
to exist

If then our diagram be assumed to represent a considerable amount of
modification species A and all the earlier varieties will have become
extinct being replaced by eight new species a14 to m14 and species
I will be replaced by six n14 to z14 new species

But we may go further than this The original species of our genus were
supposed to resemble each other in unequal degrees as is so generally
the case in nature species A being more nearly related to B C and
D than to the other species and species I more to G H K L than to
the others These two species A and I were also supposed to be very
common and widely diffused species so that they must originally have
had some advantage over most of the other species of the genus Their
modified descendants fourteen in number at the fourteenthousandth
generation will probably have inherited some of the same advantages
they have also been modified and improved in a diversified manner at
each stage of descent so as to have become adapted to many related
places in the natural economy of their country It seems therefore
extremely probable that they will have taken the places of and thus
exterminated not only their parents A and I but likewise some of
the original species which were most nearly related to their parents
Hence very few of the original species will have transmitted offspring
to the fourteenthousandth generation We may suppose that only one F
of the two species E and F which were least closely related to the
other nine original species has transmitted descendants to this late
stage of descent

The new species in our diagram descended from the original eleven
species will now be fifteen in number Owing to the divergent tendency
of natural selection the extreme amount of difference in character
between species a14 and z14 will be much greater than that between the
most distinct of the original eleven species The new species moreover
will be allied to each other in a widely different manner Of the eight
descendants from A the three marked a14 q14 p14 will be nearly
related from having recently branched off from a10 b14 and f14 from
having diverged at an earlier period from a5 will be in some degree
distinct from the three firstnamed species and lastly o14 e14 and
m14 will be nearly related one to the other but from having diverged
at the first commencement of the process of modification will be widely
different from the other five species and may constitute a subgenus or
a distinct genus

The six descendants from I will form two subgenera or genera But as
the original species I differed largely from A standing nearly
at the extreme end of the original genus the six descendants from I
will owing to inheritance alone differ considerably from the eight
descendants from A the two groups moreover are supposed to have
gone on diverging in different directions The intermediate species
also and this is a very important consideration which connected the
original species A and I have all become except F extinct and
have left no descendants Hence the six new species descended from
I and the eight descendants from A will have to be ranked as very
distinct genera or even as distinct subfamilies

Thus it is as I believe that two or more genera are produced by
descent with modification from two or more species of the same genus
And the two or more parentspecies are supposed to be descended from
some one species of an earlier genus In our diagram this is indicated
by the broken lines beneath the capital letters converging in
subbranches downwards towards a single point this point represents
a species the supposed progenitor of our several new subgenera and
genera

It is worth while to reflect for a moment on the character of the new
species F14 which is supposed not to have diverged much in character
but to have retained the form of F either unaltered or altered only
in a slight degree In this case its affinities to the other fourteen
new species will be of a curious and circuitous nature Being descended
from a form that stood between the parentspecies A and I
now supposed to be extinct and unknown it will be in some degree
intermediate in character between the two groups descended from these
two species But as these two groups have gone on diverging in character
from the type of their parents the new species F14 will not be
directly intermediate between them but rather between types of the two
groups and every naturalist will be able to call such cases before his
mind

In the diagram each horizontal line has hitherto been supposed to
represent a thousand generations but each may represent a million or
more generations it may also represent a section of the successive
strata of the earths crust including extinct remains We shall when we
come to our chapter on geology have to refer again to this subject
and I think we shall then see that the diagram throws light on the
affinities of extinct beings which though generally belonging to the
same orders families or genera with those now living yet are often
in some degree intermediate in character between existing groups and
we can understand this fact for the extinct species lived at various
remote epochs when the branching lines of descent had diverged less

I see no reason to limit the process of modification as now explained
to the formation of genera alone If in the diagram we suppose the
amount of change represented by each successive group of diverging
dotted lines to be great the forms marked a14 to p14 those marked
b14 and f14 and those marked o14 to m14 will form three very distinct
genera We shall also have two very distinct genera descended from I
differing widely from the descendants of A These two groups of genera
will thus form two distinct families or orders according to the amount
of divergent modification supposed to be represented in the diagram And
the two new families or orders are descended from two species of the
original genus and these are supposed to be descended from some still
more ancient and unknown form

We have seen that in each country it is the species belonging to the
larger genera which oftenest present varieties or incipient species
This indeed might have been expected for as natural selection acts
through one form having some advantage over other forms in the struggle
for existence it will chiefly act on those which already have some
advantage and the largeness of any group shows that its species have
inherited from a common ancestor some advantage in common Hence the
struggle for the production of new and modified descendants will mainly
lie between the larger groups which are all trying to increase in
number One large group will slowly conquer another large group
reduce its number and thus lessen its chance of further variation and
improvement Within the same large group the later and more highly
perfected subgroups from branching out and seizing on many new places
in the polity of nature will constantly tend to supplant and destroy
the earlier and less improved subgroups Small and broken groups and
subgroups will finally disappear Looking to the future we can predict
that the groups of organic beings which are now large and triumphant
and which are least broken up that is which have as yet suffered least
extinction will for a long period continue to increase But which
groups will ultimately prevail no man can predict for we know that
many groups formerly most extensively developed have now become
extinct Looking still more remotely to the future we may predict
that owing to the continued and steady increase of the larger groups
a multitude of smaller groups will become utterly extinct and leave no
modified descendants and consequently that of the species living at
any one period extremely few will transmit descendants to a remote
futurity I shall have to return to this subject in the chapter on
classification but I may add that as according to this view extremely
few of the more ancient species have transmitted descendants to the
present day and as all the descendants of the same species form a
class we can understand how it is that there exist so few classes in
each main division of the animal and vegetable kingdoms Although few of
the most ancient species have left modified descendants yet at remote
geological periods the earth may have been almost as well peopled with
species of many genera families orders and classes as at the present
day

ON THE DEGREE TO WHICH ORGANISATION TENDS TO ADVANCE

Natural selection acts exclusively by the preservation and accumulation
of variations which are beneficial under the organic and inorganic
conditions to which each creature is exposed at all periods of life
The ultimate result is that each creature tends to become more and more
improved in relation to its conditions This improvement inevitably
leads to the gradual advancement of the organisation of the greater
number of living beings throughout the world But here we enter on a
very intricate subject for naturalists have not defined to each others
satisfaction what is meant by an advance in organisation Among the
vertebrata the degree of intellect and an approach in structure to man
clearly come into play It might be thought that the amount of change
which the various parts and organs pass through in their development
from embryo to maturity would suffice as a standard of comparison but
there are cases as with certain parasitic crustaceans in which several
parts of the structure become less perfect so that the mature animal
cannot be called higher than its larva Von Baers standard seems
the most widely applicable and the best namely the amount of
differentiation of the parts of the same organic being in the adult
state as I should be inclined to add and their specialisation
for different functions or as Milne Edwards would express it the
completeness of the division of physiological labour But we shall see
how obscure this subject is if we look for instance to fishes among
which some naturalists rank those as highest which like the sharks
approach nearest to amphibians while other naturalists rank the common
bony or teleostean fishes as the highest inasmuch as they are most
strictly fishlike and differ most from the other vertebrate classes
We see still more plainly the obscurity of the subject by turning
to plants among which the standard of intellect is of course quite
excluded and here some botanists rank those plants as highest which
have every organ as sepals petals stamens and pistils fully
developed in each flower whereas other botanists probably with more
truth look at the plants which have their several organs much modified
and reduced in number as the highest

If we take as the standard of high organisation the amount of
differentiation and specialisation of the several organs in each being
when adult and this will include the advancement of the brain for
intellectual purposes natural selection clearly leads towards this
standard for all physiologists admit that the specialisation of organs
inasmuch as in this state they perform their functions better is
an advantage to each being and hence the accumulation of variations
tending towards specialisation is within the scope of natural selection
On the other hand we can see bearing in mind that all organic
beings are striving to increase at a high ratio and to seize on every
unoccupied or less well occupied place in the economy of nature that
it is quite possible for natural selection gradually to fit a being to
a situation in which several organs would be superfluous or useless in
such cases there would be retrogression in the scale of organisation
Whether organisation on the whole has actually advanced from the
remotest geological periods to the present day will be more conveniently
discussed in our chapter on Geological Succession

But it may be objected that if all organic beings thus tend to rise in
the scale how is it that throughout the world a multitude of the lowest
forms still exist and how is it that in each great class some forms
are far more highly developed than others Why have not the more highly
developed forms every where supplanted and exterminated the lower
Lamarck who believed in an innate and inevitable tendency towards
perfection in all organic beings seems to have felt this difficulty
so strongly that he was led to suppose that new and simple forms are
continually being produced by spontaneous generation Science has not as
yet proved the truth of this belief whatever the future may reveal
On our theory the continued existence of lowly organisms offers no
difficulty for natural selection or the survival of the fittest does
not necessarily include progressive development it only takes advantage
of such variations as arise and are beneficial to each creature under
its complex relations of life And it may be asked what advantage
as far as we can see would it be to an infusorian animalcule to an
intestinal worm or even to an earthworm to be highly organised If
it were no advantage these forms would be left by natural selection
unimproved or but little improved and might remain for indefinite ages
in their present lowly condition And geology tells us that some of
the lowest forms as the infusoria and rhizopods have remained for an
enormous period in nearly their present state But to suppose that most
of the many now existing low forms have not in the least advanced since
the first dawn of life would be extremely rash for every naturalist who
has dissected some of the beings now ranked as very low in the
scale must have been struck with their really wondrous and beautiful
organisation

Nearly the same remarks are applicable if we look to the different
grades of organisation within the same great group for instance in the
vertebrata to the coexistence of mammals and fish among mammalia to
the coexistence of man and the ornithorhynchus among fishes to the
coexistence of the shark and the lancelet Amphioxus which latter
fish in the extreme simplicity of its structure approaches the
invertebrate classes But mammals and fish hardly come into competition
with each other the advancement of the whole class of mammals or of
certain members in this class to the highest grade would not lead to
their taking the place of fishes Physiologists believe that the brain
must be bathed by warm blood to be highly active and this requires
aerial respiration so that warmblooded mammals when inhabiting the
water lie under a disadvantage in having to come continually to the
surface to breathe With fishes members of the shark family would not
tend to supplant the lancelet for the lancelet as I hear from Fritz
Muller has as sole companion and competitor on the barren sandy shore
of South Brazil an anomalous annelid The three lowest orders of
mammals namely marsupials edentata and rodents coexist in South
America in the same region with numerous monkeys and probably interfere
little with each other Although organisation on the whole may have
advanced and be still advancing throughout the world yet the scale will
always present many degrees of perfection for the high advancement of
certain whole classes or of certain members of each class does not at
all necessarily lead to the extinction of those groups with which
they do not enter into close competition In some cases as we shall
hereafter see lowly organised forms appear to have been preserved to
the present day from inhabiting confined or peculiar stations where
they have been subjected to less severe competition and where their
scanty numbers have retarded the chance of favourable variations
arising

Finally I believe that many lowly organised forms now exist throughout
the world from various causes In some cases variations or individual
differences of a favourable nature may never have arisen for natural
selection to act on and accumulate In no case probably has time
sufficed for the utmost possible amount of development In some few
cases there has been what we must call retrogression or organisation
But the main cause lies in the fact that under very simple conditions
of life a high organisation would be of no service possibly would be of
actual disservice as being of a more delicate nature and more liable
to be put out of order and injured

Looking to the first dawn of life when all organic beings as we may
believe presented the simplest structure how it has been asked
could the first step in the advancement or differentiation of parts
have arisen Mr Herbert Spencer would probably answer that as soon as
simple unicellular organisms came by growth or division to be compounded
of several cells or became attached to any supporting surface his law
that homologous units of any order become differentiated in proportion
as their relations to incident forces become different would come into
action But as we have no facts to guide us speculation on the subject
is almost useless It is however an error to suppose that there would
be no struggle for existence and consequently no natural selection
until many forms had been produced variations in a single species
inhabiting an isolated station might be beneficial and thus the whole
mass of individuals might be modified or two distinct forms might
arise But as I remarked towards the close of the introduction no
one ought to feel surprise at much remaining as yet unexplained on the
origin of species if we make due allowance for our profound ignorance
on the mutual relations of the inhabitants of the world at the present
time and still more so during past ages

CONVERGENCE OF CHARACTER

Mr HC Watson thinks that I have overrated the importance of
divergence of character in which however he apparently believes and
that convergence as it may be called has likewise played a part If
two species belonging to two distinct though allied genera had both
produced a large number of new and divergent forms it is conceivable
that these might approach each other so closely that they would have
all to be classed under the same genus and thus the descendants of two
distinct genera would converge into one But it would in most cases
be extremely rash to attribute to convergence a close and general
similarity of structure in the modified descendants of widely distinct
forms The shape of a crystal is determined solely by the molecular
forces and it is not surprising that dissimilar substances should
sometimes assume the same form but with organic beings we should
bear in mind that the form of each depends on an infinitude of complex
relations namely on the variations which have arisen these being due
to causes far too intricate to be followed out on the nature of the
variations which have been preserved or selected and this depends on
the surrounding physical conditions and in a still higher degree on
the surrounding organisms with which each being has come into
competition and lastly on inheritance in itself a fluctuating
element from innumerable progenitors all of which have had their forms
determined through equally complex relations It is incredible that the
descendants of two organisms which had originally differed in a marked
manner should ever afterwards converge so closely as to lead to a near
approach to identity throughout their whole organisation If this had
occurred we should meet with the same form independently of genetic
connection recurring in widely separated geological formations and the
balance of evidence is opposed to any such an admission

Mr Watson has also objected that the continued action of natural
selection together with divergence of character would tend to make an
indefinite number of specific forms As far as mere inorganic conditions
are concerned it seems probable that a sufficient number of species
would soon become adapted to all considerable diversities of heat
moisture etc but I fully admit that the mutual relations of organic
beings are more important and as the number of species in any country
goes on increasing the organic conditions of life must become more and
more complex Consequently there seems at first no limit to the amount
of profitable diversification of structure and therefore no limit to
the number of species which might be produced We do not know that even
the most prolific area is fully stocked with specific forms at the Cape
of Good Hope and in Australia which support such an astonishing number
of species many European plants have become naturalised But geology
shows us that from an early part of the tertiary period the number of
species of shells and that from the middle part of this same period
the number of mammals has not greatly or at all increased What then
checks an indefinite increase in the number of species The amount of
life I do not mean the number of specific forms supported on an
area must have a limit depending so largely as it does on physical
conditions therefore if an area be inhabited by very many species
each or nearly each species will be represented by few individuals
and such species will be liable to extermination from accidental
fluctuations in the nature of the seasons or in the number of their
enemies The process of extermination in such cases would be rapid
whereas the production of new species must always be slow Imagine the
extreme case of as many species as individuals in England and the
first severe winter or very dry summer would exterminate thousands on
thousands of species Rare species and each species will become rare
if the number of species in any country becomes indefinitely increased
will on the principal often explained present within a given period
few favourable variations consequently the process of giving birth to
new specific forms would thus be retarded When any species becomes
very rare close interbreeding will help to exterminate it authors have
thought that this comes into play in accounting for the deterioration
of the aurochs in Lithuania of red deer in Scotland and of bears
in Norway etc Lastly and this I am inclined to think is the most
important element a dominant species which has already beaten many
competitors in its own home will tend to spread and supplant many
others Alph de Candolle has shown that those species which spread
widely tend generally to spread VERY widely consequently they will tend
to supplant and exterminate several species in several areas and thus
check the inordinate increase of specific forms throughout the world
Dr Hooker has recently shown that in the southeast corner of Australia
where apparently there are many invaders from different quarters of
the globe the endemic Australian species have been greatly reduced in
number How much weight to attribute to these several considerations I
will not pretend to say but conjointly they must limit in each country
the tendency to an indefinite augmentation of specific forms

SUMMARY OF CHAPTER

If under changing conditions of life organic beings present individual
differences in almost every part of their structure and this cannot be
disputed if there be owing to their geometrical rate of increase a
severe struggle for life at some age season or year and this certainly
cannot be disputed then considering the infinite complexity of the
relations of all organic beings to each other and to their conditions
of life causing an infinite diversity in structure constitution and
habits to be advantageous to them it would be a most extraordinary
fact if no variations had ever occurred useful to each beings own
welfare in the same manner as so many variations have occurred useful
to man But if variations useful to any organic being ever do occur
assuredly individuals thus characterised will have the best chance of
being preserved in the struggle for life and from the strong principle
of inheritance these will tend to produce offspring similarly
characterised This principle of preservation or the survival of the
fittest I have called natural selection It leads to the improvement
of each creature in relation to its organic and inorganic conditions of
life and consequently in most cases to what must be regarded as an
advance in organisation Nevertheless low and simple forms will long
endure if well fitted for their simple conditions of life

Natural selection on the principle of qualities being inherited at
corresponding ages can modify the egg seed or young as easily as the
adult Among many animals sexual selection will have given its aid to
ordinary selection by assuring to the most vigorous and best adapted
males the greatest number of offspring Sexual selection will also give
characters useful to the males alone in their struggles or rivalry with
other males and these characters will be transmitted to one sex or to
both sexes according to the form of inheritance which prevails

Whether natural selection has really thus acted in adapting the various
forms of life to their several conditions and stations must be judged
by the general tenour and balance of evidence given in the following
chapters But we have already seen how it entails extinction and how
largely extinction has acted in the worlds history geology plainly
declares Natural selection also leads to divergence of character for
the more organic beings diverge in structure habits and constitution
by so much the more can a large number be supported on the area of
which we see proof by looking to the inhabitants of any small spot and
to the productions naturalised in foreign lands Therefore during
the modification of the descendants of any one species and during
the incessant struggle of all species to increase in numbers the more
diversified the descendants become the better will be their chance
of success in the battle for life Thus the small differences
distinguishing varieties of the same species steadily tend to increase
till they equal the greater differences between species of the same
genus or even of distinct genera

We have seen that it is the common the widely diffused and widely
ranging species belonging to the larger genera within each class which
vary most and these tend to transmit to their modified offspring
that superiority which now makes them dominant in their own countries
Natural selection as has just been remarked leads to divergence of
character and to much extinction of the less improved and intermediate
forms of life On these principles the nature of the affinities and
the generally well defined distinctions between the innumerable organic
beings in each class throughout the world may be explained It is a
truly wonderful fact the wonder of which we are apt to overlook from
familiarity that all animals and all plants throughout all time and
space should be related to each other in groups subordinate to groups
in the manner which we everywhere behold namely varieties of the same
species most closely related species of the same genus less closely and
unequally related forming sections and subgenera species of distinct
genera much less closely related and genera related in different
degrees forming subfamilies families orders subclasses and
classes The several subordinate groups in any class cannot be ranked
in a single file but seem clustered round points and these round
other points and so on in almost endless cycles If species had been
independently created no explanation would have been possible of this
kind of classification but it is explained through inheritance and the
complex action of natural selection entailing extinction and divergence
of character as we have seen illustrated in the diagram

The affinities of all the beings of the same class have sometimes been
represented by a great tree I believe this simile largely speaks the
truth The green and budding twigs may represent existing species and
those produced during former years may represent the long succession
of extinct species At each period of growth all the growing twigs
have tried to branch out on all sides and to overtop and kill the
surrounding twigs and branches in the same manner as species and groups
of species have at all times overmastered other species in the great
battle for life The limbs divided into great branches and these into
lesser and lesser branches were themselves once when the tree was
young budding twigs and this connexion of the former and present
buds by ramifying branches may well represent the classification of all
extinct and living species in groups subordinate to groups Of the many
twigs which flourished when the tree was a mere bush only two or three
now grown into great branches yet survive and bear the other branches
so with the species which lived during longpast geological periods
very few have left living and modified descendants From the first
growth of the tree many a limb and branch has decayed and dropped off
and these fallen branches of various sizes may represent those whole
orders families and genera which have now no living representatives
and which are known to us only in a fossil state As we here and there
see a thin straggling branch springing from a fork low down in a tree
and which by some chance has been favoured and is still alive on its
summit so we occasionally see an animal like the Ornithorhynchus or
Lepidosiren which in some small degree connects by its affinities two
large branches of life and which has apparently been saved from fatal
competition by having inhabited a protected station As buds give rise
by growth to fresh buds and these if vigorous branch out and overtop
on all sides many a feebler branch so by generation I believe it has
been with the great Tree of Life which fills with its dead and broken
branches the crust of the earth and covers the surface with its
everbranching and beautiful ramifications




CHAPTER V LAWS OF VARIATION

 Effects of changed conditions Use and disuse combined with natural
 selection organs of flight and of vision Acclimatisation Correlated
 variation Compensation and economy of growth False
 correlations Multiple rudimentary and lowly organised structures
 variable Parts developed in an unusual manner are highly variable
 specific characters more variable than generic secondary sexual
 characters variable Species of the same genus vary in an analogous
 manner Reversions to longlost characters Summary


I have hitherto sometimes spoken as if the variations so common and
multiform with organic beings under domestication and in a lesser
degree with those under nature were due to chance This of course is
a wholly incorrect expression but it serves to acknowledge plainly
our ignorance of the cause of each particular variation Some authors
believe it to be as much the function of the reproductive system to
produce individual differences or slight deviations of structure as
to make the child like its parents But the fact of variations and
monstrosities occurring much more frequently under domestication than
under nature and the greater variability of species having wide ranges
than of those with restricted ranges lead to the conclusion that
variability is generally related to the conditions of life to which each
species has been exposed during several successive generations In the
first chapter I attempted to show that changed conditions act in two
ways directly on the whole organisation or on certain parts alone and
indirectly through the reproductive system In all cases there are two
factors the nature of the organism which is much the most important of
the two and the nature of the conditions The direct action of changed
conditions leads to definite or indefinite results In the latter case
the organisation seems to become plastic and we have much fluctuating
variability In the former case the nature of the organism is such that
it yields readily when subjected to certain conditions and all or
nearly all the individuals become modified in the same way

It is very difficult to decide how far changed conditions such as of
climate food etc have acted in a definite manner There is reason
to believe that in the course of time the effects have been greater than
can be proved by clear evidence But we may safely conclude that the
innumerable complex coadaptations of structure which we see throughout
nature between various organic beings cannot be attributed simply to
such action In the following cases the conditions seem to have produced
some slight definite effect E Forbes asserts that shells at their
southern limit and when living in shallow water are more brightly
coloured than those of the same species from further north or from a
greater depth but this certainly does not always hold good Mr Gould
believes that birds of the same species are more brightly coloured under
a clear atmosphere than when living near the coast or on islands and
Wollaston is convinced that residence near the sea affects the colours
of insects MoquinTandon gives a list of plants which when growing
near the seashore have their leaves in some degree fleshy though not
elsewhere fleshy These slightly varying organisms are interesting in
as far as they present characters analogous to those possessed by the
species which are confined to similar conditions

When a variation is of the slightest use to any being we cannot tell
how much to attribute to the accumulative action of natural selection
and how much to the definite action of the conditions of life Thus it
is well known to furriers that animals of the same species have thicker
and better fur the further north they live but who can tell how much of
this difference may be due to the warmestclad individuals having been
favoured and preserved during many generations and how much to the
action of the severe climate For it would appear that climate has some
direct action on the hair of our domestic quadrupeds

Instances could be given of similar varieties being produced from the
same species under external conditions of life as different as can well
be conceived and on the other hand of dissimilar varieties being
produced under apparently the same external conditions Again
innumerable instances are known to every naturalist of species keeping
true or not varying at all although living under the most opposite
climates Such considerations as these incline me to lay less weight on
the direct action of the surrounding conditions than on a tendency to
vary due to causes of which we are quite ignorant

In one sense the conditions of life may be said not only to cause
variability either directly or indirectly but likewise to include
natural selection for the conditions determine whether this or that
variety shall survive But when man is the selecting agent we clearly
see that the two elements of change are distinct variability is in
some manner excited but it is the will of man which accumulates the
variations in certain direction and it is this latter agency which
answers to the survival of the fittest under nature

EFFECTS OF THE INCREASED USE AND DISUSE OF PARTS AS CONTROLLED BY
NATURAL SELECTION

From the facts alluded to in the first chapter I think there can be
no doubt that use in our domestic animals has strengthened and enlarged
certain parts and disuse diminished them and that such modifications
are inherited Under free nature we have no standard of comparison by
which to judge of the effects of longcontinued use or disuse for we
know not the parentforms but many animals possess structures which
can be best explained by the effects of disuse As Professor Owen has
remarked there is no greater anomaly in nature than a bird that cannot
fly yet there are several in this state The loggerheaded duck of
South America can only flap along the surface of the water and has its
wings in nearly the same condition as the domestic Aylesbury duck it is
a remarkable fact that the young birds according to Mr Cunningham can
fly while the adults have lost this power As the larger groundfeeding
birds seldom take flight except to escape danger it is probable that
the nearly wingless condition of several birds now inhabiting or which
lately inhabited several oceanic islands tenanted by no beasts of prey
has been caused by disuse The ostrich indeed inhabits continents and
is exposed to danger from which it cannot escape by flight but it
can defend itself by kicking its enemies as efficiently as many
quadrupeds We may believe that the progenitor of the ostrich genus had
habits like those of the bustard and that as the size and weight of
its body were increased during successive generations its legs were
used more and its wings less until they became incapable of flight

Kirby has remarked and I have observed the same fact that the anterior
tarsi or feet of many male dungfeeding beetles are often broken off
he examined seventeen specimens in his own collection and not one had
even a relic left In the Onites apelles the tarsi are so habitually
lost that the insect has been described as not having them In some
other genera they are present but in a rudimentary condition In the
Ateuchus or sacred beetle of the Egyptians they are totally deficient
The evidence that accidental mutilations can be inherited is at present
not decisive but the remarkable cases observed by BrownSequard in
guineapigs of the inherited effects of operations should make us
cautious in denying this tendency Hence it will perhaps be safest to
look at the entire absence of the anterior tarsi in Ateuchus and their
rudimentary condition in some other genera not as cases of inherited
mutilations but as due to the effects of longcontinued disuse for
as many dungfeeding beetles are generally found with their tarsi lost
this must happen early in life therefore the tarsi cannot be of much
importance or be much used by these insects

In some cases we might easily put down to disuse modifications of
structure which are wholly or mainly due to natural selection Mr
Wollaston has discovered the remarkable fact that 200 beetles out of
the 550 species but more are now known inhabiting Madeira are so far
deficient in wings that they cannot fly and that of the twentynine
endemic genera no less than twentythree have all their species in
this condition  Several facts namely that beetles in many parts of the
world are very frequently blown to sea and perish that the beetles in
Madeira as observed by Mr Wollaston lie much concealed until the
wind lulls and the sun shines that the proportion of wingless beetles
is larger on the exposed Desertas than in Madeira itself and especially
the extraordinary fact so strongly insisted on by Mr Wollaston that
certain large groups of beetles elsewhere excessively numerous which
absolutely require the use of their wings are here almost entirely
absent These several considerations make me believe that the wingless
condition of so many Madeira beetles is mainly due to the action of
natural selection combined probably with disuse For during many
successive generations each individual beetle which flew least either
from its wings having been ever so little less perfectly developed or
from indolent habit will have had the best chance of surviving from not
being blown out to sea and on the other hand those beetles which most
readily took to flight would oftenest have been blown to sea and thus
destroyed

The insects in Madeira which are not groundfeeders and which as
certain flowerfeeding coleoptera and lepidoptera must habitually use
their wings to gain their subsistence have as Mr Wollaston suspects
their wings not at all reduced but even enlarged This is quite
compatible with the action of natural selection For when a new insect
first arrived on the island the tendency of natural selection to
enlarge or to reduce the wings would depend on whether a greater number
of individuals were saved by successfully battling with the winds or
by giving up the attempt and rarely or never flying As with mariners
shipwrecked near a coast it would have been better for the good
swimmers if they had been able to swim still further whereas it would
have been better for the bad swimmers if they had not been able to swim
at all and had stuck to the wreck

The eyes of moles and of some burrowing rodents are rudimentary in size
and in some cases are quite covered by skin and fur This state of the
eyes is probably due to gradual reduction from disuse but aided
perhaps by natural selection In South America a burrowing rodent the
tucotuco or Ctenomys is even more subterranean in its habits than the
mole and I was assured by a Spaniard who had often caught them that
they were frequently blind One which I kept alive was certainly in
this condition the cause as appeared on dissection having been
inflammation of the nictitating membrane As frequent inflammation of
the eyes must be injurious to any animal and as eyes are certainly not
necessary to animals having subterranean habits a reduction in their
size with the adhesion of the eyelids and growth of fur over them
might in such case be an advantage and if so natural selection would
aid the effects of disuse

It is well known that several animals belonging to the most different
classes which inhabit the caves of Carniola and Kentucky are blind In
some of the crabs the footstalk for the eye remains though the eye is
gone the stand for the telescope is there though the telescope with
its glasses has been lost As it is difficult to imagine that eyes
though useless could be in any way injurious to animals living in
darkness their loss may be attributed to disuse In one of the blind
animals namely the caverat Neotoma two of which were captured by
Professor Silliman at above half a mile distance from the mouth of
the cave and therefore not in the profoundest depths the eyes were
lustrous and of large size and these animals as I am informed by
Professor Silliman after having been exposed for about a month to a
graduated light acquired a dim perception of objects

It is difficult to imagine conditions of life more similar than deep
limestone caverns under a nearly similar climate so that in accordance
with the old view of the blind animals having been separately created
for the American and European caverns very close similarity in their
organisation and affinities might have been expected This is certainly
not the case if we look at the two whole faunas with respect to the
insects alone Schiodte has remarked We are accordingly prevented
from considering the entire phenomenon in any other light than something
purely local and the similarity which is exhibited in a few forms
between the Mammoth Cave in Kentucky and the caves in Carniola
otherwise than as a very plain expression of that analogy which subsists
generally between the fauna of Europe and of North America On my view
we must suppose that American animals having in most cases ordinary
powers of vision slowly migrated by successive generations from the
outer world into the deeper and deeper recesses of the Kentucky caves
as did European animals into the caves of Europe We have some evidence
of this gradation of habit for as Schiodte remarks We accordingly
look upon the subterranean faunas as small ramifications which have
penetrated into the earth from the geographically limited faunas of the
adjacent tracts and which as they extended themselves into darkness
have been accommodated to surrounding circumstances Animals not
far remote from ordinary forms prepare the transition from light to
darkness Next follow those that are constructed for twilight and last
of all those destined for total darkness and whose formation is quite
peculiar These remarks of Schiodtes it should be understood apply
not to the same but to distinct species By the time that an animal had
reached after numberless generations the deepest recesses disuse
will on this view have more or less perfectly obliterated its eyes and
natural selection will often have effected other changes such as an
increase in the length of the antennae or palpi as a compensation for
blindness Notwithstanding such modifications we might expect still to
see in the caveanimals of America affinities to the other inhabitants
of that continent and in those of Europe to the inhabitants of the
European continent And this is the case with some of the American
caveanimals as I hear from Professor Dana and some of the European
caveinsects are very closely allied to those of the surrounding
country It would be difficult to give any rational explanation of the
affinities of the blind caveanimals to the other inhabitants of the
two continents on the ordinary view of their independent creation That
several of the inhabitants of the caves of the Old and New Worlds should
be closely related we might expect from the wellknown relationship
of most of their other productions As a blind species of Bathyscia is
found in abundance on shady rocks far from caves the loss of vision in
the cave species of this one genus has probably had no relation to its
dark habitation for it is natural that an insect already deprived of
vision should readily become adapted to dark caverns Another blind
genus Anophthalmus offers this remarkable peculiarity that the
species as Mr Murray observes have not as yet been found anywhere
except in caves yet those which inhabit the several caves of Europe and
America are distinct but it is possible that the progenitors of these
several species while they were furnished with eyes may formerly have
ranged over both continents and then have become extinct excepting in
their present secluded abodes Far from feeling surprise that some of
the caveanimals should be very anomalous as Agassiz has remarked in
regard to the blind fish the Amblyopsis and as is the case with the
blind Proteus with reference to the reptiles of Europe I am only
surprised that more wrecks of ancient life have not been preserved
owing to the less severe competition to which the scanty inhabitants of
these dark abodes will have been exposed

ACCLIMATISATION

Habit is hereditary with plants as in the period of flowering in the
time of sleep in the amount of rain requisite for seeds to germinate
etc and this leads me to say a few words on acclimatisation As it
is extremely common for distinct species belonging to the same genus to
inhabit hot and cold countries if it be true that all the species of
the same genus are descended from a single parentform acclimatisation
must be readily effected during a long course of descent It is
notorious that each species is adapted to the climate of its own home
species from an arctic or even from a temperate region cannot endure a
tropical climate or conversely So again many succulent plants cannot
endure a damp climate But the degree of adaptation of species to the
climates under which they live is often overrated We may infer this
from our frequent inability to predict whether or not an imported plant
will endure our climate and from the number of plants and animals
brought from different countries which are here perfectly healthy We
have reason to believe that species in a state of nature are closely
limited in their ranges by the competition of other organic beings quite
as much as or more than by adaptation to particular climates But
whether or not this adaptation is in most cases very close we have
evidence with some few plants of their becoming to a certain extent
naturally habituated to different temperatures that is they become
acclimatised thus the pines and rhododendrons raised from seed
collected by Dr Hooker from the same species growing at different
heights on the Himalayas were found to possess in this country
different constitutional powers of resisting cold Mr Thwaites informs
me that he has observed similar facts in Ceylon analogous observations
have been made by Mr HC Watson on European species of plants brought
from the Azores to England and I could give other cases In regard to
animals several authentic instances could be adduced of species having
largely extended within historical times their range from warmer to
colder latitudes and conversely but we do not positively know that
these animals were strictly adapted to their native climate though in
all ordinary cases we assume such to be the case nor do we know that
they have subsequently become specially acclimatised to their new homes
so as to be better fitted for them than they were at first

As we may infer that our domestic animals were originally chosen by
uncivilised man because they were useful and because they bred readily
under confinement and not because they were subsequently found capable
of farextended transportation the common and extraordinary capacity
in our domestic animals of not only withstanding the most different
climates but of being perfectly fertile a far severer test under
them may be used as an argument that a large proportion of other
animals now in a state of nature could easily be brought to bear widely
different climates We must not however push the foregoing argument
too far on account of the probable origin of some of our domestic
animals from several wild stocks the blood for instance of a tropical
and arctic wolf may perhaps be mingled in our domestic breeds The rat
and mouse cannot be considered as domestic animals but they have been
transported by man to many parts of the world and now have a far wider
range than any other rodent for they live under the cold climate of
Faroe in the north and of the Falklands in the south and on many an
island in the torrid zones Hence adaptation to any special climate may
be looked at as a quality readily grafted on an innate wide flexibility
of constitution common to most animals On this view the capacity of
enduring the most different climates by man himself and by his domestic
animals and the fact of the extinct elephant and rhinoceros having
formerly endured a glacial climate whereas the living species are now
all tropical or subtropical in their habits ought not to be looked
at as anomalies but as examples of a very common flexibility of
constitution brought under peculiar circumstances into action

How much of the acclimatisation of species to any peculiar climate is
due to mere habit and how much to the natural selection of varieties
having different innate constitutions and how much to both means
combined is an obscure question That habit or custom has some
influence I must believe both from analogy and from the incessant
advice given in agricultural works even in the ancient Encyclopaedias
of China to be very cautious in transporting animals from one district
to another And as it is not likely that man should have succeeded in
selecting so many breeds and subbreeds with constitutions specially
fitted for their own districts the result must I think be due to
habit On the other hand natural selection would inevitably tend to
preserve those individuals which were born with constitutions best
adapted to any country which they inhabited In treatises on many kinds
of cultivated plants certain varieties are said to withstand certain
climates better than others this is strikingly shown in works on
fruittrees published in the United States in which certain varieties
are habitually recommended for the northern and others for the southern
states and as most of these varieties are of recent origin they cannot
owe their constitutional differences to habit The case of the Jerusalem
artichoke which is never propagated in England by seed and of which
consequently new varieties have not been produced has even been
advanced as proving that acclimatisation cannot be effected for it
is now as tender as ever it was  The case also of the kidneybean has
been often cited for a similar purpose and with much greater weight
but until some one will sow during a score of generations his
kidneybeans so early that a very large proportion are destroyed by
frost and then collect seed from the few survivors with care
to prevent accidental crosses and then again get seed from these
seedlings with the same precautions the experiment cannot be said to
have been even tried Nor let it be supposed that differences in the
constitution of seedling kidneybeans never appear for an account has
been published how much more hardy some seedlings are than others and
of this fact I have myself observed striking instances

On the whole we may conclude that habit or use and disuse have
in some cases played a considerable part in the modification of the
constitution and structure but that the effects have often been largely
combined with and sometimes overmastered by the natural selection of
innate variations

CORRELATED VARIATION

I mean by this expression that the whole organisation is so tied
together during its growth and development that when slight variations
in any one part occur and are accumulated through natural selection
other parts become modified This is a very important subject most
imperfectly understood and no doubt wholly different classes of facts
may be here easily confounded together We shall presently see that
simple inheritance often gives the false appearance of correlation One
of the most obvious real cases is that variations of structure arising
in the young or larvae naturally tend to affect the structure of the
mature animal The several parts which are homologous and which at
an early embryonic period are identical in structure and which are
necessarily exposed to similar conditions seem eminently liable to vary
in a like manner we see this in the right and left sides of the body
varying in the same manner in the front and hind legs and even in the
jaws and limbs varying together for the lower jaw is believed by some
anatomists to be homologous with the limbs These tendencies I do not
doubt may be mastered more or less completely by natural selection
thus a family of stags once existed with an antler only on one side and
if this had been of any great use to the breed it might probably have
been rendered permanent by natural selection

Homologous parts as has been remarked by some authors tend to cohere
this is often seen in monstrous plants and nothing is more common than
the union of homologous parts in normal structures as in the union of
the petals into a tube Hard parts seem to affect the form of adjoining
soft parts it is believed by some authors that with birds the diversity
in the shape of the pelvis causes the remarkable diversity in the shape
of the kidneys Others believe that the shape of the pelvis in the human
mother influences by pressure the shape of the head of the child In
snakes according to Schlegel the shape of the body and the manner
of swallowing determine the position and form of several of the most
important viscera

The nature of the bond is frequently quite obscure M Is Geoffroy St
Hilaire has forcibly remarked that certain malconformations frequently
and that others rarely coexist without our being able to assign any
reason What can be more singular than the relation in cats between
complete whiteness and blue eyes with deafness or between the
tortoiseshell colour and the female sex or in pigeons between their
feathered feet and skin betwixt the outer toes or between the presence
of more or less down on the young pigeon when first hatched with the
future colour of its plumage or again the relation between the hair
and the teeth in the naked Turkish dog though here no doubt homology
comes into play With respect to this latter case of correlation I
think it can hardly be accidental that the two orders of mammals which
are most abnormal in their dermal covering viz Cetacea whales and
Edentata armadilloes scaly anteaters etc are likewise on the
whole the most abnormal in their teeth but there are so many exceptions
to this rule as Mr Mivart has remarked that it has little value

I know of no case better adapted to show the importance of the laws of
correlation and variation independently of utility and therefore of
natural selection than that of the difference between the outer and
inner flowers in some Compositous and Umbelliferous plants Everyone is
familiar with the difference between the ray and central florets of for
instance the daisy and this difference is often accompanied with the
partial or complete abortion of the reproductive organs But in some
of these plants the seeds also differ in shape and sculpture These
differences have sometimes been attributed to the pressure of the
involucra on the florets or to their mutual pressure and the shape of
the seeds in the rayflorets of some Compositae countenances this idea
but with the Umbelliferae it is by no means as Dr Hooker informs me
the species with the densest heads which most frequently differ in their
inner and outer flowers It might have been thought that the development
of the raypetals by drawing nourishment from the reproductive organs
causes their abortion but this can hardly be the sole case for in some
Compositae the seeds of the outer and inner florets differ without any
difference in the corolla Possibly these several differences may be
connected with the different flow of nutriment towards the central and
external flowers We know at least that with irregular flowers those
nearest to the axis are most subject to peloria that is to become
abnormally symmetrical I may add as an instance of this fact and as
a striking case of correlation that in many pelargoniums the two upper
petals in the central flower of the truss often lose their patches
of darker colour and when this occurs the adherent nectary is quite
aborted the central flower thus becoming peloric or regular When the
colour is absent from only one of the two upper petals the nectary is
not quite aborted but is much shortened

With respect to the development of the corolla Sprengels idea that
the rayflorets serve to attract insects whose agency is highly
advantageous or necessary for the fertilisation of these plants is
highly probable and if so natural selection may have come into
play But with respect to the seeds it seems impossible that their
differences in shape which are not always correlated with any
difference in the corolla can be in any way beneficial yet in the
Umbelliferae these differences are of such apparent importance the
seeds being sometimes orthospermous in the exterior flowers and
coelospermous in the central flowers that the elder De Candolle founded
his main divisions in the order on such characters Hence modifications
of structure viewed by systematists as of high value may be wholly due
to the laws of variation and correlation without being as far as we
can judge of the slightest service to the species

We may often falsely attribute to correlated variation structures which
are common to whole groups of species and which in truth are simply
due to inheritance for an ancient progenitor may have acquired through
natural selection some one modification in structure and after
thousands of generations some other and independent modification and
these two modifications having been transmitted to a whole group of
descendants with diverse habits would naturally be thought to be in
some necessary manner correlated Some other correlations are apparently
due to the manner in which natural selection can alone act For
instance Alph De Candolle has remarked that winged seeds are never
found in fruits which do not open I should explain this rule by
the impossibility of seeds gradually becoming winged through natural
selection unless the capsules were open for in this case alone could
the seeds which were a little better adapted to be wafted by the wind
gain an advantage over others less well fitted for wide dispersal

COMPENSATION AND ECONOMY OF GROWTH

The elder Geoffroy and Goethe propounded at about the same time their
law of compensation or balancement of growth or as Goethe expressed
it in order to spend on one side nature is forced to economise on
the other side I think this holds true to a certain extent with our
domestic productions if nourishment flows to one part or organ in
excess it rarely flows at least in excess to another part thus it is
difficult to get a cow to give much milk and to fatten readily The same
varieties of the cabbage do not yield abundant and nutritious foliage
and a copious supply of oilbearing seeds When the seeds in our fruits
become atrophied the fruit itself gains largely in size and quality
In our poultry a large tuft of feathers on the head is generally
accompanied by a diminished comb and a large beard by diminished
wattles With species in a state of nature it can hardly be maintained
that the law is of universal application but many good observers more
especially botanists believe in its truth I will not however here
give any instances for I see hardly any way of distinguishing between
the effects on the one hand of a part being largely developed through
natural selection and another and adjoining part being reduced by the
same process or by disuse and on the other hand the actual withdrawal
of nutriment from one part owing to the excess of growth in another and
adjoining part

I suspect also that some of the cases of compensation which have been
advanced and likewise some other facts may be merged under a more
general principle namely that natural selection is continually
trying to economise in every part of the organisation If under changed
conditions of life a structure before useful becomes less useful its
diminution will be favoured for it will profit the individual not to
have its nutriment wasted in building up a useless structure I can
thus only understand a fact with which I was much struck when examining
cirripedes and of which many other instances could be given namely
that when a cirripede is parasitic within another cirripede and is thus
protected it loses more or less completely its own shell or carapace
This is the case with the male Ibla and in a truly extraordinary manner
with the Proteolepas for the carapace in all other cirripedes consists
of the three highly important anterior segments of the head enormously
developed and furnished with great nerves and muscles but in the
parasitic and protected Proteolepas the whole anterior part of the
head is reduced to the merest rudiment attached to the bases of the
prehensile antennae Now the saving of a large and complex structure
when rendered superfluous would be a decided advantage to each
successive individual of the species for in the struggle for life
to which every animal is exposed each would have a better chance of
supporting itself by less nutriment being wasted

Thus as I believe natural selection will tend in the long run to
reduce any part of the organisation as soon as it becomes through
changed habits superfluous without by any means causing some other
part to be largely developed in a corresponding degree And conversely
that natural selection may perfectly well succeed in largely developing
an organ without requiring as a necessary compensation the reduction of
some adjoining part

MULTIPLE RUDIMENTARY AND LOWLYORGANISED STRUCTURES ARE VARIABLE

It seems to be a rule as remarked by Is Geoffroy St Hilaire both
with varieties and species that when any part or organ is repeated
many times in the same individual as the vertebrae in snakes and the
stamens in polyandrous flowers the number is variable whereas the
number of the same part or organ when it occurs in lesser numbers
is constant The same author as well as some botanists have further
remarked that multiple parts are extremely liable to vary in structure
As vegetative repetition to use Professor Owens expression is
a sign of low organisation the foregoing statements accord with the
common opinion of naturalists that beings which stand low in the scale
of nature are more variable than those which are higher I presume that
lowness here means that the several parts of the organisation have been
but little specialised for particular functions and as long as the same
part has to perform diversified work we can perhaps see why it
should remain variable that is why natural selection should not have
preserved or rejected each little deviation of form so carefully as when
the part has to serve for some one special purpose In the same way that
a knife which has to cut all sorts of things may be of almost any shape
whilst a tool for some particular purpose must be of some particular
shape Natural selection it should never be forgotten can act solely
through and for the advantage of each being

Rudimentary parts as is generally admitted are apt to be highly
variable We shall have to recur to this subject and I will here only
add that their variability seems to result from their uselessness
and consequently from natural selection having had no power to check
deviations in their structure

A PART DEVELOPED IN ANY SPECIES IN AN EXTRAORDINARY DEGREE OR MANNER
IN COMPARISON WITH THE SAME PART IN ALLIED SPECIES TENDS TO BE HIGHLY
VARIABLE

Several years ago I was much struck by a remark to the above effect made
by Mr Waterhouse Professor Owen also seems to have come to a nearly
similar conclusion It is hopeless to attempt to convince any one of the
truth of the above proposition without giving the long array of facts
which I have collected and which cannot possibly be here introduced I
can only state my conviction that it is a rule of high generality I
am aware of several causes of error but I hope that I have made due
allowances for them It should be understood that the rule by no means
applies to any part however unusually developed unless it be unusually
developed in one species or in a few species in comparison with the same
part in many closely allied species Thus the wing of the bat is a most
abnormal structure in the class of mammals but the rule would not apply
here because the whole group of bats possesses wings it would apply
only if some one species had wings developed in a remarkable manner in
comparison with the other species of the same genus The rule applies
very strongly in the case of secondary sexual characters when displayed
in any unusual manner The term secondary sexual characters used by
Hunter relates to characters which are attached to one sex but are
not directly connected with the act of reproduction The rule applies
to males and females but more rarely to females as they seldom offer
remarkable secondary sexual characters The rule being so plainly
applicable in the case of secondary sexual characters may be due to the
great variability of these characters whether or not displayed in any
unusual manner of which fact I think there can be little doubt But
that our rule is not confined to secondary sexual characters is clearly
shown in the case of hermaphrodite cirripedes I particularly attended
to Mr Waterhouses remark whilst investigating this order and I am
fully convinced that the rule almost always holds good I shall in a
future work give a list of all the more remarkable cases I will here
give only one as it illustrates the rule in its largest application
The opercular valves of sessile cirripedes rock barnacles are in
every sense of the word very important structures and they differ
extremely little even in distinct genera but in the several species
of one genus Pyrgoma these valves present a marvellous amount of
diversification the homologous valves in the different species being
sometimes wholly unlike in shape and the amount of variation in the
individuals of the same species is so great that it is no exaggeration
to state that the varieties of the same species differ more from each
other in the characters derived from these important organs than do the
species belonging to other distinct genera

As with birds the individuals of the same species inhabiting the same
country vary extremely little I have particularly attended to them
and the rule certainly seems to hold good in this class I cannot make
out that it applies to plants and this would have seriously shaken my
belief in its truth had not the great variability in plants made it
particularly difficult to compare their relative degrees of variability

When we see any part or organ developed in a remarkable degree or manner
in a species the fair presumption is that it is of high importance
to that species nevertheless it is in this case eminently liable to
variation Why should this be so On the view that each species has been
independently created with all its parts as we now see them I can see
no explanation But on the view that groups of species are descended
from some other species and have been modified through natural
selection I think we can obtain some light First let me make some
preliminary remarks If in our domestic animals any part or the
whole animal be neglected and no selection be applied that part for
instance the comb in the Dorking fowl or the whole breed will cease to
have a uniform character and the breed may be said to be degenerating
In rudimentary organs and in those which have been but little
specialised for any particular purpose and perhaps in polymorphic
groups we see a nearly parallel case for in such cases natural
selection either has not or cannot come into full play and thus the
organisation is left in a fluctuating condition But what here more
particularly concerns us is that those points in our domestic animals
which at the present time are undergoing rapid change by continued
selection are also eminently liable to variation Look at the
individuals of the same breed of the pigeon and see what a prodigious
amount of difference there is in the beak of tumblers in the beak and
wattle of carriers in the carriage and tail of fantails etc these
being the points now mainly attended to by English fanciers Even in the
same subbreed as in that of the shortfaced tumbler it is notoriously
difficult to breed nearly perfect birds many departing widely from the
standard There may truly be said to be a constant struggle going on
between on the one hand the tendency to reversion to a less perfect
state as well as an innate tendency to new variations and on the
other hand the power of steady selection to keep the breed true In
the long run selection gains the day and we do not expect to fail so
completely as to breed a bird as coarse as a common tumbler pigeon from
a good shortfaced strain But as long as selection is rapidly going
on much variability in the parts undergoing modification may always be
expected

Now let us turn to nature When a part has been developed in an
extraordinary manner in any one species compared with the other species
of the same genus we may conclude that this part has undergone an
extraordinary amount of modification since the period when the several
species branched off from the common progenitor of the genus This
period will seldom be remote in any extreme degree as species rarely
endure for more than one geological period An extraordinary amount of
modification implies an unusually large and longcontinued amount of
variability which has continually been accumulated by natural
selection for the benefit of the species But as the variability of
the extraordinarily developed part or organ has been so great and
longcontinued within a period not excessively remote we might as a
general rule still expect to find more variability in such parts than
in other parts of the organisation which have remained for a much longer
period nearly constant And this I am convinced is the case That the
struggle between natural selection on the one hand and the tendency to
reversion and variability on the other hand will in the course of
time cease and that the most abnormally developed organs may be made
constant I see no reason to doubt Hence when an organ however
abnormal it may be has been transmitted in approximately the same
condition to many modified descendants as in the case of the wing of
the bat it must have existed according to our theory for an immense
period in nearly the same state and thus it has come not to be more
variable than any other structure It is only in those cases in which
the modification has been comparatively recent and extraordinarily great
that we ought to find the GENERATIVE VARIABILITY as it may be called
still present in a high degree For in this case the variability
will seldom as yet have been fixed by the continued selection of the
individuals varying in the required manner and degree and by the
continued rejection of those tending to revert to a former and less
modified condition

SPECIFIC CHARACTERS MORE VARIABLE THAN GENERIC CHARACTERS

The principle discussed under the last heading may be applied to our
present subject It is notorious that specific characters are more
variable than generic To explain by a simple example what is meant if
in a large genus of plants some species had blue flowers and some had
red the colour would be only a specific character and no one would be
surprised at one of the blue species varying into red or conversely
but if all the species had blue flowers the colour would become
a generic character and its variation would be a more unusual
circumstance I have chosen this example because the explanation which
most naturalists would advance is not here applicable namely that
specific characters are more variable than generic because they are
taken from parts of less physiological importance than those commonly
used for classing genera I believe this explanation is partly yet only
indirectly true I shall however have to return to this point in
the chapter on Classification It would be almost superfluous to adduce
evidence in support of the statement that ordinary specific characters
are more variable than generic but with respect to important
characters I have repeatedly noticed in works on natural history that
when an author remarks with surprise that some important organ or part
which is generally very constant throughout a large group of species
DIFFERS considerably in closelyallied species it is often VARIABLE
in the individuals of the same species And this fact shows that a
character which is generally of generic value when it sinks in value
and becomes only of specific value often becomes variable though its
physiological importance may remain the same Something of the same kind
applies to monstrosities at least Is Geoffroy St Hilaire apparently
entertains no doubt that the more an organ normally differs in the
different species of the same group the more subject it is to anomalies
in the individuals

On the ordinary view of each species having been independently created
why should that part of the structure which differs from the same
part in other independently created species of the same genus be
more variable than those parts which are closely alike in the several
species I do not see that any explanation can be given But on the
view that species are only strongly marked and fixed varieties we might
expect often to find them still continuing to vary in those parts of
their structure which have varied within a moderately recent period and
which have thus come to differ Or to state the case in another manner
the points in which all the species of a genus resemble each other and
in which they differ from allied genera are called generic characters
and these characters may be attributed to inheritance from a common
progenitor for it can rarely have happened that natural selection will
have modified several distinct species fitted to more or less widely
different habits in exactly the same manner and as these socalled
generic characters have been inherited from before the period when the
several species first branched off from their common progenitor and
subsequently have not varied or come to differ in any degree or only in
a slight degree it is not probable that they should vary at the present
day On the other hand the points in which species differ from other
species of the same genus are called specific characters and as these
specific characters have varied and come to differ since the period when
the species branched off from a common progenitor it is probable
that they should still often be in some degree variable at least more
variable than those parts of the organisation which have for a very long
period remained constant

SECONDARY SEXUAL CHARACTERS VARIABLE

I think it will be admitted by naturalists without my entering on
details that secondary sexual characters are highly variable It will
also be admitted that species of the same group differ from each other
more widely in their secondary sexual characters than in other parts
of their organisation compare for instance the amount of difference
between the males of gallinaceous birds in which secondary sexual
characters are strongly displayed with the amount of difference between
the females The cause of the original variability of these characters
is not manifest but we can see why they should not have been rendered
as constant and uniform as others for they are accumulated by sexual
selection which is less rigid in its action than ordinary selection
as it does not entail death but only gives fewer offspring to the
less favoured males Whatever the cause may be of the variability
of secondary sexual characters as they are highly variable sexual
selection will have had a wide scope for action and may thus have
succeeded in giving to the species of the same group a greater amount of
difference in these than in other respects

It is a remarkable fact that the secondary differences between the two
sexes of the same species are generally displayed in the very same parts
of the organisation in which the species of the same genus differ from
each other Of this fact I will give in illustration the first two
instances which happen to stand on my list and as the differences in
these cases are of a very unusual nature the relation can hardly be
accidental The same number of joints in the tarsi is a character common
to very large groups of beetles but in the Engidae as Westwood has
remarked the number varies greatly and the number likewise differs in
the two sexes of the same species Again in the fossorial hymenoptera
the neuration of the wings is a character of the highest importance
because common to large groups but in certain genera the neuration
differs in the different species and likewise in the two sexes of the
same species Sir J Lubbock has recently remarked that several minute
crustaceans offer excellent illustrations of this law In Pontella
for instance the sexual characters are afforded mainly by the anterior
antennae and by the fifth pair of legs the specific differences also
are principally given by these organs This relation has a clear
meaning on my view I look at all the species of the same genus as
having as certainly descended from the same progenitor as have the two
sexes of any one species Consequently whatever part of the structure
of the common progenitor or of its early descendants became variable
variations of this part would it is highly probable be taken advantage
of by natural and sexual selection in order to fit the several places
in the economy of nature and likewise to fit the two sexes of the same
species to each other or to fit the males to struggle with other males
for the possession of the females

Finally then I conclude that the greater variability of specific
characters or those which distinguish species from species than of
generic characters or those which are possessed by all the species
that the frequent extreme variability of any part which is developed in
a species in an extraordinary manner in comparison with the same part in
its congeners and the slight degree of variability in a part however
extraordinarily it may be developed if it be common to a whole group of
species that the great variability of secondary sexual characters and
their great difference in closely allied species that secondary sexual
and ordinary specific differences are generally displayed in the
same parts of the organisation are all principles closely connected
together All being mainly due to the species of the same group being
the descendants of a common progenitor from whom they have inherited
much in common to parts which have recently and largely varied being
more likely still to go on varying than parts which have long been
inherited and have not varied to natural selection having more or less
completely according to the lapse of time overmastered the tendency
to reversion and to further variability to sexual selection being
less rigid than ordinary selection and to variations in the same parts
having been accumulated by natural and sexual selection and thus having
been adapted for secondary sexual and for ordinary purposes

DISTINCT SPECIES PRESENT ANALOGOUS VARIATIONS SO THAT A VARIETY OF
ONE SPECIES OFTEN ASSUMES A CHARACTER PROPER TO AN ALLIED SPECIES OR
REVERTS TO SOME OF THE CHARACTERS OF AN EARLY PROGENITOR

These propositions will be most readily understood by looking to our
domestic races The most distinct breeds of the pigeon in countries
widely apart present subvarieties with reversed feathers on the
head and with feathers on the feet characters not possessed by the
aboriginal rockpigeon these then are analogous variations in two or
more distinct races The frequent presence of fourteen or even
sixteen tailfeathers in the pouter may be considered as a variation
representing the normal structure of another race the fantail I
presume that no one will doubt that all such analogous variations are
due to the several races of the pigeon having inherited from a common
parent the same constitution and tendency to variation when acted on by
similar unknown influences In the vegetable kingdom we have a case of
analogous variation in the enlarged stems or as commonly called roots
of the Swedish turnip and rutabaga plants which several botanists rank
as varieties produced by cultivation from a common parent if this
be not so the case will then be one of analogous variation in two
socalled distinct species and to these a third may be added namely
the common turnip According to the ordinary view of each species having
been independently created we should have to attribute this similarity
in the enlarged stems of these three plants not to the vera causa
of community of descent and a consequent tendency to vary in a like
manner but to three separate yet closely related acts of creation Many
similar cases of analogous variation have been observed by Naudin in the
great gourd family and by various authors in our cereals Similar
cases occurring with insects under natural conditions have lately been
discussed with much ability by Mr Walsh who has grouped them under his
law of equable variability

With pigeons however we have another case namely the occasional
appearance in all the breeds of slatyblue birds with two black bars
on the wings white loins a bar at the end of the tail with the outer
feathers externally edged near their bases with white As all these
marks are characteristic of the parent rockpigeon I presume that no
one will doubt that this is a case of reversion and not of a new yet
analogous variation appearing in the several breeds We may I think
confidently come to this conclusion because as we have seen these
coloured marks are eminently liable to appear in the crossed offspring
of two distinct and differently coloured breeds and in this case there
is nothing in the external conditions of life to cause the reappearance
of the slatyblue with the several marks beyond the influence of the
mere act of crossing on the laws of inheritance

No doubt it is a very surprising fact that characters should reappear
after having been lost for many probably for hundreds of generations
But when a breed has been crossed only once by some other breed the
offspring occasionally show for many generations a tendency to revert in
character to the foreign breed some say for a dozen or even a score of
generations After twelve generations the proportion of blood to use a
common expression from one ancestor is only 1 in 2048 and yet as we
see it is generally believed that a tendency to reversion is retained
by this remnant of foreign blood In a breed which has not been
crossed but in which BOTH parents have lost some character which their
progenitor possessed the tendency whether strong or weak to reproduce
the lost character might as was formerly remarked for all that we
can see to the contrary be transmitted for almost any number of
generations When a character which has been lost in a breed reappears
after a great number of generations the most probable hypothesis is
not that one individual suddenly takes after an ancestor removed by
some hundred generations but that in each successive generation the
character in question has been lying latent and at last under unknown
favourable conditions is developed With the barbpigeon for instance
which very rarely produces a blue bird it is probable that there is a
latent tendency in each generation to produce blue plumage The abstract
improbability of such a tendency being transmitted through a vast number
of generations is not greater than that of quite useless or rudimentary
organs being similarly transmitted A mere tendency to produce a
rudiment is indeed sometimes thus inherited

As all the species of the same genus are supposed to be descended from
a common progenitor it might be expected that they would occasionally
vary in an analogous manner so that the varieties of two or more
species would resemble each other or that a variety of one species
would resemble in certain characters another and distinct species
this other species being according to our view only a wellmarked and
permanent variety But characters exclusively due to analogous variation
would probably be of an unimportant nature for the preservation of
all functionally important characters will have been determined through
natural selection in accordance with the different habits of the
species It might further be expected that the species of the same
genus would occasionally exhibit reversions to longlost characters
As however we do not know the common ancestor of any natural group
we cannot distinguish between reversionary and analogous characters
If for instance we did not know that the parent rockpigeon was not
featherfooted or turncrowned we could not have told whether such
characters in our domestic breeds were reversions or only analogous
variations but we might have inferred that the blue colour was a case
of reversion from the number of the markings which are correlated with
this tint and which would not probably have all appeared together from
simple variation More especially we might have inferred this from the
blue colour and the several marks so often appearing when differently
coloured breeds are crossed Hence although under nature it must
generally be left doubtful what cases are reversions to formerly
existing characters and what are new but analogous variations yet
we ought on our theory sometimes to find the varying offspring of a
species assuming characters which are already present in other members
of the same group And this undoubtedly is the case

The difficulty in distinguishing variable species is largely due to
the varieties mocking as it were other species of the same genus
A considerable catalogue also could be given of forms intermediate
between two other forms which themselves can only doubtfully be ranked
as species and this shows unless all these closely allied forms be
considered as independently created species that they have in varying
assumed some of the characters of the others But the best evidence of
analogous variations is afforded by parts or organs which are generally
constant in character but which occasionally vary so as to resemble
in some degree the same part or organ in an allied species I have
collected a long list of such cases but here as before I lie under
the great disadvantage of not being able to give them I can only repeat
that such cases certainly occur and seem to me very remarkable

I will however give one curious and complex case not indeed as
affecting any important character but from occurring in several species
of the same genus partly under domestication and partly under nature
It is a case almost certainly of reversion The ass sometimes has very
distinct transverse bars on its legs like those on the legs of a zebra
It has been asserted that these are plainest in the foal and from
inquiries which I have made I believe this to be true The stripe on
the shoulder is sometimes double and is very variable in length and
outline A white ass but NOT an albino has been described without
either spinal or shoulder stripe and these stripes are sometimes very
obscure or actually quite lost in darkcoloured asses The koulan
of Pallas is said to have been seen with a double shoulderstripe
Mr Blyth has seen a specimen of the hemionus with a distinct
shoulderstripe though it properly has none and I have been informed
by Colonel Poole that foals of this species are generally striped on the
legs and faintly on the shoulder The quagga though so plainly barred
like a zebra over the body is without bars on the legs but Dr Gray
has figured one specimen with very distinct zebralike bars on the
hocks

With respect to the horse I have collected cases in England of the
spinal stripe in horses of the most distinct breeds and of ALL colours
transverse bars on the legs are not rare in duns mouseduns and in one
instance in a chestnut a faint shoulderstripe may sometimes be seen
in duns and I have seen a trace in a bay horse My son made a careful
examination and sketch for me of a dun Belgian carthorse with a double
stripe on each shoulder and with legstripes I have myself seen a dun
Devonshire pony and a small dun Welsh pony has been carefully described
to me both with THREE parallel stripes on each shoulder

In the northwest part of India the Kattywar breed of horses is so
generally striped that as I hear from Colonel Poole who examined
this breed for the Indian Government a horse without stripes is not
considered as purely bred The spine is always striped the legs are
generally barred and the shoulderstripe which is sometimes double
and sometimes treble is common the side of the face moreover is
sometimes striped The stripes are often plainest in the foal and
sometimes quite disappear in old horses Colonel Poole has seen both
gray and bay Kattywar horses striped when first foaled I have also
reason to suspect from information given me by Mr WW Edwards that
with the English racehorse the spinal stripe is much commoner in the
foal than in the fullgrown animal I have myself recently bred a foal
from a bay mare offspring of a Turkoman horse and a Flemish mare by
a bay English racehorse This foal when a week old was marked on its
hinder quarters and on its forehead with numerous very narrow dark
zebralike bars and its legs were feebly striped All the stripes soon
disappeared completely Without here entering on further details I may
state that I have collected cases of leg and shoulder stripes in horses
of very different breeds in various countries from Britain to Eastern
China and from Norway in the north to the Malay Archipelago in the
south In all parts of the world these stripes occur far oftenest
in duns and mouseduns by the term dun a large range of colour is
included from one between brown and black to a close approach to cream
colour

I am aware that Colonel Hamilton Smith who has written on this subject
believes that the several breeds of the horse are descended from several
aboriginal species one of which the dun was striped and that the
abovedescribed appearances are all due to ancient crosses with the dun
stock But this view may be safely rejected for it is highly improbable
that the heavy Belgian carthorse Welsh ponies Norwegian cobs the
lanky Kattywar race etc inhabiting the most distant parts of the
world should have all have been crossed with one supposed aboriginal
stock

Now let us turn to the effects of crossing the several species of the
horse genus Rollin asserts that the common mule from the ass and horse
is particularly apt to have bars on its legs according to Mr Gosse
in certain parts of the United States about nine out of ten mules have
striped legs I once saw a mule with its legs so much striped that any
one might have thought that it was a hybrid zebra and Mr WC Martin
in his excellent treatise on the horse has given a figure of a similar
mule In four coloured drawings which I have seen of hybrids between
the ass and zebra the legs were much more plainly barred than the rest
of the body and in one of them there was a double shoulderstripe In
Lord Mortons famous hybrid from a chestnut mare and male quagga the
hybrid and even the pure offspring subsequently produced from the same
mare by a black Arabian sire were much more plainly barred across the
legs than is even the pure quagga Lastly and this is another most
remarkable case a hybrid has been figured by Dr Gray and he informs
me that he knows of a second case from the ass and the hemionus and
this hybrid though the ass only occasionally has stripes on his
legs and the hemionus has none and has not even a shoulderstripe
nevertheless had all four legs barred and had three short
shoulderstripes like those on the dun Devonshire and Welsh ponies and
even had some zebralike stripes on the sides of its face With respect
to this last fact I was so convinced that not even a stripe of colour
appears from what is commonly called chance that I was led solely
from the occurrence of the facestripes on this hybrid from the ass and
hemionus to ask Colonel Poole whether such facestripes ever occurred
in the eminently striped Kattywar breed of horses and was as we have
seen answered in the affirmative

What now are we to say to these several facts We see several distinct
species of the horse genus becoming by simple variation striped on the
legs like a zebra or striped on the shoulders like an ass In the horse
we see this tendency strong whenever a dun tint appears a tint which
approaches to that of the general colouring of the other species of the
genus The appearance of the stripes is not accompanied by any change
of form or by any other new character We see this tendency to become
striped most strongly displayed in hybrids from between several of the
most distinct species Now observe the case of the several breeds
of pigeons they are descended from a pigeon including two or three
subspecies or geographical races of a bluish colour with certain bars
and other marks and when any breed assumes by simple variation a bluish
tint these bars and other marks invariably reappear but without any
other change of form or character When the oldest and truest breeds of
various colours are crossed we see a strong tendency for the blue tint
and bars and marks to reappear in the mongrels I have stated that the
most probable hypothesis to account for the reappearance of very ancient
characters is that there is a TENDENCY in the young of each successive
generation to produce the longlost character and that this tendency
from unknown causes sometimes prevails And we have just seen that in
several species of the horse genus the stripes are either plainer or
appear more commonly in the young than in the old Call the breeds of
pigeons some of which have bred true for centuries species and how
exactly parallel is the case with that of the species of the horse
genus  For myself I venture confidently to look back thousands on
thousands of generations and I see an animal striped like a zebra but
perhaps otherwise very differently constructed the common parent of
our domestic horse whether or not it be descended from one or more wild
stocks of the ass the hemionus quagga and zebra

He who believes that each equine species was independently created
will I presume assert that each species has been created with a
tendency to vary both under nature and under domestication in this
particular manner so as often to become striped like the other species
of the genus and that each has been created with a strong tendency
when crossed with species inhabiting distant quarters of the world to
produce hybrids resembling in their stripes not their own parents but
other species of the genus To admit this view is as it seems to me to
reject a real for an unreal or at least for an unknown cause It makes
the works of God a mere mockery and deception I would almost as soon
believe with the old and ignorant cosmogonists that fossil shells had
never lived but had been created in stone so as to mock the shells now
living on the seashore

SUMMARY

Our ignorance of the laws of variation is profound Not in one case out
of a hundred can we pretend to assign any reason why this or that part
has varied But whenever we have the means of instituting a comparison
the same laws appear to have acted in producing the lesser differences
between varieties of the same species and the greater differences
between species of the same genus Changed conditions generally induce
mere fluctuating variability but sometimes they cause direct and
definite effects and these may become strongly marked in the course
of time though we have not sufficient evidence on this head Habit in
producing constitutional peculiarities and use in strengthening and
disuse in weakening and diminishing organs appear in many cases to have
been potent in their effects Homologous parts tend to vary in the same
manner and homologous parts tend to cohere Modifications in hard parts
and in external parts sometimes affect softer and internal parts When
one part is largely developed perhaps it tends to draw nourishment from
the adjoining parts and every part of the structure which can be saved
without detriment will be saved Changes of structure at an early age
may affect parts subsequently developed and many cases of correlated
variation the nature of which we are unable to understand undoubtedly
occur Multiple parts are variable in number and in structure perhaps
arising from such parts not having been closely specialised for any
particular function so that their modifications have not been closely
checked by natural selection It follows probably from this same cause
that organic beings low in the scale are more variable than those
standing higher in the scale and which have their whole organisation
more specialised Rudimentary organs from being useless are not
regulated by natural selection and hence are variable Specific
characters that is the characters which have come to differ since the
several species of the same genus branched off from a common parent are
more variable than generic characters or those which have long been
inherited and have not differed within this same period In these
remarks we have referred to special parts or organs being still
variable because they have recently varied and thus come to differ but
we have also seen in the second chapter that the same principle applies
to the whole individual for in a district where many species of a
genus are found that is where there has been much former variation and
differentiation or where the manufactory of new specific forms has been
actively at work in that district and among these species we now find
on an average most varieties Secondary sexual characters are highly
variable and such characters differ much in the species of the same
group Variability in the same parts of the organisation has generally
been taken advantage of in giving secondary sexual differences to the
two sexes of the same species and specific differences to the
several species of the same genus Any part or organ developed to an
extraordinary size or in an extraordinary manner in comparison with
the same part or organ in the allied species must have gone through an
extraordinary amount of modification since the genus arose and thus we
can understand why it should often still be variable in a much higher
degree than other parts for variation is a longcontinued and slow
process and natural selection will in such cases not as yet have had
time to overcome the tendency to further variability and to
reversion to a less modified state But when a species with an
extraordinarily developed organ has become the parent of many modified
descendants which on our view must be a very slow process requiring a
long lapse of time in this case natural selection has succeeded in
giving a fixed character to the organ in however extraordinary a manner
it may have been developed Species inheriting nearly the same
constitution from a common parent and exposed to similar influences
naturally tend to present analogous variations or these same species
may occasionally revert to some of the characters of their ancient
progenitors Although new and important modifications may not arise from
reversion and analogous variation such modifications will add to the
beautiful and harmonious diversity of nature

Whatever the cause may be of each slight difference between the
offspring and their parents and a cause for each must exist we have
reason to believe that it is the steady accumulation of beneficial
differences which has given rise to all the more important modifications
of structure in relation to the habits of each species




CHAPTER VI DIFFICULTIES OF THE THEORY

 Difficulties of the theory of descent with modification Absence
 or rarity of transitional varieties Transitions in habits of
 life Diversified habits in the same species Species with habits
 widely different from those of their allies Organs of extreme
 perfection Modes of transition Cases of difficulty Natura non facit
 saltum Organs of small importance Organs not in all cases absolutely
 perfect The law of Unity of Type and of the Conditions of Existence
 embraced by the theory of Natural Selection


Long before the reader has arrived at this part of my work a crowd of
difficulties will have occurred to him Some of them are so serious that
to this day I can hardly reflect on them without being in some degree
staggered but to the best of my judgment the greater number are only
apparent and those that are real are not I think fatal to the theory

These difficulties and objections may be classed under the following
heads First why if species have descended from other species by fine
gradations do we not everywhere see innumerable transitional forms Why
is not all nature in confusion instead of the species being as we see
them well defined

Secondly is it possible that an animal having for instance
the structure and habits of a bat could have been formed by the
modification of some other animal with widely different habits and
structure Can we believe that natural selection could produce on
the one hand an organ of trifling importance such as the tail of a
giraffe which serves as a flyflapper and on the other hand an organ
so wonderful as the eye

Thirdly can instincts be acquired and modified through natural
selection What shall we say to the instinct which leads the bee to make
cells and which has practically anticipated the discoveries of profound
mathematicians

Fourthly how can we account for species when crossed being sterile
and producing sterile offspring whereas when varieties are crossed
their fertility is unimpaired

The two first heads will be here discussed some miscellaneous
objections in the following chapter Instinct and Hybridism in the two
succeeding chapters

ON THE ABSENCE OR RARITY OF TRANSITIONAL VARIETIES

As natural selection acts solely by the preservation of profitable
modifications each new form will tend in a fullystocked country to
take the place of and finally to exterminate its own less improved
parentform and other lessfavoured forms with which it comes into
competition Thus extinction and natural selection go hand in hand
Hence if we look at each species as descended from some unknown form
both the parent and all the transitional varieties will generally have
been exterminated by the very process of the formation and perfection of
the new form

But as by this theory innumerable transitional forms must have existed
why do we not find them embedded in countless numbers in the crust of
the earth It will be more convenient to discuss this question in the
chapter on the imperfection of the geological record and I will here
only state that I believe the answer mainly lies in the record being
incomparably less perfect than is generally supposed The crust of
the earth is a vast museum but the natural collections have been
imperfectly made and only at long intervals of time

But it may be urged that when several closely allied species inhabit
the same territory we surely ought to find at the present time many
transitional forms Let us take a simple case in travelling from north
to south over a continent we generally meet at successive intervals
with closely allied or representative species evidently filling nearly
the same place in the natural economy of the land These representative
species often meet and interlock and as the one becomes rarer and
rarer the other becomes more and more frequent till the one replaces
the other But if we compare these species where they intermingle they
are generally as absolutely distinct from each other in every detail of
structure as are specimens taken from the metropolis inhabited by each
By my theory these allied species are descended from a common parent
and during the process of modification each has become adapted to
the conditions of life of its own region and has supplanted and
exterminated its original parentform and all the transitional varieties
between its past and present states Hence we ought not to expect at
the present time to meet with numerous transitional varieties in each
region though they must have existed there and may be embedded
there in a fossil condition But in the intermediate region having
intermediate conditions of life why do we not now find closelylinking
intermediate varieties This difficulty for a long time quite confounded
me But I think it can be in large part explained

In the first place we should be extremely cautious in inferring because
an area is now continuous that it has been continuous during a long
period Geology would lead us to believe that most continents have been
broken up into islands even during the later tertiary periods and in
such islands distinct species might have been separately formed without
the possibility of intermediate varieties existing in the intermediate
zones By changes in the form of the land and of climate marine areas
now continuous must often have existed within recent times in a far less
continuous and uniform condition than at present But I will pass
over this way of escaping from the difficulty for I believe that many
perfectly defined species have been formed on strictly continuous areas
though I do not doubt that the formerly broken condition of areas
now continuous has played an important part in the formation of new
species more especially with freelycrossing and wandering animals

In looking at species as they are now distributed over a wide area
we generally find them tolerably numerous over a large territory then
becoming somewhat abruptly rarer and rarer on the confines and finally
disappearing Hence the neutral territory between two representative
species is generally narrow in comparison with the territory proper to
each We see the same fact in ascending mountains and sometimes it
is quite remarkable how abruptly as Alph De Candolle has observed a
common alpine species disappears The same fact has been noticed by E
Forbes in sounding the depths of the sea with the dredge To those who
look at climate and the physical conditions of life as the allimportant
elements of distribution these facts ought to cause surprise as
climate and height or depth graduate away insensibly But when we
bear in mind that almost every species even in its metropolis would
increase immensely in numbers were it not for other competing species
that nearly all either prey on or serve as prey for others in short
that each organic being is either directly or indirectly related in the
most important manner to other organic beings we see that the range
of the inhabitants of any country by no means exclusively depends
on insensibly changing physical conditions but in large part on
the presence of other species on which it lives or by which it is
destroyed or with which it comes into competition and as these species
are already defined objects not blending one into another by insensible
gradations the range of any one species depending as it does on the
range of others will tend to be sharply defined Moreover each species
on the confines of its range where it exists in lessened numbers will
during fluctuations in the number of its enemies or of its prey or in
the nature of the seasons be extremely liable to utter extermination
and thus its geographical range will come to be still more sharply
defined

As allied or representative species when inhabiting a continuous area
are generally distributed in such a manner that each has a wide range
with a comparatively narrow neutral territory between them in which
they become rather suddenly rarer and rarer then as varieties do not
essentially differ from species the same rule will probably apply to
both and if we take a varying species inhabiting a very large area
we shall have to adapt two varieties to two large areas and a third
variety to a narrow intermediate zone The intermediate variety
consequently will exist in lesser numbers from inhabiting a narrow and
lesser area and practically as far as I can make out this rule holds
good with varieties in a state of nature I have met with striking
instances of the rule in the case of varieties intermediate between
wellmarked varieties in the genus Balanus And it would appear from
information given me by Mr Watson Dr Asa Gray and Mr Wollaston
that generally when varieties intermediate between two other forms
occur they are much rarer numerically than the forms which they
connect Now if we may trust these facts and inferences and conclude
that varieties linking two other varieties together generally have
existed in lesser numbers than the forms which they connect then we can
understand why intermediate varieties should not endure for very
long periods why as a general rule they should be exterminated and
disappear sooner than the forms which they originally linked together

For any form existing in lesser numbers would as already remarked
run a greater chance of being exterminated than one existing in large
numbers and in this particular case the intermediate form would be
eminently liable to the inroads of closely allied forms existing on both
sides of it But it is a far more important consideration that during
the process of further modification by which two varieties are supposed
to be converted and perfected into two distinct species the two which
exist in larger numbers from inhabiting larger areas will have a great
advantage over the intermediate variety which exists in smaller numbers
in a narrow and intermediate zone For forms existing in larger numbers
will have a better chance within any given period of presenting
further favourable variations for natural selection to seize on than
will the rarer forms which exist in lesser numbers Hence the more
common forms in the race for life will tend to beat and supplant the
less common forms for these will be more slowly modified and improved
It is the same principle which as I believe accounts for the common
species in each country as shown in the second chapter presenting on
an average a greater number of wellmarked varieties than do the rarer
species I may illustrate what I mean by supposing three varieties of
sheep to be kept one adapted to an extensive mountainous region a
second to a comparatively narrow hilly tract and a third to the wide
plains at the base and that the inhabitants are all trying with equal
steadiness and skill to improve their stocks by selection the chances
in this case will be strongly in favour of the great holders on the
mountains or on the plains improving their breeds more quickly than the
small holders on the intermediate narrow hilly tract and consequently
the improved mountain or plain breed will soon take the place of the
less improved hill breed and thus the two breeds which originally
existed in greater numbers will come into close contact with each
other without the interposition of the supplanted intermediate hill
variety

To sum up I believe that species come to be tolerably welldefined
objects and do not at any one period present an inextricable chaos of
varying and intermediate links first because new varieties are very
slowly formed for variation is a slow process and natural selection
can do nothing until favourable individual differences or variations
occur and until a place in the natural polity of the country can
be better filled by some modification of some one or more of its
inhabitants And such new places will depend on slow changes of climate
or on the occasional immigration of new inhabitants and probably in
a still more important degree on some of the old inhabitants becoming
slowly modified with the new forms thus produced and the old ones
acting and reacting on each other So that in any one region and at
any one time we ought to see only a few species presenting slight
modifications of structure in some degree permanent and this assuredly
we do see

Secondly areas now continuous must often have existed within the recent
period as isolated portions in which many forms more especially
among the classes which unite for each birth and wander much may have
separately been rendered sufficiently distinct to rank as representative
species In this case intermediate varieties between the several
representative species and their common parent must formerly have
existed within each isolated portion of the land but these links
during the process of natural selection will have been supplanted and
exterminated so that they will no longer be found in a living state

Thirdly when two or more varieties have been formed in different
portions of a strictly continuous area intermediate varieties will it
is probable at first have been formed in the intermediate zones but
they will generally have had a short duration For these intermediate
varieties will from reasons already assigned namely from what we know
of the actual distribution of closely allied or representative species
and likewise of acknowledged varieties exist in the intermediate zones
in lesser numbers than the varieties which they tend to connect From
this cause alone the intermediate varieties will be liable to accidental
extermination and during the process of further modification through
natural selection they will almost certainly be beaten and supplanted
by the forms which they connect for these from existing in greater
numbers will in the aggregate present more varieties and thus be
further improved through natural selection and gain further advantages

Lastly looking not to any one time but at all time if my theory be
true numberless intermediate varieties linking closely together all
the species of the same group must assuredly have existed but the
very process of natural selection constantly tends as has been so often
remarked to exterminate the parent forms and the intermediate links
Consequently evidence of their former existence could be found only
among fossil remains which are preserved as we shall attempt to show
in a future chapter in an extremely imperfect and intermittent record

ON THE ORIGIN AND TRANSITION OF ORGANIC BEINGS WITH PECULIAR HABITS AND
STRUCTURE

It has been asked by the opponents of such views as I hold how for
instance could a land carnivorous animal have been converted into one
with aquatic habits for how could the animal in its transitional
state have subsisted It would be easy to show that there now exist
carnivorous animals presenting close intermediate grades from strictly
terrestrial to aquatic habits and as each exists by a struggle for
life it is clear that each must be well adapted to its place in nature
Look at the Mustela vison of North America which has webbed feet
and which resembles an otter in its fur short legs and form of tail
during summer this animal dives for and preys on fish but during the
long winter it leaves the frozen waters and preys like other polecats
on mice and land animals If a different case had been taken and it
had been asked how an insectivorous quadruped could possibly have been
converted into a flying bat the question would have been far more
difficult to answer Yet I think such difficulties have little weight

Here as on other occasions I lie under a heavy disadvantage for out
of the many striking cases which I have collected I can give only
one or two instances of transitional habits and structures in allied
species and of diversified habits either constant or occasional in
the same species And it seems to me that nothing less than a long list
of such cases is sufficient to lessen the difficulty in any particular
case like that of the bat

Look at the family of squirrels here we have the finest gradation from
animals with their tails only slightly flattened and from others as
Sir J Richardson has remarked with the posterior part of their bodies
rather wide and with the skin on their flanks rather full to the
socalled flying squirrels and flying squirrels have their limbs and
even the base of the tail united by a broad expanse of skin which
serves as a parachute and allows them to glide through the air to
an astonishing distance from tree to tree We cannot doubt that each
structure is of use to each kind of squirrel in its own country by
enabling it to escape birds or beasts of prey or to collect food more
quickly or as there is reason to believe to lessen the danger
from occasional falls But it does not follow from this fact that the
structure of each squirrel is the best that it is possible to conceive
under all possible conditions Let the climate and vegetation change
let other competing rodents or new beasts of prey immigrate or old ones
become modified and all analogy would lead us to believe that some
at least of the squirrels would decrease in numbers or become
exterminated unless they also become modified and improved in structure
in a corresponding manner Therefore I can see no difficulty
more especially under changing conditions of life in the continued
preservation of individuals with fuller and fuller flankmembranes
each modification being useful each being propagated until by the
accumulated effects of this process of natural selection a perfect
socalled flying squirrel was produced

Now look at the Galeopithecus or socalled flying lemur which was
formerly ranked among bats but is now believed to belong to the
Insectivora An extremely wide flankmembrane stretches from the corners
of the jaw to the tail and includes the limbs with the elongated
fingers This flankmembrane is furnished with an extensor muscle
Although no graduated links of structure fitted for gliding through the
air now connect the Galeopithecus with the other Insectivora yet there
is no difficulty in supposing that such links formerly existed and that
each was developed in the same manner as with the less perfectly gliding
squirrels each grade of structure having been useful to its possessor
Nor can I see any insuperable difficulty in further believing it
possible that the membraneconnected fingers and forearm of the
Galeopithecus might have been greatly lengthened by natural selection
and this as far as the organs of flight are concerned would
have converted the animal into a bat In certain bats in which the
wingmembrane extends from the top of the shoulder to the tail and
includes the hindlegs we perhaps see traces of an apparatus originally
fitted for gliding through the air rather than for flight

If about a dozen genera of birds were to become extinct who would have
ventured to surmise that birds might have existed which used their wings
solely as flappers like the logger headed duck Micropterus of Eyton
as fins in the water and as front legs on the land like the penguin
as sails like the ostrich and functionally for no purpose like the
apteryx Yet the structure of each of these birds is good for it under
the conditions of life to which it is exposed for each has to live by a
struggle but it is not necessarily the best possible under all possible
conditions It must not be inferred from these remarks that any of the
grades of wingstructure here alluded to which perhaps may all be the
result of disuse indicate the steps by which birds actually acquired
their perfect power of flight but they serve to show what diversified
means of transition are at least possible

Seeing that a few members of such waterbreathing classes as the
Crustacea and Mollusca are adapted to live on the land and seeing that
we have flying birds and mammals flying insects of the most diversified
types and formerly had flying reptiles it is conceivable that
flyingfish which now glide far through the air slightly rising and
turning by the aid of their fluttering fins might have been modified
into perfectly winged animals If this had been effected who would
have ever imagined that in an early transitional state they had been
inhabitants of the open ocean and had used their incipient organs of
flight exclusively so far as we know to escape being devoured by other
fish

When we see any structure highly perfected for any particular habit
as the wings of a bird for flight we should bear in mind that animals
displaying early transitional grades of the structure will seldom have
survived to the present day for they will have been supplanted by their
successors which were gradually rendered more perfect through natural
selection Furthermore we may conclude that transitional states between
structures fitted for very different habits of life will rarely have
been developed at an early period in great numbers and under many
subordinate forms Thus to return to our imaginary illustration of
the flyingfish it does not seem probable that fishes capable of true
flight would have been developed under many subordinate forms for
taking prey of many kinds in many ways on the land and in the water
until their organs of flight had come to a high stage of perfection
so as to have given them a decided advantage over other animals in
the battle for life Hence the chance of discovering species with
transitional grades of structure in a fossil condition will always be
less from their having existed in lesser numbers than in the case of
species with fully developed structures

I will now give two or three instances both of diversified and of
changed habits in the individuals of the same species In either case
it would be easy for natural selection to adapt the structure of the
animal to its changed habits or exclusively to one of its several
habits It is however difficult to decide and immaterial for us
whether habits generally change first and structure afterwards or
whether slight modifications of structure lead to changed habits both
probably often occurring almost simultaneously Of cases of changed
habits it will suffice merely to allude to that of the many British
insects which now feed on exotic plants or exclusively on artificial
substances Of diversified habits innumerable instances could be given
I have often watched a tyrant flycatcher Saurophagus sulphuratus in
South America hovering over one spot and then proceeding to another
like a kestrel and at other times standing stationary on the margin of
water and then dashing into it like a kingfisher at a fish In our own
country the larger titmouse Parus major may be seen climbing branches
almost like a creeper it sometimes like a shrike kills small birds by
blows on the head and I have many times seen and heard it hammering the
seeds of the yew on a branch and thus breaking them like a nuthatch In
North America the black bear was seen by Hearne swimming for hours with
widely open mouth thus catching almost like a whale insects in the
water

As we sometimes see individuals following habits different from those
proper to their species and to the other species of the same genus we
might expect that such individuals would occasionally give rise to
new species having anomalous habits and with their structure either
slightly or considerably modified from that of their type And such
instances occur in nature Can a more striking instance of adaptation be
given than that of a woodpecker for climbing trees and seizing insects
in the chinks of the bark Yet in North America there are woodpeckers
which feed largely on fruit and others with elongated wings which chase
insects on the wing On the plains of La Plata where hardly a tree
grows there is a woodpecker Colaptes campestris which has two toes
before and two behind a longpointed tongue pointed tailfeathers
sufficiently stiff to support the bird in a vertical position on a post
but not so stiff as in the typical woodpeckers and a straight strong
beak The beak however is not so straight or so strong as in the
typical woodpeckers but it is strong enough to bore into wood Hence
this Colaptes in all the essential parts of its structure is a
woodpecker Even in such trifling characters as the colouring the harsh
tone of the voice and undulatory flight its close bloodrelationship
to our common woodpecker is plainly declared yet as I can assert not
only from my own observations but from those of the accurate Azara in
certain large districts it does not climb trees and it makes its
nest in holes in banks  In certain other districts however this same
woodpecker as Mr Hudson states frequents trees and bores holes in
the trunk for its nest I may mention as another illustration of the
varied habits of this genus that a Mexican Colaptes has been described
by De Saussure as boring holes into hard wood in order to lay up a store
of acorns

Petrels are the most aerial and oceanic of birds but in the quiet
sounds of Tierra del Fuego the Puffinuria berardi in its general
habits in its astonishing power of diving in its manner of swimming
and of flying when made to take flight would be mistaken by any one for
an auk or a grebe nevertheless it is essentially a petrel but with
many parts of its organisation profoundly modified in relation to its
new habits of life whereas the woodpecker of La Plata has had its
structure only slightly modified In the case of the waterouzel the
acutest observer by examining its dead body would never have suspected
its subaquatic habits yet this bird which is allied to the thrush
family subsists by diving using its wings under water and
grasping stones with its feet All the members of the great order of
Hymenopterous insects are terrestrial excepting the genus Proctotrupes
which Sir John Lubbock has discovered to be aquatic in its habits it
often enters the water and dives about by the use not of its legs but of
its wings and remains as long as four hours beneath the surface yet
it exhibits no modification in structure in accordance with its abnormal
habits

He who believes that each being has been created as we now see it must
occasionally have felt surprise when he has met with an animal having
habits and structure not in agreement What can be plainer than that the
webbed feet of ducks and geese are formed for swimming Yet there are
upland geese with webbed feet which rarely go near the water and no one
except Audubon has seen the frigatebird which has all its four toes
webbed alight on the surface of the ocean On the other hand grebes
and coots are eminently aquatic although their toes are only bordered
by membrane What seems plainer than that the long toes not furnished
with membrane of the Grallatores are formed for walking over swamps
and floating plants The waterhen and landrail are members of this
order yet the first is nearly as aquatic as the coot and the second is
nearly as terrestrial as the quail or partridge In such cases and
many others could be given habits have changed without a corresponding
change of structure The webbed feet of the upland goose may be said to
have become almost rudimentary in function though not in structure
In the frigatebird the deeply scooped membrane between the toes shows
that structure has begun to change

He who believes in separate and innumerable acts of creation may say
that in these cases it has pleased the Creator to cause a being of one
type to take the place of one belonging to another type but this seems
to me only restating the fact in dignified language He who believes in
the struggle for existence and in the principle of natural selection
will acknowledge that every organic being is constantly endeavouring to
increase in numbers and that if any one being varies ever so little
either in habits or structure and thus gains an advantage over some
other inhabitant of the same country it will seize on the place of that
inhabitant however different that may be from its own place Hence it
will cause him no surprise that there should be geese and frigatebirds
with webbed feet living on the dry land and rarely alighting on the
water that there should be longtoed corncrakes living in meadows
instead of in swamps that there should be woodpeckers where hardly a
tree grows that there should be diving thrushes and diving Hymenoptera
and petrels with the habits of auks

ORGANS OF EXTREME PERFECTION AND COMPLICATION

To suppose that the eye with all its inimitable contrivances for
adjusting the focus to different distances for admitting different
amounts of light and for the correction of spherical and chromatic
aberration could have been formed by natural selection seems I freely
confess absurd in the highest degree When it was first said that the
sun stood still and the world turned round the common sense of mankind
declared the doctrine false but the old saying of Vox populi vox Dei
as every philosopher knows cannot be trusted in science Reason tells
me that if numerous gradations from a simple and imperfect eye to one
complex and perfect can be shown to exist each grade being useful to
its possessor as is certainly the case if further the eye ever varies
and the variations be inherited as is likewise certainly the case
and if such variations should be useful to any animal under changing
conditions of life then the difficulty of believing that a perfect and
complex eye could be formed by natural selection though insuperable by
our imagination should not be considered as subversive of the theory
How a nerve comes to be sensitive to light hardly concerns us more than
how life itself originated but I may remark that as some of the lowest
organisms in which nerves cannot be detected are capable of perceiving
light it does not seem impossible that certain sensitive elements
in their sarcode should become aggregated and developed into nerves
endowed with this special sensibility

In searching for the gradations through which an organ in any species
has been perfected we ought to look exclusively to its lineal
progenitors but this is scarcely ever possible and we are forced
to look to other species and genera of the same group that is to the
collateral descendants from the same parentform in order to see what
gradations are possible and for the chance of some gradations having
been transmitted in an unaltered or little altered condition But the
state of the same organ in distinct classes may incidentally throw light
on the steps by which it has been perfected

The simplest organ which can be called an eye consists of an optic
nerve surrounded by pigmentcells and covered by translucent skin but
without any lens or other refractive body We may however according
to M Jourdain descend even a step lower and find aggregates of
pigmentcells apparently serving as organs of vision without any
nerves and resting merely on sarcodic tissue Eyes of the above simple
nature are not capable of distinct vision and serve only to distinguish
light from darkness In certain starfishes small depressions in the
layer of pigment which surrounds the nerve are filled as described by
the author just quoted with transparent gelatinous matter projecting
with a convex surface like the cornea in the higher animals He
suggests that this serves not to form an image but only to concentrate
the luminous rays and render their perception more easy In this
concentration of the rays we gain the first and by far the most
important step towards the formation of a true pictureforming eye for
we have only to place the naked extremity of the optic nerve which in
some of the lower animals lies deeply buried in the body and in
some near the surface at the right distance from the concentrating
apparatus and an image will be formed on it

In the great class of the Articulata we may start from an optic nerve
simply coated with pigment the latter sometimes forming a sort of
pupil but destitute of lens or other optical contrivance With insects
it is now known that the numerous facets on the cornea of their great
compound eyes form true lenses and that the cones include curiously
modified nervous filaments But these organs in the Articulata are so
much diversified that Muller formerly made three main classes with seven
subdivisions besides a fourth main class of aggregated simple eyes

When we reflect on these facts here given much too briefly with
respect to the wide diversified and graduated range of structure in
the eyes of the lower animals and when we bear in mind how small the
number of all living forms must be in comparison with those which have
become extinct the difficulty ceases to be very great in believing that
natural selection may have converted the simple apparatus of an optic
nerve coated with pigment and invested by transparent membrane into
an optical instrument as perfect as is possessed by any member of the
Articulata class

He who will go thus far ought not to hesitate to go one step further
if he finds on finishing this volume that large bodies of facts
otherwise inexplicable can be explained by the theory of modification
through natural selection he ought to admit that a structure even as
perfect as an eagles eye might thus be formed although in this case
he does not know the transitional states It has been objected that in
order to modify the eye and still preserve it as a perfect instrument
many changes would have to be effected simultaneously which it is
assumed could not be done through natural selection but as I have
attempted to show in my work on the variation of domestic animals it is
not necessary to suppose that the modifications were all simultaneous
if they were extremely slight and gradual Different kinds of
modification would also serve for the same general purpose as Mr
Wallace has remarked If a lens has too short or too long a focus it
may be amended either by an alteration of curvature or an alteration of
density if the curvature be irregular and the rays do not converge
to a point then any increased regularity of curvature will be an
improvement So the contraction of the iris and the muscular
movements of the eye are neither of them essential to vision but only
improvements which might have been added and perfected at any stage of
the construction of the instrument Within the highest division of
the animal kingdom namely the Vertebrata we can start from an eye
so simple that it consists as in the lancelet of a little sack of
transparent skin furnished with a nerve and lined with pigment but
destitute of any other apparatus In fishes and reptiles as Owen has
remarked The range of gradation of dioptric structures is very
great It is a significant fact that even in man according to the high
authority of Virchow the beautiful crystalline lens is formed in the
embryo by an accumulation of epidermic cells lying in a sacklike fold
of the skin and the vitreous body is formed from embryonic subcutaneous
tissue To arrive however at a just conclusion regarding the
formation of the eye with all its marvellous yet not absolutely perfect
characters it is indispensable that the reason should conquer the
imagination but I have felt the difficulty far to keenly to be
surprised at others hesitating to extend the principle of natural
selection to so startling a length

It is scarcely possible to avoid comparing the eye with a telescope
We know that this instrument has been perfected by the longcontinued
efforts of the highest human intellects and we naturally infer that the
eye has been formed by a somewhat analogous process But may not this
inference be presumptuous Have we any right to assume that the Creator
works by intellectual powers like those of man If we must compare the
eye to an optical instrument we ought in imagination to take a thick
layer of transparent tissue with spaces filled with fluid and with a
nerve sensitive to light beneath and then suppose every part of this
layer to be continually changing slowly in density so as to separate
into layers of different densities and thicknesses placed at different
distances from each other and with the surfaces of each layer slowly
changing in form Further we must suppose that there is a power
represented by natural selection or the survival of the fittest always
intently watching each slight alteration in the transparent layers and
carefully preserving each which under varied circumstances in any way
or degree tends to produce a distincter image We must suppose each
new state of the instrument to be multiplied by the million each to be
preserved until a better is produced and then the old ones to be all
destroyed In living bodies variation will cause the slight alteration
generation will multiply them almost infinitely and natural selection
will pick out with unerring skill each improvement Let this process
go on for millions of years and during each year on millions of
individuals of many kinds and may we not believe that a living optical
instrument might thus be formed as superior to one of glass as the
works of the Creator are to those of man

MODES Of TRANSITION

If it could be demonstrated that any complex organ existed which
could not possibly have been formed by numerous successive slight
modifications my theory would absolutely break down But I can find
out no such case No doubt many organs exist of which we do not know
the transitional grades more especially if we look to muchisolated
species around which according to the theory there has been much
extinction Or again if we take an organ common to all the members of
a class for in this latter case the organ must have been originally
formed at a remote period since which all the many members of the class
have been developed and in order to discover the early transitional
grades through which the organ has passed we should have to look to
very ancient ancestral forms long since become extinct

We should be extremely cautious in concluding that an organ could not
have been formed by transitional gradations of some kind Numerous cases
could be given among the lower animals of the same organ performing
at the same time wholly distinct functions thus in the larva of the
dragonfly and in the fish Cobites the alimentary canal respires
digests and excretes In the Hydra the animal may be turned inside
out and the exterior surface will then digest and the stomach respire
In such cases natural selection might specialise if any advantage
were thus gained the whole or part of an organ which had previously
performed two functions for one function alone and thus by insensible
steps greatly change its nature Many plants are known which regularly
produce at the same time differently constructed flowers and if such
plants were to produce one kind alone a great change would be effected
with comparative suddenness in the character of the species It is
however probable that the two sorts of flowers borne by the same plant
were originally differentiated by finely graduated steps which may
still be followed in some few cases

Again two distinct organs or the same organ under two very different
forms may simultaneously perform in the same individual the same
function and this is an extremely important means of transition to
give one instance there are fish with gills or branchiae that breathe
the air dissolved in the water at the same time that they breathe free
air in their swimbladders this latter organ being divided by highly
vascular partitions and having a ductus pneumaticus for the supply of
air To give another instance from the vegetable kingdom plants climb
by three distinct means by spirally twining by clasping a support with
their sensitive tendrils and by the emission of aerial rootlets these
three means are usually found in distinct groups but some few species
exhibit two of the means or even all three combined in the same
individual In all such cases one of the two organs might readily be
modified and perfected so as to perform all the work being aided during
the progress of modification by the other organ and then this other
organ might be modified for some other and quite distinct purpose or be
wholly obliterated

The illustration of the swimbladder in fishes is a good one because
it shows us clearly the highly important fact that an organ originally
constructed for one purpose namely flotation may be converted into
one for a widely different purpose namely respiration The swimbladder
has also been worked in as an accessory to the auditory organs
of certain fishes All physiologists admit that the swimbladder is
homologous or ideally similar in position and structure with the
lungs of the higher vertebrate animals hence there is no reason to
doubt that the swimbladder has actually been converted into lungs or
an organ used exclusively for respiration

According to this view it may be inferred that all vertebrate animals
with true lungs are descended by ordinary generation from an ancient
and unknown prototype which was furnished with a floating apparatus or
swimbladder We can thus as I infer from Professor Owens interesting
description of these parts understand the strange fact that every
particle of food and drink which we swallow has to pass over the
orifice of the trachea with some risk of falling into the lungs
notwithstanding the beautiful contrivance by which the glottis
is closed In the higher Vertebrata the branchiae have wholly
disappeared but in the embryo the slits on the sides of the neck and
the looplike course of the arteries still mark their former position
But it is conceivable that the now utterly lost branchiae might have
been gradually worked in by natural selection for some distinct purpose
for instance Landois has shown that the wings of insects are developed
from the trachea it is therefore highly probable that in this great
class organs which once served for respiration have been actually
converted into organs for flight

In considering transitions of organs it is so important to bear in mind
the probability of conversion from one function to another that I will
give another instance Pedunculated cirripedes have two minute folds of
skin called by me the ovigerous frena which serve through the means
of a sticky secretion to retain the eggs until they are hatched within
the sack These cirripedes have no branchiae the whole surface of
the body and of the sack together with the small frena serving for
respiration The Balanidae or sessile cirripedes on the other hand
have no ovigerous frena the eggs lying loose at the bottom of the sack
within the wellenclosed shell but they have in the same relative
position with the frena large muchfolded membranes which freely
communicate with the circulatory lacunae of the sack and body and which
have been considered by all naturalists to act as branchiae Now I
think no one will dispute that the ovigerous frena in the one family are
strictly homologous with the branchiae of the other family indeed they
graduate into each other Therefore it need not be doubted that the two
little folds of skin which originally served as ovigerous frena but
which likewise very slightly aided in the act of respiration have
been gradually converted by natural selection into branchiae simply
through an increase in their size and the obliteration of their adhesive
glands If all pedunculated cirripedes had become extinct and they have
suffered far more extinction than have sessile cirripedes who would
ever have imagined that the branchiae in this latter family had
originally existed as organs for preventing the ova from being washed
out of the sack

There is another possible mode of transition namely through the
acceleration or retardation of the period of reproduction This has
lately been insisted on by Professor Cope and others in the United
States It is now known that some animals are capable of reproduction
at a very early age before they have acquired their perfect characters
and if this power became thoroughly well developed in a species it
seems probable that the adult stage of development would sooner or later
be lost and in this case especially if the larva differed much from
the mature form the character of the species would be greatly changed
and degraded Again not a few animals after arriving at maturity go
on changing in character during nearly their whole lives With mammals
for instance the form of the skull is often much altered with age of
which Dr Murie has given some striking instances with seals Every
one knows how the horns of stags become more and more branched and the
plumes of some birds become more finely developed as they grow older
Professor Cope states that the teeth of certain lizards change much in
shape with advancing years With crustaceans not only many trivial
but some important parts assume a new character as recorded by Fritz
Muller after maturity In all such cases and many could be given if
the age for reproduction were retarded the character of the species at
least in its adult state would be modified nor is it improbable that
the previous and earlier stages of development would in some cases be
hurried through and finally lost Whether species have often or ever
been modified through this comparatively sudden mode of transition I
can form no opinion but if this has occurred it is probable that the
differences between the young and the mature and between the mature and
the old were primordially acquired by graduated steps

SPECIAL DIFFICULTIES OF THE THEORY OF NATURAL SELECTION

Although we must be extremely cautious in concluding that any organ
could not have been produced by successive small transitional
gradations yet undoubtedly serious cases of difficulty occur

One of the most serious is that of neuter insects which are often
differently constructed from either the males or fertile females but
this case will be treated of in the next chapter The electric organs of
fishes offer another case of special difficulty for it is impossible
to conceive by what steps these wondrous organs have been produced But
this is not surprising for we do not even know of what use they are
In the gymnotus and torpedo they no doubt serve as powerful means of
defence and perhaps for securing prey yet in the ray as observed
by Matteucci an analogous organ in the tail manifests but little
electricity even when the animal is greatly irritated so little that
it can hardly be of any use for the above purposes Moreover in the
ray besides the organ just referred to there is as Dr R McDonnell
has shown another organ near the head not known to be electrical but
which appears to be the real homologue of the electric battery in the
torpedo It is generally admitted that there exists between these organs
and ordinary muscle a close analogy in intimate structure in the
distribution of the nerves and in the manner in which they are acted
on by various reagents It should also be especially observed that
muscular contraction is accompanied by an electrical discharge and
as Dr Radcliffe insists in the electrical apparatus of the torpedo
during rest there would seem to be a charge in every respect like that
which is met with in muscle and nerve during the rest and the discharge
of the torpedo instead of being peculiar may be only another form of
the discharge which attends upon the action of muscle and motor nerve
Beyond this we cannot at present go in the way of explanation but as
we know so little about the uses of these organs and as we know nothing
about the habits and structure of the progenitors of the existing
electric fishes it would be extremely bold to maintain that no
serviceable transitions are possible by which these organs might have
been gradually developed

These organs appear at first to offer another and far more serious
difficulty for they occur in about a dozen kinds of fish of which
several are widely remote in their affinities When the same organ is
found in several members of the same class especially if in members
having very different habits of life we may generally attribute its
presence to inheritance from a common ancestor and its absence in some
of the members to loss through disuse or natural selection So that if
the electric organs had been inherited from some one ancient progenitor
we might have expected that all electric fishes would have been
specially related to each other but this is far from the case Nor does
geology at all lead to the belief that most fishes formerly possessed
electric organs which their modified descendants have now lost But
when we look at the subject more closely we find in the several fishes
provided with electric organs that these are situated in different
parts of the body that they differ in construction as in the
arrangement of the plates and according to Pacini in the process or
means by which the electricity is excited and lastly in being supplied
with nerves proceeding from different sources and this is perhaps
the most important of all the differences Hence in the several
fishes furnished with electric organs these cannot be considered as
homologous but only as analogous in function Consequently there is
no reason to suppose that they have been inherited from a common
progenitor for had this been the case they would have closely resembled
each other in all respects Thus the difficulty of an organ apparently
the same arising in several remotely allied species disappears
leaving only the lesser yet still great difficulty namely by what
graduated steps these organs have been developed in each separate group
of fishes

The luminous organs which occur in a few insects belonging to widely
different families and which are situated in different parts of the
body offer under our present state of ignorance a difficulty almost
exactly parallel with that of the electric organs Other similar cases
could be given for instance in plants the very curious contrivance of
a mass of pollengrains borne on a footstalk with an adhesive gland
is apparently the same in Orchis and Asclepias genera almost as remote
as is possible among flowering plants but here again the parts are not
homologous In all cases of beings far removed from each other in the
scale of organisation which are furnished with similar and peculiar
organs it will be found that although the general appearance and
function of the organs may be the same yet fundamental differences
between them can always be detected For instance the eyes of
Cephalopods or cuttlefish and of vertebrate animals appear wonderfully
alike and in such widely sundered groups no part of this resemblance
can be due to inheritance from a common progenitor Mr Mivart has
advanced this case as one of special difficulty but I am unable to
see the force of his argument An organ for vision must be formed of
transparent tissue and must include some sort of lens for throwing
an image at the back of a darkened chamber Beyond this superficial
resemblance there is hardly any real similarity between the eyes of
cuttlefish and vertebrates as may be seen by consulting Hensens
admirable memoir on these organs in the Cephalopoda It is impossible
for me here to enter on details but I may specify a few of the points
of difference The crystalline lens in the higher cuttlefish consists
of two parts placed one behind the other like two lenses both having
a very different structure and disposition to what occurs in the
vertebrata The retina is wholly different with an actual inversion of
the elemental parts and with a large nervous ganglion included within
the membranes of the eye The relations of the muscles are as different
as it is possible to conceive and so in other points Hence it is not
a little difficult to decide how far even the same terms ought to be
employed in describing the eyes of the Cephalopoda and Vertebrata It
is of course open to any one to deny that the eye in either case could
have been developed through the natural selection of successive slight
variations but if this be admitted in the one case it is clearly
possible in the other and fundamental differences of structure in the
visual organs of two groups might have been anticipated in accordance
with this view of their manner of formation As two men have sometimes
independently hit on the same invention so in the several foregoing
cases it appears that natural selection working for the good of each
being and taking advantage of all favourable variations has produced
similar organs as far as function is concerned in distinct organic
beings which owe none of their structure in common to inheritance from
a common progenitor

Fritz Muller in order to test the conclusions arrived at in this
volume has followed out with much care a nearly similar line of
argument Several families of crustaceans include a few species
possessing an airbreathing apparatus and fitted to live out of the
water In two of these families which were more especially examined by
Muller and which are nearly related to each other the species agree
most closely in all important characters namely in their sense organs
circulating systems in the position of the tufts of hair within
their complex stomachs and lastly in the whole structure of the
waterbreathing branchiae even to the microscopical hooks by which they
are cleansed Hence it might have been expected that in the few species
belonging to both families which live on the land the equally important
airbreathing apparatus would have been the same for why should this
one apparatus given for the same purpose have been made to differ
while all the other important organs were closely similar or rather
identical

Fritz Muller argues that this close similarity in so many points
of structure must in accordance with the views advanced by me be
accounted for by inheritance from a common progenitor But as the vast
majority of the species in the above two families as well as most
other crustaceans are aquatic in their habits it is improbable in the
highest degree that their common progenitor should have been adapted for
breathing air Muller was thus led carefully to examine the apparatus in
the airbreathing species and he found it to differ in each in several
important points as in the position of the orifices in the manner in
which they are opened and closed and in some accessory details Now
such differences are intelligible and might even have been expected on
the supposition that species belonging to distinct families had slowly
become adapted to live more and more out of water and to breathe the
air For these species from belonging to distinct families would have
differed to a certain extent and in accordance with the principle that
the nature of each variation depends on two factors viz the nature of
the organism and that of the surrounding conditions their variability
assuredly would not have been exactly the same Consequently natural
selection would have had different materials or variations to work on
in order to arrive at the same functional result and the structures
thus acquired would almost necessarily have differed On the hypothesis
of separate acts of creation the whole case remains unintelligible This
line of argument seems to have had great weight in leading Fritz Muller
to accept the views maintained by me in this volume

Another distinguished zoologist the late Professor Claparede has
argued in the same manner and has arrived at the same result He
shows that there are parasitic mites Acaridae belonging to distinct
subfamilies and families which are furnished with hairclaspers These
organs must have been independently developed as they could not have
been inherited from a common progenitor and in the several groups they
are formed by the modification of the fore legs of the hind legs of
the maxillae or lips and of appendages on the under side of the hind
part of the body

In the foregoing cases we see the same end gained and the same function
performed in beings not at all or only remotely allied by organs in
appearance though not in development closely similar On the other
hand it is a common rule throughout nature that the same end should
be gained even sometimes in the case of closely related beings by the
most diversified means How differently constructed is the feathered
wing of a bird and the membranecovered wing of a bat and still more so
the four wings of a butterfly the two wings of a fly and the two wings
with the elytra of a beetle Bivalve shells are made to open and shut
but on what a number of patterns is the hinge constructed from the long
row of neatly interlocking teeth in a Nucula to the simple ligament of
a Mussel  Seeds are disseminated by their minuteness by their capsule
being converted into a light balloonlike envelope by being embedded
in pulp or flesh formed of the most diverse parts and rendered
nutritious as well as conspicuously coloured so as to attract and
be devoured by birds by having hooks and grapnels of many kinds and
serrated awns so as to adhere to the fur of quadrupeds and by being
furnished with wings and plumes as different in shape as they are
elegant in structure so as to be wafted by every breeze I will give
one other instance for this subject of the same end being gained by the
most diversified means well deserves attention Some authors maintain
that organic beings have been formed in many ways for the sake of
mere variety almost like toys in a shop but such a view of nature is
incredible With plants having separated sexes and with those in which
though hermaphrodites the pollen does not spontaneously fall on the
stigma some aid is necessary for their fertilisation With several
kinds this is effected by the pollengrains which are light and
incoherent being blown by the wind through mere chance on to the
stigma and this is the simplest plan which can well be conceived An
almost equally simple though very different plan occurs in many plants
in which a symmetrical flower secretes a few drops of nectar and is
consequently visited by insects and these carry the pollen from the
anthers to the stigma

From this simple stage we may pass through an inexhaustible number of
contrivances all for the same purpose and effected in essentially the
same manner but entailing changes in every part of the flower The
nectar may be stored in variously shaped receptacles with the
stamens and pistils modified in many ways sometimes forming traplike
contrivances and sometimes capable of neatly adapted movements through
irritability or elasticity From such structures we may advance till we
come to such a case of extraordinary adaptation as that lately described
by Dr Cruger in the Coryanthes This orchid has part of its labellum or
lower lip hollowed out into a great bucket into which drops of almost
pure water continually fall from two secreting horns which stand above
it and when the bucket is halffull the water overflows by a spout on
one side The basal part of the labellum stands over the bucket and is
itself hollowed out into a sort of chamber with two lateral entrances
within this chamber there are curious fleshy ridges The most ingenious
man if he had not witnessed what takes place could never have imagined
what purpose all these parts serve But Dr Cruger saw crowds of large
humblebees visiting the gigantic flowers of this orchid not in order
to suck nectar but to gnaw off the ridges within the chamber above the
bucket in doing this they frequently pushed each other into the bucket
and their wings being thus wetted they could not fly away but were
compelled to crawl out through the passage formed by the spout or
overflow Dr Cruger saw a continual procession of bees thus crawling
out of their involuntary bath The passage is narrow and is roofed over
by the column so that a bee in forcing its way out first rubs its
back against the viscid stigma and then against the viscid glands of the
pollenmasses The pollenmasses are thus glued to the back of the
bee which first happens to crawl out through the passage of a lately
expanded flower and are thus carried away Dr Cruger sent me a flower
in spirits of wine with a bee which he had killed before it had quite
crawled out with a pollenmass still fastened to its back When the
bee thus provided flies to another flower or to the same flower a
second time and is pushed by its comrades into the bucket and then
crawls out by the passage the pollenmass necessarily comes first into
contact with the viscid stigma and adheres to it and the flower is
fertilised Now at last we see the full use of every part of the flower
of the watersecreting horns of the bucket halffull of water which
prevents the bees from flying away and forces them to crawl out through
the spout and rub against the properly placed viscid pollenmasses and
the viscid stigma

The construction of the flower in another closely allied orchid namely
the Catasetum is widely different though serving the same end and is
equally curious Bees visit these flowers like those of the Coryanthes
in order to gnaw the labellum in doing this they inevitably touch
a long tapering sensitive projection or as I have called it the
antenna This antenna when touched transmits a sensation or vibration
to a certain membrane which is instantly ruptured this sets free a
spring by which the pollenmass is shot forth like an arrow in the
right direction and adheres by its viscid extremity to the back of the
bee The pollenmass of the male plant for the sexes are separate in
this orchid is thus carried to the flower of the female plant where it
is brought into contact with the stigma which is viscid enough to
break certain elastic threads and retain the pollen thus effecting
fertilisation

How it may be asked in the foregoing and in innumerable other
instances can we understand the graduated scale of complexity and the
multifarious means for gaining the same end The answer no doubt is as
already remarked that when two forms vary which already differ from
each other in some slight degree the variability will not be of the
same exact nature and consequently the results obtained through natural
selection for the same general purpose will not be the same We should
also bear in mind that every highly developed organism has passed
through many changes and that each modified structure tends to be
inherited so that each modification will not readily be quite lost
but may be again and again further altered Hence the structure of each
part of each species for whatever purpose it may serve is the sum of
many inherited changes through which the species has passed during its
successive adaptations to changed habits and conditions of life

Finally then although in many cases it is most difficult even to
conjecture by what transitions organs could have arrived at their
present state yet considering how small the proportion of living and
known forms is to the extinct and unknown I have been astonished how
rarely an organ can be named towards which no transitional grade is
known to lead It is certainly true that new organs appearing as if
created for some special purpose rarely or never appear in any being as
indeed is shown by that old but somewhat exaggerated canon in natural
history of Natura non facit saltum We meet with this admission in the
writings of almost every experienced naturalist or as Milne Edwards
has well expressed it Nature is prodigal in variety but niggard in
innovation Why on the theory of Creation should there be so much
variety and so little real novelty Why should all the parts and organs
of many independent beings each supposed to have been separately
created for its own proper place in nature be so commonly linked
together by graduated steps Why should not Nature take a sudden leap
from structure to structure On the theory of natural selection we can
clearly understand why she should not for natural selection acts only
by taking advantage of slight successive variations she can never take
a great and sudden leap but must advance by the short and sure though
slow steps

ORGANS OF LITTLE APPARENT IMPORTANCE AS AFFECTED BY NATURAL SELECTION

As natural selection acts by life and death by the survival of the
fittest and by the destruction of the less wellfitted individuals
I have sometimes felt great difficulty in understanding the origin or
formation of parts of little importance almost as great though of
a very different kind as in the case of the most perfect and complex
organs

In the first place we are much too ignorant in regard to the whole
economy of any one organic being to say what slight modifications would
be of importance or not In a former chapter I have given instances of
very trifling characters such as the down on fruit and the colour of
its flesh the colour of the skin and hair of quadrupeds which from
being correlated with constitutional differences or from determining
the attacks of insects might assuredly be acted on by natural
selection The tail of the giraffe looks like an artificially
constructed flyflapper and it seems at first incredible that this
could have been adapted for its present purpose by successive slight
modifications each better and better fitted for so trifling an object
as to drive away flies yet we should pause before being too positive
even in this case for we know that the distribution and existence of
cattle and other animals in South America absolutely depend on their
power of resisting the attacks of insects so that individuals which
could by any means defend themselves from these small enemies would be
able to range into new pastures and thus gain a great advantage It is
not that the larger quadrupeds are actually destroyed except in some
rare cases by flies but they are incessantly harassed and their
strength reduced so that they are more subject to disease or not so
well enabled in a coming dearth to search for food or to escape from
beasts of prey

Organs now of trifling importance have probably in some cases been of
high importance to an early progenitor and after having been slowly
perfected at a former period have been transmitted to existing species
in nearly the same state although now of very slight use but any
actually injurious deviations in their structure would of course have
been checked by natural selection Seeing how important an organ of
locomotion the tail is in most aquatic animals its general presence and
use for many purposes in so many land animals which in their lungs or
modified swimbladders betray their aquatic origin may perhaps be thus
accounted for A welldeveloped tail having been formed in an aquatic
animal it might subsequently come to be worked in for all sorts of
purposes as a flyflapper an organ of prehension or as an aid in
turning as in the case of the dog though the aid in this latter
respect must be slight for the hare with hardly any tail can double
still more quickly

In the second place we may easily err in attributing importance to
characters and in believing that they have been developed through
natural selection We must by no means overlook the effects of the
definite action of changed conditions of life of socalled spontaneous
variations which seem to depend in a quite subordinate degree on the
nature of the conditions of the tendency to reversion to longlost
characters of the complex laws of growth such as of correlation
comprehension of the pressure of one part on another etc and finally
of sexual selection by which characters of use to one sex are often
gained and then transmitted more or less perfectly to the other sex
though of no use to the sex But structures thus indirectly gained
although at first of no advantage to a species may subsequently
have been taken advantage of by its modified descendants under new
conditions of life and newly acquired habits

If green woodpeckers alone had existed and we did not know that there
were many black and pied kinds I dare say that we should have thought
that the green colour was a beautiful adaptation to conceal this
treefrequenting bird from its enemies and consequently that it was
a character of importance and had been acquired through natural
selection as it is the colour is probably in chief part due to sexual
selection A trailing palm in the Malay Archipelago climbs the loftiest
trees by the aid of exquisitely constructed hooks clustered around the
ends of the branches and this contrivance no doubt is of the highest
service to the plant but as we see nearly similar hooks on many trees
which are not climbers and which as there is reason to believe from
the distribution of the thornbearing species in Africa and South
America serve as a defence against browsing quadrupeds so the spikes
on the palm may at first have been developed for this object and
subsequently have been improved and taken advantage of by the plant as
it underwent further modification and became a climber The naked skin
on the head of a vulture is generally considered as a direct adaptation
for wallowing in putridity and so it may be or it may possibly be due
to the direct action of putrid matter but we should be very cautious in
drawing any such inference when we see that the skin on the head of the
cleanfeeding male turkey is likewise naked The sutures in the skulls
of young mammals have been advanced as a beautiful adaptation for aiding
parturition and no doubt they facilitate or may be indispensable
for this act but as sutures occur in the skulls of young birds and
reptiles which have only to escape from a broken egg we may infer that
this structure has arisen from the laws of growth and has been taken
advantage of in the parturition of the higher animals

We are profoundly ignorant of the cause of each slight variation or
individual difference and we are immediately made conscious of this
by reflecting on the differences between the breeds of our domesticated
animals in different countries more especially in the less civilized
countries where there has been but little methodical selection Animals
kept by savages in different countries often have to struggle for
their own subsistence and are exposed to a certain extent to natural
selection and individuals with slightly different constitutions would
succeed best under different climates With cattle susceptibility to the
attacks of flies is correlated with colour as is the liability to be
poisoned by certain plants so that even colour would be thus subjected
to the action of natural selection Some observers are convinced that a
damp climate affects the growth of the hair and that with the hair the
horns are correlated Mountain breeds always differ from lowland breeds
and a mountainous country would probably affect the hind limbs from
exercising them more and possibly even the form of the pelvis and then
by the law of homologous variation the front limbs and the head would
probably be affected The shape also of the pelvis might affect
by pressure the shape of certain parts of the young in the womb The
laborious breathing necessary in high regions tends as we have
good reason to believe to increase the size of the chest and again
correlation would come into play The effects of lessened exercise
together with abundant food on the whole organisation is probably still
more important and this as H von Nathusius has lately shown in
his excellent Treatise is apparently one chief cause of the great
modification which the breeds of swine have undergone But we are far
too ignorant to speculate on the relative importance of the several
known and unknown causes of variation and I have made these remarks
only to show that if we are unable to account for the characteristic
differences of our several domestic breeds which nevertheless are
generally admitted to have arisen through ordinary generation from
one or a few parentstocks we ought not to lay too much stress on
our ignorance of the precise cause of the slight analogous differences
between true species

UTILITARIAN DOCTRINE HOW FAR TRUE BEAUTY HOW ACQUIRED

The foregoing remarks lead me to say a few words on the protest lately
made by some naturalists against the utilitarian doctrine that every
detail of structure has been produced for the good of its possessor
They believe that many structures have been created for the sake of
beauty to delight man or the Creator but this latter point is beyond
the scope of scientific discussion or for the sake of mere variety
a view already discussed Such doctrines if true would be absolutely
fatal to my theory I fully admit that many structures are now of no
direct use to their possessors and may never have been of any use to
their progenitors but this does not prove that they were formed
solely for beauty or variety No doubt the definite action of changed
conditions and the various causes of modifications lately specified
have all produced an effect probably a great effect independently of
any advantage thus gained But a still more important consideration is
that the chief part of the organisation of every living creature is due
to inheritance and consequently though each being assuredly is well
fitted for its place in nature many structures have now no very close
and direct relation to present habits of life Thus we can
hardly believe that the webbed feet of the upland goose or of the
frigatebird are of special use to these birds we cannot believe
that the similar bones in the arm of the monkey in the fore leg of the
horse in the wing of the bat and in the flipper of the seal are of
special use to these animals We may safely attribute these structures
to inheritance But webbed feet no doubt were as useful to the
progenitor of the upland goose and of the frigatebird as they now
are to the most aquatic of living birds So we may believe that the
progenitor of the seal did not possess a flipper but a foot with five
toes fitted for walking or grasping and we may further venture to
believe that the several bones in the limbs of the monkey horse and
bat were originally developed on the principle of utility probably
through the reduction of more numerous bones in the fin of some ancient
fishlike progenitor of the whole class It is scarcely possible to
decide how much allowance ought to be made for such causes of change
as the definite action of external conditions socalled spontaneous
variations and the complex laws of growth but with these important
exceptions we may conclude that the structure of every living creature
either now is or was formerly of some direct or indirect use to its
possessor

With respect to the belief that organic beings have been created
beautiful for the delight of man a belief which it has been pronounced
is subversive of my whole theory I may first remark that the sense of
beauty obviously depends on the nature of the mind irrespective of
any real quality in the admired object and that the idea of what is
beautiful is not innate or unalterable We see this for instance in
the men of different races admiring an entirely different standard of
beauty in their women If beautiful objects had been created solely for
mans gratification it ought to be shown that before man appeared
there was less beauty on the face of the earth than since he came on the
stage Were the beautiful volute and cone shells of the Eocene epoch
and the gracefully sculptured ammonites of the Secondary period created
that man might ages afterwards admire them in his cabinet Few objects
are more beautiful than the minute siliceous cases of the diatomaceae
were these created that they might be examined and admired under the
higher powers of the microscope The beauty in this latter case and
in many others is apparently wholly due to symmetry of growth Flowers
rank among the most beautiful productions of nature but they have
been rendered conspicuous in contrast with the green leaves and in
consequence at the same time beautiful so that they may be easily
observed by insects I have come to this conclusion from finding it an
invariable rule that when a flower is fertilised by the wind it never
has a gailycoloured corolla Several plants habitually produce two
kinds of flowers one kind open and coloured so as to attract insects
the other closed not coloured destitute of nectar and never visited
by insects Hence we may conclude that if insects had not been
developed on the face of the earth our plants would not have been
decked with beautiful flowers but would have produced only such poor
flowers as we see on our fir oak nut and ash trees on grasses
spinach docks and nettles which are all fertilised through the agency
of the wind A similar line of argument holds good with fruits that
a ripe strawberry or cherry is as pleasing to the eye as to the
palate that the gailycoloured fruit of the spindlewood tree and the
scarlet berries of the holly are beautiful objects will be admitted by
everyone But this beauty serves merely as a guide to birds and
beasts in order that the fruit may be devoured and the matured seeds
disseminated I infer that this is the case from having as yet found
no exception to the rule that seeds are always thus disseminated when
embedded within a fruit of any kind that is within a fleshy or
pulpy envelope if it be coloured of any brilliant tint or rendered
conspicuous by being white or black

On the other hand I willingly admit that a great number of male
animals as all our most gorgeous birds some fishes reptiles and
mammals and a host of magnificently coloured butterflies have been
rendered beautiful for beautys sake But this has been effected through
sexual selection that is by the more beautiful males having been
continually preferred by the females and not for the delight of man So
it is with the music of birds We may infer from all this that a nearly
similar taste for beautiful colours and for musical sounds runs through
a large part of the animal kingdom When the female is as beautifully
coloured as the male which is not rarely the case with birds and
butterflies the cause apparently lies in the colours acquired through
sexual selection having been transmitted to both sexes instead of to
the males alone How the sense of beauty in its simplest form that is
the reception of a peculiar kind of pleasure from certain colours forms
and sounds was first developed in the mind of man and of the lower
animals is a very obscure subject The same sort of difficulty is
presented if we enquire how it is that certain flavours and odours give
pleasure and others displeasure Habit in all these cases appears
to have come to a certain extent into play but there must be some
fundamental cause in the constitution of the nervous system in each
species

Natural selection cannot possibly produce any modification in a species
exclusively for the good of another species though throughout
nature one species incessantly takes advantage of and profits by the
structures of others But natural selection can and does often produce
structures for the direct injury of other animals as we see in the fang
of the adder and in the ovipositor of the ichneumon by which its eggs
are deposited in the living bodies of other insects If it could be
proved that any part of the structure of any one species had been
formed for the exclusive good of another species it would annihilate my
theory for such could not have been produced through natural selection
Although many statements may be found in works on natural history to
this effect I cannot find even one which seems to me of any weight It
is admitted that the rattlesnake has a poisonfang for its own defence
and for the destruction of its prey but some authors suppose that at
the same time it is furnished with a rattle for its own injury namely
to warn its prey I would almost as soon believe that the cat curls the
end of its tail when preparing to spring in order to warn the doomed
mouse It is a much more probable view that the rattlesnake uses its
rattle the cobra expands its frill and the puffadder swells while
hissing so loudly and harshly in order to alarm the many birds and
beasts which are known to attack even the most venomous species Snakes
act on the same principle which makes the hen ruffle her feathers and
expand her wings when a dog approaches her chickens But I have not
space here to enlarge on the many ways by which animals endeavour to
frighten away their enemies

Natural selection will never produce in a being any structure more
injurious than beneficial to that being for natural selection acts
solely by and for the good of each No organ will be formed as Paley
has remarked for the purpose of causing pain or for doing an injury
to its possessor If a fair balance be struck between the good and evil
caused by each part each will be found on the whole advantageous After
the lapse of time under changing conditions of life if any part comes
to be injurious it will be modified or if it be not so the being will
become extinct as myriads have become extinct

Natural selection tends only to make each organic being as perfect as
or slightly more perfect than the other inhabitants of the same country
with which it comes into competition And we see that this is the
standard of perfection attained under nature The endemic productions of
New Zealand for instance are perfect one compared with another but
they are now rapidly yielding before the advancing legions of plants
and animals introduced from Europe Natural selection will not produce
absolute perfection nor do we always meet as far as we can judge with
this high standard under nature The correction for the aberration of
light is said by Muller not to be perfect even in that most perfect
organ the human eye Helmholtz whose judgment no one will dispute
after describing in the strongest terms the wonderful powers of the
human eye adds these remarkable words That which we have discovered
in the way of inexactness and imperfection in the optical machine and
in the image on the retina is as nothing in comparison with the
incongruities which we have just come across in the domain of the
sensations One might say that nature has taken delight in accumulating
contradictions in order to remove all foundation from the theory of a
preexisting harmony between the external and internal worlds If our
reason leads us to admire with enthusiasm a multitude of inimitable
contrivances in nature this same reason tells us though we may easily
err on both sides that some other contrivances are less perfect Can we
consider the sting of the bee as perfect which when used against many
kinds of enemies cannot be withdrawn owing to the backward serratures
and thus inevitably causes the death of the insect by tearing out its
viscera

If we look at the sting of the bee as having existed in a remote
progenitor as a boring and serrated instrument like that in so many
members of the same great order and that it has since been modified
but not perfected for its present purpose with the poison originally
adapted for some other object such as to produce galls since
intensified we can perhaps understand how it is that the use of the
sting should so often cause the insects own death for if on the whole
the power of stinging be useful to the social community it will fulfil
all the requirements of natural selection though it may cause the death
of some few members If we admire the truly wonderful power of scent by
which the males of many insects find their females can we admire the
production for this single purpose of thousands of drones which are
utterly useless to the community for any other purpose and which are
ultimately slaughtered by their industrious and sterile sisters It may
be difficult but we ought to admire the savage instinctive hatred
of the queenbee which urges her to destroy the young queens her
daughters as soon as they are born or to perish herself in the combat
for undoubtedly this is for the good of the community and maternal love
or maternal hatred though the latter fortunately is most rare is all
the same to the inexorable principles of natural selection If we admire
the several ingenious contrivances by which orchids and many other
plants are fertilised through insect agency can we consider as equally
perfect the elaboration of dense clouds of pollen by our firtrees so
that a few granules may be wafted by chance on to the ovules

SUMMARY THE LAW OF UNITY OF TYPE AND OF THE CONDITIONS OF EXISTENCE
EMBRACED BY THE THEORY OF NATURAL SELECTION

We have in this chapter discussed some of the difficulties and
objections which may be urged against the theory Many of them are
serious but I think that in the discussion light has been thrown on
several facts which on the belief of independent acts of creation are
utterly obscure We have seen that species at any one period are not
indefinitely variable and are not linked together by a multitude of
intermediate gradations partly because the process of natural selection
is always very slow and at any one time acts only on a few forms
and partly because the very process of natural selection implies the
continual supplanting and extinction of preceding and intermediate
gradations Closely allied species now living on a continuous area
must often have been formed when the area was not continuous and when
the conditions of life did not insensibly graduate away from one part to
another When two varieties are formed in two districts of a continuous
area an intermediate variety will often be formed fitted for an
intermediate zone but from reasons assigned the intermediate variety
will usually exist in lesser numbers than the two forms which it
connects consequently the two latter during the course of further
modification from existing in greater numbers will have a great
advantage over the less numerous intermediate variety and will thus
generally succeed in supplanting and exterminating it

We have seen in this chapter how cautious we should be in concluding
that the most different habits of life could not graduate into each
other that a bat for instance could not have been formed by natural
selection from an animal which at first only glided through the air

We have seen that a species under new conditions of life may change its
habits or it may have diversified habits with some very unlike those
of its nearest congeners Hence we can understand bearing in mind that
each organic being is trying to live wherever it can live how it has
arisen that there are upland geese with webbed feet ground woodpeckers
diving thrushes and petrels with the habits of auks

Although the belief that an organ so perfect as the eye could have been
formed by natural selection is enough to stagger any one yet in
the case of any organ if we know of a long series of gradations in
complexity each good for its possessor then under changing conditions
of life there is no logical impossibility in the acquirement of any
conceivable degree of perfection through natural selection In the cases
in which we know of no intermediate or transitional states we should
be extremely cautious in concluding that none can have existed for the
metamorphoses of many organs show what wonderful changes in function
are at least possible For instance a swimbladder has apparently been
converted into an airbreathing lung The same organ having performed
simultaneously very different functions and then having been in part
or in whole specialised for one function and two distinct organs
having performed at the same time the same function the one having been
perfected whilst aided by the other must often have largely facilitated
transitions

We have seen that in two beings widely remote from each other in the
natural scale organs serving for the same purpose and in external
appearance closely similar may have been separately and independently
formed but when such organs are closely examined essential differences
in their structure can almost always be detected and this naturally
follows from the principle of natural selection On the other hand the
common rule throughout nature is infinite diversity of structure for
gaining the same end and this again naturally follows from the same
great principle

In many cases we are far too ignorant to be enabled to assert that
a part or organ is so unimportant for the welfare of a species that
modifications in its structure could not have been slowly accumulated
by means of natural selection In many other cases modifications
are probably the direct result of the laws of variation or of growth
independently of any good having been thus gained But even such
structures have often as we may feel assured been subsequently taken
advantage of and still further modified for the good of species under
new conditions of life We may also believe that a part formerly of
high importance has frequently been retained as the tail of an aquatic
animal by its terrestrial descendants though it has become of such
small importance that it could not in its present state have been
acquired by means of natural selection

Natural selection can produce nothing in one species for the exclusive
good or injury of another though it may well produce parts organs and
excretions highly useful or even indispensable or highly injurious
to another species but in all cases at the same time useful to the
possessor In each wellstocked country natural selection acts through
the competition of the inhabitants and consequently leads to success
in the battle for life only in accordance with the standard of that
particular country Hence the inhabitants of one country generally the
smaller one often yield to the inhabitants of another and generally the
larger country For in the larger country there will have existed more
individuals and more diversified forms and the competition will
have been severer and thus the standard of perfection will have been
rendered higher Natural selection will not necessarily lead to absolute
perfection nor as far as we can judge by our limited faculties can
absolute perfection be everywhere predicated

On the theory of natural selection we can clearly understand the full
meaning of that old canon in natural history Natura non facit saltum
This canon if we look to the present inhabitants alone of the world is
not strictly correct but if we include all those of past times whether
known or unknown it must on this theory be strictly true

It is generally acknowledged that all organic beings have been formed on
two great laws Unity of Type and the Conditions of Existence By unity
of type is meant that fundamental agreement in structure which we see
in organic beings of the same class and which is quite independent of
their habits of life On my theory unity of type is explained by unity
of descent The expression of conditions of existence so often insisted
on by the illustrious Cuvier is fully embraced by the principle of
natural selection For natural selection acts by either now adapting the
varying parts of each being to its organic and inorganic conditions
of life or by having adapted them during past periods of time the
adaptations being aided in many cases by the increased use or disuse
of parts being affected by the direct action of external conditions
of life and subjected in all cases to the several laws of growth and
variation Hence in fact the law of the Conditions of Existence is the
higher law as it includes through the inheritance of former variations
and adaptations that of Unity of Type




CHAPTER VII MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL SELECTION

 Longevity Modifications not necessarily simultaneous Modifications
 apparently of no direct service Progressive development Characters of
 small functional importance the most constant Supposed incompetence
 of natural selection to account for the incipient stages of useful
 structures Causes which interfere with the acquisition through natural
 selection of useful structures Gradations of structure with changed
 functions Widely different organs in members of the same class
 developed from one and the same source Reasons for disbelieving in
 great and abrupt modifications


I will devote this chapter to the consideration of various miscellaneous
objections which have been advanced against my views as some of the
previous discussions may thus be made clearer but it would be useless
to discuss all of them as many have been made by writers who have not
taken the trouble to understand the subject Thus a distinguished German
naturalist has asserted that the weakest part of my theory is that I
consider all organic beings as imperfect what I have really said is
that all are not as perfect as they might have been in relation to their
conditions and this is shown to be the case by so many native forms
in many quarters of the world having yielded their places to intruding
foreigners Nor can organic beings even if they were at any one time
perfectly adapted to their conditions of life have remained so when
their conditions changed unless they themselves likewise changed and
no one will dispute that the physical conditions of each country as
well as the number and kinds of its inhabitants have undergone many
mutations

A critic has lately insisted with some parade of mathematical accuracy
that longevity is a great advantage to all species so that he who
believes in natural selection must arrange his genealogical tree in
such a manner that all the descendants have longer lives than their
progenitors  Cannot our critics conceive that a biennial plant or one of
the lower animals might range into a cold climate and perish there every
winter and yet owing to advantages gained through natural selection
survive from year to year by means of its seeds or ova Mr E Ray
Lankester has recently discussed this subject and he concludes as far
as its extreme complexity allows him to form a judgment that longevity
is generally related to the standard of each species in the scale of
organisation as well as to the amount of expenditure in reproduction
and in general activity And these conditions have it is probable been
largely determined through natural selection

It has been argued that as none of the animals and plants of Egypt
of which we know anything have changed during the last three or four
thousand years so probably have none in any part of the world But as
Mr GH Lewes has remarked this line of argument proves too much
for the ancient domestic races figured on the Egyptian monuments or
embalmed are closely similar or even identical with those now living
yet all naturalists admit that such races have been produced through
the modification of their original types The many animals which have
remained unchanged since the commencement of the glacial period would
have been an incomparably stronger case for these have been exposed
to great changes of climate and have migrated over great distances
whereas in Egypt during the last several thousand years the
conditions of life as far as we know have remained absolutely uniform
The fact of little or no modification having been effected since the
glacial period would have been of some avail against those who believe
in an innate and necessary law of development but is powerless against
the doctrine of natural selection or the survival of the fittest which
implies that when variations or individual differences of a beneficial
nature happen to arise these will be preserved but this will be
effected only under certain favourable circumstances

The celebrated palaeontologist Bronn at the close of his German
translation of this work asks how on the principle of natural
selection can a variety live side by side with the parent species
If both have become fitted for slightly different habits of life
or conditions they might live together and if we lay on one side
polymorphic species in which the variability seems to be of a peculiar
nature and all mere temporary variations such as size albinism
etc the more permanent varieties are generally found as far as I can
discover inhabiting distinct stations such as high land or low land
dry or moist districts Moreover in the case of animals which wander
much about and cross freely their varieties seem to be generally
confined to distinct regions

Bronn also insists that distinct species never differ from each other in
single characters but in many parts and he asks how it always comes
that many parts of the organisation should have been modified at the
same time through variation and natural selection But there is no
necessity for supposing that all the parts of any being have been
simultaneously modified The most striking modifications excellently
adapted for some purpose might as was formerly remarked be acquired
by successive variations if slight first in one part and then in
another and as they would be transmitted all together they would
appear to us as if they had been simultaneously developed The best
answer however to the above objection is afforded by those domestic
races which have been modified chiefly through mans power of
selection for some special purpose Look at the race and drayhorse or
at the greyhound and mastiff Their whole frames and even their mental
characteristics have been modified but if we could trace each step
in the history of their transformation and the latter steps can be
traced we should not see great and simultaneous changes but first
one part and then another slightly modified and improved Even when
selection has been applied by man to some one character alone of which
our cultivated plants offer the best instances it will invariably be
found that although this one part whether it be the flower fruit or
leaves has been greatly changed almost all the other parts have been
slightly modified This may be attributed partly to the principle of
correlated growth and partly to socalled spontaneous variation

A much more serious objection has been urged by Bronn and recently by
Broca namely that many characters appear to be of no service whatever
to their possessors and therefore cannot have been influenced through
natural selection Bronn adduces the length of the ears and tails in the
different species of hares and mice the complex folds of enamel in the
teeth of many animals and a multitude of analogous cases With respect
to plants this subject has been discussed by Nageli in an admirable
essay He admits that natural selection has effected much but he
insists that the families of plants differ chiefly from each other in
morphological characters which appear to be quite unimportant for the
welfare of the species He consequently believes in an innate tendency
towards progressive and more perfect development He specifies the
arrangement of the cells in the tissues and of the leaves on the axis
as cases in which natural selection could not have acted To these
may be added the numerical divisions in the parts of the flower the
position of the ovules the shape of the seed when not of any use for
dissemination etc

There is much force in the above objection Nevertheless we ought in
the first place to be extremely cautious in pretending to decide what
structures now are or have formerly been of use to each species In
the second place it should always be borne in mind that when one part
is modified so will be other parts through certain dimly seen causes
such as an increased or diminished flow of nutriment to a part mutual
pressure an early developed part affecting one subsequently developed
and so forth as well as through other causes which lead to the
many mysterious cases of correlation which we do not in the least
understand These agencies may be all grouped together for the sake of
brevity under the expression of the laws of growth In the third
place we have to allow for the direct and definite action of changed
conditions of life and for socalled spontaneous variations in which
the nature of the conditions apparently plays a quite subordinate part
Budvariations such as the appearance of a mossrose on a common rose
or of a nectarine on a peachtree offer good instances of spontaneous
variations but even in these cases if we bear in mind the power of a
minute drop of poison in producing complex galls we ought not to feel
too sure that the above variations are not the effect of some local
change in the nature of the sap due to some change in the conditions
There must be some efficient cause for each slight individual
difference as well as for more strongly marked variations which
occasionally arise and if the unknown cause were to act persistently
it is almost certain that all the individuals of the species would be
similarly modified

In the earlier editions of this work I underrated as it now seems
probable the frequency and importance of modifications due to
spontaneous variability But it is impossible to attribute to this cause
the innumerable structures which are so well adapted to the habits
of life of each species I can no more believe in this than that
the welladapted form of a racehorse or greyhound which before the
principle of selection by man was well understood excited so much
surprise in the minds of the older naturalists can thus be explained

It may be worth while to illustrate some of the foregoing remarks With
respect to the assumed inutility of various parts and organs it is
hardly necessary to observe that even in the higher and bestknown
animals many structures exist which are so highly developed that no one
doubts that they are of importance yet their use has not been or has
only recently been ascertained As Bronn gives the length of the ears
and tail in the several species of mice as instances though trifling
ones of differences in structure which can be of no special use I may
mention that according to Dr Schobl the external ears of the common
mouse are supplied in an extraordinary manner with nerves so that
they no doubt serve as tactile organs hence the length of the ears can
hardly be quite unimportant We shall also presently see that the tail
is a highly useful prehensile organ to some of the species and its use
would be much influence by its length

With respect to plants to which on account of Nagelis essay I shall
confine myself in the following remarks it will be admitted that the
flowers of the orchids present a multitude of curious structures
which a few years ago would have been considered as mere morphological
differences without any special function but they are now known to be
of the highest importance for the fertilisation of the species through
the aid of insects and have probably been gained through natural
selection No one until lately would have imagined that in dimorphic and
trimorphic plants the different lengths of the stamens and pistils and
their arrangement could have been of any service but now we know this
to be the case

In certain whole groups of plants the ovules stand erect and in others
they are suspended and within the same ovarium of some few plants one
ovule holds the former and a second ovule the latter position These
positions seem at first purely morphological or of no physiological
signification but Dr Hooker informs me that within the same ovarium
the upper ovules alone in some cases and in others the lower ones
alone are fertilised and he suggests that this probably depends on
the direction in which the pollentubes enter the ovarium If so the
position of the ovules even when one is erect and the other suspended
within the same ovarium would follow the selection of any slight
deviations in position which favoured their fertilisation and the
production of seed

Several plants belonging to distinct orders habitually produce flowers
of two kinds the one open of the ordinary structure the other closed
and imperfect These two kinds of flowers sometimes differ wonderfully
in structure yet may be seen to graduate into each other on the same
plant The ordinary and open flowers can be intercrossed and the
benefits which certainly are derived from this process are thus secured
The closed and imperfect flowers are however manifestly of high
importance as they yield with the utmost safety a large stock of seed
with the expenditure of wonderfully little pollen The two kinds of
flowers often differ much as just stated in structure The petals in
the imperfect flowers almost always consist of mere rudiments and the
pollengrains are reduced in diameter In Ononis columnae five of the
alternate stamens are rudimentary and in some species of Viola three
stamens are in this state two retaining their proper function but
being of very small size In six out of thirty of the closed flowers in
an Indian violet name unknown for the plants have never produced with
me perfect flowers the sepals are reduced from the normal number of
five to three In one section of the Malpighiaceae the closed flowers
according to A de Jussieu are still further modified for the five
stamens which stand opposite to the sepals are all aborted a sixth
stamen standing opposite to a petal being alone developed and this
stamen is not present in the ordinary flowers of this species the style
is aborted and the ovaria are reduced from three to two Now although
natural selection may well have had the power to prevent some of
the flowers from expanding and to reduce the amount of pollen when
rendered by the closure of the flowers superfluous yet hardly any of
the above special modifications can have been thus determined but
must have followed from the laws of growth including the functional
inactivity of parts during the progress of the reduction of the pollen
and the closure of the flowers

It is so necessary to appreciate the important effects of the laws of
growth that I will give some additional cases of another kind namely
of differences in the same part or organ due to differences in relative
position on the same plant In the Spanish chestnut and in certain
firtrees the angles of divergence of the leaves differ according to
Schacht in the nearly horizontal and in the upright branches In the
common rue and some other plants one flower usually the central or
terminal one opens first and has five sepals and petals and five
divisions to the ovarium while all the other flowers on the plant are
tetramerous In the British Adoxa the uppermost flower generally has
two calyxlobes with the other organs tetramerous while the surrounding
flowers generally have three calyxlobes with the other organs
pentamerous In many Compositae and Umbelliferae and in some other
plants the circumferential flowers have their corollas much more
developed than those of the centre and this seems often connected with
the abortion of the reproductive organs It is a more curious fact
previously referred to that the achenes or seeds of the circumference
and centre sometimes differ greatly in form colour and other
characters In Carthamus and some other Compositae the central achenes
alone are furnished with a pappus and in Hyoseris the same head yields
achenes of three different forms In certain Umbelliferae the exterior
seeds according to Tausch are orthospermous and the central one
coelospermous and this is a character which was considered by De
Candolle to be in other species of the highest systematic importance
Professor Braun mentions a Fumariaceous genus in which the flowers in
the lower part of the spike bear oval ribbed oneseeded nutlets and
in the upper part of the spike lanceolate twovalved and twoseeded
siliques In these several cases with the exception of that of the
welldeveloped rayflorets which are of service in making the flowers
conspicuous to insects natural selection cannot as far as we can
judge have come into play or only in a quite subordinate manner All
these modifications follow from the relative position and interaction
of the parts and it can hardly be doubted that if all the flowers and
leaves on the same plant had been subjected to the same external and
internal condition as are the flowers and leaves in certain positions
all would have been modified in the same manner

In numerous other cases we find modifications of structure which are
considered by botanists to be generally of a highly important nature
affecting only some of the flowers on the same plant or occurring on
distinct plants which grow close together under the same conditions As
these variations seem of no special use to the plants they cannot
have been influenced by natural selection Of their cause we are quite
ignorant we cannot even attribute them as in the last class of cases
to any proximate agency such as relative position I will give only
a few instances It is so common to observe on the same plant flowers
indifferently tetramerous pentamerous etc that I need not give
examples but as numerical variations are comparatively rare when the
parts are few I may mention that according to De Candolle the flowers
of Papaver bracteatum offer either two sepals with four petals which
is the common type with poppies or three sepals with six petals The
manner in which the petals are folded in the bud is in most groups a
very constant morphological character but Professor Asa Gray states
that with some species of Mimulus the aestivation is almost as
frequently that of the Rhinanthideae as of the Antirrhinideae to which
latter tribe the genus belongs Aug St Hilaire gives the following
cases the genus Zanthoxylon belongs to a division of the Rutaceae with
a single ovary but in some species flowers may be found on the same
plant and even in the same panicle with either one or two ovaries
In Helianthemum the capsule has been described as unilocular or
trilocular and in H mutabile Une lame PLUS OU MOINS LARGE
setend entre le pericarpe et le placenta In the flowers of Saponaria
officinalis Dr Masters has observed instances of both marginal and free
central placentation Lastly St Hilaire found towards the southern
extreme of the range of Gomphia oleaeformis two forms which he did
not at first doubt were distinct species but he subsequently saw them
growing on the same bush and he then adds Voila donc dans un meme
individu des loges et un style qui se rattachent tantot a un axe
verticale et tantot a un gynobase

We thus see that with plants many morphological changes may be
attributed to the laws of growth and the interaction of parts
independently of natural selection But with respect to Nagelis
doctrine of an innate tendency towards perfection or progressive
development can it be said in the case of these strongly pronounced
variations that the plants have been caught in the act of progressing
towards a higher state of development On the contrary I should infer
from the mere fact of the parts in question differing or varying greatly
on the same plant that such modifications were of extremely small
importance to the plants themselves of whatever importance they may
generally be to us for our classifications The acquisition of a useless
part can hardly be said to raise an organism in the natural scale and
in the case of the imperfect closed flowers above described if any
new principle has to be invoked it must be one of retrogression rather
than of progression and so it must be with many parasitic and degraded
animals We are ignorant of the exciting cause of the above specified
modifications but if the unknown cause were to act almost uniformly for
a length of time we may infer that the result would be almost uniform
and in this case all the individuals of the species would be modified in
the same manner

From the fact of the above characters being unimportant for the welfare
of the species any slight variations which occurred in them would
not have been accumulated and augmented through natural selection A
structure which has been developed through longcontinued selection
when it ceases to be of service to a species generally becomes
variable as we see with rudimentary organs for it will no longer be
regulated by this same power of selection But when from the nature
of the organism and of the conditions modifications have been induced
which are unimportant for the welfare of the species they may be and
apparently often have been transmitted in nearly the same state to
numerous otherwise modified descendants It cannot have been of much
importance to the greater number of mammals birds or reptiles whether
they were clothed with hair feathers or scales yet hair has been
transmitted to almost all mammals feathers to all birds and scales to
all true reptiles A structure whatever it may be which is common to
many allied forms is ranked by us as of high systematic importance
and consequently is often assumed to be of high vital importance to the
species Thus as I am inclined to believe morphological differences
which we consider as important such as the arrangement of the leaves
the divisions of the flower or of the ovarium the position of the
ovules etc first appeared in many cases as fluctuating variations
which sooner or later became constant through the nature of the organism
and of the surrounding conditions as well as through the intercrossing
of distinct individuals but not through natural selection for as these
morphological characters do not affect the welfare of the species any
slight deviations in them could not have been governed or accumulated
through this latter agency It is a strange result which we thus arrive
at namely that characters of slight vital importance to the species
are the most important to the systematist but as we shall hereafter
see when we treat of the genetic principle of classification this is by
no means so paradoxical as it may at first appear

Although we have no good evidence of the existence in organic beings of
an innate tendency towards progressive development yet this necessarily
follows as I have attempted to show in the fourth chapter through the
continued action of natural selection For the best definition which
has ever been given of a high standard of organisation is the degree
to which the parts have been specialised or differentiated and natural
selection tends towards this end inasmuch as the parts are thus enabled
to perform their functions more efficiently

A distinguished zoologist Mr St George Mivart has recently collected
all the objections which have ever been advanced by myself and others
against the theory of natural selection as propounded by Mr Wallace
and myself and has illustrated them with admirable art and force When
thus marshalled they make a formidable array and as it forms no
part of Mr Mivarts plan to give the various facts and considerations
opposed to his conclusions no slight effort of reason and memory is
left to the reader who may wish to weigh the evidence on both sides
When discussing special cases Mr Mivart passes over the effects of the
increased use and disuse of parts which I have always maintained to be
highly important and have treated in my Variation under Domestication
at greater length than as I believe any other writer He likewise
often assumes that I attribute nothing to variation independently of
natural selection whereas in the work just referred to I have collected
a greater number of wellestablished cases than can be found in any
other work known to me My judgment may not be trustworthy but after
reading with care Mr Mivarts book and comparing each section with
what I have said on the same head I never before felt so strongly
convinced of the general truth of the conclusions here arrived at
subject of course in so intricate a subject to much partial error

All Mr Mivarts objections will be or have been considered in the
present volume The one new point which appears to have struck many
readers is That natural selection is incompetent to account for the
incipient stages of useful structures This subject is intimately
connected with that of the gradation of the characters often
accompanied by a change of function for instance the conversion of a
swimbladder into lungs points which were discussed in the last chapter
under two headings Nevertheless I will here consider in some detail
several of the cases advanced by Mr Mivart selecting those which are
the most illustrative as want of space prevents me from considering
all

The giraffe by its lofty stature much elongated neck fore legs head
and tongue has its whole frame beautifully adapted for browsing on the
higher branches of trees It can thus obtain food beyond the reach of
the other Ungulata or hoofed animals inhabiting the same country and
this must be a great advantage to it during dearths The Niata cattle
in South America show us how small a difference in structure may make
during such periods a great difference in preserving an animals
life These cattle can browse as well as others on grass but from the
projection of the lower jaw they cannot during the often recurrent
droughts browse on the twigs of trees reeds etc to which food the
common cattle and horses are then driven so that at these times the
Niatas perish if not fed by their owners Before coming to Mr Mivarts
objections it may be well to explain once again how natural selection
will act in all ordinary cases Man has modified some of his animals
without necessarily having attended to special points of structure by
simply preserving and breeding from the fleetest individuals as with
the racehorse and greyhound or as with the gamecock by breeding
from the victorious birds So under nature with the nascent giraffe the
individuals which were the highest browsers and were able during dearths
to reach even an inch or two above the others will often have been
preserved for they will have roamed over the whole country in search of
food That the individuals of the same species often differ slightly
in the relative lengths of all their parts may be seen in many works of
natural history in which careful measurements are given These slight
proportional differences due to the laws of growth and variation are
not of the slightest use or importance to most species But it will have
been otherwise with the nascent giraffe considering its probable habits
of life for those individuals which had some one part or several parts
of their bodies rather more elongated than usual would generally
have survived These will have intercrossed and left offspring either
inheriting the same bodily peculiarities or with a tendency to vary
again in the same manner while the individuals less favoured in the
same respects will have been the most liable to perish

We here see that there is no need to separate single pairs as man does
when he methodically improves a breed natural selection will preserve
and thus separate all the superior individuals allowing them freely
to intercross and will destroy all the inferior individuals By this
process longcontinued which exactly corresponds with what I have
called unconscious selection by man combined no doubt in a most
important manner with the inherited effects of the increased use of
parts it seems to me almost certain that an ordinary hoofed quadruped
might be converted into a giraffe

To this conclusion Mr Mivart brings forward two objections One is
that the increased size of the body would obviously require an increased
supply of food and he considers it as very problematical whether the
disadvantages thence arising would not in times of scarcity more than
counterbalance the advantages But as the giraffe does actually exist
in large numbers in Africa and as some of the largest antelopes in the
world taller than an ox abound there why should we doubt that as
far as size is concerned intermediate gradations could formerly have
existed there subjected as now to severe dearths Assuredly the being
able to reach at each stage of increased size to a supply of food
left untouched by the other hoofed quadrupeds of the country would have
been of some advantage to the nascent giraffe Nor must we overlook the
fact that increased bulk would act as a protection against almost all
beasts of prey excepting the lion and against this animal its tall
neck and the taller the better would as Mr Chauncey Wright has
remarked serve as a watchtower It is from this cause as Sir S Baker
remarks that no animal is more difficult to stalk than the giraffe
This animal also uses its long neck as a means of offence or defence
by violently swinging its head armed with stumplike horns The
preservation of each species can rarely be determined by any one
advantage but by the union of all great and small

Mr Mivart then asks and this is his second objection if natural
selection be so potent and if high browsing be so great an advantage
why has not any other hoofed quadruped acquired a long neck and lofty
stature besides the giraffe and in a lesser degree the camel
guanaco and macrauchenia Or again why has not any member of the
group acquired a long proboscis With respect to South Africa which was
formerly inhabited by numerous herds of the giraffe the answer is not
difficult and can best be given by an illustration In every meadow
in England in which trees grow we see the lower branches trimmed or
planed to an exact level by the browsing of the horses or cattle and
what advantage would it be for instance to sheep if kept there to
acquire slightly longer necks In every district some one kind of animal
will almost certainly be able to browse higher than the others and it
is almost equally certain that this one kind alone could have its neck
elongated for this purpose through natural selection and the effects
of increased use In South Africa the competition for browsing on the
higher branches of the acacias and other trees must be between giraffe
and giraffe and not with the other ungulate animals

Why in other quarters of the world various animals belonging to this
same order have not acquired either an elongated neck or a proboscis
cannot be distinctly answered but it is as unreasonable to expect a
distinct answer to such a question as why some event in the history of
mankind did not occur in one country while it did in another We are
ignorant with respect to the conditions which determine the numbers and
range of each species and we cannot even conjecture what changes of
structure would be favourable to its increase in some new country We
can however see in a general manner that various causes might have
interfered with the development of a long neck or proboscis To reach
the foliage at a considerable height without climbing for which hoofed
animals are singularly illconstructed implies greatly increased
bulk of body and we know that some areas support singularly few large
quadrupeds for instance South America though it is so luxuriant
while South Africa abounds with them to an unparalleled degree Why this
should be so we do not know nor why the later tertiary periods should
have been much more favourable for their existence than the present
time Whatever the causes may have been we can see that certain
districts and times would have been much more favourable than others for
the development of so large a quadruped as the giraffe

In order that an animal should acquire some structure specially and
largely developed it is almost indispensable that several other parts
should be modified and coadapted Although every part of the body varies
slightly it does not follow that the necessary parts should always
vary in the right direction and to the right degree With the different
species of our domesticated animals we know that the parts vary in
a different manner and degree and that some species are much more
variable than others Even if the fitting variations did arise it
does not follow that natural selection would be able to act on them and
produce a structure which apparently would be beneficial to the species
For instance if the number of individuals existing in a country is
determined chiefly through destruction by beasts of prey by external
or internal parasites etc as seems often to be the case then natural
selection will be able to do little or will be greatly retarded in
modifying any particular structure for obtaining food Lastly natural
selection is a slow process and the same favourable conditions must
long endure in order that any marked effect should thus be produced
Except by assigning such general and vague reasons we cannot explain
why in many quarters of the world hoofed quadrupeds have not acquired
much elongated necks or other means for browsing on the higher branches
of trees

Objections of the same nature as the foregoing have been advanced by
many writers In each case various causes besides the general ones just
indicated have probably interfered with the acquisition through natural
selection of structures which it is thought would be beneficial to
certain species One writer asks why has not the ostrich acquired the
power of flight But a moments reflection will show what an enormous
supply of food would be necessary to give to this bird of the desert
force to move its huge body through the air Oceanic islands are
inhabited by bats and seals but by no terrestrial mammals yet as some
of these bats are peculiar species they must have long inhabited their
present homes Therefore Sir C Lyell asks and assigns certain reasons
in answer why have not seals and bats given birth on such islands to
forms fitted to live on the land But seals would necessarily be first
converted into terrestrial carnivorous animals of considerable size and
bats into terrestrial insectivorous animals for the former there would
be no prey for the bats groundinsects would serve as food but these
would already be largely preyed on by the reptiles or birds which first
colonise and abound on most oceanic islands Gradations of structure
with each stage beneficial to a changing species will be favoured only
under certain peculiar conditions A strictly terrestrial animal by
occasionally hunting for food in shallow water then in streams or
lakes might at last be converted into an animal so thoroughly aquatic
as to brave the open ocean But seals would not find on oceanic
islands the conditions favourable to their gradual reconversion into a
terrestrial form Bats as formerly shown probably acquired their
wings by at first gliding through the air from tree to tree like the
socalled flying squirrels for the sake of escaping from their enemies
or for avoiding falls but when the power of true flight had once been
acquired it would never be reconverted back at least for the above
purposes into the less efficient power of gliding through the air
Bats might indeed like many birds have had their wings greatly
reduced in size or completely lost through disuse but in this case
it would be necessary that they should first have acquired the power of
running quickly on the ground by the aid of their hind legs alone so
as to compete with birds or other ground animals and for such a change
a bat seems singularly illfitted These conjectural remarks have been
made merely to show that a transition of structure with each step
beneficial is a highly complex affair and that there is nothing
strange in a transition not having occurred in any particular case

Lastly more than one writer has asked why have some animals had their
mental powers more highly developed than others as such development
would be advantageous to all Why have not apes acquired the
intellectual powers of man Various causes could be assigned but as
they are conjectural and their relative probability cannot be weighed
it would be useless to give them A definite answer to the latter
question ought not to be expected seeing that no one can solve the
simpler problem why of two races of savages one has risen higher in
the scale of civilisation than the other and this apparently implies
increased brain power

We will return to Mr Mivarts other objections Insects often resemble
for the sake of protection various objects such as green or decayed
leaves dead twigs bits of lichen flowers spines excrement of birds
and living insects but to this latter point I shall hereafter recur
The resemblance is often wonderfully close and is not confined to
colour but extends to form and even to the manner in which the insects
hold themselves The caterpillars which project motionless like dead
twigs from the bushes on which they feed offer an excellent instance of
a resemblance of this kind The cases of the imitation of such objects
as the excrement of birds are rare and exceptional On this head
Mr Mivart remarks As according to Mr Darwins theory there is a
constant tendency to indefinite variation and as the minute incipient
variations will be in ALL DIRECTIONS they must tend to neutralize
each other and at first to form such unstable modifications that it is
difficult if not impossible to see how such indefinite oscillations
of infinitesimal beginnings can ever build up a sufficiently appreciable
resemblance to a leaf bamboo or other object for natural selection to
seize upon and perpetuate

But in all the foregoing cases the insects in their original state
no doubt presented some rude and accidental resemblance to an object
commonly found in the stations frequented by them Nor is this at
all improbable considering the almost infinite number of surrounding
objects and the diversity in form and colour of the hosts of insects
which exist As some rude resemblance is necessary for the first start
we can understand how it is that the larger and higher animals do not
with the exception as far as I know of one fish resemble for the
sake of protection special objects but only the surface which commonly
surrounds them and this chiefly in colour Assuming that an insect
originally happened to resemble in some degree a dead twig or a decayed
leaf and that it varied slightly in many ways then all the variations
which rendered the insect at all more like any such object and thus
favoured its escape would be preserved while other variations would
be neglected and ultimately lost or if they rendered the insect at
all less like the imitated object they would be eliminated There would
indeed be force in Mr Mivarts objection if we were to attempt to
account for the above resemblances independently of natural selection
through mere fluctuating variability but as the case stands there is
none

Nor can I see any force in Mr Mivarts difficulty with respect to the
last touches of perfection in the mimicry as in the case given by
Mr Wallace of a walkingstick insect Ceroxylus laceratus which
resembles a stick grown over by a creeping moss or jungermannia
So close was this resemblance that a native Dyak maintained that the
foliaceous excrescences were really moss Insects are preyed on by birds
and other enemies whose sight is probably sharper than ours and
every grade in resemblance which aided an insect to escape notice or
detection would tend towards its preservation and the more perfect the
resemblance so much the better for the insect Considering the nature
of the differences between the species in the group which includes
the above Ceroxylus there is nothing improbable in this insect having
varied in the irregularities on its surface and in these having become
more or less greencoloured for in every group the characters which
differ in the several species are the most apt to vary while the
generic characters or those common to all the species are the most
constant

The Greenland whale is one of the most wonderful animals in the world
and the baleen or whalebone one of its greatest peculiarities The
baleen consists of a row on each side of the upper jaw of about 300
plates or laminae which stand close together transversely to the longer
axis of the mouth Within the main row there are some subsidiary rows
The extremities and inner margins of all the plates are frayed into
stiff bristles which clothe the whole gigantic palate and serve to
strain or sift the water and thus to secure the minute prey on which
these great animals subsist The middle and longest lamina in the
Greenland whale is ten twelve or even fifteen feet in length but in
the different species of Cetaceans there are gradations in length the
middle lamina being in one species according to Scoresby four feet
in another three in another eighteen inches and in the Balaenoptera
rostrata only about nine inches in length The quality of the whalebone
also differs in the different species

With respect to the baleen Mr Mivart remarks that if it had once
attained such a size and development as to be at all useful then
its preservation and augmentation within serviceable limits would be
promoted by natural selection alone But how to obtain the beginning of
such useful development In answer it may be asked why should not
the early progenitors of the whales with baleen have possessed a mouth
constructed something like the lamellated beak of a duck Ducks
like whales subsist by sifting the mud and water and the family has
sometimes been called Criblatores or sifters I hope that I may not
be misconstrued into saying that the progenitors of whales did actually
possess mouths lamellated like the beak of a duck I wish only to show
that this is not incredible and that the immense plates of baleen in
the Greenland whale might have been developed from such lamellae by
finely graduated steps each of service to its possessor

The beak of a shovellerduck Spatula clypeata is a more beautiful
and complex structure than the mouth of a whale The upper mandible is
furnished on each side in the specimen examined by me with a row or
comb formed of 188 thin elastic lamellae obliquely bevelled so as to
be pointed and placed transversely to the longer axis of the mouth
They arise from the palate and are attached by flexible membrane to
the sides of the mandible Those standing towards the middle are the
longest being about onethird of an inch in length and they project
fourteen onehundredths of an inch beneath the edge At their bases
there is a short subsidiary row of obliquely transverse lamellae In
these several respects they resemble the plates of baleen in the mouth
of a whale But towards the extremity of the beak they differ much as
they project inward instead of straight downward The entire head of
the shoveller though incomparably less bulky is about oneeighteenth
of the length of the head of a moderately large Balaenoptera rostrata
in which species the baleen is only nine inches long so that if we were
to make the head of the shoveller as long as that of the Balaenoptera
the lamellae would be six inches in length that is twothirds of the
length of the baleen in this species of whale The lower mandible of
the shovellerduck is furnished with lamellae of equal length with these
above but finer and in being thus furnished it differs conspicuously
from the lower jaw of a whale which is destitute of baleen On the
other hand the extremities of these lower lamellae are frayed into
fine bristly points so that they thus curiously resemble the plates
of baleen In the genus Prion a member of the distinct family of the
Petrels the upper mandible alone is furnished with lamellae which are
well developed and project beneath the margin so that the beak of this
bird resembles in this respect the mouth of a whale

From the highly developed structure of the shovellers beak we may
proceed as I have learned from information and specimens sent to me by
Mr Salvin without any great break as far as fitness for sifting
is concerned through the beak of the Merganetta armata and in some
respects through that of the Aix sponsa to the beak of the common
duck In this latter species the lamellae are much coarser than in the
shoveller and are firmly attached to the sides of the mandible they
are only about fifty in number on each side and do not project at
all beneath the margin They are squaretopped and are edged with
translucent hardish tissue as if for crushing food The edges of the
lower mandible are crossed by numerous fine ridges which project very
little Although the beak is thus very inferior as a sifter to that of
a shoveller yet this bird as every one knows constantly uses it for
this purpose There are other species as I hear from Mr Salvin in
which the lamellae are considerably less developed than in the common
duck but I do not know whether they use their beaks for sifting the
water

Turning to another group of the same family In the Egyptian goose
Chenalopex the beak closely resembles that of the common duck but the
lamellae are not so numerous nor so distinct from each other nor do
they project so much inward yet this goose as I am informed by Mr E
Bartlett uses its bill like a duck by throwing the water out at the
corners Its chief food however is grass which it crops like the
common goose In this latter bird the lamellae of the upper mandible
are much coarser than in the common duck almost confluent about
twentyseven in number on each side and terminating upward in
teethlike knobs The palate is also covered with hard rounded knobs
The edges of the lower mandible are serrated with teeth much more
prominent coarser and sharper than in the duck The common goose does
not sift the water but uses its beak exclusively for tearing or cutting
herbage for which purpose it is so well fitted that it can crop grass
closer than almost any other animal There are other species of geese
as I hear from Mr Bartlett in which the lamellae are less developed
than in the common goose

We thus see that a member of the duck family with a beak constructed
like that of a common goose and adapted solely for grazing or even
a member with a beak having less welldeveloped lamellae might be
converted by small changes into a species like the Egyptian goose this
into one like the common duck and lastly into one like the shoveller
provided with a beak almost exclusively adapted for sifting the water
for this bird could hardly use any part of its beak except the hooked
tip for seizing or tearing solid food The beak of a goose as I may
add might also be converted by small changes into one provided with
prominent recurved teeth like those of the Merganser a member of the
same family serving for the widely different purpose of securing live
fish

Returning to the whales The Hyperoodon bidens is destitute of true
teeth in an efficient condition but its palate is roughened according
to Lacepede with small unequal hard points of horn There is
therefore nothing improbable in supposing that some early Cetacean form
was provided with similar points of horn on the palate but rather more
regularly placed and which like the knobs on the beak of the goose
aided it in seizing or tearing its food If so it will hardly be denied
that the points might have been converted through variation and natural
selection into lamellae as welldeveloped as those of the Egyptian
goose in which case they would have been used both for seizing objects
and for sifting the water then into lamellae like those of the domestic
duck and so onward until they became as well constructed as those of
the shoveller in which case they would have served exclusively as
a sifting apparatus From this stage in which the lamellae would be
twothirds of the length of the plates of baleen in the Balaenoptera
rostrata gradations which may be observed in stillexisting Cetaceans
lead us onward to the enormous plates of baleen in the Greenland whale
Nor is there the least reason to doubt that each step in this scale
might have been as serviceable to certain ancient Cetaceans with
the functions of the parts slowly changing during the progress of
development as are the gradations in the beaks of the different
existing members of the duckfamily We should bear in mind that each
species of duck is subjected to a severe struggle for existence and
that the structure of every part of its frame must be well adapted to
its conditions of life

The Pleuronectidae or Flatfish are remarkable for their asymmetrical
bodies They rest on one side in the greater number of species on the
left but in some on the right side and occasionally reversed adult
specimens occur The lower or restingsurface resembles at first sight
the ventral surface of an ordinary fish it is of a white colour less
developed in many ways than the upper side with the lateral fins often
of smaller size But the eyes offer the most remarkable peculiarity for
they are both placed on the upper side of the head During early youth
however they stand opposite to each other and the whole body is then
symmetrical with both sides equally coloured Soon the eye proper to
the lower side begins to glide slowly round the head to the upper side
but does not pass right through the skull as was formerly thought to be
the case It is obvious that unless the lower eye did thus travel round
it could not be used by the fish while lying in its habitual position on
one side The lower eye would also have been liable to be abraded by
the sandy bottom That the Pleuronectidae are admirably adapted by
their flattened and asymmetrical structure for their habits of life
is manifest from several species such as soles flounders etc being
extremely common The chief advantages thus gained seem to be protection
from their enemies and facility for feeding on the ground The
different members however of the family present as Schiodte
remarks a long series of forms exhibiting a gradual transition from
Hippoglossus pinguis which does not in any considerable degree alter
the shape in which it leaves the ovum to the soles which are entirely
thrown to one side

Mr Mivart has taken up this case and remarks that a sudden spontaneous
transformation in the position of the eyes is hardly conceivable in
which I quite agree with him He then adds If the transit was gradual
then how such transit of one eye a minute fraction of the journey
towards the other side of the head could benefit the individual
is indeed far from clear It seems even that such an incipient
transformation must rather have been injurious But he might have found
an answer to this objection in the excellent observations published
in 1867 by Malm The Pleuronectidae while very young and still
symmetrical with their eyes standing on opposite sides of the head
cannot long retain a vertical position owing to the excessive depth of
their bodies the small size of their lateral fins and to their being
destitute of a swimbladder Hence soon growing tired they fall to
the bottom on one side While thus at rest they often twist as Malm
observed the lower eye upward to see above them and they do this so
vigorously that the eye is pressed hard against the upper part of the
orbit The forehead between the eyes consequently becomes as could be
plainly seen temporarily contracted in breadth On one occasion Malm
saw a young fish raise and depress the lower eye through an angular
distance of about seventy degrees

We should remember that the skull at this early age is cartilaginous and
flexible so that it readily yields to muscular action It is also known
with the higher animals even after early youth that the skull
yields and is altered in shape if the skin or muscles be permanently
contracted through disease or some accident With longeared rabbits
if one ear flops forward and downward its weight drags forward all the
bones of the skull on the same side of which I have given a figure
Malm states that the newlyhatched young of perches salmon and several
other symmetrical fishes have the habit of occasionally resting on
one side at the bottom and he has observed that they often then
strain their lower eyes so as to look upward and their skulls are thus
rendered rather crooked These fishes however are soon able to hold
themselves in a vertical position and no permanent effect is thus
produced With the Pleuronectidae on the other hand the older they
grow the more habitually they rest on one side owing to the increasing
flatness of their bodies and a permanent effect is thus produced on the
form of the head and on the position of the eyes Judging from analogy
the tendency to distortion would no doubt be increased through the
principle of inheritance Schiodte believes in opposition to some other
naturalists that the Pleuronectidae are not quite symmetrical even
in the embryo and if this be so we could understand how it is that
certain species while young habitually fall over and rest on the left
side and other species on the right side Malm adds in confirmation
of the above view that the adult Trachypterus arcticus which is not a
member of the Pleuronectidae rests on its left side at the bottom and
swims diagonally through the water and in this fish the two sides
of the head are said to be somewhat dissimilar Our great authority
on Fishes Dr Gunther concludes his abstract of Malms paper by
remarking that the author gives a very simple explanation of the
abnormal condition of the Pleuronectoids

We thus see that the first stages of the transit of the eye from one
side of the head to the other which Mr Mivart considers would be
injurious may be attributed to the habit no doubt beneficial to the
individual and to the species of endeavouring to look upward with both
eyes while resting on one side at the bottom We may also attribute to
the inherited effects of use the fact of the mouth in several kinds
of flatfish being bent towards the lower surface with the jaw bones
stronger and more effective on this the eyeless side of the head than
on the other for the sake as Dr Traquair supposes of feeding with
ease on the ground Disuse on the other hand will account for the less
developed condition of the whole inferior half of the body including
the lateral fins though Yarrel thinks that the reduced size of these
fins is advantageous to the fish as there is so much less room for
their action than with the larger fins above Perhaps the lesser number
of teeth in the proportion of four to seven in the upper halves of the
two jaws of the plaice to twentyfive to thirty in the lower halves
may likewise be accounted for by disuse From the colourless state of
the ventral surface of most fishes and of many other animals we may
reasonably suppose that the absence of colour in flatfish on the side
whether it be the right or left which is undermost is due to the
exclusion of light But it cannot be supposed that the peculiar speckled
appearance of the upper side of the sole so like the sandy bed of the
sea or the power in some species as recently shown by Pouchet of
changing their colour in accordance with the surrounding surface or the
presence of bony tubercles on the upper side of the turbot are due to
the action of the light Here natural selection has probably come into
play as well as in adapting the general shape of the body of these
fishes and many other peculiarities to their habits of life We should
keep in mind as I have before insisted that the inherited effects
of the increased use of parts and perhaps of their disuse will be
strengthened by natural selection For all spontaneous variations in the
right direction will thus be preserved as will those individuals
which inherit in the highest degree the effects of the increased and
beneficial use of any part How much to attribute in each particular
case to the effects of use and how much to natural selection it seems
impossible to decide

I may give another instance of a structure which apparently owes its
origin exclusively to use or habit The extremity of the tail in
some American monkeys has been converted into a wonderfully perfect
prehensile organ and serves as a fifth hand A reviewer who agrees
with Mr Mivart in every detail remarks on this structure It is
impossible to believe that in any number of ages the first slight
incipient tendency to grasp could preserve the lives of the individuals
possessing it or favour their chance of having and of rearing
offspring But there is no necessity for any such belief Habit and
this almost implies that some benefit great or small is thus derived
would in all probability suffice for the work Brehm saw the young of
an African monkey Cercopithecus clinging to the under surface of their
mother by their hands and at the same time they hooked their little
tails round that of their mother Professor Henslow kept in confinement
some harvest mice Mus messorius which do not possess a structurally
prehensive tail but he frequently observed that they curled their
tails round the branches of a bush placed in the cage and thus aided
themselves in climbing I have received an analogous account from Dr
Gunther who has seen a mouse thus suspend itself If the harvest mouse
had been more strictly arboreal it would perhaps have had its tail
rendered structurally prehensile as is the case with some members of
the same order Why Cercopithecus considering its habits while young
has not become thus provided it would be difficult to say It is
however possible that the long tail of this monkey may be of more
service to it as a balancing organ in making its prodigious leaps than
as a prehensile organ

The mammary glands are common to the whole class of mammals and are
indispensable for their existence they must therefore have been
developed at an extremely remote period and we can know nothing
positively about their manner of development Mr Mivart asks Is it
conceivable that the young of any animal was ever saved from destruction
by accidentally sucking a drop of scarcely nutritious fluid from an
accidentally hypertrophied cutaneous gland of its mother And even
if one was so what chance was there of the perpetuation of such a
variation But the case is not here put fairly It is admitted by most
evolutionists that mammals are descended from a marsupial form and
if so the mammary glands will have been at first developed within
the marsupial sack In the case of the fish Hippocampus the eggs are
hatched and the young are reared for a time within a sack of this
nature and an American naturalist Mr Lockwood believes from what he
has seen of the development of the young that they are nourished by
a secretion from the cutaneous glands of the sack Now with the
early progenitors of mammals almost before they deserved to be thus
designated is it not at least possible that the young might have been
similarly nourished And in this case the individuals which secreted a
fluid in some degree or manner the most nutritious so as to partake of
the nature of milk would in the long run have reared a larger number
of wellnourished offspring than would the individuals which secreted a
poorer fluid and thus the cutaneous glands which are the homologues of
the mammary glands would have been improved or rendered more effective
It accords with the widely extended principle of specialisation that
the glands over a certain space of the sack should have become more
highly developed than the remainder and they would then have formed a
breast but at first without a nipple as we see in the Ornithorhyncus
at the base of the mammalian series Through what agency the glands over
a certain space became more highly specialised than the others I will
not pretend to decide whether in part through compensation of growth
the effects of use or of natural selection

The development of the mammary glands would have been of no service and
could not have been affected through natural selection unless the young
at the same time were able to partake of the secretion There is no
greater difficulty in understanding how young mammals have instinctively
learned to suck the breast than in understanding how unhatched chickens
have learned to break the eggshell by tapping against it with their
specially adapted beaks or how a few hours after leaving the shell they
have learned to pick up grains of food In such cases the most probable
solution seems to be that the habit was at first acquired by practice
at a more advanced age and afterwards transmitted to the offspring
at an earlier age But the young kangaroo is said not to suck only to
cling to the nipple of its mother who has the power of injecting milk
into the mouth of her helpless halfformed offspring On this head
Mr Mivart remarks Did no special provision exist the young one must
infallibly be choked by the intrusion of the milk into the windpipe
But there IS a special provision The larynx is so elongated that
it rises up into the posterior end of the nasal passage and is thus
enabled to give free entrance to the air for the lungs while the milk
passes harmlessly on each side of this elongated larynx and so safely
attains the gullet behind it Mr Mivart then asks how did natural
selection remove in the adult kangaroo and in most other mammals on
the assumption that they are descended from a marsupial form this at
least perfectly innocent and harmless structure It may be suggested
in answer that the voice which is certainly of high importance to many
animals could hardly have been used with full force as long as the
larynx entered the nasal passage and Professor Flower has suggested
to me that this structure would have greatly interfered with an animal
swallowing solid food

We will now turn for a short space to the lower divisions of the
animal kingdom The Echinodermata starfishes seaurchins etc are
furnished with remarkable organs called pedicellariae which consist
when well developed of a tridactyle forceps that is of one formed of
three serrated arms neatly fitting together and placed on the summit of
a flexible stem moved by muscles These forceps can seize firmly hold
of any object and Alexander Agassiz has seen an Echinus or seaurchin
rapidly passing particles of excrement from forceps to forceps down
certain lines of its body in order that its shell should not be fouled
But there is no doubt that besides removing dirt of all kinds they
subserve other functions and one of these apparently is defence

With respect to these organs Mr Mivart as on so many previous
occasions asks What would be the utility of the FIRST RUDIMENTARY
BEGINNINGS of such structures and how could such insipient buddings
have ever preserved the life of a single Echinus He adds not even
the SUDDEN development of the snapping action would have been beneficial
without the freely movable stalk nor could the latter have been
efficient without the snapping jaws yet no minute nearly indefinite
variations could simultaneously evolve these complex coordinations of
structure to deny this seems to do no less than to affirm a startling
paradox Paradoxical as this may appear to Mr Mivart tridactyle
forcepses immovably fixed at the base but capable of a snapping
action certainly exist on some starfishes and this is intelligible
if they serve at least in part as a means of defence Mr Agassiz to
whose great kindness I am indebted for much information on the subject
informs me that there are other starfishes in which one of the three
arms of the forceps is reduced to a support for the other two and
again other genera in which the third arm is completely lost In
Echinoneus the shell is described by M Perrier as bearing two kinds of
pedicellariae one resembling those of Echinus and the other those of
Spatangus and such cases are always interesting as affording the means
of apparently sudden transitions through the abortion of one of the two
states of an organ

With respect to the steps by which these curious organs have been
evolved Mr Agassiz infers from his own researches and those of Mr
Muller that both in starfishes and seaurchins the pedicellariae must
undoubtedly be looked at as modified spines This may be inferred from
their manner of development in the individual as well as from a long
and perfect series of gradations in different species and genera from
simple granules to ordinary spines to perfect tridactyle pedicellariae
The gradation extends even to the manner in which ordinary spines
and the pedicellariae with their supporting calcareous rods are
articulated to the shell In certain genera of starfishes the very
combinations needed to show that the pedicellariae are only modified
branching spines may be found Thus we have fixed spines with three
equidistant serrated movable branches articulated to near their
bases and higher up on the same spine three other movable branches
Now when the latter arise from the summit of a spine they form in fact
a rude tridactyle pedicellariae and such may be seen on the same spine
together with the three lower branches In this case the identity in
nature between the arms of the pedicellariae and the movable branches
of a spine is unmistakable It is generally admitted that the ordinary
spines serve as a protection and if so there can be no reason to doubt
that those furnished with serrated and movable branches likewise serve
for the same purpose and they would thus serve still more effectively
as soon as by meeting together they acted as a prehensile or snapping
apparatus Thus every gradation from an ordinary fixed spine to a fixed
pedicellariae would be of service

In certain genera of starfishes these organs instead of being fixed
or borne on an immovable support are placed on the summit of a flexible
and muscular though short stem and in this case they probably
subserve some additional function besides defence In the seaurchins
the steps can be followed by which a fixed spine becomes articulated to
the shell and is thus rendered movable I wish I had space here to
give a fuller abstract of Mr Agassizs interesting observations on the
development of the pedicellariae All possible gradations as he adds
may likewise be found between the pedicellariae of the starfishes and
the hooks of the Ophiurians another group of the Echinodermata and
again between the pedicellariae of seaurchins and the anchors of the
Holothuriae also belonging to the same great class

Certain compound animals or zoophytes as they have been termed namely
the Polyzoa are provided with curious organs called avicularia These
differ much in structure in the different species In their most perfect
condition they curiously resemble the head and beak of a vulture in
miniature seated on a neck and capable of movement as is likewise the
lower jaw or mandible In one species observed by me all the avicularia
on the same branch often moved simultaneously backwards and forwards
with the lower jaw widely open through an angle of about 90 degrees
in the course of five seconds and their movement caused the whole
polyzoary to tremble When the jaws are touched with a needle they seize
it so firmly that the branch can thus be shaken

Mr Mivart adduces this case chiefly on account of the supposed
difficulty of organs namely the avicularia of the Polyzoa and the
pedicellariae of the Echinodermata which he considers as essentially
similar having been developed through natural selection in widely
distinct divisions of the animal kingdom But as far as structure is
concerned I can see no similarity between tridactyle pedicellariae and
avicularia The latter resembles somewhat more closely the chelae or
pincers of Crustaceans and Mr Mivart might have adduced with equal
appropriateness this resemblance as a special difficulty or even their
resemblance to the head and beak of a bird The avicularia are believed
by Mr Busk Dr Smitt and Dr Nitsche naturalists who have carefully
studied this group to be homologous with the zooids and their
cells which compose the zoophyte the movable lip or lid of the cell
corresponding with the lower and movable mandible of the avicularium
Mr Busk however does not know of any gradations now existing between
a zooid and an avicularium It is therefore impossible to conjecture by
what serviceable gradations the one could have been converted into the
other but it by no means follows from this that such gradations have
not existed

As the chelae of Crustaceans resemble in some degree the avicularia of
Polyzoa both serving as pincers it may be worth while to show that
with the former a long series of serviceable gradations still exists In
the first and simplest stage the terminal segment of a limb shuts down
either on the square summit of the broad penultimate segment or against
one whole side and is thus enabled to catch hold of an object but the
limb still serves as an organ of locomotion We next find one corner of
the broad penultimate segment slightly prominent sometimes furnished
with irregular teeth and against these the terminal segment shuts down
By an increase in the size of this projection with its shape as well
as that of the terminal segment slightly modified and improved the
pincers are rendered more and more perfect until we have at last
an instrument as efficient as the chelae of a lobster And all these
gradations can be actually traced

Besides the avicularia the polyzoa possess curious organs called
vibracula These generally consist of long bristles capable of movement
and easily excited In one species examined by me the vibracula were
slightly curved and serrated along the outer margin and all of them on
the same polyzoary often moved simultaneously so that acting like
long oars they swept a branch rapidly across the objectglass of my
microscope When a branch was placed on its face the vibracula became
entangled and they made violent efforts to free themselves They are
supposed to serve as a defence and may be seen as Mr Busk remarks
to sweep slowly and carefully over the surface of the polyzoary
removing what might be noxious to the delicate inhabitants of the cells
when their tentacula are protruded The avicularia like the vibracula
probably serve for defence but they also catch and kill small living
animals which it is believed are afterwards swept by the currents
within reach of the tentacula of the zooids Some species are provided
with avicularia and vibracula some with avicularia alone and a few with
vibracula alone

It is not easy to imagine two objects more widely different in
appearance than a bristle or vibraculum and an avicularium like the
head of a bird yet they are almost certainly homologous and have been
developed from the same common source namely a zooid with its cell
Hence we can understand how it is that these organs graduate in some
cases as I am informed by Mr Busk into each other Thus with the
avicularia of several species of Lepralia the movable mandible is so
much produced and is so like a bristle that the presence of the upper
or fixed beak alone serves to determine its avicularian nature The
vibracula may have been directly developed from the lips of the cells
without having passed through the avicularian stage but it seems more
probable that they have passed through this stage as during the early
stages of the transformation the other parts of the cell with the
included zooid could hardly have disappeared at once In many cases the
vibracula have a grooved support at the base which seems to represent
the fixed beak though this support in some species is quite absent
This view of the development of the vibracula if trustworthy is
interesting for supposing that all the species provided with avicularia
had become extinct no one with the most vivid imagination would ever
have thought that the vibracula had originally existed as part of an
organ resembling a birds head or an irregular box or hood It is
interesting to see two such widely different organs developed from a
common origin and as the movable lip of the cell serves as a protection
to the zooid there is no difficulty in believing that all the
gradations by which the lip became converted first into the lower
mandible of an avicularium and then into an elongated bristle
likewise served as a protection in different ways and under different
circumstances

In the vegetable kingdom Mr Mivart only alludes to two cases namely
the structure of the flowers of orchids and the movements of climbing
plants With respect to the former he says The explanation of their
ORIGIN is deemed thoroughly unsatisfactory utterly insufficient to
explain the incipient infinitesimal beginnings of structures which are
of utility only when they are considerably developed As I have fully
treated this subject in another work I will here give only a few
details on one alone of the most striking peculiarities of the flowers
of orchids namely their pollinia A pollinium when highly developed
consists of a mass of pollengrains affixed to an elastic footstalk
or caudicle and this to a little mass of extremely viscid matter The
pollinia are by this means transported by insects from one flower to
the stigma of another In some orchids there is no caudicle to the
pollenmasses and the grains are merely tied together by fine threads
but as these are not confined to orchids they need not here be
considered yet I may mention that at the base of the orchidaceous
series in Cypripedium we can see how the threads were probably
first developed In other orchids the threads cohere at one end of the
pollenmasses and this forms the first or nascent trace of a caudicle
That this is the origin of the caudicle even when of considerable
length and highly developed we have good evidence in the aborted
pollengrains which can sometimes be detected embedded within the
central and solid parts

With respect to the second chief peculiarity namely the little mass
of viscid matter attached to the end of the caudicle a long series of
gradations can be specified each of plain service to the plant In most
flowers belonging to other orders the stigma secretes a little viscid
matter Now in certain orchids similar viscid matter is secreted but
in much larger quantities by one alone of the three stigmas and this
stigma perhaps in consequence of the copious secretion is rendered
sterile When an insect visits a flower of this kind it rubs off some
of the viscid matter and thus at the same time drags away some of the
pollengrains From this simple condition which differs but
little from that of a multitude of common flowers there are endless
gradations to species in which the pollenmass terminates in a very
short free caudicle to others in which the caudicle becomes firmly
attached to the viscid matter with the sterile stigma itself much
modified In this latter case we have a pollinium in its most highly
developed and perfect condition He who will carefully examine the
flowers of orchids for himself will not deny the existence of the above
series of gradations from a mass of pollengrains merely tied together
by threads with the stigma differing but little from that of the
ordinary flowers to a highly complex pollinium admirably adapted for
transportal by insects nor will he deny that all the gradations in
the several species are admirably adapted in relation to the general
structure of each flower for its fertilisation by different insects In
this and in almost every other case the enquiry may be pushed further
backwards and it may be asked how did the stigma of an ordinary flower
become viscid but as we do not know the full history of any one
group of beings it is as useless to ask as it is hopeless to attempt
answering such questions

We will now turn to climbing plants These can be arranged in a long
series from those which simply twine round a support to those which I
have called leafclimbers and to those provided with tendrils In these
two latter classes the stems have generally but not always lost the
power of twining though they retain the power of revolving which the
tendrils likewise possess The gradations from leafclimbers to tendril
bearers are wonderfully close and certain plants may be differently
placed in either class But in ascending the series from simple twiners
to leafclimbers an important quality is added namely sensitiveness
to a touch by which means the footstalks of the leaves or flowers or
these modified and converted into tendrils are excited to bend round
and clasp the touching object He who will read my memoir on these
plants will I think admit that all the many gradations in function and
structure between simple twiners and tendrilbearers are in each case
beneficial in a high degree to the species For instance it is clearly
a great advantage to a twining plant to become a leafclimber and it is
probable that every twiner which possessed leaves with long footstalks
would have been developed into a leafclimber if the footstalks had
possessed in any slight degree the requisite sensitiveness to a touch

As twining is the simplest means of ascending a support and forms the
basis of our series it may naturally be asked how did plants acquire
this power in an incipient degree afterwards to be improved and
increased through natural selection The power of twining depends
firstly on the stems while young being extremely flexible but this
is a character common to many plants which are not climbers and
secondly on their continually bending to all points of the compass one
after the other in succession in the same order By this movement the
stems are inclined to all sides and are made to move round and round
As soon as the lower part of a stem strikes against any object and is
stopped the upper part still goes on bending and revolving and thus
necessarily twines round and up the support The revolving movement
ceases after the early growth of each shoot As in many widely separated
families of plants single species and single genera possess the power
of revolving and have thus become twiners they must have independently
acquired it and cannot have inherited it from a common progenitor
Hence I was led to predict that some slight tendency to a movement of
this kind would be found to be far from uncommon with plants which did
not climb and that this had afforded the basis for natural selection
to work on and improve When I made this prediction I knew of only one
imperfect case namely of the young flowerpeduncles of a Maurandia
which revolved slightly and irregularly like the stems of twining
plants but without making any use of this habit Soon afterwards
Fritz Muller discovered that the young stems of an Alisma and of a
Linum plants which do not climb and are widely separated in the natural
system revolved plainly though irregularly and he states that he has
reason to suspect that this occurs with some other plants These slight
movements appear to be of no service to the plants in question anyhow
they are not of the least use in the way of climbing which is the point
that concerns us Nevertheless we can see that if the stems of these
plants had been flexible and if under the conditions to which they are
exposed it had profited them to ascend to a height then the habit
of slightly and irregularly revolving might have been increased and
utilised through natural selection until they had become converted into
welldeveloped twining species

With respect to the sensitiveness of the footstalks of the leaves and
flowers and of tendrils nearly the same remarks are applicable as in
the case of the revolving movements of twining plants As a vast number
of species belonging to widely distinct groups are endowed with this
kind of sensitiveness it ought to be found in a nascent condition in
many plants which have not become climbers This is the case I observed
that the young flowerpeduncles of the above Maurandia curved themselves
a little towards the side which was touched Morren found in several
species of Oxalis that the leaves and their footstalks moved
especially after exposure to a hot sun when they were gently and
repeatedly touched or when the plant was shaken I repeated these
observations on some other species of Oxalis with the same result in
some of them the movement was distinct but was best seen in the young
leaves in others it was extremely slight It is a more important fact
that according to the high authority of Hofmeister the young shoots and
leaves of all plants move after being shaken and with climbing plants
it is as we know only during the early stages of growth that the
footstalks and tendrils are sensitive

It is scarcely possible that the above slight movements due to a touch
or shake in the young and growing organs of plants can be of any
functional importance to them But plants possess in obedience to
various stimuli powers of movement which are of manifest importance
to them for instance towards and more rarely from the light in
opposition to and more rarely in the direction of the attraction
of gravity When the nerves and muscles of an animal are excited by
galvanism or by the absorption of strychnine the consequent movements
may be called an incidental result for the nerves and muscles have not
been rendered specially sensitive to these stimuli So with plants it
appears that from having the power of movement in obedience to certain
stimuli they are excited in an incidental manner by a touch or by
being shaken Hence there is no great difficulty in admitting that in
the case of leafclimbers and tendrilbearers it is this tendency which
has been taken advantage of and increased through natural selection It
is however probable from reasons which I have assigned in my memoir
that this will have occurred only with plants which had already acquired
the power of revolving and had thus become twiners

I have already endeavoured to explain how plants became twiners
namely by the increase of a tendency to slight and irregular revolving
movements which were at first of no use to them this movement as
well as that due to a touch or shake being the incidental result of
the power of moving gained for other and beneficial purposes Whether
during the gradual development of climbing plants natural selection
has been aided by the inherited effects of use I will not pretend to
decide but we know that certain periodical movements for instance the
socalled sleep of plants are governed by habit

I have now considered enough perhaps more than enough of the cases
selected with care by a skilful naturalist to prove that natural
selection is incompetent to account for the incipient stages of
useful structures and I have shown as I hope that there is no great
difficulty on this head A good opportunity has thus been afforded for
enlarging a little on gradations of structure often associated with
strange functions an important subject which was not treated at
sufficient length in the former editions of this work I will now
briefly recapitulate the foregoing cases

With the giraffe the continued preservation of the individuals of some
extinct highreaching ruminant which had the longest necks legs etc
and could browse a little above the average height and the continued
destruction of those which could not browse so high would have sufficed
for the production of this remarkable quadruped but the prolonged
use of all the parts together with inheritance will have aided in an
important manner in their coordination With the many insects which
imitate various objects there is no improbability in the belief that
an accidental resemblance to some common object was in each case the
foundation for the work of natural selection since perfected through
the occasional preservation of slight variations which made the
resemblance at all closer and this will have been carried on as long
as the insect continued to vary and as long as a more and more perfect
resemblance led to its escape from sharpsighted enemies In certain
species of whales there is a tendency to the formation of irregular
little points of horn on the palate and it seems to be quite within the
scope of natural selection to preserve all favourable variations until
the points were converted first into lamellated knobs or teeth like
those on the beak of a goose then into short lamellae like those of
the domestic ducks and then into lamellae as perfect as those of the
shovellerduck and finally into the gigantic plates of baleen as
in the mouth of the Greenland whale In the family of the ducks the
lamellae are first used as teeth then partly as teeth and partly as
a sifting apparatus and at last almost exclusively for this latter
purpose

With such structures as the above lamellae of horn or whalebone habit
or use can have done little or nothing as far as we can judge towards
their development On the other hand the transportal of the lower eye
of a flatfish to the upper side of the head and the formation of
a prehensile tail may be attributed almost wholly to continued use
together with inheritance With respect to the mammae of the higher
animals the most probable conjecture is that primordially the cutaneous
glands over the whole surface of a marsupial sack secreted a nutritious
fluid and that these glands were improved in function through natural
selection and concentrated into a confined area in which case they
would have formed a mamma There is no more difficulty in understanding
how the branched spines of some ancient Echinoderm which served as
a defence became developed through natural selection into tridactyle
pedicellariae than in understanding the development of the pincers of
crustaceans through slight serviceable modifications in the ultimate
and penultimate segments of a limb which was at first used solely
for locomotion In the avicularia and vibracula of the Polyzoa we have
organs widely different in appearance developed from the same source
and with the vibracula we can understand how the successive gradations
might have been of service With the pollinia of orchids the threads
which originally served to tie together the pollengrains can be traced
cohering into caudicles and the steps can likewise be followed by which
viscid matter such as that secreted by the stigmas of ordinary flowers
and still subserving nearly but not quite the same purpose became
attached to the free ends of the caudicles all these gradations being
of manifest benefit to the plants in question With respect to climbing
plants I need not repeat what has been so lately said

It has often been asked if natural selection be so potent why has not
this or that structure been gained by certain species to which it would
apparently have been advantageous But it is unreasonable to expect a
precise answer to such questions considering our ignorance of the past
history of each species and of the conditions which at the present day
determine its numbers and range In most cases only general reasons
but in some few cases special reasons can be assigned Thus to adapt
a species to new habits of life many coordinated modifications are
almost indispensable and it may often have happened that the requisite
parts did not vary in the right manner or to the right degree Many
species must have been prevented from increasing in numbers through
destructive agencies which stood in no relation to certain structures
which we imagine would have been gained through natural selection
from appearing to us advantageous to the species In this case as the
struggle for life did not depend on such structures they could not
have been acquired through natural selection In many cases complex and
longenduring conditions often of a peculiar nature are necessary for
the development of a structure and the requisite conditions may seldom
have concurred The belief that any given structure which we think
often erroneously would have been beneficial to a species would
have been gained under all circumstances through natural selection is
opposed to what we can understand of its manner of action Mr Mivart
does not deny that natural selection has effected something but he
considers it as demonstrably insufficient to account for the phenomena
which I explain by its agency His chief arguments have now been
considered and the others will hereafter be considered They seem to me
to partake little of the character of demonstration and to have little
weight in comparison with those in favour of the power of natural
selection aided by the other agencies often specified I am bound to
add that some of the facts and arguments here used by me have been
advanced for the same purpose in an able article lately published in the
MedicoChirurgical Review

At the present day almost all naturalists admit evolution under some
form Mr Mivart believes that species change through an internal force
or tendency about which it is not pretended that anything is known
That species have a capacity for change will be admitted by all
evolutionists but there is no need as it seems to me to invoke
any internal force beyond the tendency to ordinary variability which
through the aid of selection by man has given rise to many welladapted
domestic races and which through the aid of natural selection would
equally well give rise by graduated steps to natural races or species
The final result will generally have been as already explained an
advance but in some few cases a retrogression in organisation

Mr Mivart is further inclined to believe and some naturalists agree
with him that new species manifest themselves with suddenness and by
modifications appearing at once For instance he supposes that the
differences between the extinct threetoed Hipparion and the horse arose
suddenly He thinks it difficult to believe that the wing of a bird was
developed in any other way than by a comparatively sudden modification
of a marked and important kind and apparently he would extend the
same view to the wings of bats and pterodactyles This conclusion
which implies great breaks or discontinuity in the series appears to me
improbable in the highest degree

Everyone who believes in slow and gradual evolution will of course
admit that specific changes may have been as abrupt and as great as
any single variation which we meet with under nature or even under
domestication But as species are more variable when domesticated or
cultivated than under their natural conditions it is not probable that
such great and abrupt variations have often occurred under nature as
are known occasionally to arise under domestication Of these latter
variations several may be attributed to reversion and the characters
which thus reappear were it is probable in many cases at first
gained in a gradual manner A still greater number must be called
monstrosities such as sixfingered men porcupine men Ancon sheep
Niata cattle etc and as they are widely different in character from
natural species they throw very little light on our subject Excluding
such cases of abrupt variations the few which remain would at best
constitute if found in a state of nature doubtful species closely
related to their parental types

My reasons for doubting whether natural species have changed as abruptly
as have occasionally domestic races and for entirely disbelieving that
they have changed in the wonderful manner indicated by Mr Mivart are
as follows According to our experience abrupt and strongly marked
variations occur in our domesticated productions singly and at rather
long intervals of time If such occurred under nature they would
be liable as formerly explained to be lost by accidental causes of
destruction and by subsequent intercrossing and so it is known to be
under domestication unless abrupt variations of this kind are specially
preserved and separated by the care of man Hence in order that a new
species should suddenly appear in the manner supposed by Mr Mivart
it is almost necessary to believe in opposition to all analogy that
several wonderfully changed individuals appeared simultaneously within
the same district This difficulty as in the case of unconscious
selection by man is avoided on the theory of gradual evolution through
the preservation of a large number of individuals which varied more
or less in any favourable direction and of the destruction of a large
number which varied in an opposite manner

That many species have been evolved in an extremely gradual manner
there can hardly be a doubt The species and even the genera of many
large natural families are so closely allied together that it is
difficult to distinguish not a few of them On every continent in
proceeding from north to south from lowland to upland etc we meet
with a host of closely related or representative species as we likewise
do on certain distinct continents which we have reason to believe were
formerly connected But in making these and the following remarks I am
compelled to allude to subjects hereafter to be discussed Look at
the many outlying islands round a continent and see how many of their
inhabitants can be raised only to the rank of doubtful species So it is
if we look to past times and compare the species which have just passed
away with those still living within the same areas or if we compare
the fossil species embedded in the substages of the same geological
formation It is indeed manifest that multitudes of species are related
in the closest manner to other species that still exist or have lately
existed and it will hardly be maintained that such species have been
developed in an abrupt or sudden manner Nor should it be forgotten
when we look to the special parts of allied species instead of to
distinct species that numerous and wonderfully fine gradations can be
traced connecting together widely different structures

Many large groups of facts are intelligible only on the principle that
species have been evolved by very small steps For instance the fact
that the species included in the larger genera are more closely related
to each other and present a greater number of varieties than do the
species in the smaller genera The former are also grouped in little
clusters like varieties round species and they present other analogies
with varieties as was shown in our second chapter On this same
principle we can understand how it is that specific characters are more
variable than generic characters and how the parts which are developed
in an extraordinary degree or manner are more variable than other parts
of the same species Many analogous facts all pointing in the same
direction could be added

Although very many species have almost certainly been produced by
steps not greater than those separating fine varieties yet it may
be maintained that some have been developed in a different and abrupt
manner Such an admission however ought not to be made without strong
evidence being assigned The vague and in some respects false analogies
as they have been shown to be by Mr Chauncey Wright which have been
advanced in favour of this view such as the sudden crystallisation of
inorganic substances or the falling of a facetted spheroid from one
facet to another hardly deserve consideration One class of facts
however namely the sudden appearance of new and distinct forms of
life in our geological formations supports at first sight the belief in
abrupt development But the value of this evidence depends entirely on
the perfection of the geological record in relation to periods remote
in the history of the world If the record is as fragmentary as many
geologists strenuously assert there is nothing strange in new forms
appearing as if suddenly developed

Unless we admit transformations as prodigious as those advocated by Mr
Mivart such as the sudden development of the wings of birds or bats or
the sudden conversion of a Hipparion into a horse hardly any light
is thrown by the belief in abrupt modifications on the deficiency of
connecting links in our geological formations But against the belief in
such abrupt changes embryology enters a strong protest It is notorious
that the wings of birds and bats and the legs of horses or other
quadrupeds are undistinguishable at an early embryonic period and
that they become differentiated by insensibly fine steps Embryological
resemblances of all kinds can be accounted for as we shall hereafter
see by the progenitors of our existing species having varied after
early youth and having transmitted their newlyacquired characters to
their offspring at a corresponding age The embryo is thus left almost
unaffected and serves as a record of the past condition of the species
Hence it is that existing species during the early stages of their
development so often resemble ancient and extinct forms belonging to the
same class On this view of the meaning of embryological resemblances
and indeed on any view it is incredible that an animal should have
undergone such momentous and abrupt transformations as those above
indicated and yet should not bear even a trace in its embryonic
condition of any sudden modification every detail in its structure
being developed by insensibly fine steps

He who believes that some ancient form was transformed suddenly through
an internal force or tendency into for instance one furnished with
wings will be almost compelled to assume in opposition to all analogy
that many individuals varied simultaneously It cannot be denied that
such abrupt and great changes of structure are widely different from
those which most species apparently have undergone He will further be
compelled to believe that many structures beautifully adapted to all the
other parts of the same creature and to the surrounding conditions
have been suddenly produced and of such complex and wonderful
coadaptations he will not be able to assign a shadow of an
explanation He will be forced to admit that these great and sudden
transformations have left no trace of their action on the embryo
To admit all this is as it seems to me to enter into the realms of
miracle and to leave those of science




CHAPTER VIII INSTINCT

 Instincts comparable with habits but different in their
 origin Instincts graduated Aphides and ants Instincts
 variable Domestic instincts their origin Natural instincts of
 the cuckoo molothrus ostrich and parasitic bees Slavemaking
 ants Hivebee its cellmaking instinct Changes of instinct and
 structure not necessarily simultaneous Difficulties of the theory of
 the Natural Selection of instincts Neuter or sterile insects Summary


Many instincts are so wonderful that their development will probably
appear to the reader a difficulty sufficient to overthrow my whole
theory I may here premise that I have nothing to do with the origin of
the mental powers any more than I have with that of life itself We are
concerned only with the diversities of instinct and of the other mental
faculties in animals of the same class

I will not attempt any definition of instinct It would be easy to show
that several distinct mental actions are commonly embraced by this term
but every one understands what is meant when it is said that instinct
impels the cuckoo to migrate and to lay her eggs in other birds
nests An action which we ourselves require experience to enable us to
perform when performed by an animal more especially by a very young
one without experience and when performed by many individuals in the
same way without their knowing for what purpose it is performed is
usually said to be instinctive But I could show that none of these
characters are universal A little dose of judgment or reason as Pierre
Huber expresses it often comes into play even with animals low in the
scale of nature

Frederick Cuvier and several of the older metaphysicians have compared
instinct with habit This comparison gives I think an accurate notion
of the frame of mind under which an instinctive action is performed but
not necessarily of its origin How unconsciously many habitual actions
are performed indeed not rarely in direct opposition to our conscious
will  yet they may be modified by the will or reason Habits easily
become associated with other habits with certain periods of time and
states of the body When once acquired they often remain constant
throughout life Several other points of resemblance between instincts
and habits could be pointed out As in repeating a wellknown song
so in instincts one action follows another by a sort of rhythm if a
person be interrupted in a song or in repeating anything by rote he is
generally forced to go back to recover the habitual train of thought so
P Huber found it was with a caterpillar which makes a very complicated
hammock for if he took a caterpillar which had completed its hammock
up to say the sixth stage of construction and put it into a
hammock completed up only to the third stage the caterpillar simply
reperformed the fourth fifth and sixth stages of construction
If however a caterpillar were taken out of a hammock made up for
instance to the third stage and were put into one finished up to the
sixth stage so that much of its work was already done for it far from
deriving any benefit from this it was much embarrassed and in order
to complete its hammock seemed forced to start from the third stage
where it had left off and thus tried to complete the already finished
work

If we suppose any habitual action to become inherited and it can be
shown that this does sometimes happen then the resemblance between what
originally was a habit and an instinct becomes so close as not to be
distinguished If Mozart instead of playing the pianoforte at three
years old with wonderfully little practice had played a tune with no
practice at all be might truly be said to have done so instinctively
But it would be a serious error to suppose that the greater number
of instincts have been acquired by habit in one generation and then
transmitted by inheritance to succeeding generations It can be clearly
shown that the most wonderful instincts with which we are acquainted
namely those of the hivebee and of many ants could not possibly have
been acquired by habit

It will be universally admitted that instincts are as important as
corporeal structures for the welfare of each species under its present
conditions of life Under changed conditions of life it is at least
possible that slight modifications of instinct might be profitable to a
species and if it can be shown that instincts do vary ever so little
then I can see no difficulty in natural selection preserving and
continually accumulating variations of instinct to any extent that was
profitable It is thus as I believe that all the most complex and
wonderful instincts have originated As modifications of corporeal
structure arise from and are increased by use or habit and are
diminished or lost by disuse so I do not doubt it has been with
instincts But I believe that the effects of habit are in many cases of
subordinate importance to the effects of the natural selection of
what may be called spontaneous variations of instincts that is of
variations produced by the same unknown causes which produce slight
deviations of bodily structure

No complex instinct can possibly be produced through natural selection
except by the slow and gradual accumulation of numerous slight yet
profitable variations Hence as in the case of corporeal structures
we ought to find in nature not the actual transitional gradations by
which each complex instinct has been acquired for these could be found
only in the lineal ancestors of each species but we ought to find in
the collateral lines of descent some evidence of such gradations or
we ought at least to be able to show that gradations of some kind are
possible and this we certainly can do I have been surprised to find
making allowance for the instincts of animals having been but little
observed except in Europe and North America and for no instinct being
known among extinct species how very generally gradations leading to
the most complex instincts can be discovered Changes of instinct may
sometimes be facilitated by the same species having different instincts
at different periods of life or at different seasons of the year or
when placed under different circumstances etc in which case either
the one or the other instinct might be preserved by natural selection
And such instances of diversity of instinct in the same species can be
shown to occur in nature

Again as in the case of corporeal structure and conformably to my
theory the instinct of each species is good for itself but has never
as far as we can judge been produced for the exclusive good of others
One of the strongest instances of an animal apparently performing an
action for the sole good of another with which I am acquainted is that
of aphides voluntarily yielding as was first observed by Huber their
sweet excretion to ants that they do so voluntarily the following
facts show I removed all the ants from a group of about a dozen aphides
on a dockplant and prevented their attendance during several hours
After this interval I felt sure that the aphides would want to excrete
I watched them for some time through a lens but not one excreted I
then tickled and stroked them with a hair in the same manner as well
as I could as the ants do with their antennae but not one excreted
Afterwards I allowed an ant to visit them and it immediately seemed
by its eager way of running about to be well aware what a rich flock it
had discovered it then began to play with its antennae on the abdomen
first of one aphis and then of another and each as soon as it felt the
antennae immediately lifted up its abdomen and excreted a limpid drop
of sweet juice which was eagerly devoured by the ant Even the quite
young aphides behaved in this manner showing that the action was
instinctive and not the result of experience It is certain from the
observations of Huber that the aphides show no dislike to the ants
if the latter be not present they are at last compelled to eject their
excretion But as the excretion is extremely viscid it is no doubt a
convenience to the aphides to have it removed therefore probably they
do not excrete solely for the good of the ants Although there is no
evidence that any animal performs an action for the exclusive good of
another species yet each tries to take advantage of the instincts of
others as each takes advantage of the weaker bodily structure of other
species So again certain instincts cannot be considered as absolutely
perfect but as details on this and other such points are not
indispensable they may be here passed over

As some degree of variation in instincts under a state of nature and
the inheritance of such variations are indispensable for the action of
natural selection as many instances as possible ought to be given but
want of space prevents me I can only assert that instincts certainly
do vary for instance the migratory instinct both in extent and
direction and in its total loss So it is with the nests of birds
which vary partly in dependence on the situations chosen and on the
nature and temperature of the country inhabited but often from causes
wholly unknown to us Audubon has given several remarkable cases
of differences in the nests of the same species in the northern and
southern United States Why it has been asked if instinct be variable
has it not granted to the bee the ability to use some other material
when wax was deficient But what other natural material could bees
use They will work as I have seen with wax hardened with vermilion
or softened with lard Andrew Knight observed that his bees instead of
laboriously collecting propolis used a cement of wax and turpentine
with which he had covered decorticated trees It has lately been shown
that bees instead of searching for pollen will gladly use a very
different substance namely oatmeal Fear of any particular enemy is
certainly an instinctive quality as may be seen in nestling birds
though it is strengthened by experience and by the sight of fear of the
same enemy in other animals The fear of man is slowly acquired as
I have elsewhere shown by the various animals which inhabit desert
islands and we see an instance of this even in England in the greater
wildness of all our large birds in comparison with our small birds
for the large birds have been most persecuted by man We may safely
attribute the greater wildness of our large birds to this cause for in
uninhabited islands large birds are not more fearful than small and the
magpie so wary in England is tame in Norway as is the hooded crow in
Egypt

That the mental qualities of animals of the same kind born in a state
of nature vary much could be shown by many facts Several cases could
also be adduced of occasional and strange habits in wild animals which
if advantageous to the species might have given rise through natural
selection to new instincts But I am well aware that these general
statements without the facts in detail can produce but a feeble effect
on the readers mind I can only repeat my assurance that I do not
speak without good evidence

INHERITED CHANGES OF HABIT OR INSTINCT IN DOMESTICATED ANIMALS

The possibility or even probability of inherited variations
of instinct in a state of nature will be strengthened by briefly
considering a few cases under domestication We shall thus be enabled
to see the part which habit and the selection of socalled spontaneous
variations have played in modifying the mental qualities of our domestic
animals It is notorious how much domestic animals vary in their mental
qualities With cats for instance one naturally takes to catching
rats and another mice and these tendencies are known to be inherited
One cat according to Mr St John always brought home game birds
another hares or rabbits and another hunted on marshy ground and almost
nightly caught woodcocks or snipes A number of curious and authentic
instances could be given of various shades of disposition and taste and
likewise of the oddest tricks associated with certain frames of mind or
periods of time But let us look to the familiar case of the breeds
of dogs it cannot be doubted that young pointers I have myself seen
striking instances will sometimes point and even back other dogs the
very first time that they are taken out retrieving is certainly in some
degree inherited by retrievers and a tendency to run round instead of
at a flock of sheep by shepherddogs I cannot see that these actions
performed without experience by the young and in nearly the same manner
by each individual performed with eager delight by each breed and
without the end being known for the young pointer can no more know that
he points to aid his master than the white butterfly knows why she lays
her eggs on the leaf of the cabbage I cannot see that these actions
differ essentially from true instincts If we were to behold one kind
of wolf when young and without any training as soon as it scented its
prey stand motionless like a statue and then slowly crawl forward with
a peculiar gait and another kind of wolf rushing round instead of at
a herd of deer and driving them to a distant point we should assuredly
call these actions instinctive Domestic instincts as they may be
called are certainly far less fixed than natural instincts but
they have been acted on by far less rigorous selection and have
been transmitted for an incomparably shorter period under less fixed
conditions of life

How strongly these domestic instincts habits and dispositions are
inherited and how curiously they become mingled is well shown when
different breeds of dogs are crossed Thus it is known that a cross with
a bulldog has affected for many generations the courage and obstinacy
of greyhounds and a cross with a greyhound has given to a whole family
of shepherddogs a tendency to hunt hares These domestic instincts
when thus tested by crossing resemble natural instincts which in a
like manner become curiously blended together and for a long period
exhibit traces of the instincts of either parent for example Le Roy
describes a dog whose greatgrandfather was a wolf and this dog
showed a trace of its wild parentage only in one way by not coming in a
straight line to his master when called

Domestic instincts are sometimes spoken of as actions which have become
inherited solely from longcontinued and compulsory habit but this is
not true No one would ever have thought of teaching or probably could
have taught the tumblerpigeon to tumble an action which as I have
witnessed is performed by young birds that have never seen a pigeon
tumble We may believe that some one pigeon showed a slight tendency to
this strange habit and that the longcontinued selection of the best
individuals in successive generations made tumblers what they now are
and near Glasgow there are housetumblers as I hear from Mr Brent
which cannot fly eighteen inches high without going head over heels It
may be doubted whether any one would have thought of training a dog to
point had not some one dog naturally shown a tendency in this line and
this is known occasionally to happen as I once saw in a pure terrier
the act of pointing is probably as many have thought only the
exaggerated pause of an animal preparing to spring on its prey When the
first tendency to point was once displayed methodical selection and the
inherited effects of compulsory training in each successive generation
would soon complete the work and unconscious selection is still in
progress as each man tries to procure without intending to improve the
breed dogs which stand and hunt best On the other hand habit alone
in some cases has sufficed hardly any animal is more difficult to tame
than the young of the wild rabbit scarcely any animal is tamer than the
young of the tame rabbit but I can hardly suppose that domestic rabbits
have often been selected for tameness alone so that we must attribute
at least the greater part of the inherited change from extreme wildness
to extreme tameness to habit and longcontinued close confinement

Natural instincts are lost under domestication a remarkable instance of
this is seen in those breeds of fowls which very rarely or never become
broody that is never wish to sit on their eggs Familiarity alone
prevents our seeing how largely and how permanently the minds of our
domestic animals have been modified It is scarcely possible to doubt
that the love of man has become instinctive in the dog All wolves
foxes jackals and species of the cat genus when kept tame are most
eager to attack poultry sheep and pigs and this tendency has been
found incurable in dogs which have been brought home as puppies from
countries such as Tierra del Fuego and Australia where the savages do
not keep these domestic animals How rarely on the other hand do
our civilised dogs even when quite young require to be taught not to
attack poultry sheep and pigs  No doubt they occasionally do make an
attack and are then beaten and if not cured they are destroyed
so that habit and some degree of selection have probably concurred in
civilising by inheritance our dogs On the other hand young chickens
have lost wholly by habit that fear of the dog and cat which no doubt
was originally instinctive in them for I am informed by Captain Hutton
that the young chickens of the parent stock the Gallus bankiva when
reared in India under a hen are at first excessively wild So it is
with young pheasants reared in England under a hen It is not that
chickens have lost all fear but fear only of dogs and cats for if
the hen gives the danger chuckle they will run more especially young
turkeys from under her and conceal themselves in the surrounding grass
or thickets and this is evidently done for the instinctive purpose of
allowing as we see in wild groundbirds their mother to fly away
But this instinct retained by our chickens has become useless under
domestication for the motherhen has almost lost by disuse the power of
flight

Hence we may conclude that under domestication instincts have been
acquired and natural instincts have been lost partly by habit and
partly by man selecting and accumulating during successive generations
peculiar mental habits and actions which at first appeared from what we
must in our ignorance call an accident In some cases compulsory habit
alone has sufficed to produce inherited mental changes in other cases
compulsory habit has done nothing and all has been the result of
selection pursued both methodically and unconsciously but in most
cases habit and selection have probably concurred

SPECIAL INSTINCTS

We shall perhaps best understand how instincts in a state of nature
have become modified by selection by considering a few cases I will
select only three namely the instinct which leads the cuckoo to lay
her eggs in other birds nests the slavemaking instinct of certain
ants and the cellmaking power of the hivebee these two latter
instincts have generally and justly been ranked by naturalists as the
most wonderful of all known instincts

INSTINCTS OF THE CUCKOO

It is supposed by some naturalists that the more immediate cause of
the instinct of the cuckoo is that she lays her eggs not daily but
at intervals of two or three days so that if she were to make her own
nest and sit on her own eggs those first laid would have to be left
for some time unincubated or there would be eggs and young birds of
different ages in the same nest If this were the case the process of
laying and hatching might be inconveniently long more especially as
she migrates at a very early period and the first hatched young would
probably have to be fed by the male alone But the American cuckoo is
in this predicament for she makes her own nest and has eggs and young
successively hatched all at the same time It has been both asserted
and denied that the American cuckoo occasionally lays her eggs in other
birds nests but I have lately heard from Dr Merrill of Iowa that he
once found in Illinois a young cuckoo together with a young jay in the
nest of a blue jay Garrulus cristatus and as both were nearly full
feathered there could be no mistake in their identification I could
also give several instances of various birds which have been known
occasionally to lay their eggs in other birds nests Now let us suppose
that the ancient progenitor of our European cuckoo had the habits of the
American cuckoo and that she occasionally laid an egg in another birds
nest If the old bird profited by this occasional habit through being
enabled to emigrate earlier or through any other cause or if the
young were made more vigorous by advantage being taken of the mistaken
instinct of another species than when reared by their own mother
encumbered as she could hardly fail to be by having eggs and young of
different ages at the same time then the old birds or the fostered
young would gain an advantage And analogy would lead us to believe
that the young thus reared would be apt to follow by inheritance the
occasional and aberrant habit of their mother and in their turn
would be apt to lay their eggs in other birds nests and thus be
more successful in rearing their young By a continued process of this
nature I believe that the strange instinct of our cuckoo has been
generated It has also recently been ascertained on sufficient
evidence by Adolf Muller that the cuckoo occasionally lays her eggs
on the bare ground sits on them and feeds her young This rare event
is probably a case of reversion to the longlost aboriginal instinct of
nidification

It has been objected that I have not noticed other related instincts
and adaptations of structure in the cuckoo which are spoken of as
necessarily coordinated But in all cases speculation on an instinct
known to us only in a single species is useless for we have hitherto
had no facts to guide us Until recently the instincts of the European
and of the nonparasitic American cuckoo alone were known now owing
to Mr Ramsays observations we have learned something about three
Australian species which lay their eggs in other birds nests The
chief points to be referred to are three first that the common cuckoo
with rare exceptions lays only one egg in a nest so that the large and
voracious young bird receives ample food Secondly that the eggs are
remarkably small not exceeding those of the skylark a bird about
onefourth as large as the cuckoo That the small size of the egg is a
real case of adaptation we may infer from the fact of the monparasitic
American cuckoo laying fullsized eggs Thirdly that the young cuckoo
soon after birth has the instinct the strength and a properly shaped
back for ejecting its fosterbrothers which then perish from cold and
hunger This has been boldly called a beneficent arrangement in
order that the young cuckoo may get sufficient food and that its
fosterbrothers may perish before they had acquired much feeling 

Turning now to the Australian species though these birds generally lay
only one egg in a nest it is not rare to find two and even three eggs
in the same nest In the bronze cuckoo the eggs vary greatly in size
from eight to ten lines in length Now if it had been of an advantage
to this species to have laid eggs even smaller than those now laid so
as to have deceived certain fosterparents or as is more probable to
have been hatched within a shorter period for it is asserted that
there is a relation between the size of eggs and the period of their
incubation then there is no difficulty in believing that a race or
species might have been formed which would have laid smaller and smaller
eggs for these would have been more safely hatched and reared Mr
Ramsay remarks that two of the Australian cuckoos when they lay their
eggs in an open nest manifest a decided preference for nests containing
eggs similar in colour to their own The European species apparently
manifests some tendency towards a similar instinct but not rarely
departs from it as is shown by her laying her dull and palecoloured
eggs in the nest of the hedgewarbler with bright greenishblue eggs
Had our cuckoo invariably displayed the above instinct it would
assuredly have been added to those which it is assumed must all have
been acquired together The eggs of the Australian bronze cuckoo vary
according to Mr Ramsay to an extraordinary degree in colour so
that in this respect as well as in size natural selection might have
secured and fixed any advantageous variation

In the case of the European cuckoo the offspring of the fosterparents
are commonly ejected from the nest within three days after the cuckoo is
hatched and as the latter at this age is in a most helpless condition
Mr Gould was formerly inclined to believe that the act of ejection was
performed by the fosterparents themselves But he has now received a
trustworthy account of a young cuckoo which was actually seen while
still blind and not able even to hold up its own head in the act of
ejecting its fosterbrothers One of these was replaced in the nest by
the observer and was again thrown out With respect to the means by
which this strange and odious instinct was acquired if it were of great
importance for the young cuckoo as is probably the case to receive as
much food as possible soon after birth I can see no special difficulty
in its having gradually acquired during successive generations the
blind desire the strength and structure necessary for the work of
ejection for those cuckoos which had such habits and structure best
developed would be the most securely reared The first step towards the
acquisition of the proper instinct might have been mere unintentional
restlessness on the part of the young bird when somewhat advanced
in age and strength the habit having been afterwards improved and
transmitted to an earlier age I can see no more difficulty in this than
in the unhatched young of other birds acquiring the instinct to break
through their own shells or than in young snakes acquiring in their
upper jaws as Owen has remarked a transitory sharp tooth for cutting
through the tough eggshell For if each part is liable to individual
variations at all ages and the variations tend to be inherited at
a corresponding or earlier age propositions which cannot be
disputed then the instincts and structure of the young could be slowly
modified as surely as those of the adult and both cases must stand or
fall together with the whole theory of natural selection

Some species of Molothrus a widely distinct genus of American birds
allied to our starlings have parasitic habits like those of the cuckoo
and the species present an interesting gradation in the perfection
of their instincts The sexes of Molothrus badius are stated by an
excellent observer Mr Hudson sometimes to live promiscuously together
in flocks and sometimes to pair They either build a nest of their own
or seize on one belonging to some other bird occasionally throwing out
the nestlings of the stranger They either lay their eggs in the nest
thus appropriated or oddly enough build one for themselves on the top
of it They usually sit on their own eggs and rear their own young but
Mr Hudson says it is probable that they are occasionally parasitic for
he has seen the young of this species following old birds of a distinct
kind and clamouring to be fed by them The parasitic habits of another
species of Molothrus the M bonariensis are much more highly developed
than those of the last but are still far from perfect This bird as
far as it is known invariably lays its eggs in the nests of strangers
but it is remarkable that several together sometimes commence to build
an irregular untidy nest of their own placed in singular illadapted
situations as on the leaves of a large thistle They never however as
far as Mr Hudson has ascertained complete a nest for themselves They
often lay so many eggs from fifteen to twenty in the same fosternest
that few or none can possibly be hatched They have moreover the
extraordinary habit of pecking holes in the eggs whether of their own
species or of their foster parents which they find in the appropriated
nests They drop also many eggs on the bare ground which are thus
wasted A third species the M pecoris of North America has acquired
instincts as perfect as those of the cuckoo for it never lays more than
one egg in a fosternest so that the young bird is securely reared Mr
Hudson is a strong disbeliever in evolution but he appears to have been
so much struck by the imperfect instincts of the Molothrus bonariensis
that he quotes my words and asks Must we consider these habits not
as especially endowed or created instincts but as small consequences of
one general law namely transition

Various birds as has already been remarked occasionally lay their eggs
in the nests of other birds This habit is not very uncommon with the
Gallinaceae and throws some light on the singular instinct of the
ostrich In this family several hen birds unite and lay first a few eggs
in one nest and then in another and these are hatched by the males
This instinct may probably be accounted for by the fact of the hens
laying a large number of eggs but as with the cuckoo at intervals of
two or three days The instinct however of the American ostrich as
in the case of the Molothrus bonariensis has not as yet been perfected
for a surprising number of eggs lie strewed over the plains so that in
one days hunting I picked up no less than twenty lost and wasted eggs

Many bees are parasitic and regularly lay their eggs in the nests
of other kinds of bees This case is more remarkable than that of the
cuckoo for these bees have not only had their instincts but their
structure modified in accordance with their parasitic habits for they
do not possess the pollencollecting apparatus which would have been
indispensable if they had stored up food for their own young Some
species of Sphegidae wasplike insects are likewise parasitic and
M Fabre has lately shown good reason for believing that although
the Tachytes nigra generally makes its own burrow and stores it with
paralysed prey for its own larvae yet that when this insect finds a
burrow already made and stored by another sphex it takes advantage of
the prize and becomes for the occasion parasitic In this case as
with that of the Molothrus or cuckoo I can see no difficulty in natural
selection making an occasional habit permanent if of advantage to the
species and if the insect whose nest and stored food are feloniously
appropriated be not thus exterminated

SLAVEMAKING INSTINCT

This remarkable instinct was first discovered in the Formica Polyerges
rufescens by Pierre Huber a better observer even than his celebrated
father This ant is absolutely dependent on its slaves without their
aid the species would certainly become extinct in a single year The
males and fertile females do no work of any kind and the workers or
sterile females though most energetic and courageous in capturing
slaves do no other work They are incapable of making their own nests
or of feeding their own larvae When the old nest is found inconvenient
and they have to migrate it is the slaves which determine the
migration and actually carry their masters in their jaws So utterly
helpless are the masters that when Huber shut up thirty of them without
a slave but with plenty of the food which they like best and with
their larvae and pupae to stimulate them to work they did nothing they
could not even feed themselves and many perished of hunger Huber then
introduced a single slave F fusca and she instantly set to work fed
and saved the survivors made some cells and tended the larvae and
put all to rights What can be more extraordinary than these
wellascertained facts If we had not known of any other slavemaking
ant it would have been hopeless to speculate how so wonderful an
instinct could have been perfected

Another species Formica sanguinea was likewise first discovered by P
Huber to be a slavemaking ant This species is found in the southern
parts of England and its habits have been attended to by Mr F Smith
of the British Museum to whom I am much indebted for information on
this and other subjects Although fully trusting to the statements of
Huber and Mr Smith I tried to approach the subject in a sceptical
frame of mind as any one may well be excused for doubting the existence
of so extraordinary an instinct as that of making slaves Hence I
will give the observations which I made in some little detail I opened
fourteen nests of F sanguinea and found a few slaves in all Males and
fertile females of the slavespecies F fusca are found only in their
own proper communities and have never been observed in the nests of F
sanguinea The slaves are black and not above half the size of their
red masters so that the contrast in their appearance is great When the
nest is slightly disturbed the slaves occasionally come out and like
their masters are much agitated and defend the nest when the nest is
much disturbed and the larvae and pupae are exposed the slaves work
energetically together with their masters in carrying them away to a
place of safety Hence it is clear that the slaves feel quite at home
During the months of June and July on three successive years I watched
for many hours several nests in Surrey and Sussex and never saw a slave
either leave or enter a nest As during these months the slaves are
very few in number I thought that they might behave differently when
more numerous but Mr Smith informs me that he has watched the nests at
various hours during May June and August both in Surrey and Hampshire
and has never seen the slaves though present in large numbers in
August either leave or enter the nest Hence he considers them as
strictly household slaves The masters on the other hand may be
constantly seen bringing in materials for the nest and food of all
kinds During the year 1860 however in the month of July I came
across a community with an unusually large stock of slaves and I
observed a few slaves mingled with their masters leaving the nest and
marching along the same road to a tall Scotchfir tree twentyfive
yards distant which they ascended together probably in search of
aphides or cocci According to Huber who had ample opportunities
for observation the slaves in Switzerland habitually work with their
masters in making the nest and they alone open and close the doors in
the morning and evening and as Huber expressly states their principal
office is to search for aphides This difference in the usual habits of
the masters and slaves in the two countries probably depends merely
on the slaves being captured in greater numbers in Switzerland than in
England

One day I fortunately witnessed a migration of F sanguinea from one
nest to another and it was a most interesting spectacle to behold the
masters carefully carrying their slaves in their jaws instead of
being carried by them as in the case of F rufescens Another day my
attention was struck by about a score of the slavemakers haunting the
same spot and evidently not in search of food they approached and were
vigorously repulsed by an independent community of the slave species F
fusca sometimes as many as three of these ants clinging to the legs of
the slavemaking F sanguinea The latter ruthlessly killed their
small opponents and carried their dead bodies as food to their nest
twentynine yards distant but they were prevented from getting any
pupae to rear as slaves I then dug up a small parcel of the pupae of F
fusca from another nest and put them down on a bare spot near the place
of combat they were eagerly seized and carried off by the tyrants who
perhaps fancied that after all they had been victorious in their late
combat

At the same time I laid on the same place a small parcel of the pupae of
another species F flava with a few of these little yellow ants still
clinging to the fragments of their nest This species is sometimes
though rarely made into slaves as has been described by Mr Smith
Although so small a species it is very courageous and I have seen it
ferociously attack other ants In one instance I found to my surprise
an independent community of F flava under a stone beneath a nest of the
slavemaking F sanguinea and when I had accidentally disturbed both
nests the little ants attacked their big neighbours with surprising
courage Now I was curious to ascertain whether F sanguinea could
distinguish the pupae of F fusca which they habitually make into
slaves from those of the little and furious F flava which they rarely
capture and it was evident that they did at once distinguish them
for we have seen that they eagerly and instantly seized the pupae of F
fusca whereas they were much terrified when they came across the pupae
or even the earth from the nest of F flava and quickly ran away but
in about a quarter of an hour shortly after all the little yellow ants
had crawled away they took heart and carried off the pupae

One evening I visited another community of F sanguinea and found a
number of these ants returning home and entering their nests carrying
the dead bodies of F fusca showing that it was not a migration and
numerous pupae I traced a long file of ants burdened with booty for
about forty yards back to a very thick clump of heath whence I saw the
last individual of F sanguinea emerge carrying a pupa but I was not
able to find the desolated nest in the thick heath The nest however
must have been close at hand for two or three individuals of F fusca
were rushing about in the greatest agitation and one was perched
motionless with its own pupa in its mouth on the top of a spray of
heath an image of despair over its ravaged home

Such are the facts though they did not need confirmation by me in
regard to the wonderful instinct of making slaves Let it be observed
what a contrast the instinctive habits of F sanguinea present with
those of the continental F rufescens The latter does not build its own
nest does not determine its own migrations does not collect food
for itself or its young and cannot even feed itself it is absolutely
dependent on its numerous slaves Formica sanguinea on the other
hand possesses much fewer slaves and in the early part of the summer
extremely few The masters determine when and where a new nest shall
be formed and when they migrate the masters carry the slaves Both in
Switzerland and England the slaves seem to have the exclusive care of
the larvae and the masters alone go on slavemaking expeditions In
Switzerland the slaves and masters work together making and bringing
materials for the nest both but chiefly the slaves tend and milk
as it may be called their aphides and thus both collect food for
the community In England the masters alone usually leave the nest to
collect building materials and food for themselves their slaves and
larvae So that the masters in this country receive much less service
from their slaves than they do in Switzerland

By what steps the instinct of F sanguinea originated I will not pretend
to conjecture But as ants which are not slavemakers will as I have
seen carry off pupae of other species if scattered near their nests
it is possible that such pupae originally stored as food might become
developed and the foreign ants thus unintentionally reared would then
follow their proper instincts and do what work they could If their
presence proved useful to the species which had seized them if it were
more advantageous to this species to capture workers than to procreate
them the habit of collecting pupae originally for food might by
natural selection be strengthened and rendered permanent for the
very different purpose of raising slaves When the instinct was once
acquired if carried out to a much less extent even than in our British
F sanguinea which as we have seen is less aided by its slaves than
the same species in Switzerland natural selection might increase and
modify the instinct always supposing each modification to be of use to
the species until an ant was formed as abjectly dependent on its slaves
as is the Formica rufescens

CELLMAKING INSTINCT OF THE HIVEBEE

I will not here enter on minute details on this subject but will merely
give an outline of the conclusions at which I have arrived He must be
a dull man who can examine the exquisite structure of a comb so
beautifully adapted to its end without enthusiastic admiration We
hear from mathematicians that bees have practically solved a recondite
problem and have made their cells of the proper shape to hold the
greatest possible amount of honey with the least possible consumption
of precious wax in their construction It has been remarked that a
skilful workman with fitting tools and measures would find it very
difficult to make cells of wax of the true form though this is effected
by a crowd of bees working in a dark hive Granting whatever instincts
you please it seems at first quite inconceivable how they can make
all the necessary angles and planes or even perceive when they are
correctly made But the difficulty is not nearly so great as at first
appears all this beautiful work can be shown I think to follow from a
few simple instincts

I was led to investigate this subject by Mr Waterhouse who has shown
that the form of the cell stands in close relation to the presence of
adjoining cells and the following view may perhaps be considered only
as a modification of his theory Let us look to the great principle of
gradation and see whether Nature does not reveal to us her method of
work At one end of a short series we have humblebees which use their
old cocoons to hold honey sometimes adding to them short tubes of wax
and likewise making separate and very irregular rounded cells of wax At
the other end of the series we have the cells of the hivebee placed in
a double layer each cell as is well known is an hexagonal prism
with the basal edges of its six sides bevelled so as to join an inverted
pyramid of three rhombs These rhombs have certain angles and the
three which form the pyramidal base of a single cell on one side of the
comb enter into the composition of the bases of three adjoining cells
on the opposite side In the series between the extreme perfection of
the cells of the hivebee and the simplicity of those of the humblebee
we have the cells of the Mexican Melipona domestica carefully described
and figured by Pierre Huber The Melipona itself is intermediate in
structure between the hive and humble bee but more nearly related to
the latter it forms a nearly regular waxen comb of cylindrical cells
in which the young are hatched and in addition some large cells of
wax for holding honey These latter cells are nearly spherical and of
nearly equal sizes and are aggregated into an irregular mass But the
important point to notice is that these cells are always made at that
degree of nearness to each other that they would have intersected or
broken into each other if the spheres had been completed but this is
never permitted the bees building perfectly flat walls of wax between
the spheres which thus tend to intersect Hence each cell consists of
an outer spherical portion and of two three or more flat surfaces
according as the cell adjoins two three or more other cells When one
cell rests on three other cells which from the spheres being nearly
of the same size is very frequently and necessarily the case the three
flat surfaces are united into a pyramid and this pyramid as Huber has
remarked is manifestly a gross imitation of the threesided pyramidal
base of the cell of the hivebee As in the cells of the hivebee so
here the three plane surfaces in any one cell necessarily enter into
the construction of three adjoining cells It is obvious that the
Melipona saves wax and what is more important labour by this manner
of building for the flat walls between the adjoining cells are not
double but are of the same thickness as the outer spherical portions
and yet each flat portion forms a part of two cells

Reflecting on this case it occurred to me that if the Melipona had made
its spheres at some given distance from each other and had made them of
equal sizes and had arranged them symmetrically in a double layer
the resulting structure would have been as perfect as the comb of the
hivebee Accordingly I wrote to Professor Miller of Cambridge and
this geometer has kindly read over the following statement drawn up
from his information and tells me that it is strictly correct 

If a number of equal spheres be described with their centres placed in
two parallel layers with the centre of each sphere at the distance of
radius x sqrt2 or radius x 141421 or at some lesser distance from
the centres of the six surrounding spheres in the same layer and at the
same distance from the centres of the adjoining spheres in the other and
parallel layer then if planes of intersection between the several
spheres in both layers be formed there will result a double layer of
hexagonal prisms united together by pyramidal bases formed of three
rhombs and the rhombs and the sides of the hexagonal prisms will have
every angle identically the same with the best measurements which have
been made of the cells of the hivebee But I hear from Professor Wyman
who has made numerous careful measurements that the accuracy of the
workmanship of the bee has been greatly exaggerated so much so that
whatever the typical form of the cell may be it is rarely if ever
realised

Hence we may safely conclude that if we could slightly modify the
instincts already possessed by the Melipona and in themselves not very
wonderful this bee would make a structure as wonderfully perfect as
that of the hivebee We must suppose the Melipona to have the power of
forming her cells truly spherical and of equal sizes and this would
not be very surprising seeing that she already does so to a certain
extent and seeing what perfectly cylindrical burrows many insects make
in wood apparently by turning round on a fixed point We must suppose
the Melipona to arrange her cells in level layers as she already does
her cylindrical cells and we must further suppose and this is the
greatest difficulty that she can somehow judge accurately at what
distance to stand from her fellowlabourers when several are making
their spheres but she is already so far enabled to judge of distance
that she always describes her spheres so as to intersect to a certain
extent and then she unites the points of intersection by perfectly flat
surfaces By such modifications of instincts which in themselves are not
very wonderful hardly more wonderful than those which guide a bird to
make its nest I believe that the hivebee has acquired through natural
selection her inimitable architectural powers

But this theory can be tested by experiment Following the example of
Mr Tegetmeier I separated two combs and put between them a long
thick rectangular strip of wax the bees instantly began to excavate
minute circular pits in it and as they deepened these little pits they
made them wider and wider until they were converted into shallow basins
appearing to the eye perfectly true or parts of a sphere and of
about the diameter of a cell It was most interesting to observe that
wherever several bees had begun to excavate these basins near together
they had begun their work at such a distance from each other that by
the time the basins had acquired the above stated width ie about the
width of an ordinary cell and were in depth about one sixth of the
diameter of the sphere of which they formed a part the rims of the
basins intersected or broke into each other As soon as this occurred
the bees ceased to excavate and began to build up flat walls of wax
on the lines of intersection between the basins so that each hexagonal
prism was built upon the scalloped edge of a smooth basin instead of on
the straight edges of a threesided pyramid as in the case of ordinary
cells

I then put into the hive instead of a thick rectangular piece of wax
a thin and narrow knifeedged ridge coloured with vermilion The bees
instantly began on both sides to excavate little basins near to each
other in the same way as before but the ridge of wax was so thin that
the bottoms of the basins if they had been excavated to the same depth
as in the former experiment would have broken into each other from the
opposite sides The bees however did not suffer this to happen and
they stopped their excavations in due time so that the basins as soon
as they had been a little deepened came to have flat bases and these
flat bases formed by thin little plates of the vermilion wax left
ungnawed were situated as far as the eye could judge exactly along
the planes of imaginary intersection between the basins on the opposite
side of the ridge of wax In some parts only small portions in other
parts large portions of a rhombic plate were thus left between the
opposed basins but the work from the unnatural state of things had
not been neatly performed The bees must have worked at very nearly the
same rate in circularly gnawing away and deepening the basins on both
sides of the ridge of vermilion wax in order to have thus succeeded in
leaving flat plates between the basins by stopping work at the planes
of intersection

Considering how flexible thin wax is I do not see that there is any
difficulty in the bees whilst at work on the two sides of a strip
of wax perceiving when they have gnawed the wax away to the proper
thinness and then stopping their work In ordinary combs it has
appeared to me that the bees do not always succeed in working at exactly
the same rate from the opposite sides for I have noticed halfcompleted
rhombs at the base of a justcommenced cell which were slightly concave
on one side where I suppose that the bees had excavated too quickly
and convex on the opposed side where the bees had worked less quickly
In one wellmarked instance I put the comb back into the hive and
allowed the bees to go on working for a short time and again examined
the cell and I found that the rhombic plate had been completed and had
become PERFECTLY FLAT it was absolutely impossible from the extreme
thinness of the little plate that they could have effected this by
gnawing away the convex side and I suspect that the bees in such cases
stand in the opposed cells and push and bend the ductile and warm wax
which as I have tried is easily done into its proper intermediate
plane and thus flatten it

From the experiment of the ridge of vermilion wax we can see that if
the bees were to build for themselves a thin wall of wax they could
make their cells of the proper shape by standing at the proper distance
from each other by excavating at the same rate and by endeavouring to
make equal spherical hollows but never allowing the spheres to break
into each other Now bees as may be clearly seen by examining the edge
of a growing comb do make a rough circumferential wall or rim all
round the comb and they gnaw this away from the opposite sides always
working circularly as they deepen each cell They do not make the whole
threesided pyramidal base of any one cell at the same time but only
that one rhombic plate which stands on the extreme growing margin or
the two plates as the case may be and they never complete the upper
edges of the rhombic plates until the hexagonal walls are commenced
Some of these statements differ from those made by the justly celebrated
elder Huber but I am convinced of their accuracy and if I had space I
could show that they are conformable with my theory

Hubers statement that the very first cell is excavated out of a little
parallelsided wall of wax is not as far as I have seen strictly
correct the first commencement having always been a little hood of
wax but I will not here enter on details We see how important a part
excavation plays in the construction of the cells but it would be a
great error to suppose that the bees cannot build up a rough wall of wax
in the proper position that is along the plane of intersection between
two adjoining spheres I have several specimens showing clearly that
they can do this Even in the rude circumferential rim or wall of wax
round a growing comb flexures may sometimes be observed corresponding
in position to the planes of the rhombic basal plates of future cells
But the rough wall of wax has in every case to be finished off by being
largely gnawed away on both sides The manner in which the bees build is
curious they always make the first rough wall from ten to twenty times
thicker than the excessively thin finished wall of the cell which will
ultimately be left We shall understand how they work by supposing
masons first to pile up a broad ridge of cement and then to begin
cutting it away equally on both sides near the ground till a smooth
very thin wall is left in the middle the masons always piling up the
cutaway cement and adding fresh cement on the summit of the ridge We
shall thus have a thin wall steadily growing upward but always crowned
by a gigantic coping From all the cells both those just commenced and
those completed being thus crowned by a strong coping of wax the
bees can cluster and crawl over the comb without injuring the delicate
hexagonal walls These walls as Professor Miller has kindly ascertained
for me vary greatly in thickness being on an average of twelve
measurements made near the border of the comb 1/352 of an inch in
thickness whereas the basal rhomboidal plates are thicker nearly in
the proportion of three to two having a mean thickness from twentyone
measurements of 1/229 of an inch By the above singular manner of
building strength is continually given to the comb with the utmost
ultimate economy of wax

It seems at first to add to the difficulty of understanding how the
cells are made that a multitude of bees all work together one bee
after working a short time at one cell going to another so that as
Huber has stated a score of individuals work even at the commencement
of the first cell I was able practically to show this fact by covering
the edges of the hexagonal walls of a single cell or the extreme margin
of the circumferential rim of a growing comb with an extremely thin
layer of melted vermilion wax and I invariably found that the colour
was most delicately diffused by the bees as delicately as a painter
could have done it with his brush by atoms of the coloured wax having
been taken from the spot on which it had been placed and worked into
the growing edges of the cells all round The work of construction seems
to be a sort of balance struck between many bees all instinctively
standing at the same relative distance from each other all trying to
sweep equal spheres and then building up or leaving ungnawed the
planes of intersection between these spheres It was really curious to
note in cases of difficulty as when two pieces of comb met at an angle
how often the bees would pull down and rebuild in different ways the
same cell sometimes recurring to a shape which they had at first
rejected

When bees have a place on which they can stand in their proper positions
for working for instance on a slip of wood placed directly under the
middle of a comb growing downwards so that the comb has to be built
over one face of the slip in this case the bees can lay the foundations
of one wall of a new hexagon in its strictly proper place projecting
beyond the other completed cells It suffices that the bees should be
enabled to stand at their proper relative distances from each other
and from the walls of the last completed cells and then by striking
imaginary spheres they can build up a wall intermediate between two
adjoining spheres but as far as I have seen they never gnaw away and
finish off the angles of a cell till a large part both of that cell and
of the adjoining cells has been built This capacity in bees of laying
down under certain circumstances a rough wall in its proper place
between two justcommenced cells is important as it bears on a fact
which seems at first subversive of the foregoing theory namely that
the cells on the extreme margin of waspcombs are sometimes strictly
hexagonal but I have not space here to enter on this subject Nor does
there seem to me any great difficulty in a single insect as in the case
of a queenwasp making hexagonal cells if she were to work alternately
on the inside and outside of two or three cells commenced at the same
time always standing at the proper relative distance from the parts
of the cells just begun sweeping spheres or cylinders and building up
intermediate planes

As natural selection acts only by the accumulation of slight
modifications of structure or instinct each profitable to the
individual under its conditions of life it may reasonably be asked how
a long and graduated succession of modified architectural instincts
all tending towards the present perfect plan of construction could
have profited the progenitors of the hivebee I think the answer is not
difficult cells constructed like those of the bee or the wasp gain in
strength and save much in labour and space and in the materials of
which they are constructed With respect to the formation of wax it is
known that bees are often hard pressed to get sufficient nectar and
I am informed by Mr Tegetmeier that it has been experimentally proved
that from twelve to fifteen pounds of dry sugar are consumed by a
hive of bees for the secretion of a pound of wax so that a prodigious
quantity of fluid nectar must be collected and consumed by the bees in
a hive for the secretion of the wax necessary for the construction
of their combs Moreover many bees have to remain idle for many days
during the process of secretion A large store of honey is indispensable
to support a large stock of bees during the winter and the security
of the hive is known mainly to depend on a large number of bees being
supported Hence the saving of wax by largely saving honey and the
time consumed in collecting the honey must be an important element of
success any family of bees Of course the success of the species may
be dependent on the number of its enemies or parasites or on quite
distinct causes and so be altogether independent of the quantity of
honey which the bees can collect But let us suppose that this latter
circumstance determined as it probably often has determined whether
a bee allied to our humblebees could exist in large numbers in any
country and let us further suppose that the community lived through the
winter and consequently required a store of honey there can in
this case be no doubt that it would be an advantage to our imaginary
humblebee if a slight modification of her instincts led her to make her
waxen cells near together so as to intersect a little for a wall in
common even to two adjoining cells would save some little labour and
wax Hence it would continually be more and more advantageous to our
humblebees if they were to make their cells more and more regular
nearer together and aggregated into a mass like the cells of the
Melipona for in this case a large part of the bounding surface of each
cell would serve to bound the adjoining cells and much labour and wax
would be saved Again from the same cause it would be advantageous to
the Melipona if she were to make her cells closer together and more
regular in every way than at present for then as we have seen the
spherical surfaces would wholly disappear and be replaced by plane
surfaces and the Melipona would make a comb as perfect as that of
the hivebee Beyond this stage of perfection in architecture natural
selection could not lead for the comb of the hivebee as far as we can
see is absolutely perfect in economising labour and wax

Thus as I believe the most wonderful of all known instincts that
of the hivebee can be explained by natural selection having taken
advantage of numerous successive slight modifications of simpler
instincts natural selection having by slow degrees more and more
perfectly led the bees to sweep equal spheres at a given distance from
each other in a double layer and to build up and excavate the wax along
the planes of intersection The bees of course no more knowing that
they swept their spheres at one particular distance from each other
than they know what are the several angles of the hexagonal prisms and
of the basal rhombic plates the motive power of the process of natural
selection having been the construction of cells of due strength and of
the proper size and shape for the larvae this being effected with the
greatest possible economy of labour and wax that individual swarm which
thus made the best cells with least labour and least waste of honey
in the secretion of wax having succeeded best and having transmitted
their newlyacquired economical instincts to new swarms which in their
turn will have had the best chance of succeeding in the struggle for
existence

OBJECTIONS TO THE THEORY OF NATURAL SELECTION AS APPLIED TO INSTINCTS
NEUTER AND STERILE INSECTS

It has been objected to the foregoing view of the origin of instincts
that the variations of structure and of instinct must have been
simultaneous and accurately adjusted to each other as a modification
in the one without an immediate corresponding change in the other would
have been fatal The force of this objection rests entirely on the
assumption that the changes in the instincts and structure are abrupt
To take as an illustration the case of the larger titmouse Parus
major alluded to in a previous chapter this bird often holds the seeds
of the yew between its feet on a branch and hammers with its beak till
it gets at the kernel Now what special difficulty would there be in
natural selection preserving all the slight individual variations in the
shape of the beak which were better and better adapted to break open
the seeds until a beak was formed as well constructed for this purpose
as that of the nuthatch at the same time that habit or compulsion or
spontaneous variations of taste led the bird to become more and more of
a seedeater In this case the beak is supposed to be slowly modified
by natural selection subsequently to but in accordance with slowly
changing habits or taste but let the feet of the titmouse vary and grow
larger from correlation with the beak or from any other unknown cause
and it is not improbable that such larger feet would lead the bird to
climb more and more until it acquired the remarkable climbing instinct
and power of the nuthatch In this case a gradual change of structure is
supposed to lead to changed instinctive habits To take one more case
few instincts are more remarkable than that which leads the swift of
the Eastern Islands to make its nest wholly of inspissated saliva Some
birds build their nests of mud believed to be moistened with saliva
and one of the swifts of North America makes its nest as I have
seen of sticks agglutinated with saliva and even with flakes of this
substance Is it then very improbable that the natural selection of
individual swifts which secreted more and more saliva should at last
produce a species with instincts leading it to neglect other materials
and to make its nest exclusively of inspissated saliva And so in other
cases It must however be admitted that in many instances we cannot
conjecture whether it was instinct or structure which first varied

No doubt many instincts of very difficult explanation could be opposed
to the theory of natural selection cases in which we cannot see how
an instinct could have originated cases in which no intermediate
gradations are known to exist cases of instincts of such trifling
importance that they could hardly have been acted on by natural
selection cases of instincts almost identically the same in animals
so remote in the scale of nature that we cannot account for their
similarity by inheritance from a common progenitor and consequently
must believe that they were independently acquired through natural
selection I will not here enter on these several cases but will
confine myself to one special difficulty which at first appeared to
me insuperable and actually fatal to the whole theory I allude to
the neuters or sterile females in insect communities for these neuters
often differ widely in instinct and in structure from both the males
and fertile females and yet from being sterile they cannot propagate
their kind

The subject well deserves to be discussed at great length but I will
here take only a single case that of working or sterile ants How the
workers have been rendered sterile is a difficulty but not much greater
than that of any other striking modification of structure for it can
be shown that some insects and other articulate animals in a state of
nature occasionally become sterile and if such insects had been social
and it had been profitable to the community that a number should have
been annually born capable of work but incapable of procreation I can
see no especial difficulty in this having been effected through natural
selection But I must pass over this preliminary difficulty The great
difficulty lies in the working ants differing widely from both the males
and the fertile females in structure as in the shape of the thorax and
in being destitute of wings and sometimes of eyes and in instinct As
far as instinct alone is concerned the wonderful difference in this
respect between the workers and the perfect females would have been
better exemplified by the hivebee If a working ant or other neuter
insect had been an ordinary animal I should have unhesitatingly
assumed that all its characters had been slowly acquired through
natural selection namely by individuals having been born with slight
profitable modifications which were inherited by the offspring and
that these again varied and again were selected and so onwards But
with the working ant we have an insect differing greatly from its
parents yet absolutely sterile so that it could never have transmitted
successively acquired modifications of structure or instinct to its
progeny It may well be asked how it is possible to reconcile this case
with the theory of natural selection

First let it be remembered that we have innumerable instances both in
our domestic productions and in those in a state of nature of all sorts
of differences of inherited structure which are correlated with certain
ages and with either sex We have differences correlated not only with
one sex but with that short period when the reproductive system is
active as in the nuptial plumage of many birds and in the hooked jaws
of the male salmon We have even slight differences in the horns of
different breeds of cattle in relation to an artificially imperfect
state of the male sex for oxen of certain breeds have longer horns than
the oxen of other breeds relatively to the length of the horns in
both the bulls and cows of these same breeds Hence I can see no
great difficulty in any character becoming correlated with the sterile
condition of certain members of insect communities the difficulty lies
in understanding how such correlated modifications of structure could
have been slowly accumulated by natural selection

This difficulty though appearing insuperable is lessened or as I
believe disappears when it is remembered that selection may be applied
to the family as well as to the individual and may thus gain the
desired end Breeders of cattle wish the flesh and fat to be well
marbled together An animal thus characterized has been slaughtered
but the breeder has gone with confidence to the same stock and has
succeeded Such faith may be placed in the power of selection that a
breed of cattle always yielding oxen with extraordinarily long horns
could it is probable be formed by carefully watching which individual
bulls and cows when matched produced oxen with the longest horns and
yet no one ox would ever have propagated its kind Here is a better and
real illustration According to M Verlot some varieties of the double
annual stock from having been long and carefully selected to the right
degree always produce a large proportion of seedlings bearing double
and quite sterile flowers but they likewise yield some single and
fertile plants These latter by which alone the variety can be
propagated may be compared with the fertile male and female ants and
the double sterile plants with the neuters of the same community As
with the varieties of the stock so with social insects selection has
been applied to the family and not to the individual for the sake
of gaining a serviceable end Hence we may conclude that slight
modifications of structure or of instinct correlated with the sterile
condition of certain members of the community have proved advantageous
consequently the fertile males and females have flourished and
transmitted to their fertile offspring a tendency to produce sterile
members with the same modifications This process must have been
repeated many times until that prodigious amount of difference between
the fertile and sterile females of the same species has been produced
which we see in many social insects

But we have not as yet touched on the acme of the difficulty namely
the fact that the neuters of several ants differ not only from the
fertile females and males but from each other sometimes to an almost
incredible degree and are thus divided into two or even three castes
The castes moreover do not generally graduate into each other but are
perfectly well defined being as distinct from each other as are any
two species of the same genus or rather as any two genera of the same
family Thus in Eciton there are working and soldier neuters with
jaws and instincts extraordinarily different in Cryptocerus the
workers of one caste alone carry a wonderful sort of shield on their
heads the use of which is quite unknown in the Mexican Myrmecocystus
the workers of one caste never leave the nest they are fed by the
workers of another caste and they have an enormously developed abdomen
which secretes a sort of honey supplying the place of that excreted
by the aphides or the domestic cattle as they may be called which our
European ants guard and imprison

It will indeed be thought that I have an overweening confidence in the
principle of natural selection when I do not admit that such wonderful
and wellestablished facts at once annihilate the theory In the simpler
case of neuter insects all of one caste which as I believe have been
rendered different from the fertile males and females through natural
selection we may conclude from the analogy of ordinary variations that
the successive slight profitable modifications did not first arise in
all the neuters in the same nest but in some few alone and that by
the survival of the communities with females which produced most neuters
having the advantageous modification all the neuters ultimately came to
be thus characterized According to this view we ought occasionally
to find in the same nest neuterinsects presenting gradations of
structure and this we do find even not rarely considering how few
neuterinsects out of Europe have been carefully examined Mr F Smith
has shown that the neuters of several British ants differ surprisingly
from each other in size and sometimes in colour and that the extreme
forms can be linked together by individuals taken out of the same nest
I have myself compared perfect gradations of this kind It sometimes
happens that the larger or the smaller sized workers are the most
numerous or that both large and small are numerous while those of an
intermediate size are scanty in numbers Formica flava has larger
and smaller workers with some few of intermediate size and in this
species as Mr F Smith has observed the larger workers have simple
eyes ocelli which though small can be plainly distinguished
whereas the smaller workers have their ocelli rudimentary Having
carefully dissected several specimens of these workers I can affirm
that the eyes are far more rudimentary in the smaller workers than can
be accounted for merely by their proportionately lesser size and I
fully believe though I dare not assert so positively that the workers
of intermediate size have their ocelli in an exactly intermediate
condition So that here we have two bodies of sterile workers in the
same nest differing not only in size but in their organs of vision
yet connected by some few members in an intermediate condition I may
digress by adding that if the smaller workers had been the most useful
to the community and those males and females had been continually
selected which produced more and more of the smaller workers until all
the workers were in this condition we should then have had a species of
ant with neuters in nearly the same condition as those of Myrmica For
the workers of Myrmica have not even rudiments of ocelli though the
male and female ants of this genus have welldeveloped ocelli

I may give one other case so confidently did I expect occasionally to
find gradations of important structures between the different castes
of neuters in the same species that I gladly availed myself of Mr F
Smiths offer of numerous specimens from the same nest of the driver
ant Anomma of West Africa The reader will perhaps best appreciate
the amount of difference in these workers by my giving not the actual
measurements but a strictly accurate illustration the difference was
the same as if we were to see a set of workmen building a house of whom
many were five feet four inches high and many sixteen feet high but we
must in addition suppose that the larger workmen had heads four instead
of three times as big as those of the smaller men and jaws nearly five
times as big The jaws moreover of the working ants of the several
sizes differed wonderfully in shape and in the form and number of the
teeth But the important fact for us is that though the workers can
be grouped into castes of different sizes yet they graduate insensibly
into each other as does the widelydifferent structure of their jaws I
speak confidently on this latter point as Sir J Lubbock made drawings
for me with the camera lucida of the jaws which I dissected from the
workers of the several sizes Mr Bates in his interesting Naturalist
on the Amazons has described analogous cases

With these facts before me I believe that natural selection by acting
on the fertile ants or parents could form a species which should
regularly produce neuters all of large size with one form of jaw or
all of small size with widely different jaws or lastly and this is the
greatest difficulty one set of workers of one size and structure and
simultaneously another set of workers of a different size and structure
a graduated series having first been formed as in the case of the
driver ant and then the extreme forms having been produced in greater
and greater numbers through the survival of the parents which generated
them until none with an intermediate structure were produced

An analogous explanation has been given by Mr Wallace of the equally
complex case of certain Malayan butterflies regularly appearing under
two or even three distinct female forms and by Fritz Muller of certain
Brazilian crustaceans likewise appearing under two widely distinct male
forms But this subject need not here be discussed

I have now explained how I believe the wonderful fact of two
distinctly defined castes of sterile workers existing in the same
nest both widely different from each other and from their parents has
originated We can see how useful their production may have been to a
social community of ants on the same principle that the division of
labour is useful to civilised man Ants however work by inherited
instincts and by inherited organs or tools while man works by acquired
knowledge and manufactured instruments But I must confess that with
all my faith in natural selection I should never have anticipated that
this principle could have been efficient in so high a degree had not
the case of these neuter insects led me to this conclusion I have
therefore discussed this case at some little but wholly insufficient
length in order to show the power of natural selection and likewise
because this is by far the most serious special difficulty which my
theory has encountered The case also is very interesting as it
proves that with animals as with plants any amount of modification
may be effected by the accumulation of numerous slight spontaneous
variations which are in any way profitable without exercise or habit
having been brought into play For peculiar habits confined to the
workers of sterile females however long they might be followed could
not possibly affect the males and fertile females which alone leave
descendants I am surprised that no one has advanced this demonstrative
case of neuter insects against the wellknown doctrine of inherited
habit as advanced by Lamarck

SUMMARY

I have endeavoured in this chapter briefly to show that the mental
qualities of our domestic animals vary and that the variations are
inherited Still more briefly I have attempted to show that instincts
vary slightly in a state of nature No one will dispute that instincts
are of the highest importance to each animal Therefore there is no
real difficulty under changing conditions of life in natural selection
accumulating to any extent slight modifications of instinct which are in
any way useful In many cases habit or use and disuse have probably
come into play I do not pretend that the facts given in this chapter
strengthen in any great degree my theory but none of the cases of
difficulty to the best of my judgment annihilate it On the other
hand the fact that instincts are not always absolutely perfect and are
liable to mistakes that no instinct can be shown to have been produced
for the good of other animals though animals take advantage of the
instincts of others that the canon in natural history of Natura
non facit saltum is applicable to instincts as well as to corporeal
structure and is plainly explicable on the foregoing views but is
otherwise inexplicable all tend to corroborate the theory of natural
selection

This theory is also strengthened by some few other facts in regard
to instincts as by that common case of closely allied but distinct
species when inhabiting distant parts of the world and living under
considerably different conditions of life yet often retaining nearly
the same instincts For instance we can understand on the principle of
inheritance how it is that the thrush of tropical South America lines
its nest with mud in the same peculiar manner as does our British
thrush how it is that the Hornbills of Africa and India have the same
extraordinary instinct of plastering up and imprisoning the females in a
hole in a tree with only a small hole left in the plaster through which
the males feed them and their young when hatched how it is that the
male wrens Troglodytes of North America build cocknests to roost
in like the males of our Kittywrens a habit wholly unlike that of
any other known bird Finally it may not be a logical deduction but to
my imagination it is far more satisfactory to look at such instincts as
the young cuckoo ejecting its fosterbrothers ants making slaves the
larvae of ichneumonidae feeding within the live bodies of caterpillars
not as specially endowed or created instincts but as small consequences
of one general law leading to the advancement of all organic
beings namely multiply vary let the strongest live and the weakest
die




CHAPTER IX HYBRIDISM

 Distinction between the sterility of first crosses and of
 hybrids Sterility various in degree not universal affected by close
 interbreeding removed by domestication Laws governing the sterility
 of hybrids Sterility not a special endowment but incidental on
 other differences not accumulated by natural selection Causes of
 the sterility of first crosses and of hybrids Parallelism between the
 effects of changed conditions of life and of crossing Dimorphism and
 trimorphism Fertility of varieties when crossed and of their mongrel
 offspring not universal Hybrids and mongrels compared independently of
 their fertility Summary


The view commonly entertained by naturalists is that species when
intercrossed have been specially endowed with sterility in order
to prevent their confusion This view certainly seems at first highly
probable for species living together could hardly have been kept
distinct had they been capable of freely crossing The subject is in
many ways important for us more especially as the sterility of species
when first crossed and that of their hybrid offspring cannot have been
acquired as I shall show by the preservation of successive profitable
degrees of sterility It is an incidental result of differences in the
reproductive systems of the parentspecies

In treating this subject two classes of facts to a large extent
fundamentally different have generally been confounded namely the
sterility of species when first crossed and the sterility of the
hybrids produced from them

Pure species have of course their organs of reproduction in a perfect
condition yet when intercrossed they produce either few or no
offspring Hybrids on the other hand have their reproductive organs
functionally impotent as may be clearly seen in the state of the
male element in both plants and animals though the formative organs
themselves are perfect in structure as far as the microscope reveals
In the first case the two sexual elements which go to form the embryo
are perfect in the second case they are either not at all developed or
are imperfectly developed This distinction is important when the
cause of the sterility which is common to the two cases has to be
considered The distinction probably has been slurred over owing to the
sterility in both cases being looked on as a special endowment beyond
the province of our reasoning powers

The fertility of varieties that is of the forms known or believed to be
descended from common parents when crossed and likewise the fertility
of their mongrel offspring is with reference to my theory of equal
importance with the sterility of species for it seems to make a broad
and clear distinction between varieties and species

DEGREES OF STERILITY

First for the sterility of species when crossed and of their hybrid
offspring It is impossible to study the several memoirs and works of
those two conscientious and admirable observers Kolreuter and Gartner
who almost devoted their lives to this subject without being deeply
impressed with the high generality of some degree of sterility
Kolreuter makes the rule universal but then he cuts the knot for in
ten cases in which he found two forms considered by most authors as
distinct species quite fertile together he unhesitatingly ranks them
as varieties Gartner also makes the rule equally universal and he
disputes the entire fertility of Kolreuters ten cases But in these and
in many other cases Gartner is obliged carefully to count the seeds in
order to show that there is any degree of sterility He always compares
the maximum number of seeds produced by two species when first crossed
and the maximum produced by their hybrid offspring with the average
number produced by both pure parentspecies in a state of nature But
causes of serious error here intervene a plant to be hybridised must
be castrated and what is often more important must be secluded
in order to prevent pollen being brought to it by insects from other
plants Nearly all the plants experimented on by Gartner were potted
and were kept in a chamber in his house That these processes are often
injurious to the fertility of a plant cannot be doubted for Gartner
gives in his table about a score of cases of plants which he castrated
and artificially fertilised with their own pollen and excluding
all cases such as the Leguminosae in which there is an acknowledged
difficulty in the manipulation half of these twenty plants had their
fertility in some degree impaired Moreover as Gartner repeatedly
crossed some forms such as the common red and blue pimpernels
Anagallis arvensis and coerulea which the best botanists rank as
varieties and found them absolutely sterile we may doubt whether many
species are really so sterile when intercrossed as he believed

It is certain on the one hand that the sterility of various species
when crossed is so different in degree and graduates away so insensibly
and on the other hand that the fertility of pure species is so easily
affected by various circumstances that for all practical purposes it is
most difficult to say where perfect fertility ends and sterility begins
I think no better evidence of this can be required than that the two
most experienced observers who have ever lived namely Kolreuter and
Gartner arrived at diametrically opposite conclusions in regard to some
of the very same forms It is also most instructive to compare but I
have not space here to enter on details the evidence advanced by our
best botanists on the question whether certain doubtful forms should be
ranked as species or varieties with the evidence from fertility adduced
by different hybridisers or by the same observer from experiments made
during different years It can thus be shown that neither sterility nor
fertility affords any certain distinction between species and varieties
The evidence from this source graduates away and is doubtful in the
same degree as is the evidence derived from other constitutional and
structural differences

In regard to the sterility of hybrids in successive generations though
Gartner was enabled to rear some hybrids carefully guarding them from a
cross with either pure parent for six or seven and in one case for
ten generations yet he asserts positively that their fertility never
increases but generally decreases greatly and suddenly With respect
to this decrease it may first be noticed that when any deviation in
structure or constitution is common to both parents this is often
transmitted in an augmented degree to the offspring and both sexual
elements in hybrid plants are already affected in some degree But I
believe that their fertility has been diminished in nearly all these
cases by an independent cause namely by too close interbreeding I
have made so many experiments and collected so many facts showing on
the one hand that an occasional cross with a distinct individual or
variety increases the vigour and fertility of the offspring and on
the other hand that very close interbreeding lessens their vigour and
fertility that I cannot doubt the correctness of this conclusion
Hybrids are seldom raised by experimentalists in great numbers and as
the parentspecies or other allied hybrids generally grow in the same
garden the visits of insects must be carefully prevented during the
flowering season hence hybrids if left to themselves will generally
be fertilised during each generation by pollen from the same flower and
this would probably be injurious to their fertility already lessened
by their hybrid origin I am strengthened in this conviction by a
remarkable statement repeatedly made by Gartner namely that if even
the less fertile hybrids be artificially fertilised with hybrid pollen
of the same kind their fertility notwithstanding the frequent ill
effects from manipulation sometimes decidedly increases and goes on
increasing Now in the process of artificial fertilisation pollen is
as often taken by chance as I know from my own experience from the
anthers of another flower as from the anthers of the flower itself
which is to be fertilised so that a cross between two flowers though
probably often on the same plant would be thus effected Moreover
whenever complicated experiments are in progress so careful an observer
as Gartner would have castrated his hybrids and this would have insured
in each generation a cross with pollen from a distinct flower either
from the same plant or from another plant of the same hybrid nature
And thus the strange fact of an increase of fertility in the successive
generations of ARTIFICIALLY FERTILISED hybrids in contrast with those
spontaneously selffertilised may as I believe be accounted for by
too close interbreeding having been avoided

Now let us turn to the results arrived at by a third most experienced
hybridiser namely the Hon and Rev W Herbert He is as emphatic in
his conclusion that some hybrids are perfectly fertile as fertile as
the pure parentspecies as are Kolreuter and Gartner that some degree
of sterility between distinct species is a universal law of nature
He experimented on some of the very same species as did Gartner The
difference in their results may I think be in part accounted for by
Herberts great horticultural skill and by his having hothouses at his
command Of his many important statements I will here give only a single
one as an example namely that every ovule in a pod of Crinum capense
fertilised by C revolutum produced a plant which I never saw to occur
in a case of its natural fecundation So that here we have perfect or
even more than commonly perfect fertility in a first cross between two
distinct species

This case of the Crinum leads me to refer to a singular fact namely
that individual plants of certain species of Lobelia Verbascum and
Passiflora can easily be fertilised by the pollen from a distinct
species but not by pollen from the same plant though this pollen can
be proved to be perfectly sound by fertilising other plants or species
In the genus Hippeastrum in Corydalis as shown by Professor Hildebrand
in various orchids as shown by Mr Scott and Fritz Muller all the
individuals are in this peculiar condition So that with some species
certain abnormal individuals and in other species all the individuals
can actually be hybridised much more readily than they can be fertilised
by pollen from the same individual plant  To give one instance a bulb
of Hippeastrum aulicum produced four flowers three were fertilised
by Herbert with their own pollen and the fourth was subsequently
fertilised by the pollen of a compound hybrid descended from three
distinct species the result was that the ovaries of the three first
flowers soon ceased to grow and after a few days perished entirely
whereas the pod impregnated by the pollen of the hybrid made vigorous
growth and rapid progress to maturity and bore good seed which
vegetated freely Mr Herbert tried similar experiments during many
years and always with the same result These cases serve to show on
what slight and mysterious causes the lesser or greater fertility of a
species sometimes depends

The practical experiments of horticulturists though not made with
scientific precision deserve some notice It is notorious in how
complicated a manner the species of Pelargonium Fuchsia Calceolaria
Petunia Rhododendron etc have been crossed yet many of these
hybrids seed freely For instance Herbert asserts that a hybrid from
Calceolaria integrifolia and plantaginea species most widely dissimilar
in general habit reproduces itself as perfectly as if it had been a
natural species from the mountains of Chile I have taken some pains
to ascertain the degree of fertility of some of the complex crosses of
Rhododendrons and I am assured that many of them are perfectly fertile
Mr C Noble for instance informs me that he raises stocks for
grafting from a hybrid between Rhod ponticum and catawbiense and that
this hybrid seeds as freely as it is possible to imagine Had hybrids
when fairly treated always gone on decreasing in fertility in each
successive generation as Gartner believed to be the case the fact
would have been notorious to nurserymen Horticulturists raise large
beds of the same hybrid and such alone are fairly treated for by
insect agency the several individuals are allowed to cross freely with
each other and the injurious influence of close interbreeding is thus
prevented Any one may readily convince himself of the efficiency of
insect agency by examining the flowers of the more sterile kinds of
hybrid Rhododendrons which produce no pollen for he will find on their
stigmas plenty of pollen brought from other flowers

In regard to animals much fewer experiments have been carefully tried
than with plants If our systematic arrangements can be trusted that
is if the genera of animals are as distinct from each other as are the
genera of plants then we may infer that animals more widely distinct
in the scale of nature can be crossed more easily than in the case
of plants but the hybrids themselves are I think more sterile It
should however be borne in mind that owing to few animals breeding
freely under confinement few experiments have been fairly tried for
instance the canarybird has been crossed with nine distinct species of
finches but as not one of these breeds freely in confinement we have
no right to expect that the first crosses between them and the canary
or that their hybrids should be perfectly fertile Again with respect
to the fertility in successive generations of the more fertile hybrid
animals I hardly know of an instance in which two families of the same
hybrid have been raised at the same time from different parents so
as to avoid the ill effects of close interbreeding On the contrary
brothers and sisters have usually been crossed in each successive
generation in opposition to the constantly repeated admonition of every
breeder And in this case it is not at all surprising that the inherent
sterility in the hybrids should have gone on increasing

Although I know of hardly any thoroughly wellauthenticated cases of
perfectly fertile hybrid animals I have reason to believe that the
hybrids from Cervulus vaginalis and Reevesii and from Phasianus
colchicus with P torquatus are perfectly fertile M Quatrefages
states that the hybrids from two moths Bombyx cynthia and arrindia
were proved in Paris to be fertile inter se for eight generations It
has lately been asserted that two such distinct species as the hare and
rabbit when they can be got to breed together produce offspring which
are highly fertile when crossed with one of the parentspecies The
hybrids from the common and Chinese geese A cygnoides species which
are so different that they are generally ranked in distinct genera have
often bred in this country with either pure parent and in one single
instance they have bred inter se This was effected by Mr Eyton who
raised two hybrids from the same parents but from different hatches
and from these two birds he raised no less than eight hybrids
grandchildren of the pure geese from one nest In India however
these crossbred geese must be far more fertile for I am assured by
two eminently capable judges namely Mr Blyth and Captain Hutton that
whole flocks of these crossed geese are kept in various parts of
the country and as they are kept for profit where neither pure
parentspecies exists they must certainly be highly or perfectly
fertile

With our domesticated animals the various races when crossed together
are quite fertile yet in many cases they are descended from two or more
wild species From this fact we must conclude either that the aboriginal
parentspecies at first produced perfectly fertile hybrids or that the
hybrids subsequently reared under domestication became quite fertile
This latter alternative which was first propounded by Pallas seems by
far the most probable and can indeed hardly be doubted It is for
instance almost certain that our dogs are descended from several wild
stocks yet with perhaps the exception of certain indigenous domestic
dogs of South America all are quite fertile together but analogy makes
me greatly doubt whether the several aboriginal species would at first
have freely bred together and have produced quite fertile hybrids
So again I have lately acquired decisive evidence that the crossed
offspring from the Indian humped and common cattle are inter se
perfectly fertile and from the observations by Rutimeyer on their
important osteological differences as well as from those by Mr Blyth
on their differences in habits voice constitution etc these two
forms must be regarded as good and distinct species The same remarks
may be extended to the two chief races of the pig We must therefore
either give up the belief of the universal sterility of species when
crossed or we must look at this sterility in animals not as an
indelible characteristic but as one capable of being removed by
domestication

Finally considering all the ascertained facts on the intercrossing of
plants and animals it may be concluded that some degree of sterility
both in first crosses and in hybrids is an extremely general result
but that it cannot under our present state of knowledge be considered
as absolutely universal

LAWS GOVERNING THE STERILITY OF FIRST CROSSES AND OF HYBRIDS

We will now consider a little more in detail the laws governing the
sterility of first crosses and of hybrids Our chief object will be to
see whether or not these laws indicate that species have been specially
endowed with this quality in order to prevent their crossing and
blending together in utter confusion The following conclusions are
drawn up chiefly from Gartners admirable work on the hybridisation
of plants I have taken much pains to ascertain how far they apply
to animals and considering how scanty our knowledge is in regard to
hybrid animals I have been surprised to find how generally the same
rules apply to both kingdoms

It has been already remarked that the degree of fertility both of
first crosses and of hybrids graduates from zero to perfect fertility
It is surprising in how many curious ways this gradation can be shown
but only the barest outline of the facts can here be given When pollen
from a plant of one family is placed on the stigma of a plant of a
distinct family it exerts no more influence than so much inorganic
dust From this absolute zero of fertility the pollen of different
species applied to the stigma of some one species of the same genus
yields a perfect gradation in the number of seeds produced up to nearly
complete or even quite complete fertility and as we have seen in
certain abnormal cases even to an excess of fertility beyond that
which the plants own pollen produces So in hybrids themselves there
are some which never have produced and probably never would produce
even with the pollen of the pure parents a single fertile seed but in
some of these cases a first trace of fertility may be detected by
the pollen of one of the pure parentspecies causing the flower of the
hybrid to wither earlier than it otherwise would have done and the
early withering of the flower is well known to be a sign of incipient
fertilisation From this extreme degree of sterility we have
selffertilised hybrids producing a greater and greater number of seeds
up to perfect fertility

The hybrids raised from two species which are very difficult to cross
and which rarely produce any offspring are generally very sterile but
the parallelism between the difficulty of making a first cross and the
sterility of the hybrids thus produced two classes of facts which are
generally confounded together is by no means strict There are many
cases in which two pure species as in the genus Verbascum can be
united with unusual facility and produce numerous hybrid offspring
yet these hybrids are remarkably sterile On the other hand there are
species which can be crossed very rarely or with extreme difficulty
but the hybrids when at last produced are very fertile Even within
the limits of the same genus for instance in Dianthus these two
opposite cases occur

The fertility both of first crosses and of hybrids is more easily
affected by unfavourable conditions than is that of pure species But
the fertility of first crosses is likewise innately variable for it
is not always the same in degree when the same two species are crossed
under the same circumstances it depends in part upon the constitution
of the individuals which happen to have been chosen for the experiment
So it is with hybrids for their degree of fertility is often found to
differ greatly in the several individuals raised from seed out of the
same capsule and exposed to the same conditions

By the term systematic affinity is meant the general resemblance
between species in structure and constitution Now the fertility
of first crosses and of the hybrids produced from them is largely
governed by their systematic affinity This is clearly shown by hybrids
never having been raised between species ranked by systematists in
distinct families and on the other hand by very closely allied
species generally uniting with facility But the correspondence between
systematic affinity and the facility of crossing is by no means strict
A multitude of cases could be given of very closely allied species which
will not unite or only with extreme difficulty and on the other hand
of very distinct species which unite with the utmost facility In
the same family there may be a genus as Dianthus in which very many
species can most readily be crossed and another genus as Silene
in which the most persevering efforts have failed to produce between
extremely close species a single hybrid Even within the limits of the
same genus we meet with this same difference for instance the many
species of Nicotiana have been more largely crossed than the species of
almost any other genus but Gartner found that N acuminata which is
not a particularly distinct species obstinately failed to fertilise or
to be fertilised by no less than eight other species of Nicotiana Many
analogous facts could be given

No one has been able to point out what kind or what amount of
difference in any recognisable character is sufficient to prevent two
species crossing It can be shown that plants most widely different in
habit and general appearance and having strongly marked differences in
every part of the flower even in the pollen in the fruit and in the
cotyledons can be crossed Annual and perennial plants deciduous and
evergreen trees plants inhabiting different stations and fitted for
extremely different climates can often be crossed with ease

By a reciprocal cross between two species I mean the case for
instance of a femaleass being first crossed by a stallion and then
a mare by a maleass these two species may then be said to have been
reciprocally crossed There is often the widest possible difference
in the facility of making reciprocal crosses Such cases are highly
important for they prove that the capacity in any two species to cross
is often completely independent of their systematic affinity that is
of any difference in their structure or constitution excepting in their
reproductive systems The diversity of the result in reciprocal crosses
between the same two species was long ago observed by Kolreuter To give
an instance Mirabilis jalapa can easily be fertilised by the pollen of
M longiflora and the hybrids thus produced are sufficiently fertile
but Kolreuter tried more than two hundred times during eight following
years to fertilise reciprocally M longiflora with the pollen of M
jalapa and utterly failed Several other equally striking cases could
be given Thuret has observed the same fact with certain seaweeds
or Fuci Gartner moreover found that this difference of facility in
making reciprocal crosses is extremely common in a lesser degree He has
observed it even between closely related forms as Matthiola annua
and glabra which many botanists rank only as varieties It is also a
remarkable fact that hybrids raised from reciprocal crosses though of
course compounded of the very same two species the one species having
first been used as the father and then as the mother though they rarely
differ in external characters yet generally differ in fertility in a
small and occasionally in a high degree

Several other singular rules could be given from Gartner for instance
some species have a remarkable power of crossing with other species
other species of the same genus have a remarkable power of impressing
their likeness on their hybrid offspring but these two powers do not at
all necessarily go together There are certain hybrids which instead
of having as is usual an intermediate character between their two
parents always closely resemble one of them and such hybrids though
externally so like one of their pure parentspecies are with rare
exceptions extremely sterile So again among hybrids which are usually
intermediate in structure between their parents exceptional and
abnormal individuals sometimes are born which closely resemble one of
their pure parents and these hybrids are almost always utterly sterile
even when the other hybrids raised from seed from the same capsule have
a considerable degree of fertility These facts show how completely the
fertility of a hybrid may be independent of its external resemblance to
either pure parent

Considering the several rules now given which govern the fertility
of first crosses and of hybrids we see that when forms which must be
considered as good and distinct species are united their fertility
graduates from zero to perfect fertility or even to fertility under
certain conditions in excess that their fertility besides being
eminently susceptible to favourable and unfavourable conditions is
innately variable that it is by no means always the same in degree in
the first cross and in the hybrids produced from this cross that the
fertility of hybrids is not related to the degree in which they resemble
in external appearance either parent and lastly that the facility of
making a first cross between any two species is not always governed by
their systematic affinity or degree of resemblance to each other This
latter statement is clearly proved by the difference in the result of
reciprocal crosses between the same two species for according as the
one species or the other is used as the father or the mother there
is generally some difference and occasionally the widest possible
difference in the facility of effecting an union The hybrids
moreover produced from reciprocal crosses often differ in fertility

Now do these complex and singular rules indicate that species have been
endowed with sterility simply to prevent their becoming confounded
in nature I think not For why should the sterility be so extremely
different in degree when various species are crossed all of which
we must suppose it would be equally important to keep from blending
together Why should the degree of sterility be innately variable in
the individuals of the same species Why should some species cross with
facility and yet produce very sterile hybrids and other species cross
with extreme difficulty and yet produce fairly fertile hybrids
Why should there often be so great a difference in the result of a
reciprocal cross between the same two species Why it may even be
asked has the production of hybrids been permitted To grant to species
the special power of producing hybrids and then to stop their further
propagation by different degrees of sterility not strictly related to
the facility of the first union between their parents seems a strange
arrangement

The foregoing rules and facts on the other hand appear to me clearly
to indicate that the sterility both of first crosses and of hybrids
is simply incidental or dependent on unknown differences in their
reproductive systems the differences being of so peculiar and limited
a nature that in reciprocal crosses between the same two species
the male sexual element of the one will often freely act on the female
sexual element of the other but not in a reversed direction It will be
advisable to explain a little more fully by an example what I mean
by sterility being incidental on other differences and not a specially
endowed quality As the capacity of one plant to be grafted or budded on
another is unimportant for their welfare in a state of nature I presume
that no one will suppose that this capacity is a SPECIALLY endowed
quality but will admit that it is incidental on differences in the laws
of growth of the two plants We can sometimes see the reason why one
tree will not take on another from differences in their rate of growth
in the hardness of their wood in the period of the flow or nature of
their sap etc but in a multitude of cases we can assign no reason
whatever Great diversity in the size of two plants one being woody and
the other herbaceous one being evergreen and the other deciduous and
adaptation to widely different climates does not always prevent the two
grafting together As in hybridisation so with grafting the capacity
is limited by systematic affinity for no one has been able to graft
together trees belonging to quite distinct families and on the other
hand closely allied species and varieties of the same species can
usually but not invariably be grafted with ease But this capacity
as in hybridisation is by no means absolutely governed by systematic
affinity Although many distinct genera within the same family have been
grafted together in other cases species of the same genus will not take
on each other The pear can be grafted far more readily on the quince
which is ranked as a distinct genus than on the apple which is a
member of the same genus Even different varieties of the pear take with
different degrees of facility on the quince so do different varieties
of the apricot and peach on certain varieties of the plum

As Gartner found that there was sometimes an innate difference in
different INDIVIDUALS of the same two species in crossing so Sagaret
believes this to be the case with different individuals of the same
two species in being grafted together As in reciprocal crosses the
facility of effecting an union is often very far from equal so it
sometimes is in grafting The common gooseberry for instance cannot
be grafted on the currant whereas the currant will take though with
difficulty on the gooseberry

We have seen that the sterility of hybrids which have their reproductive
organs in an imperfect condition is a different case from the
difficulty of uniting two pure species which have their reproductive
organs perfect yet these two distinct classes of cases run to a large
extent parallel Something analogous occurs in grafting for Thouin
found that three species of Robinia which seeded freely on their own
roots and which could be grafted with no great difficulty on a fourth
species when thus grafted were rendered barren On the other hand
certain species of Sorbus when grafted on other species yielded twice
as much fruit as when on their own roots We are reminded by this latter
fact of the extraordinary cases of Hippeastrum Passiflora etc which
seed much more freely when fertilised with the pollen of a distinct
species than when fertilised with pollen from the same plant

We thus see that although there is a clear and great difference between
the mere adhesion of grafted stocks and the union of the male and female
elements in the act of reproduction yet that there is a rude degree of
parallelism in the results of grafting and of crossing distinct species
And as we must look at the curious and complex laws governing the
facility with which trees can be grafted on each other as incidental on
unknown differences in their vegetative systems so I believe that the
still more complex laws governing the facility of first crosses are
incidental on unknown differences in their reproductive systems These
differences in both cases follow to a certain extent as might
have been expected systematic affinity by which term every kind of
resemblance and dissimilarity between organic beings is attempted to be
expressed The facts by no means seem to indicate that the greater or
lesser difficulty of either grafting or crossing various species
has been a special endowment although in the case of crossing the
difficulty is as important for the endurance and stability of specific
forms as in the case of grafting it is unimportant for their welfare

ORIGIN AND CAUSES OF THE STERILITY OF FIRST CROSSES AND OF HYBRIDS

At one time it appeared to me probable as it has to others that
the sterility of first crosses and of hybrids might have been slowly
acquired through the natural selection of slightly lessened degrees of
fertility which like any other variation spontaneously appeared in
certain individuals of one variety when crossed with those of another
variety For it would clearly be advantageous to two varieties or
incipient species if they could be kept from blending on the same
principle that when man is selecting at the same time two varieties it
is necessary that he should keep them separate In the first place
it may be remarked that species inhabiting distinct regions are often
sterile when crossed now it could clearly have been of no advantage
to such separated species to have been rendered mutually sterile
and consequently this could not have been effected through natural
selection but it may perhaps be argued that if a species was rendered
sterile with some one compatriot sterility with other species would
follow as a necessary contingency In the second place it is almost as
much opposed to the theory of natural selection as to that of special
creation that in reciprocal crosses the male element of one form should
have been rendered utterly impotent on a second form while at the same
time the male element of this second form is enabled freely to fertilise
the first form for this peculiar state of the reproductive system could
hardly have been advantageous to either species

In considering the probability of natural selection having come into
action in rendering species mutually sterile the greatest difficulty
will be found to lie in the existence of many graduated steps from
slightly lessened fertility to absolute sterility It may be admitted
that it would profit an incipient species if it were rendered in some
slight degree sterile when crossed with its parent form or with some
other variety for thus fewer bastardised and deteriorated offspring
would be produced to commingle their blood with the new species in
process of formation But he who will take the trouble to reflect on the
steps by which this first degree of sterility could be increased through
natural selection to that high degree which is common with so
many species and which is universal with species which have been
differentiated to a generic or family rank will find the subject
extraordinarily complex After mature reflection it seems to me that
this could not have been effected through natural selection Take the
case of any two species which when crossed produced few and sterile
offspring now what is there which could favour the survival of those
individuals which happened to be endowed in a slightly higher degree
with mutual infertility and which thus approached by one small step
towards absolute sterility Yet an advance of this kind if the theory
of natural selection be brought to bear must have incessantly occurred
with many species for a multitude are mutually quite barren With
sterile neuter insects we have reason to believe that modifications in
their structure and fertility have been slowly accumulated by natural
selection from an advantage having been thus indirectly given to the
community to which they belonged over other communities of the same
species but an individual animal not belonging to a social community
if rendered slightly sterile when crossed with some other variety would
not thus itself gain any advantage or indirectly give any advantage
to the other individuals of the same variety thus leading to their
preservation

But it would be superfluous to discuss this question in detail for with
plants we have conclusive evidence that the sterility of crossed species
must be due to some principle quite independent of natural selection
Both Gartner and Kolreuter have proved that in genera including numerous
species a series can be formed from species which when crossed yield
fewer and fewer seeds to species which never produce a single seed but
yet are affected by the pollen of certain other species for the germen
swells It is here manifestly impossible to select the more sterile
individuals which have already ceased to yield seeds so that this acme
of sterility when the germen alone is effected cannot have been gained
through selection and from the laws governing the various grades of
sterility being so uniform throughout the animal and vegetable kingdoms
we may infer that the cause whatever it may be is the same or nearly
the same in all cases

We will now look a little closer at the probable nature of the
differences between species which induce sterility in first crosses and
in hybrids In the case of first crosses the greater or less difficulty
in effecting a union and in obtaining offspring apparently depends
on several distinct causes There must sometimes be a physical
impossibility in the male element reaching the ovule as would be the
case with a plant having a pistil too long for the pollentubes to
reach the ovarium It has also been observed that when the pollen of one
species is placed on the stigma of a distantly allied species though
the pollentubes protrude they do not penetrate the stigmatic surface
Again the male element may reach the female element but be incapable
of causing an embryo to be developed as seems to have been the case
with some of Thurets experiments on Fuci No explanation can be given
of these facts any more than why certain trees cannot be grafted on
others Lastly an embryo may be developed and then perish at an early
period This latter alternative has not been sufficiently attended to
but I believe from observations communicated to me by Mr Hewitt who
has had great experience in hybridising pheasants and fowls that the
early death of the embryo is a very frequent cause of sterility in first
crosses Mr Salter has recently given the results of an examination of
about 500 eggs produced from various crosses between three species
of Gallus and their hybrids the majority of these eggs had been
fertilised and in the majority of the fertilised eggs the embryos had
either been partially developed and had then perished or had become
nearly mature but the young chickens had been unable to break through
the shell Of the chickens which were born more than fourfifths died
within the first few days or at latest weeks without any obvious
cause apparently from mere inability to live so that from the 500
eggs only twelve chickens were reared With plants hybridized embryos
probably often perish in a like manner at least it is known that
hybrids raised from very distinct species are sometimes weak and
dwarfed and perish at an early age of which fact Max Wichura has
recently given some striking cases with hybrid willows It may be here
worth noticing that in some cases of parthenogenesis the embryos within
the eggs of silk moths which had not been fertilised pass through their
early stages of development and then perish like the embryos produced by
a cross between distinct species Until becoming acquainted with these
facts I was unwilling to believe in the frequent early death of
hybrid embryos for hybrids when once born are generally healthy and
longlived as we see in the case of the common mule Hybrids however
are differently circumstanced before and after birth when born and
living in a country where their two parents live they are generally
placed under suitable conditions of life But a hybrid partakes of only
half of the nature and constitution of its mother it may therefore
before birth as long as it is nourished within its mothers womb or
within the egg or seed produced by the mother be exposed to conditions
in some degree unsuitable and consequently be liable to perish at an
early period more especially as all very young beings are eminently
sensitive to injurious or unnatural conditions of life But after all
the cause more probably lies in some imperfection in the original act
of impregnation causing the embryo to be imperfectly developed rather
than in the conditions to which it is subsequently exposed

In regard to the sterility of hybrids in which the sexual elements are
imperfectly developed the case is somewhat different I have more than
once alluded to a large body of facts showing that when animals and
plants are removed from their natural conditions they are extremely
liable to have their reproductive systems seriously affected This
in fact is the great bar to the domestication of animals Between the
sterility thus superinduced and that of hybrids there are many points
of similarity In both cases the sterility is independent of general
health and is often accompanied by excess of size or great luxuriance
In both cases the sterility occurs in various degrees in both the male
element is the most liable to be affected but sometimes the female
more than the male In both the tendency goes to a certain extent with
systematic affinity for whole groups of animals and plants are rendered
impotent by the same unnatural conditions and whole groups of species
tend to produce sterile hybrids On the other hand one species in a
group will sometimes resist great changes of conditions with unimpaired
fertility and certain species in a group will produce unusually fertile
hybrids No one can tell till he tries whether any particular animal
will breed under confinement or any exotic plant seed freely under
culture nor can he tell till he tries whether any two species of a
genus will produce more or less sterile hybrids Lastly when organic
beings are placed during several generations under conditions not
natural to them they are extremely liable to vary which seems to be
partly due to their reproductive systems having been specially affected
though in a lesser degree than when sterility ensues So it is with
hybrids for their offspring in successive generations are eminently
liable to vary as every experimentalist has observed

Thus we see that when organic beings are placed under new and unnatural
conditions and when hybrids are produced by the unnatural crossing of
two species the reproductive system independently of the general state
of health is affected in a very similar manner In the one case the
conditions of life have been disturbed though often in so slight a
degree as to be inappreciable by us in the other case or that of
hybrids the external conditions have remained the same but the
organisation has been disturbed by two distinct structures and
constitutions including of course the reproductive systems having been
blended into one For it is scarcely possible that two organisations
should be compounded into one without some disturbance occurring in the
development or periodical action or mutual relations of the different
parts and organs one to another or to the conditions of life When
hybrids are able to breed inter se they transmit to their offspring
from generation to generation the same compounded organisation and
hence we need not be surprised that their sterility though in some
degree variable does not diminish it is even apt to increase
this being generally the result as before explained of too close
interbreeding The above view of the sterility of hybrids being caused
by two constitutions being compounded into one has been strongly
maintained by Max Wichura

It must however be owned that we cannot understand on the above or
any other view several facts with respect to the sterility of hybrids
for instance the unequal fertility of hybrids produced from reciprocal
crosses or the increased sterility in those hybrids which occasionally
and exceptionally resemble closely either pure parent Nor do I pretend
that the foregoing remarks go to the root of the matter no explanation
is offered why an organism when placed under unnatural conditions
is rendered sterile All that I have attempted to show is that in two
cases in some respects allied sterility is the common result in the
one case from the conditions of life having been disturbed in the other
case from the organisation having been disturbed by two organisations
being compounded into one

A similar parallelism holds good with an allied yet very different
class of facts It is an old and almost universal belief founded on a
considerable body of evidence which I have elsewhere given that slight
changes in the conditions of life are beneficial to all living things
We see this acted on by farmers and gardeners in their frequent
exchanges of seed tubers etc from one soil or climate to another
and back again During the convalescence of animals great benefit is
derived from almost any change in their habits of life Again both with
plants and animals there is the clearest evidence that a cross between
individuals of the same species which differ to a certain extent gives
vigour and fertility to the offspring and that close interbreeding
continued during several generations between the nearest relations if
these be kept under the same conditions of life almost always leads to
decreased size weakness or sterility

Hence it seems that on the one hand slight changes in the conditions
of life benefit all organic beings and on the other hand that slight
crosses that is crosses between the males and females of the same
species which have been subjected to slightly different conditions or
which have slightly varied give vigour and fertility to the offspring
But as we have seen organic beings long habituated to certain
uniform conditions under a state of nature when subjected as under
confinement to a considerable change in their conditions very
frequently are rendered more or less sterile and we know that a cross
between two forms that have become widely or specifically different
produce hybrids which are almost always in some degree sterile I am
fully persuaded that this double parallelism is by no means an accident
or an illusion He who is able to explain why the elephant and a
multitude of other animals are incapable of breeding when kept under
only partial confinement in their native country will be able to
explain the primary cause of hybrids being so generally sterile He will
at the same time be able to explain how it is that the races of some of
our domesticated animals which have often been subjected to new and
not uniform conditions are quite fertile together although they are
descended from distinct species which would probably have been sterile
if aboriginally crossed The above two parallel series of facts seem
to be connected together by some common but unknown bond which is
essentially related to the principle of life this principle according
to Mr Herbert Spencer being that life depends on or consists in the
incessant action and reaction of various forces which as throughout
nature are always tending towards an equilibrium and when this
tendency is slightly disturbed by any change the vital forces gain in
power

RECIPROCAL DIMORPHISM AND TRIMORPHISM

This subject may be here briefly discussed and will be found to throw
some light on hybridism Several plants belonging to distinct orders
present two forms which exist in about equal numbers and which differ
in no respect except in their reproductive organs one form having
a long pistil with short stamens the other a short pistil with long
stamens the two having differently sized pollengrains With trimorphic
plants there are three forms likewise differing in the lengths of their
pistils and stamens in the size and colour of the pollengrains and
in some other respects and as in each of the three forms there are two
sets of stamens the three forms possess altogether six sets of stamens
and three kinds of pistils These organs are so proportioned in length
to each other that half the stamens in two of the forms stand on a level
with the stigma of the third form Now I have shown and the result
has been confirmed by other observers that in order to obtain full
fertility with these plants it is necessary that the stigma of the
one form should be fertilised by pollen taken from the stamens of
corresponding height in another form So that with dimorphic species
two unions which may be called legitimate are fully fertile and
two which may be called illegitimate are more or less infertile With
trimorphic species six unions are legitimate or fully fertile and
twelve are illegitimate or more or less infertile

The infertility which may be observed in various dimorphic and
trimorphic plants when they are illegitimately fertilised that is by
pollen taken from stamens not corresponding in height with the pistil
differs much in degree up to absolute and utter sterility just in the
same manner as occurs in crossing distinct species As the degree
of sterility in the latter case depends in an eminent degree on the
conditions of life being more or less favourable so I have found it
with illegitimate unions It is well known that if pollen of a distinct
species be placed on the stigma of a flower and its own pollen be
afterwards even after a considerable interval of time placed on the
same stigma its action is so strongly prepotent that it generally
annihilates the effect of the foreign pollen so it is with the pollen
of the several forms of the same species for legitimate pollen is
strongly prepotent over illegitimate pollen when both are placed on the
same stigma I ascertained this by fertilising several flowers first
illegitimately and twentyfour hours afterwards legitimately with
pollen taken from a peculiarly coloured variety and all the seedlings
were similarly coloured this shows that the legitimate pollen
though applied twentyfour hours subsequently had wholly destroyed
or prevented the action of the previously applied illegitimate pollen
Again as in making reciprocal crosses between the same two species
there is occasionally a great difference in the result so the same
thing occurs with trimorphic plants for instance the midstyled form
of Lythrum salicaria was illegitimately fertilised with the greatest
ease by pollen from the longer stamens of the shortstyled form and
yielded many seeds but the latter form did not yield a single seed when
fertilised by the longer stamens of the midstyled form

In all these respects and in others which might be added the forms
of the same undoubted species when illegitimately united behave in
exactly the same manner as do two distinct species when crossed This
led me carefully to observe during four years many seedlings raised
from several illegitimate unions The chief result is that these
illegitimate plants as they may be called are not fully fertile It
is possible to raise from dimorphic species both longstyled and
shortstyled illegitimate plants and from trimorphic plants all three
illegitimate forms These can then be properly united in a legitimate
manner When this is done there is no apparent reason why they
should not yield as many seeds as did their parents when legitimately
fertilised But such is not the case They are all infertile in various
degrees some being so utterly and incurably sterile that they did
not yield during four seasons a single seed or even seedcapsule The
sterility of these illegitimate plants when united with each other in
a legitimate manner may be strictly compared with that of hybrids when
crossed inter se If on the other hand a hybrid is crossed with either
pure parentspecies the sterility is usually much lessened and so it
is when an illegitimate plant is fertilised by a legitimate plant In
the same manner as the sterility of hybrids does not always run
parallel with the difficulty of making the first cross between the two
parentspecies so that sterility of certain illegitimate plants was
unusually great while the sterility of the union from which they
were derived was by no means great With hybrids raised from the same
seedcapsule the degree of sterility is innately variable so it is in a
marked manner with illegitimate plants Lastly many hybrids are profuse
and persistent flowerers while other and more sterile hybrids produce
few flowers and are weak miserable dwarfs exactly similar cases occur
with the illegitimate offspring of various dimorphic and trimorphic
plants

Altogether there is the closest identity in character and behaviour
between illegitimate plants and hybrids It is hardly an exaggeration
to maintain that illegitimate plants are hybrids produced within the
limits of the same species by the improper union of certain forms while
ordinary hybrids are produced from an improper union between socalled
distinct species We have also already seen that there is the closest
similarity in all respects between first illegitimate unions and first
crosses between distinct species This will perhaps be made more fully
apparent by an illustration we may suppose that a botanist found two
wellmarked varieties and such occur of the longstyled form of the
trimorphic Lythrum salicaria and that he determined to try by crossing
whether they were specifically distinct He would find that they yielded
only about onefifth of the proper number of seed and that they behaved
in all the other above specified respects as if they had been two
distinct species But to make the case sure he would raise plants from
his supposed hybridised seed and he would find that the seedlings were
miserably dwarfed and utterly sterile and that they behaved in all
other respects like ordinary hybrids He might then maintain that he
had actually proved in accordance with the common view that his two
varieties were as good and as distinct species as any in the world but
he would be completely mistaken

The facts now given on dimorphic and trimorphic plants are important
because they show us first that the physiological test of lessened
fertility both in first crosses and in hybrids is no safe criterion
of specific distinction secondly because we may conclude that there is
some unknown bond which connects the infertility of illegitimate unions
with that of their illegitimate offspring and we are led to extend the
same view to first crosses and hybrids thirdly because we find and
this seems to me of especial importance that two or three forms of the
same species may exist and may differ in no respect whatever either in
structure or in constitution relatively to external conditions and yet
be sterile when united in certain ways For we must remember that it is
the union of the sexual elements of individuals of the same form for
instance of two longstyled forms which results in sterility while it
is the union of the sexual elements proper to two distinct forms which
is fertile Hence the case appears at first sight exactly the reverse
of what occurs in the ordinary unions of the individuals of the same
species and with crosses between distinct species It is however
doubtful whether this is really so but I will not enlarge on this
obscure subject

We may however infer as probable from the consideration of dimorphic
and trimorphic plants that the sterility of distinct species when
crossed and of their hybrid progeny depends exclusively on the nature
of their sexual elements and not on any difference in their structure
or general constitution We are also led to this same conclusion by
considering reciprocal crosses in which the male of one species cannot
be united or can be united with great difficulty with the female of
a second species while the converse cross can be effected with perfect
facility That excellent observer Gartner likewise concluded that
species when crossed are sterile owing to differences confined to their
reproductive systems

FERTILITY OF VARIETIES WHEN CROSSED AND OF THEIR MONGREL OFFSPRING NOT
UNIVERSAL

It may be urged as an overwhelming argument that there must be some
essential distinction between species and varieties inasmuch as the
latter however much they may differ from each other in external
appearance cross with perfect facility and yield perfectly fertile
offspring With some exceptions presently to be given I fully admit
that this is the rule But the subject is surrounded by difficulties
for looking to varieties produced under nature if two forms hitherto
reputed to be varieties be found in any degree sterile together they
are at once ranked by most naturalists as species For instance the
blue and red pimpernel which are considered by most botanists as
varieties are said by Gartner to be quite sterile when crossed and
he consequently ranks them as undoubted species If we thus argue in
a circle the fertility of all varieties produced under nature will
assuredly have to be granted

If we turn to varieties produced or supposed to have been produced
under domestication we are still involved in some doubt For when it
is stated for instance that certain South American indigenous domestic
dogs do not readily unite with European dogs the explanation which will
occur to everyone and probably the true one is that they are descended
from aboriginally distinct species Nevertheless the perfect fertility
of so many domestic races differing widely from each other in
appearance for instance those of the pigeon or of the cabbage is a
remarkable fact more especially when we reflect how many species there
are which though resembling each other most closely are utterly
sterile when intercrossed Several considerations however render the
fertility of domestic varieties less remarkable In the first place
it may be observed that the amount of external difference between two
species is no sure guide to their degree of mutual sterility so that
similar differences in the case of varieties would be no sure guide It
is certain that with species the cause lies exclusively in differences
in their sexual constitution Now the varying conditions to which
domesticated animals and cultivated plants have been subjected have had
so little tendency towards modifying the reproductive system in a manner
leading to mutual sterility that we have good grounds for admitting
the directly opposite doctrine of Pallas namely that such conditions
generally eliminate this tendency so that the domesticated descendants
of species which in their natural state probably would have been in
some degree sterile when crossed become perfectly fertile together
With plants so far is cultivation from giving a tendency towards
sterility between distinct species that in several wellauthenticated
cases already alluded to certain plants have been affected in an
opposite manner for they have become selfimpotent while still
retaining the capacity of fertilising and being fertilised by other
species If the Pallasian doctrine of the elimination of sterility
through longcontinued domestication be admitted and it can hardly
be rejected it becomes in the highest degree improbable that similar
conditions longcontinued should likewise induce this tendency though
in certain cases with species having a peculiar constitution sterility
might occasionally be thus caused Thus as I believe we can understand
why with domesticated animals varieties have not been produced
which are mutually sterile and why with plants only a few such cases
immediately to be given have been observed

The real difficulty in our present subject is not as it appears to me
why domestic varieties have not become mutually infertile when crossed
but why this has so generally occurred with natural varieties as soon
as they have been permanently modified in a sufficient degree to take
rank as species We are far from precisely knowing the cause nor is
this surprising seeing how profoundly ignorant we are in regard to the
normal and abnormal action of the reproductive system But we can
see that species owing to their struggle for existence with numerous
competitors will have been exposed during long periods of time to more
uniform conditions than have domestic varieties and this may well make
a wide difference in the result For we know how commonly wild animals
and plants when taken from their natural conditions and subjected
to captivity are rendered sterile and the reproductive functions of
organic beings which have always lived under natural conditions would
probably in like manner be eminently sensitive to the influence of an
unnatural cross Domesticated productions on the other hand which
as shown by the mere fact of their domestication were not originally
highly sensitive to changes in their conditions of life and which can
now generally resist with undiminished fertility repeated changes of
conditions might be expected to produce varieties which would be
little liable to have their reproductive powers injuriously affected by
the act of crossing with other varieties which had originated in a like
manner

I have as yet spoken as if the varieties of the same species were
invariably fertile when intercrossed But it is impossible to resist the
evidence of the existence of a certain amount of sterility in the few
following cases which I will briefly abstract The evidence is at least
as good as that from which we believe in the sterility of a multitude of
species The evidence is also derived from hostile witnesses who in
all other cases consider fertility and sterility as safe criterions of
specific distinction Gartner kept during several years a dwarf kind
of maize with yellow seeds and a tall variety with red seeds growing
near each other in his garden and although these plants have separated
sexes they never naturally crossed He then fertilised thirteen
flowers of the one kind with pollen of the other but only a single
head produced any seed and this one head produced only five grains
Manipulation in this case could not have been injurious as the plants
have separated sexes No one I believe has suspected that these
varieties of maize are distinct species and it is important to notice
that the hybrid plants thus raised were themselves PERFECTLY fertile
so that even Gartner did not venture to consider the two varieties as
specifically distinct

Girou de Buzareingues crossed three varieties of gourd which like
the maize has separated sexes and he asserts that their mutual
fertilisation is by so much the less easy as their differences are
greater How far these experiments may be trusted I know not but
the forms experimented on are ranked by Sagaret who mainly founds his
classification by the test of infertility as varieties and Naudin has
come to the same conclusion

The following case is far more remarkable and seems at first
incredible but it is the result of an astonishing number of experiments
made during many years on nine species of Verbascum by so good an
observer and so hostile a witness as Gartner namely that the yellow
and white varieties when crossed produce less seed than the similarly
coloured varieties of the same species Moreover he asserts that when
yellow and white varieties of one species are crossed with yellow and
white varieties of a DISTINCT species more seed is produced by the
crosses between the similarly coloured flowers than between those which
are differently coloured Mr Scott also has experimented on the species
and varieties of Verbascum and although unable to confirm Gartners
results on the crossing of the distinct species he finds that the
dissimilarly coloured varieties of the same species yield fewer seeds
in the proportion of eightysix to 100 than the similarly coloured
varieties Yet these varieties differ in no respect except in the
colour of their flowers and one variety can sometimes be raised from
the seed of another

Kolreuter whose accuracy has been confirmed by every subsequent
observer has proved the remarkable fact that one particular variety
of the common tobacco was more fertile than the other varieties when
crossed with a widely distinct species He experimented on five forms
which are commonly reputed to be varieties and which he tested by
the severest trial namely by reciprocal crosses and he found their
mongrel offspring perfectly fertile But one of these five varieties
when used either as the father or mother and crossed with the Nicotiana
glutinosa always yielded hybrids not so sterile as those which were
produced from the four other varieties when crossed with N glutinosa
Hence the reproductive system of this one variety must have been in some
manner and in some degree modified

From these facts it can no longer be maintained that varieties when
crossed are invariably quite fertile From the great difficulty of
ascertaining the infertility of varieties in a state of nature for a
supposed variety if proved to be infertile in any degree would almost
universally be ranked as a species from man attending only to external
characters in his domestic varieties and from such varieties not having
been exposed for very long periods to uniform conditions of life from
these several considerations we may conclude that fertility does not
constitute a fundamental distinction between varieties and species when
crossed The general sterility of crossed species may safely be looked
at not as a special acquirement or endowment but as incidental on
changes of an unknown nature in their sexual elements

HYBRIDS AND MONGRELS COMPARED INDEPENDENTLY OF THEIR FERTILITY

Independently of the question of fertility the offspring of species
and of varieties when crossed may be compared in several other respects
Gartner whose strong wish it was to draw a distinct line between
species and varieties could find very few and as it seems to me
quite unimportant differences between the socalled hybrid offspring of
species and the socalled mongrel offspring of varieties And on the
other hand they agree most closely in many important respects

I shall here discuss this subject with extreme brevity The most
important distinction is that in the first generation mongrels are
more variable than hybrids but Gartner admits that hybrids from
species which have long been cultivated are often variable in the first
generation and I have myself seen striking instances of this fact
Gartner further admits that hybrids between very closely allied species
are more variable than those from very distinct species and this shows
that the difference in the degree of variability graduates away
When mongrels and the more fertile hybrids are propagated for several
generations an extreme amount of variability in the offspring in both
cases is notorious but some few instances of both hybrids and mongrels
long retaining a uniform character could be given The variability
however in the successive generations of mongrels is perhaps greater
than in hybrids

This greater variability in mongrels than in hybrids does not seem at
all surprising For the parents of mongrels are varieties and mostly
domestic varieties very few experiments having been tried on natural
varieties and this implies that there has been recent variability
which would often continue and would augment that arising from the act
of crossing The slight variability of hybrids in the first generation
in contrast with that in the succeeding generations is a curious fact
and deserves attention For it bears on the view which I have taken of
one of the causes of ordinary variability namely that the reproductive
system from being eminently sensitive to changed conditions of life
fails under these circumstances to perform its proper function of
producing offspring closely similar in all respects to the parentform
Now hybrids in the first generation are descended from species
excluding those long cultivated which have not had their reproductive
systems in any way affected and they are not variable but hybrids
themselves have their reproductive systems seriously affected and their
descendants are highly variable

But to return to our comparison of mongrels and hybrids Gartner states
that mongrels are more liable than hybrids to revert to either parent
form but this if it be true is certainly only a difference in degree
Moreover Gartner expressly states that the hybrids from long cultivated
plants are more subject to reversion than hybrids from species in their
natural state and this probably explains the singular difference in
the results arrived at by different observers Thus Max Wichura doubts
whether hybrids ever revert to their parent forms and he experimented
on uncultivated species of willows while Naudin on the other hand
insists in the strongest terms on the almost universal tendency to
reversion in hybrids and he experimented chiefly on cultivated plants
Gartner further states that when any two species although most closely
allied to each other are crossed with a third species the hybrids are
widely different from each other whereas if two very distinct varieties
of one species are crossed with another species the hybrids do not
differ much But this conclusion as far as I can make out is founded
on a single experiment and seems directly opposed to the results of
several experiments made by Kolreuter

Such alone are the unimportant differences which Gartner is able to
point out between hybrid and mongrel plants On the other hand the
degrees and kinds of resemblance in mongrels and in hybrids to their
respective parents more especially in hybrids produced from nearly
related species follow according to Gartner the same laws When two
species are crossed one has sometimes a prepotent power of impressing
its likeness on the hybrid So I believe it to be with varieties of
plants and with animals one variety certainly often has this prepotent
power over another variety Hybrid plants produced from a reciprocal
cross generally resemble each other closely and so it is with mongrel
plants from a reciprocal cross Both hybrids and mongrels can be
reduced to either pure parent form by repeated crosses in successive
generations with either parent

These several remarks are apparently applicable to animals but the
subject is here much complicated partly owing to the existence of
secondary sexual characters but more especially owing to prepotency
in transmitting likeness running more strongly in one sex than in
the other both when one species is crossed with another and when one
variety is crossed with another variety For instance I think those
authors are right who maintain that the ass has a prepotent power over
the horse so that both the mule and the hinny resemble more closely the
ass than the horse but that the prepotency runs more strongly in the
male than in the female ass so that the mule which is an offspring of
the male ass and mare is more like an ass than is the hinny which is
the offspring of the femaleass and stallion

Much stress has been laid by some authors on the supposed fact that
it is only with mongrels that the offspring are not intermediate in
character but closely resemble one of their parents but this does
sometimes occur with hybrids yet I grant much less frequently than
with mongrels Looking to the cases which I have collected of crossbred
animals closely resembling one parent the resemblances seem chiefly
confined to characters almost monstrous in their nature and which have
suddenly appeared such as albinism melanism deficiency of tail or
horns or additional fingers and toes and do not relate to characters
which have been slowly acquired through selection A tendency to sudden
reversions to the perfect character of either parent would also
be much more likely to occur with mongrels which are descended from
varieties often suddenly produced and semimonstrous in character than
with hybrids which are descended from species slowly and naturally
produced On the whole I entirely agree with Dr Prosper Lucas who
after arranging an enormous body of facts with respect to animals
comes to the conclusion that the laws of resemblance of the child to its
parents are the same whether the two parents differ little or much from
each other namely in the union of individuals of the same variety or
of different varieties or of distinct species

Independently of the question of fertility and sterility in all
other respects there seems to be a general and close similarity in the
offspring of crossed species and of crossed varieties If we look at
species as having been specially created and at varieties as having
been produced by secondary laws this similarity would be an astonishing
fact But it harmonises perfectly with the view that there is no
essential distinction between species and varieties

SUMMARY OF CHAPTER

First crosses between forms sufficiently distinct to be ranked as
species and their hybrids are very generally but not universally
sterile The sterility is of all degrees and is often so slight that
the most careful experimentalists have arrived at diametrically opposite
conclusions in ranking forms by this test The sterility is innately
variable in individuals of the same species and is eminently
susceptible to action of favourable and unfavourable conditions The
degree of sterility does not strictly follow systematic affinity but is
governed by several curious and complex laws It is generally different
and sometimes widely different in reciprocal crosses between the same
two species It is not always equal in degree in a first cross and in
the hybrids produced from this cross

In the same manner as in grafting trees the capacity in one species or
variety to take on another is incidental on differences generally
of an unknown nature in their vegetative systems so in crossing
the greater or less facility of one species to unite with another is
incidental on unknown differences in their reproductive systems There
is no more reason to think that species have been specially endowed with
various degrees of sterility to prevent their crossing and blending
in nature than to think that trees have been specially endowed with
various and somewhat analogous degrees of difficulty in being grafted
together in order to prevent their inarching in our forests

The sterility of first crosses and of their hybrid progeny has not been
acquired through natural selection In the case of first crosses it
seems to depend on several circumstances in some instances in chief
part on the early death of the embryo In the case of hybrids it
apparently depends on their whole organisation having been disturbed by
being compounded from two distinct forms the sterility being closely
allied to that which so frequently affects pure species when exposed to
new and unnatural conditions of life He who will explain these latter
cases will be able to explain the sterility of hybrids This view is
strongly supported by a parallelism of another kind namely that
firstly slight changes in the conditions of life add to the vigour
and fertility of all organic beings and secondly that the crossing of
forms which have been exposed to slightly different conditions of life
or which have varied favours the size vigour and fertility of their
offspring The facts given on the sterility of the illegitimate unions
of dimorphic and trimorphic plants and of their illegitimate progeny
perhaps render it probable that some unknown bond in all cases connects
the degree of fertility of first unions with that of their offspring
The consideration of these facts on dimorphism as well as of the
results of reciprocal crosses clearly leads to the conclusion that
the primary cause of the sterility of crossed species is confined to
differences in their sexual elements But why in the case of distinct
species the sexual elements should so generally have become more or
less modified leading to their mutual infertility we do not know but
it seems to stand in some close relation to species having been exposed
for long periods of time to nearly uniform conditions of life

It is not surprising that the difficulty in crossing any two species
and the sterility of their hybrid offspring should in most cases
correspond even if due to distinct causes for both depend on the
amount of difference between the species which are crossed Nor is
it surprising that the facility of effecting a first cross and the
fertility of the hybrids thus produced and the capacity of being
grafted together though this latter capacity evidently depends on
widely different circumstances should all run to a certain extent
parallel with the systematic affinity of the forms subjected to
experiment for systematic affinity includes resemblances of all kinds

First crosses between forms known to be varieties or sufficiently alike
to be considered as varieties and their mongrel offspring are very
generally but not as is so often stated invariably fertile Nor
is this almost universal and perfect fertility surprising when it
is remembered how liable we are to argue in a circle with respect to
varieties in a state of nature and when we remember that the greater
number of varieties have been produced under domestication by the
selection of mere external differences and that they have not been long
exposed to uniform conditions of life It should also be especially kept
in mind that longcontinued domestication tends to eliminate
sterility and is therefore little likely to induce this same quality
Independently of the question of fertility in all other respects there
is the closest general resemblance between hybrids and mongrels in
their variability in their power of absorbing each other by repeated
crosses and in their inheritance of characters from both parentforms
Finally then although we are as ignorant of the precise cause of the
sterility of first crosses and of hybrids as we are why animals and
plants removed from their natural conditions become sterile yet the
facts given in this chapter do not seem to me opposed to the belief that
species aboriginally existed as varieties




CHAPTER X ON THE IMPERFECTION OF THE GEOLOGICAL RECORD

 On the absence of intermediate varieties at the present day On the
 nature of extinct intermediate varieties on their number On the lapse
 of time as inferred from the rate of denudation and of deposition
 number On the lapse of time as estimated by years On the poorness of
 our palaeontological collections On the intermittence of geological
 formations On the denudation of granitic areas On the absence of
 intermediate varieties in any one formation On the sudden appearance
 of groups of species On their sudden appearance in the lowest known
 fossiliferous strata Antiquity of the habitable earth


In the sixth chapter I enumerated the chief objections which might be
justly urged against the views maintained in this volume Most of them
have now been discussed One namely the distinctness of specific forms
and their not being blended together by innumerable transitional links
is a very obvious difficulty I assigned reasons why such links do not
commonly occur at the present day under the circumstances apparently
most favourable for their presence namely on an extensive and
continuous area with graduated physical conditions I endeavoured to
show that the life of each species depends in a more important manner
on the presence of other already defined organic forms than on climate
and therefore that the really governing conditions of life do not
graduate away quite insensibly like heat or moisture I endeavoured
also to show that intermediate varieties from existing in lesser
numbers than the forms which they connect will generally be beaten
out and exterminated during the course of further modification and
improvement The main cause however of innumerable intermediate links
not now occurring everywhere throughout nature depends on the very
process of natural selection through which new varieties continually
take the places of and supplant their parentforms But just in
proportion as this process of extermination has acted on an enormous
scale so must the number of intermediate varieties which have formerly
existed be truly enormous Why then is not every geological formation
and every stratum full of such intermediate links Geology assuredly
does not reveal any such finely graduated organic chain and this
perhaps is the most obvious and serious objection which can be urged
against my theory The explanation lies as I believe in the extreme
imperfection of the geological record

In the first place it should always be borne in mind what sort of
intermediate forms must on the theory have formerly existed I have
found it difficult when looking at any two species to avoid picturing
to myself forms DIRECTLY intermediate between them But this is a wholly
false view we should always look for forms intermediate between each
species and a common but unknown progenitor and the progenitor
will generally have differed in some respects from all its modified
descendants To give a simple illustration the fantail and pouter
pigeons are both descended from the rockpigeon if we possessed all
the intermediate varieties which have ever existed we should have an
extremely close series between both and the rockpigeon but we should
have no varieties directly intermediate between the fantail and pouter
none for instance combining a tail somewhat expanded with a crop
somewhat enlarged the characteristic features of these two breeds
These two breeds moreover have become so much modified that if we
had no historical or indirect evidence regarding their origin it would
not have been possible to have determined from a mere comparison of
their structure with that of the rockpigeon C livia whether they had
descended from this species or from some other allied species such as
C oenas

So with natural species if we look to forms very distinct for instance
to the horse and tapir we have no reason to suppose that links directly
intermediate between them ever existed but between each and an unknown
common parent The common parent will have had in its whole organisation
much general resemblance to the tapir and to the horse but in some
points of structure may have differed considerably from both even
perhaps more than they differ from each other Hence in all such cases
we should be unable to recognise the parentform of any two or more
species even if we closely compared the structure of the parent with
that of its modified descendants unless at the same time we had a
nearly perfect chain of the intermediate links

It is just possible by the theory that one of two living forms might
have descended from the other for instance a horse from a tapir and
in this case DIRECT intermediate links will have existed between them
But such a case would imply that one form had remained for a very long
period unaltered whilst its descendants had undergone a vast amount of
change and the principle of competition between organism and organism
between child and parent will render this a very rare event for in all
cases the new and improved forms of life tend to supplant the old and
unimproved forms

By the theory of natural selection all living species have been
connected with the parentspecies of each genus by differences not
greater than we see between the natural and domestic varieties of the
same species at the present day and these parentspecies now generally
extinct have in their turn been similarly connected with more ancient
forms and so on backwards always converging to the common ancestor of
each great class So that the number of intermediate and transitional
links between all living and extinct species must have been
inconceivably great But assuredly if this theory be true such have
lived upon the earth

ON THE LAPSE OF TIME AS INFERRED FROM THE RATE OF DEPOSITION AND EXTENT
OF DENUDATION

Independently of our not finding fossil remains of such infinitely
numerous connecting links it may be objected that time cannot have
sufficed for so great an amount of organic change all changes having
been effected slowly It is hardly possible for me to recall to the
reader who is not a practical geologist the facts leading the mind
feebly to comprehend the lapse of time He who can read Sir Charles
Lyells grand work on the Principles of Geology which the future
historian will recognise as having produced a revolution in natural
science and yet does not admit how vast have been the past periods of
time may at once close this volume Not that it suffices to study
the Principles of Geology or to read special treatises by different
observers on separate formations and to mark how each author attempts
to give an inadequate idea of the duration of each formation or even
of each stratum We can best gain some idea of past time by knowing the
agencies at work and learning how deeply the surface of the land has
been denuded and how much sediment has been deposited As Lyell has
well remarked the extent and thickness of our sedimentary formations
are the result and the measure of the denudation which the earths crust
has elsewhere undergone Therefore a man should examine for himself the
great piles of superimposed strata and watch the rivulets bringing down
mud and the waves wearing away the seacliffs in order to comprehend
something about the duration of past time the monuments of which we see
all around us

It is good to wander along the coast when formed of moderately hard
rocks and mark the process of degradation The tides in most cases
reach the cliffs only for a short time twice a day and the waves eat
into them only when they are charged with sand or pebbles for there is
good evidence that pure water effects nothing in wearing away rock At
last the base of the cliff is undermined huge fragments fall down and
these remaining fixed have to be worn away atom by atom until after
being reduced in size they can be rolled about by the waves and then
they are more quickly ground into pebbles sand or mud But how often
do we see along the bases of retreating cliffs rounded boulders all
thickly clothed by marine productions showing how little they are
abraded and how seldom they are rolled about  Moreover if we follow for
a few miles any line of rocky cliff which is undergoing degradation
we find that it is only here and there along a short length or round
a promontory that the cliffs are at the present time suffering The
appearance of the surface and the vegetation show that elsewhere years
have elapsed since the waters washed their base

We have however recently learned from the observations of Ramsay in
the van of many excellent observers of Jukes Geikie Croll and
others that subaerial degradation is a much more important agency than
coastaction or the power of the waves The whole surface of the land
is exposed to the chemical action of the air and of the rainwater
with its dissolved carbonic acid and in colder countries to frost the
disintegrated matter is carried down even gentle slopes during heavy
rain and to a greater extent than might be supposed especially in
arid districts by the wind it is then transported by the streams
and rivers which when rapid deepen their channels and triturate the
fragments On a rainy day even in a gently undulating country we see
the effects of subaerial degradation in the muddy rills which flow down
every slope Messrs Ramsay and Whitaker have shown and the observation
is a most striking one that the great lines of escarpment in the
Wealden district and those ranging across England which formerly were
looked at as ancient seacoasts cannot have been thus formed for each
line is composed of one and the same formation while our seacliffs are
everywhere formed by the intersection of various formations This being
the case we are compelled to admit that the escarpments owe their
origin in chief part to the rocks of which they are composed having
resisted subaerial denudation better than the surrounding surface
this surface consequently has been gradually lowered with the lines of
harder rock left projecting Nothing impresses the mind with the vast
duration of time according to our ideas of time more forcibly than the
conviction thus gained that subaerial agencies which apparently have
so little power and which seem to work so slowly have produced great
results

When thus impressed with the slow rate at which the land is worn
away through subaerial and littoral action it is good in order to
appreciate the past duration of time to consider on the one hand the
masses of rock which have been removed over many extensive areas and on
the other hand the thickness of our sedimentary formations I remember
having been much struck when viewing volcanic islands which have been
worn by the waves and pared all round into perpendicular cliffs of
one or two thousand feet in height for the gentle slope of the
lavastreams due to their formerly liquid state showed at a glance how
far the hard rocky beds had once extended into the open ocean The same
story is told still more plainly by faults those great cracks along
which the strata have been upheaved on one side or thrown down on the
other to the height or depth of thousands of feet for since the crust
cracked and it makes no great difference whether the upheaval was
sudden or as most geologists now believe was slow and effected by
many starts the surface of the land has been so completely planed down
that no trace of these vast dislocations is externally visible The
Craven fault for instance extends for upward of thirty miles and
along this line the vertical displacement of the strata varies from 600
to 3000 feet Professor Ramsay has published an account of a downthrow
in Anglesea of 2300 feet and he informs me that he fully believes that
there is one in Merionethshire of 12000 feet yet in these cases there
is nothing on the surface of the land to show such prodigious movements
the pile of rocks on either side of the crack having been smoothly swept
away

On the other hand in all parts of the world the piles of sedimentary
strata are of wonderful thickness In the Cordillera I estimated one
mass of conglomerate at ten thousand feet and although conglomerates
have probably been accumulated at a quicker rate than finer sediments
yet from being formed of worn and rounded pebbles each of which bears
the stamp of time they are good to show how slowly the mass must
have been heaped together Professor Ramsay has given me the maximum
thickness from actual measurement in most cases of the successive
formations in DIFFERENT parts of Great Britain and this is the
result 

                                                  Feet

 Palaeozoic strata not including igneous beds57154
 Secondary strata13190
 Tertiary strata2240

  making altogether 72584 feet


that is very nearly thirteen and threequarters British miles
Some of these formations which are represented in England by thin beds
are thousands of feet in thickness on the Continent Moreover between
each successive formation we have in the opinion of most geologists
blank periods of enormous length So that the lofty pile of sedimentary
rocks in Britain gives but an inadequate idea of the time which has
elapsed during their accumulation The consideration of these various
facts impresses the mind almost in the same manner as does the vain
endeavour to grapple with the idea of eternity

Nevertheless this impression is partly false Mr Croll in an
interesting paper remarks that we do not err in forming too great a
conception of the length of geological periods but in estimating them
by years When geologists look at large and complicated phenomena and
then at the figures representing several million years the two produce
a totally different effect on the mind and the figures are at once
pronounced too small In regard to subaerial denudation Mr Croll
shows by calculating the known amount of sediment annually brought down
by certain rivers relatively to their areas of drainage that 1000
feet of solid rock as it became gradually disintegrated would thus
be removed from the mean level of the whole area in the course of six
million years This seems an astonishing result and some considerations
lead to the suspicion that it may be too large but if halved or
quartered it is still very surprising Few of us however know what a
million really means Mr Croll gives the following illustration Take
a narrow strip of paper eightythree feet four inches in length and
stretch it along the wall of a large hall then mark off at one end
the tenth of an inch This tenth of an inch will represent one hundred
years and the entire strip a million years But let it be borne in
mind in relation to the subject of this work what a hundred years
implies represented as it is by a measure utterly insignificant in a
hall of the above dimensions Several eminent breeders during a single
lifetime have so largely modified some of the higher animals which
propagate their kind much more slowly than most of the lower animals
that they have formed what well deserves to be called a new subbreed
Few men have attended with due care to any one strain for more than half
a century so that a hundred years represents the work of two breeders
in succession It is not to be supposed that species in a state of
nature ever change so quickly as domestic animals under the guidance of
methodical selection The comparison would be in every way fairer
with the effects which follow from unconscious selection that is the
preservation of the most useful or beautiful animals with no intention
of modifying the breed but by this process of unconscious selection
various breeds have been sensibly changed in the course of two or three
centuries

Species however probably change much more slowly and within the same
country only a few change at the same time This slowness follows from
all the inhabitants of the same country being already so well adapted to
each other that new places in the polity of nature do not occur until
after long intervals due to the occurrence of physical changes of some
kind or through the immigration of new forms Moreover variations
or individual differences of the right nature by which some of the
inhabitants might be better fitted to their new places under the altered
circumstance would not always occur at once Unfortunately we have no
means of determining according to the standard of years how long a
period it takes to modify a species but to the subject of time we must
return

ON THE POORNESS OF PALAEONTOLOGICAL COLLECTIONS

Now let us turn to our richest museums and what a paltry display we
behold  That our collections are imperfect is admitted by every one The
remark of that admirable palaeontologist Edward Forbes should never
be forgotten namely that very many fossil species are known and
named from single and often broken specimens or from a few specimens
collected on some one spot Only a small portion of the surface of the
earth has been geologically explored and no part with sufficient
care as the important discoveries made every year in Europe prove
No organism wholly soft can be preserved Shells and bones decay and
disappear when left on the bottom of the sea where sediment is not
accumulating We probably take a quite erroneous view when we assume
that sediment is being deposited over nearly the whole bed of the sea
at a rate sufficiently quick to embed and preserve fossil remains
Throughout an enormously large proportion of the ocean the bright blue
tint of the water bespeaks its purity The many cases on record of a
formation conformably covered after an immense interval of time by
another and later formation without the underlying bed having suffered
in the interval any wear and tear seem explicable only on the view
of the bottom of the sea not rarely lying for ages in an unaltered
condition The remains which do become embedded if in sand or gravel
will when the beds are upraised generally be dissolved by the
percolation of rain water charged with carbonic acid Some of the many
kinds of animals which live on the beach between high and low water mark
seem to be rarely preserved For instance the several species of the
Chthamalinae a subfamily of sessile cirripedes coat the rocks all
over the world in infinite numbers they are all strictly littoral with
the exception of a single Mediterranean species which inhabits deep
water and this has been found fossil in Sicily whereas not one other
species has hitherto been found in any tertiary formation yet it is
known that the genus Chthamalus existed during the Chalk period
Lastly many great deposits requiring a vast length of time for their
accumulation are entirely destitute of organic remains without our
being able to assign any reason one of the most striking instances is
that of the Flysch formation which consists of shale and sandstone
several thousand occasionally even six thousand feet in thickness
and extending for at least 300 miles from Vienna to Switzerland and
although this great mass has been most carefully searched no fossils
except a few vegetable remains have been found

With respect to the terrestrial productions which lived during the
Secondary and Palaeozoic periods it is superfluous to state that
our evidence is fragmentary in an extreme degree For instance until
recently not a landshell was known belonging to either of these vast
periods with the exception of one species discovered by Sir C Lyell
and Dr Dawson in the carboniferous strata of North America but now
landshells have been found in the lias In regard to mammiferous
remains a glance at the historical table published in Lyells
Manual will bring home the truth how accidental and rare is their
preservation far better than pages of detail Nor is their rarity
surprising when we remember how large a proportion of the bones of
tertiary mammals have been discovered either in caves or in lacustrine
deposits and that not a cave or true lacustrine bed is known belonging
to the age of our secondary or palaeozoic formations

But the imperfection in the geological record largely results from
another and more important cause than any of the foregoing namely from
the several formations being separated from each other by wide intervals
of time This doctrine has been emphatically admitted by many geologists
and palaeontologists who like E Forbes entirely disbelieve in the
change of species When we see the formations tabulated in written
works or when we follow them in nature it is difficult to avoid
believing that they are closely consecutive But we know for instance
from Sir R Murchisons great work on Russia what wide gaps there are
in that country between the superimposed formations so it is in
North America and in many other parts of the world The most skilful
geologist if his attention had been confined exclusively to these large
territories would never have suspected that during the periods which
were blank and barren in his own country great piles of sediment
charged with new and peculiar forms of life had elsewhere been
accumulated And if in every separate territory hardly any idea can be
formed of the length of time which has elapsed between the consecutive
formations we may infer that this could nowhere be ascertained
The frequent and great changes in the mineralogical composition
of consecutive formations generally implying great changes in the
geography of the surrounding lands whence the sediment was derived
accord with the belief of vast intervals of time having elapsed between
each formation

We can I think see why the geological formations of each region are
almost invariably intermittent that is have not followed each other
in close sequence Scarcely any fact struck me more when examining many
hundred miles of the South American coasts which have been upraised
several hundred feet within the recent period than the absence of
any recent deposits sufficiently extensive to last for even a short
geological period Along the whole west coast which is inhabited by
a peculiar marine fauna tertiary beds are so poorly developed that no
record of several successive and peculiar marine faunas will probably be
preserved to a distant age A little reflection will explain why along
the rising coast of the western side of South America no extensive
formations with recent or tertiary remains can anywhere be found though
the supply of sediment must for ages have been great from the enormous
degradation of the coast rocks and from the muddy streams entering the
sea The explanation no doubt is that the littoral and sublittoral
deposits are continually worn away as soon as they are brought up by
the slow and gradual rising of the land within the grinding action of
the coastwaves

We may I think conclude that sediment must be accumulated in extremely
thick solid or extensive masses in order to withstand the incessant
action of the waves when first upraised and during subsequent
oscillations of level as well as the subsequent subaerial degradation
Such thick and extensive accumulations of sediment may be formed in two
ways either in profound depths of the sea in which case the bottom
will not be inhabited by so many and such varied forms of life as the
more shallow seas and the mass when upraised will give an imperfect
record of the organisms which existed in the neighbourhood during
the period of its accumulation Or sediment may be deposited to any
thickness and extent over a shallow bottom if it continue slowly to
subside In this latter case as long as the rate of subsidence and
supply of sediment nearly balance each other the sea will remain
shallow and favourable for many and varied forms and thus a rich
fossiliferous formation thick enough when upraised to resist a large
amount of denudation may be formed

I am convinced that nearly all our ancient formations which are
throughout the greater part of their thickness RICH IN FOSSILS have
thus been formed during subsidence Since publishing my views on this
subject in 1845 I have watched the progress of geology and have been
surprised to note how author after author in treating of this or that
great formation has come to the conclusion that it was accumulated
during subsidence I may add that the only ancient tertiary formation
on the west coast of South America which has been bulky enough to
resist such degradation as it has as yet suffered but which will
hardly last to a distant geological age was deposited during a downward
oscillation of level and thus gained considerable thickness

All geological facts tell us plainly that each area has undergone
numerous slow oscillations of level and apparently these oscillations
have affected wide spaces Consequently formations rich in fossils and
sufficiently thick and extensive to resist subsequent degradation will
have been formed over wide spaces during periods of subsidence but only
where the supply of sediment was sufficient to keep the sea shallow and
to embed and preserve the remains before they had time to decay On the
other hand as long as the bed of the sea remained stationary THICK
deposits cannot have been accumulated in the shallow parts which are
the most favourable to life Still less can this have happened during
the alternate periods of elevation or to speak more accurately the
beds which were then accumulated will generally have been destroyed by
being upraised and brought within the limits of the coastaction

These remarks apply chiefly to littoral and sublittoral deposits In the
case of an extensive and shallow sea such as that within a large part
of the Malay Archipelago where the depth varies from thirty or forty
to sixty fathoms a widely extended formation might be formed during
a period of elevation and yet not suffer excessively from denudation
during its slow upheaval but the thickness of the formation could not
be great for owing to the elevatory movement it would be less than
the depth in which it was formed nor would the deposit be much
consolidated nor be capped by overlying formations so that it would
run a good chance of being worn away by atmospheric degradation and by
the action of the sea during subsequent oscillations of level It has
however been suggested by Mr Hopkins that if one part of the area
after rising and before being denuded subsided the deposit formed
during the rising movement though not thick might afterwards become
protected by fresh accumulations and thus be preserved for a long
period

Mr Hopkins also expresses his belief that sedimentary beds of
considerable horizontal extent have rarely been completely destroyed
But all geologists excepting the few who believe that our present
metamorphic schists and plutonic rocks once formed the primordial
nucleus of the globe will admit that these latter rocks have been
stripped of their covering to an enormous extent For it is scarcely
possible that such rocks could have been solidified and crystallised
while uncovered but if the metamorphic action occurred at profound
depths of the ocean the former protecting mantle of rock may not have
been very thick Admitting then that gneiss micaschist granite
diorite etc were once necessarily covered up how can we account for
the naked and extensive areas of such rocks in many parts of the world
except on the belief that they have subsequently been completely denuded
of all overlying strata That such extensive areas do exist cannot be
doubted the granitic region of Parime is described by Humboldt as being
at least nineteen times as large as Switzerland South of the Amazon
Boue colours an area composed of rocks of this nature as equal to that
of Spain France Italy part of Germany and the British Islands all
conjoined This region has not been carefully explored but from the
concurrent testimony of travellers the granitic area is very large
thus Von Eschwege gives a detailed section of these rocks stretching
from Rio de Janeiro for 260 geographical miles inland in a straight
line and I travelled for 150 miles in another direction and saw
nothing but granitic rocks Numerous specimens collected along the
whole coast from near Rio de Janeiro to the mouth of the Plata a
distance of 1100 geographical miles were examined by me and they all
belonged to this class Inland along the whole northern bank of the
Plata I saw besides modern tertiary beds only one small patch of
slightly metamorphosed rock which alone could have formed a part of the
original capping of the granitic series Turning to a wellknown region
namely to the United States and Canada as shown in Professor HD
Rogers beautiful map I have estimated the areas by cutting out and
weighing the paper and I find that the metamorphic excluding the
semimetamorphic and granite rocks exceed in the proportion of 19 to
125 the whole of the newer Palaeozoic formations In many regions the
metamorphic and granite rocks would be found much more widely extended
than they appear to be if all the sedimentary beds were removed which
rest unconformably on them and which could not have formed part of
the original mantle under which they were crystallised Hence it is
probable that in some parts of the world whole formations have been
completely denuded with not a wreck left behind


One remark is here worth a passing notice During periods of elevation
the area of the land and of the adjoining shoal parts of the sea will
be increased and new stations will often be formed all circumstances
favourable as previously explained for the formation of new varieties
and species but during such periods there will generally be a blank
in the geological record On the other hand during subsidence the
inhabited area and number of inhabitants will decrease excepting on
the shores of a continent when first broken up into an archipelago and
consequently during subsidence though there will be much extinction
few new varieties or species will be formed and it is during these very
periods of subsidence that the deposits which are richest in fossils
have been accumulated

ON THE ABSENCE OF NUMEROUS INTERMEDIATE VARIETIES IN ANY SINGLE
FORMATION

From these several considerations it cannot be doubted that the
geological record viewed as a whole is extremely imperfect but if
we confine our attention to any one formation it becomes much more
difficult to understand why we do not therein find closely graduated
varieties between the allied species which lived at its commencement and
at its close Several cases are on record of the same species presenting
varieties in the upper and lower parts of the same formation Thus
Trautschold gives a number of instances with Ammonites and Hilgendorf
has described a most curious case of ten graduated forms of Planorbis
multiformis in the successive beds of a freshwater formation in
Switzerland Although each formation has indisputably required a vast
number of years for its deposition several reasons can be given why
each should not commonly include a graduated series of links between the
species which lived at its commencement and close but I cannot assign
due proportional weight to the following considerations

Although each formation may mark a very long lapse of years each
probably is short compared with the period requisite to change one
species into another I am aware that two palaeontologists whose
opinions are worthy of much deference namely Bronn and Woodward have
concluded that the average duration of each formation is twice or thrice
as long as the average duration of specific forms But insuperable
difficulties as it seems to me prevent us from coming to any just
conclusion on this head When we see a species first appearing in the
middle of any formation it would be rash in the extreme to infer
that it had not elsewhere previously existed So again when we find
a species disappearing before the last layers have been deposited it
would be equally rash to suppose that it then became extinct We forget
how small the area of Europe is compared with the rest of the world
nor have the several stages of the same formation throughout Europe been
correlated with perfect accuracy

We may safely infer that with marine animals of all kinds there has been
a large amount of migration due to climatal and other changes and when
we see a species first appearing in any formation the probability is
that it only then first immigrated into that area It is well known for
instance that several species appear somewhat earlier in the palaeozoic
beds of North America than in those of Europe time having apparently
been required for their migration from the American to the European
seas In examining the latest deposits in various quarters of the
world it has everywhere been noted that some few still existing
species are common in the deposit but have become extinct in the
immediately surrounding sea or conversely that some are now abundant
in the neighbouring sea but are rare or absent in this particular
deposit It is an excellent lesson to reflect on the ascertained amount
of migration of the inhabitants of Europe during the glacial epoch
which forms only a part of one whole geological period and likewise to
reflect on the changes of level on the extreme change of climate
and on the great lapse of time all included within this same glacial
period Yet it may be doubted whether in any quarter of the
world sedimentary deposits INCLUDING FOSSIL REMAINS have gone on
accumulating within the same area during the whole of this period It is
not for instance probable that sediment was deposited during the whole
of the glacial period near the mouth of the Mississippi within that
limit of depth at which marine animals can best flourish for we know
that great geographical changes occurred in other parts of America
during this space of time When such beds as were deposited in shallow
water near the mouth of the Mississippi during some part of the glacial
period shall have been upraised organic remains will probably first
appear and disappear at different levels owing to the migrations
of species and to geographical changes And in the distant future a
geologist examining these beds would be tempted to conclude that the
average duration of life of the embedded fossils had been less than that
of the glacial period instead of having been really far greater that
is extending from before the glacial epoch to the present day

In order to get a perfect gradation between two forms in the upper
and lower parts of the same formation the deposit must have gone on
continuously accumulating during a long period sufficient for the slow
process of modification hence the deposit must be a very thick one
and the species undergoing change must have lived in the same district
throughout the whole time But we have seen that a thick formation
fossiliferous throughout its entire thickness can accumulate only
during a period of subsidence and to keep the depth approximately the
same which is necessary that the same marine species may live on the
same space the supply of sediment must nearly counterbalance the
amount of subsidence But this same movement of subsidence will tend to
submerge the area whence the sediment is derived and thus diminish the
supply whilst the downward movement continues In fact this nearly
exact balancing between the supply of sediment and the amount of
subsidence is probably a rare contingency for it has been observed
by more than one palaeontologist that very thick deposits are usually
barren of organic remains except near their upper or lower limits

It would seem that each separate formation like the whole pile of
formations in any country has generally been intermittent in its
accumulation When we see as is so often the case a formation composed
of beds of widely different mineralogical composition we may
reasonably suspect that the process of deposition has been more or less
interrupted Nor will the closest inspection of a formation give us any
idea of the length of time which its deposition may have consumed
Many instances could be given of beds only a few feet in thickness
representing formations which are elsewhere thousands of feet in
thickness and which must have required an enormous period for their
accumulation yet no one ignorant of this fact would have even suspected
the vast lapse of time represented by the thinner formation Many cases
could be given of the lower beds of a formation having been upraised
denuded submerged and then recovered by the upper beds of the same
formation facts showing what wide yet easily overlooked intervals
have occurred in its accumulation In other cases we have the plainest
evidence in great fossilised trees still standing upright as they grew
of many long intervals of time and changes of level during the process
of deposition which would not have been suspected had not the trees
been preserved thus Sir C Lyell and Dr Dawson found carboniferous
beds 1400 feet thick in Nova Scotia with ancient rootbearing strata
one above the other at no less than sixtyeight different levels
Hence when the same species occurs at the bottom middle and top of
a formation the probability is that it has not lived on the same
spot during the whole period of deposition but has disappeared and
reappeared perhaps many times during the same geological period
Consequently if it were to undergo a considerable amount of modification
during the deposition of any one geological formation a section would
not include all the fine intermediate gradations which must on our
theory have existed but abrupt though perhaps slight changes of form

It is allimportant to remember that naturalists have no golden rule
by which to distinguish species and varieties they grant some little
variability to each species but when they meet with a somewhat greater
amount of difference between any two forms they rank both as species
unless they are enabled to connect them together by the closest
intermediate gradations and this from the reasons just assigned we
can seldom hope to effect in any one geological section Supposing B
and C to be two species and a third A to be found in an older and
underlying bed even if A were strictly intermediate between B and C
it would simply be ranked as a third and distinct species unless at the
same time it could be closely connected by intermediate varieties
with either one or both forms Nor should it be forgotten as before
explained that A might be the actual progenitor of B and C and yet
would not necessarily be strictly intermediate between them in all
respects So that we might obtain the parentspecies and its several
modified descendants from the lower and upper beds of the same
formation and unless we obtained numerous transitional gradations we
should not recognise their bloodrelationship and should consequently
rank them as distinct species

It is notorious on what excessively slight differences many
palaeontologists have founded their species and they do this the more
readily if the specimens come from different substages of the same
formation Some experienced conchologists are now sinking many of the
very fine species of DOrbigny and others into the rank of varieties
and on this view we do find the kind of evidence of change which on
the theory we ought to find Look again at the later tertiary deposits
which include many shells believed by the majority of naturalists to
be identical with existing species but some excellent naturalists
as Agassiz and Pictet maintain that all these tertiary species are
specifically distinct though the distinction is admitted to be very
slight so that here unless we believe that these eminent naturalists
have been misled by their imaginations and that these late tertiary
species really present no difference whatever from their living
representatives or unless we admit in opposition to the judgment of
most naturalists that these tertiary species are all truly distinct
from the recent we have evidence of the frequent occurrence of slight
modifications of the kind required If we look to rather wider intervals
of time namely to distinct but consecutive stages of the same great
formation we find that the embedded fossils though universally ranked
as specifically different yet are far more closely related to each
other than are the species found in more widely separated formations
so that here again we have undoubted evidence of change in the direction
required by the theory but to this latter subject I shall return in the
following chapter

With animals and plants that propagate rapidly and do not wander
much there is reason to suspect as we have formerly seen that their
varieties are generally at first local and that such local varieties
do not spread widely and supplant their parentform until they have been
modified and perfected in some considerable degree According to this
view the chance of discovering in a formation in any one country all
the early stages of transition between any two forms is small for the
successive changes are supposed to have been local or confined to some
one spot Most marine animals have a wide range and we have seen that
with plants it is those which have the widest range that oftenest
present varieties so that with shells and other marine animals it is
probable that those which had the widest range far exceeding the limits
of the known geological formations in Europe have oftenest given rise
first to local varieties and ultimately to new species and this again
would greatly lessen the chance of our being able to trace the stages of
transition in any one geological formation

It is a more important consideration leading to the same result as
lately insisted on by Dr Falconer namely that the period during which
each species underwent modification though long as measured by years
was probably short in comparison with that during which it remained
without undergoing any change

It should not be forgotten that at the present day with perfect
specimens for examination two forms can seldom be connected by
intermediate varieties and thus proved to be the same species until
many specimens are collected from many places and with fossil
species this can rarely be done We shall perhaps best perceive the
improbability of our being enabled to connect species by numerous fine
intermediate fossil links by asking ourselves whether for instance
geologists at some future period will be able to prove that our
different breeds of cattle sheep horses and dogs are descended from
a single stock or from several aboriginal stocks or again whether
certain seashells inhabiting the shores of North America which are
ranked by some conchologists as distinct species from their European
representatives and by other conchologists as only varieties are
really varieties or are as it is called specifically distinct This
could be effected by the future geologist only by his discovering in
a fossil state numerous intermediate gradations and such success is
improbable in the highest degree

It has been asserted over and over again by writers who believe in
the immutability of species that geology yields no linking forms This
assertion as we shall see in the next chapter is certainly erroneous
As Sir J Lubbock has remarked Every species is a link between other
allied forms If we take a genus having a score of species recent
and extinct and destroy fourfifths of them no one doubts that the
remainder will stand much more distinct from each other If the extreme
forms in the genus happen to have been thus destroyed the genus itself
will stand more distinct from other allied genera What geological
research has not revealed is the former existence of infinitely
numerous gradations as fine as existing varieties connecting together
nearly all existing and extinct species But this ought not to be
expected yet this has been repeatedly advanced as a most serious
objection against my views

It may be worth while to sum up the foregoing remarks on the causes
of the imperfection of the geological record under an imaginary
illustration The Malay Archipelago is about the size of Europe from
the North Cape to the Mediterranean and from Britain to Russia and
therefore equals all the geological formations which have been examined
with any accuracy excepting those of the United States of America I
fully agree with Mr GodwinAusten that the present condition of the
Malay Archipelago with its numerous large islands separated by wide and
shallow seas probably represents the former state of Europe while most
of our formations were accumulating The Malay Archipelago is one of
the richest regions in organic beings yet if all the species were to
be collected which have ever lived there how imperfectly would they
represent the natural history of the world 

But we have every reason to believe that the terrestrial productions of
the archipelago would be preserved in an extremely imperfect manner in
the formations which we suppose to be there accumulating Not many
of the strictly littoral animals or of those which lived on naked
submarine rocks would be embedded and those embedded in gravel or
sand would not endure to a distant epoch Wherever sediment did not
accumulate on the bed of the sea or where it did not accumulate at a
sufficient rate to protect organic bodies from decay no remains could
be preserved

Formations rich in fossils of many kinds and of thickness sufficient to
last to an age as distant in futurity as the secondary formations lie
in the past would generally be formed in the archipelago only during
periods of subsidence These periods of subsidence would be separated
from each other by immense intervals of time during which the area
would be either stationary or rising whilst rising the fossiliferous
formations on the steeper shores would be destroyed almost as soon as
accumulated by the incessant coastaction as we now see on the shores
of South America Even throughout the extensive and shallow seas within
the archipelago sedimentary beds could hardly be accumulated of
great thickness during the periods of elevation or become capped
and protected by subsequent deposits so as to have a good chance of
enduring to a very distant future During the periods of subsidence
there would probably be much extinction of life during the periods
of elevation there would be much variation but the geological record
would then be less perfect

It may be doubted whether the duration of any one great period of
subsidence over the whole or part of the archipelago together with
a contemporaneous accumulation of sediment would EXCEED the average
duration of the same specific forms and these contingencies are
indispensable for the preservation of all the transitional gradations
between any two or more species If such gradations were not all fully
preserved transitional varieties would merely appear as so many new
though closely allied species It is also probable that each great
period of subsidence would be interrupted by oscillations of level
and that slight climatical changes would intervene during such lengthy
periods and in these cases the inhabitants of the archipelago would
migrate and no closely consecutive record of their modifications could
be preserved in any one formation

Very many of the marine inhabitants of the archipelago now range
thousands of miles beyond its confines and analogy plainly leads to the
belief that it would be chiefly these farranging species though
only some of them which would oftenest produce new varieties and
the varieties would at first be local or confined to one place but
if possessed of any decided advantage or when further modified and
improved they would slowly spread and supplant their parentforms When
such varieties returned to their ancient homes as they would differ
from their former state in a nearly uniform though perhaps extremely
slight degree and as they would be found embedded in slightly
different substages of the same formation they would according to
the principles followed by many palaeontologists be ranked as new and
distinct species

If then there be some degree of truth in these remarks we have no right
to expect to find in our geological formations an infinite number of
those fine transitional forms which on our theory have connected
all the past and present species of the same group into one long and
branching chain of life We ought only to look for a few links and such
assuredly we do find some more distantly some more closely related
to each other and these links let them be ever so close if found in
different stages of the same formation would by many palaeontologists
be ranked as distinct species But I do not pretend that I should ever
have suspected how poor was the record in the best preserved geological
sections had not the absence of innumerable transitional links between
the species which lived at the commencement and close of each formation
pressed so hardly on my theory

ON THE SUDDEN APPEARANCE OF WHOLE GROUPS OF ALLIED SPECIES

The abrupt manner in which whole groups of species suddenly appear in
certain formations has been urged by several palaeontologists for
instance by Agassiz Pictet and Sedgwick as a fatal objection to the
belief in the transmutation of species If numerous species belonging
to the same genera or families have really started into life at once
the fact would be fatal to the theory of evolution through natural
selection For the development by this means of a group of forms all
of which are descended from some one progenitor must have been an
extremely slow process and the progenitors must have lived long before
their modified descendants But we continually overrate the perfection
of the geological record and falsely infer because certain genera or
families have not been found beneath a certain stage that they did not
exist before that stage In all cases positive palaeontological evidence
may be implicitly trusted negative evidence is worthless as experience
has so often shown We continually forget how large the world is
compared with the area over which our geological formations have been
carefully examined we forget that groups of species may elsewhere
have long existed and have slowly multiplied before they invaded the
ancient archipelagoes of Europe and the United States We do not make
due allowance for the enormous intervals of time which have elapsed
between our consecutive formations longer perhaps in many cases
than the time required for the accumulation of each formation These
intervals will have given time for the multiplication of species from
some one parentform and in the succeeding formation such groups or
species will appear as if suddenly created

I may here recall a remark formerly made namely that it might require
a long succession of ages to adapt an organism to some new and peculiar
line of life for instance to fly through the air and consequently
that the transitional forms would often long remain confined to some one
region but that when this adaptation had once been effected and a
few species had thus acquired a great advantage over other organisms
a comparatively short time would be necessary to produce many divergent
forms which would spread rapidly and widely throughout the world
Professor Pictet in his excellent Review of this work in commenting
on early transitional forms and taking birds as an illustration cannot
see how the successive modifications of the anterior limbs of a supposed
prototype could possibly have been of any advantage But look at the
penguins of the Southern Ocean have not these birds their front limbs
in this precise intermediate state of neither true arms nor true
wings Yet these birds hold their place victoriously in the battle for
life for they exist in infinite numbers and of many kinds I do not
suppose that we here see the real transitional grades through which
the wings of birds have passed but what special difficulty is there in
believing that it might profit the modified descendants of the penguin
first to become enabled to flap along the surface of the sea like the
loggerheaded duck and ultimately to rise from its surface and glide
through the air

I will now give a few examples to illustrate the foregoing remarks and
to show how liable we are to error in supposing that whole groups of
species have suddenly been produced Even in so short an interval as
that between the first and second editions of Pictets great work on
Palaeontology published in 184446 and in 185357 the conclusions on
the first appearance and disappearance of several groups of animals
have been considerably modified and a third edition would require still
further changes I may recall the wellknown fact that in geological
treatises published not many years ago mammals were always spoken of
as having abruptly come in at the commencement of the tertiary series
And now one of the richest known accumulations of fossil mammals belongs
to the middle of the secondary series and true mammals have been
discovered in the new red sandstone at nearly the commencement of
this great series Cuvier used to urge that no monkey occurred in any
tertiary stratum but now extinct species have been discovered in India
South America and in Europe as far back as the miocene stage Had it
not been for the rare accident of the preservation of footsteps in
the new red sandstone of the United States who would have ventured to
suppose that no less than at least thirty different birdlike animals
some of gigantic size existed during that period Not a fragment of
bone has been discovered in these beds Not long ago palaeontologists
maintained that the whole class of birds came suddenly into existence
during the eocene period but now we know on the authority of Professor
Owen that a bird certainly lived during the deposition of the upper
greensand and still more recently that strange bird the Archeopteryx
with a long lizardlike tail bearing a pair of feathers on each joint
and with its wings furnished with two free claws has been discovered in
the oolitic slates of Solenhofen Hardly any recent discovery shows more
forcibly than this how little we as yet know of the former inhabitants
of the world

I may give another instance which from having passed under my own eyes
has much struck me In a memoir on Fossil Sessile Cirripedes I stated
that from the large number of existing and extinct tertiary species
from the extraordinary abundance of the individuals of many species
all over the world from the Arctic regions to the equator inhabiting
various zones of depths from the upper tidal limits to fifty fathoms
from the perfect manner in which specimens are preserved in the oldest
tertiary beds from the ease with which even a fragment of a valve
can be recognised from all these circumstances I inferred that had
sessile cirripedes existed during the secondary periods they would
certainly have been preserved and discovered and as not one species had
then been discovered in beds of this age I concluded that this great
group had been suddenly developed at the commencement of the tertiary
series This was a sore trouble to me adding as I then thought one
more instance of the abrupt appearance of a great group of species But
my work had hardly been published when a skilful palaeontologist M
Bosquet sent me a drawing of a perfect specimen of an unmistakable
sessile cirripede which he had himself extracted from the chalk of
Belgium And as if to make the case as striking as possible this
cirripede was a Chthamalus a very common large and ubiquitous genus
of which not one species has as yet been found even in any tertiary
stratum Still more recently a Pyrgoma a member of a distinct
subfamily of sessile cirripedes has been discovered by Mr Woodward in
the upper chalk so that we now have abundant evidence of the existence
of this group of animals during the secondary period

The case most frequently insisted on by palaeontologists of the
apparently sudden appearance of a whole group of species is that of the
teleostean fishes low down according to Agassiz in the Chalk period
This group includes the large majority of existing species But certain
Jurassic and Triassic forms are now commonly admitted to be teleostean
and even some palaeozoic forms have thus been classed by one high
authority If the teleosteans had really appeared suddenly in the
northern hemisphere at the commencement of the chalk formation the
fact would have been highly remarkable but it would not have formed an
insuperable difficulty unless it could likewise have been shown that at
the same period the species were suddenly and simultaneously developed
in other quarters of the world It is almost superfluous to remark
that hardly any fossilfish are known from south of the equator and
by running through Pictets Palaeontology it will be seen that very few
species are known from several formations in Europe Some few families
of fish now have a confined range the teleostean fishes might formerly
have had a similarly confined range and after having been largely
developed in some one sea have spread widely Nor have we any right to
suppose that the seas of the world have always been so freely open from
south to north as they are at present Even at this day if the Malay
Archipelago were converted into land the tropical parts of the Indian
Ocean would form a large and perfectly enclosed basin in which any
great group of marine animals might be multiplied and here they would
remain confined until some of the species became adapted to a cooler
climate and were enabled to double the southern capes of Africa or
Australia and thus reach other and distant seas

From these considerations from our ignorance of the geology of other
countries beyond the confines of Europe and the United States and
from the revolution in our palaeontological knowledge effected by the
discoveries of the last dozen years it seems to me to be about as rash
to dogmatize on the succession of organic forms throughout the world as
it would be for a naturalist to land for five minutes on a barren
point in Australia and then to discuss the number and range of its
productions

ON THE SUDDEN APPEARANCE OF GROUPS OF ALLIED SPECIES IN THE LOWEST KNOWN
FOSSILIFEROUS STRATA

There is another and allied difficulty which is much more serious I
allude to the manner in which species belonging to several of the main
divisions of the animal kingdom suddenly appear in the lowest known
fossiliferous rocks Most of the arguments which have convinced me that
all the existing species of the same group are descended from a single
progenitor apply with equal force to the earliest known species
For instance it cannot be doubted that all the Cambrian and Silurian
trilobites are descended from some one crustacean which must have lived
long before the Cambrian age and which probably differed greatly from
any known animal Some of the most ancient animals as the Nautilus
Lingula etc do not differ much from living species and it cannot on
our theory be supposed that these old species were the progenitors of
all the species belonging to the same groups which have subsequently
appeared for they are not in any degree intermediate in character

Consequently if the theory be true it is indisputable that before the
lowest Cambrian stratum was deposited long periods elapsed as long as
or probably far longer than the whole interval from the Cambrian age
to the present day and that during these vast periods the world swarmed
with living creatures Here we encounter a formidable objection for it
seems doubtful whether the earth in a fit state for the habitation of
living creatures has lasted long enough Sir W Thompson concludes that
the consolidation of the crust can hardly have occurred less than twenty
or more than four hundred million years ago but probably not less than
ninetyeight or more than two hundred million years These very wide
limits show how doubtful the data are and other elements may have
hereafter to be introduced into the problem Mr Croll estimates that
about sixty million years have elapsed since the Cambrian period
but this judging from the small amount of organic change since the
commencement of the Glacial epoch appears a very short time for the
many and great mutations of life which have certainly occurred since
the Cambrian formation and the previous one hundred and forty million
years can hardly be considered as sufficient for the development of the
varied forms of life which already existed during the Cambrian period
It is however probable as Sir William Thompson insists that the
world at a very early period was subjected to more rapid and violent
changes in its physical conditions than those now occurring and such
changes would have tended to induce changes at a corresponding rate in
the organisms which then existed

To the question why we do not find rich fossiliferous deposits belonging
to these assumed earliest periods prior to the Cambrian system I can
give no satisfactory answer Several eminent geologists with Sir R
Murchison at their head were until recently convinced that we beheld
in the organic remains of the lowest Silurian stratum the first dawn
of life Other highly competent judges as Lyell and E Forbes have
disputed this conclusion We should not forget that only a small portion
of the world is known with accuracy Not very long ago M Barrande
added another and lower stage abounding with new and peculiar species
beneath the then known Silurian system and now still lower down in the
Lower Cambrian formation Mr Hicks has found South Wales beds rich in
trilobites and containing various molluscs and annelids The presence
of phosphatic nodules and bituminous matter even in some of the
lowest azotic rocks probably indicates life at these periods and
the existence of the Eozoon in the Laurentian formation of Canada is
generally admitted There are three great series of strata beneath the
Silurian system in Canada in the lowest of which the Eozoon is found
Sir W Logan states that their united thickness may possibly far
surpass that of all the succeeding rocks from the base of the
palaeozoic series to the present time We are thus carried back to a
period so remote that the appearance of the socalled primordial
fauna of Barrande may by some be considered as a comparatively modern
event The Eozoon belongs to the most lowly organised of all classes of
animals but is highly organised for its class it existed in countless
numbers and as Dr Dawson has remarked certainly preyed on other
minute organic beings which must have lived in great numbers Thus the
words which I wrote in 1859 about the existence of living beings long
before the Cambrian period and which are almost the same with those
since used by Sir W Logan have proved true Nevertheless the
difficulty of assigning any good reason for the absence of vast piles
of strata rich in fossils beneath the Cambrian system is very great It
does not seem probable that the most ancient beds have been quite worn
away by denudation or that their fossils have been wholly obliterated
by metamorphic action for if this had been the case we should have
found only small remnants of the formations next succeeding them in
age and these would always have existed in a partially metamorphosed
condition But the descriptions which we possess of the Silurian
deposits over immense territories in Russia and in North America do not
support the view that the older a formation is the more invariably it
has suffered extreme denudation and metamorphism

The case at present must remain inexplicable and may be truly urged as
a valid argument against the views here entertained To show that it
may hereafter receive some explanation I will give the following
hypothesis From the nature of the organic remains which do not appear
to have inhabited profound depths in the several formations of Europe
and of the United States and from the amount of sediment miles in
thickness of which the formations are composed we may infer that from
first to last large islands or tracts of land whence the sediment was
derived occurred in the neighbourhood of the now existing continents
of Europe and North America This same view has since been maintained by
Agassiz and others But we do not know what was the state of things in
the intervals between the several successive formations whether Europe
and the United States during these intervals existed as dry land or as
a submarine surface near land on which sediment was not deposited or
as the bed of an open and unfathomable sea

Looking to the existing oceans which are thrice as extensive as the
land we see them studded with many islands but hardly one truly
oceanic island with the exception of New Zealand if this can be called
a truly oceanic island is as yet known to afford even a remnant of any
palaeozoic or secondary formation Hence we may perhaps infer that
during the palaeozoic and secondary periods neither continents nor
continental islands existed where our oceans now extend for had they
existed palaeozoic and secondary formations would in all probability
have been accumulated from sediment derived from their wear and tear
and would have been at least partially upheaved by the oscillations of
level which must have intervened during these enormously long periods
If then we may infer anything from these facts we may infer that
where our oceans now extend oceans have extended from the remotest
period of which we have any record and on the other hand that where
continents now exist large tracts of land have existed subjected no
doubt to great oscillations of level since the Cambrian period The
coloured map appended to my volume on Coral Reefs led me to conclude
that the great oceans are still mainly areas of subsidence the great
archipelagoes still areas of oscillations of level and the continents
areas of elevation But we have no reason to assume that things have
thus remained from the beginning of the world Our continents seem to
have been formed by a preponderance during many oscillations of
level of the force of elevation But may not the areas of preponderant
movement have changed in the lapse of ages At a period long antecedent
to the Cambrian epoch continents may have existed where oceans are
now spread out and clear and open oceans may have existed where our
continents now stand Nor should we be justified in assuming that if
for instance the bed of the Pacific Ocean were now converted into a
continent we should there find sedimentary formations in recognisable
condition older than the Cambrian strata supposing such to have been
formerly deposited for it might well happen that strata which had
subsided some miles nearer to the centre of the earth and which had
been pressed on by an enormous weight of superincumbent water might
have undergone far more metamorphic action than strata which have always
remained nearer to the surface The immense areas in some parts of the
world for instance in South America of naked metamorphic rocks which
must have been heated under great pressure have always seemed to me to
require some special explanation and we may perhaps believe that we see
in these large areas the many formations long anterior to the Cambrian
epoch in a completely metamorphosed and denuded condition

The several difficulties here discussed namely that though we find in
our geological formations many links between the species which now exist
and which formerly existed we do not find infinitely numerous fine
transitional forms closely joining them all together The sudden
manner in which several groups of species first appear in our European
formations the almost entire absence as at present known of
formations rich in fossils beneath the Cambrian strata are all
undoubtedly of the most serious nature We see this in the fact that
the most eminent palaeontologists namely Cuvier Agassiz Barrande
Pictet Falconer E Forbes etc and all our greatest geologists as
Lyell Murchison Sedgwick etc have unanimously often vehemently
maintained the immutability of species But Sir Charles Lyell now
gives the support of his high authority to the opposite side and most
geologists and palaeontologists are much shaken in their former belief
Those who believe that the geological record is in any degree perfect
will undoubtedly at once reject my theory For my part following out
Lyells metaphor I look at the geological record as a history of
the world imperfectly kept and written in a changing dialect Of this
history we possess the last volume alone relating only to two or three
countries Of this volume only here and there a short chapter has been
preserved and of each page only here and there a few lines Each
word of the slowlychanging language more or less different in the
successive chapters may represent the forms of life which are entombed
in our consecutive formations and which falsely appear to have been
abruptly introduced On this view the difficulties above discussed are
greatly diminished or even disappear




CHAPTER XI ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS

 On the slow and successive appearance of new species On their different
 rates of change Species once lost do not reappear Groups of species
 follow the same general rules in their appearance and disappearance as
 do single species On extinction On simultaneous changes in the forms
 of life throughout the world On the affinities of extinct species to
 each other and to living species On the state of development of
 ancient forms On the succession of the same types within the same
 areas Summary of preceding and present chapters


Let us now see whether the several facts and laws relating to the
geological succession of organic beings accord best with the common view
of the immutability of species or with that of their slow and gradual
modification through variation and natural selection

New species have appeared very slowly one after another both on the
land and in the waters Lyell has shown that it is hardly possible to
resist the evidence on this head in the case of the several tertiary
stages and every year tends to fill up the blanks between the stages
and to make the proportion between the lost and existing forms more
gradual In some of the most recent beds though undoubtedly of high
antiquity if measured by years only one or two species are extinct
and only one or two are new having appeared there for the first time
either locally or as far as we know on the face of the earth The
secondary formations are more broken but as Bronn has remarked
neither the appearance nor disappearance of the many species embedded in
each formation has been simultaneous

Species belonging to different genera and classes have not changed at
the same rate or in the same degree In the older tertiary beds a few
living shells may still be found in the midst of a multitude of extinct
forms Falconer has given a striking instance of a similar fact for an
existing crocodile is associated with many lost mammals and reptiles in
the subHimalayan deposits The Silurian Lingula differs but little from
the living species of this genus whereas most of the other Silurian
Molluscs and all the Crustaceans have changed greatly The productions
of the land seem to have changed at a quicker rate than those of the
sea of which a striking instance has been observed in Switzerland
There is some reason to believe that organisms high in the scale change
more quickly than those that are low though there are exceptions to
this rule The amount of organic change as Pictet has remarked is not
the same in each successive socalled formation Yet if we compare any
but the most closely related formations all the species will be found
to have undergone some change When a species has once disappeared
from the face of the earth we have no reason to believe that the same
identical form ever reappears The strongest apparent exception to this
latter rule is that of the socalled colonies of M Barrande which
intrude for a period in the midst of an older formation and then allow
the preexisting fauna to reappear but Lyells explanation namely
that it is a case of temporary migration from a distinct geographical
province seems satisfactory

These several facts accord well with our theory which includes no fixed
law of development causing all the inhabitants of an area to change
abruptly or simultaneously or to an equal degree The process of
modification must be slow and will generally affect only a few species
at the same time for the variability of each species is independent of
that of all others Whether such variations or individual differences as
may arise will be accumulated through natural selection in a greater
or less degree thus causing a greater or less amount of permanent
modification will depend on many complex contingencies on
the variations being of a beneficial nature on the freedom of
intercrossing on the slowly changing physical conditions of the
country on the immigration of new colonists and on the nature of the
other inhabitants with which the varying species come into competition
Hence it is by no means surprising that one species should retain the
same identical form much longer than others or if changing should
change in a less degree We find similar relations between the existing
inhabitants of distinct countries for instance the landshells and
coleopterous insects of Madeira have come to differ considerably from
their nearest allies on the continent of Europe whereas the marine
shells and birds have remained unaltered We can perhaps understand
the apparently quicker rate of change in terrestrial and in more highly
organised productions compared with marine and lower productions by
the more complex relations of the higher beings to their organic and
inorganic conditions of life as explained in a former chapter When
many of the inhabitants of any area have become modified and improved
we can understand on the principle of competition and from the
allimportant relations of organism to organism in the struggle for
life that any form which did not become in some degree modified and
improved would be liable to extermination Hence we see why all
the species in the same region do at last if we look to long enough
intervals of time become modified for otherwise they would become
extinct

In members of the same class the average amount of change during long
and equal periods of time may perhaps be nearly the same but as the
accumulation of enduring formations rich in fossils depends on great
masses of sediment being deposited on subsiding areas our formations
have been almost necessarily accumulated at wide and irregularly
intermittent intervals of time consequently the amount of organic
change exhibited by the fossils embedded in consecutive formations
is not equal Each formation on this view does not mark a new and
complete act of creation but only an occasional scene taken almost at
hazard in an ever slowly changing drama

We can clearly understand why a species when once lost should never
reappear even if the very same conditions of life organic and
inorganic should recur For though the offspring of one species might
be adapted and no doubt this has occurred in innumerable instances
to fill the place of another species in the economy of nature and
thus supplant it yet the two forms the old and the new would not be
identically the same for both would almost certainly inherit different
characters from their distinct progenitors and organisms already
differing would vary in a different manner For instance it is
possible if all our fantailpigeons were destroyed that fanciers might
make a new breed hardly distinguishable from the present breed but if
the parent rockpigeon were likewise destroyed and under nature we have
every reason to believe that parent forms are generally supplanted
and exterminated by their improved offspring it is incredible that a
fantail identical with the existing breed could be raised from any
other species of pigeon or even from any other well established race
of the domestic pigeon for the successive variations would almost
certainly be in some degree different and the newlyformed variety
would probably inherit from its progenitor some characteristic
differences

Groups of species that is genera and families follow the same general
rules in their appearance and disappearance as do single species
changing more or less quickly and in a greater or lesser degree A
group when it has once disappeared never reappears that is its
existence as long as it lasts is continuous I am aware that there
are some apparent exceptions to this rule but the exceptions are
surprisingly few so few that E Forbes Pictet and Woodward though
all strongly opposed to such views as I maintain admit its truth and
the rule strictly accords with the theory For all the species of
the same group however long it may have lasted are the modified
descendants one from the other and all from a common progenitor In
the genus Lingula for instance the species which have successively
appeared at all ages must have been connected by an unbroken series of
generations from the lowest Silurian stratum to the present day

We have seen in the last chapter that whole groups of species sometimes
falsely appear to have been abruptly developed and I have attempted
to give an explanation of this fact which if true would be fatal to my
views But such cases are certainly exceptional the general rule being
a gradual increase in number until the group reaches its maximum and
then sooner or later a gradual decrease If the number of the species
included within a genus or the number of the genera within a family be
represented by a vertical line of varying thickness ascending through
the successive geological formations in which the species are found
the line will sometimes falsely appear to begin at its lower end not in
a sharp point but abruptly it then gradually thickens upwards often
keeping of equal thickness for a space and ultimately thins out in the
upper beds marking the decrease and final extinction of the species
This gradual increase in number of the species of a group is strictly
conformable with the theory for the species of the same genus and the
genera of the same family can increase only slowly and progressively
the process of modification and the production of a number of allied
forms necessarily being a slow and gradual process one species first
giving rise to two or three varieties these being slowly converted
into species which in their turn produce by equally slow steps other
varieties and species and so on like the branching of a great tree
from a single stem till the group becomes large

ON EXTINCTION

We have as yet only spoken incidentally of the disappearance of species
and of groups of species On the theory of natural selection the
extinction of old forms and the production of new and improved forms are
intimately connected together The old notion of all the inhabitants of
the earth having been swept away by catastrophes at successive periods
is very generally given up even by those geologists as Elie de
Beaumont Murchison Barrande etc whose general views would naturally
lead them to this conclusion On the contrary we have every reason to
believe from the study of the tertiary formations that species and
groups of species gradually disappear one after another first from one
spot then from another and finally from the world In some few cases
however as by the breaking of an isthmus and the consequent irruption
of a multitude of new inhabitants into an adjoining sea or by the final
subsidence of an island the process of extinction may have been rapid
Both single species and whole groups of species last for very unequal
periods some groups as we have seen have endured from the earliest
known dawn of life to the present day some have disappeared before
the close of the palaeozoic period No fixed law seems to determine
the length of time during which any single species or any single genus
endures There is reason to believe that the extinction of a whole group
of species is generally a slower process than their production if their
appearance and disappearance be represented as before by a vertical
line of varying thickness the line is found to taper more gradually at
its upper end which marks the progress of extermination than at its
lower end which marks the first appearance and the early increase in
number of the species In some cases however the extermination of
whole groups as of ammonites towards the close of the secondary
period has been wonderfully sudden

The extinction of species has been involved in the most gratuitous
mystery Some authors have even supposed that as the individual has a
definite length of life so have species a definite duration No one can
have marvelled more than I have done at the extinction of species When
I found in La Plata the tooth of a horse embedded with the remains of
Mastodon Megatherium Toxodon and other extinct monsters which all
coexisted with still living shells at a very late geological period
I was filled with astonishment for seeing that the horse since its
introduction by the Spaniards into South America has run wild over the
whole country and has increased in numbers at an unparalleled rate I
asked myself what could so recently have exterminated the former horse
under conditions of life apparently so favourable But my astonishment
was groundless Professor Owen soon perceived that the tooth though
so like that of the existing horse belonged to an extinct species Had
this horse been still living but in some degree rare no naturalist
would have felt the least surprise at its rarity for rarity is the
attribute of a vast number of species of all classes in all countries
If we ask ourselves why this or that species is rare we answer that
something is unfavourable in its conditions of life but what that
something is we can hardly ever tell On the supposition of the fossil
horse still existing as a rare species we might have felt certain from
the analogy of all other mammals even of the slowbreeding elephant
and from the history of the naturalisation of the domestic horse in
South America that under more favourable conditions it would in a very
few years have stocked the whole continent But we could not have
told what the unfavourable conditions were which checked its increase
whether some one or several contingencies and at what period of the
horses life and in what degree they severally acted If the conditions
had gone on however slowly becoming less and less favourable we
assuredly should not have perceived the fact yet the fossil horse would
certainly have become rarer and rarer and finally extinct its place
being seized on by some more successful competitor

It is most difficult always to remember that the increase of every
living creature is constantly being checked by unperceived hostile
agencies and that these same unperceived agencies are amply sufficient
to cause rarity and finally extinction So little is this subject
understood that I have heard surprise repeatedly expressed at such
great monsters as the Mastodon and the more ancient Dinosaurians having
become extinct as if mere bodily strength gave victory in the battle of
life Mere size on the contrary would in some cases determine as has
been remarked by Owen quicker extermination from the greater amount
of requisite food Before man inhabited India or Africa some cause must
have checked the continued increase of the existing elephant A highly
capable judge Dr Falconer believes that it is chiefly insects which
from incessantly harassing and weakening the elephant in India check
its increase and this was Bruces conclusion with respect to
the African elephant in Abyssinia It is certain that insects and
bloodsucking bats determine the existence of the larger naturalised
quadrupeds in several parts of South America

We see in many cases in the more recent tertiary formations that rarity
precedes extinction and we know that this has been the progress of
events with those animals which have been exterminated either locally
or wholly through mans agency I may repeat what I published in 1845
namely that to admit that species generally become rare before they
become extinct to feel no surprise at the rarity of a species and yet
to marvel greatly when the species ceases to exist is much the same as
to admit that sickness in the individual is the forerunner of death to
feel no surprise at sickness but when the sick man dies to wonder and
to suspect that he died by some deed of violence

The theory of natural selection is grounded on the belief that each new
variety and ultimately each new species is produced and maintained by
having some advantage over those with which it comes into competition
and the consequent extinction of lessfavoured forms almost inevitably
follows It is the same with our domestic productions when a new and
slightly improved variety has been raised it at first supplants the
less improved varieties in the same neighbourhood when much improved it
is transported far and near like our shorthorn cattle and takes the
place of other breeds in other countries Thus the appearance of new
forms and the disappearance of old forms both those naturally and
artificially produced are bound together In flourishing groups the
number of new specific forms which have been produced within a given
time has at some periods probably been greater than the number of
the old specific forms which have been exterminated but we know that
species have not gone on indefinitely increasing at least during the
later geological epochs so that looking to later times we may believe
that the production of new forms has caused the extinction of about the
same number of old forms

The competition will generally be most severe as formerly explained
and illustrated by examples between the forms which are most like each
other in all respects Hence the improved and modified descendants of
a species will generally cause the extermination of the parentspecies
and if many new forms have been developed from any one species the
nearest allies of that species ie the species of the same genus will
be the most liable to extermination Thus as I believe a number of
new species descended from one species that is a new genus comes to
supplant an old genus belonging to the same family But it must often
have happened that a new species belonging to some one group has seized
on the place occupied by a species belonging to a distinct group and
thus have caused its extermination If many allied forms be developed
from the successful intruder many will have to yield their places
and it will generally be the allied forms which will suffer from some
inherited inferiority in common But whether it be species belonging
to the same or to a distinct class which have yielded their places to
other modified and improved species a few of the sufferers may often
be preserved for a long time from being fitted to some peculiar line of
life or from inhabiting some distant and isolated station where they
will have escaped severe competition For instance some species of
Trigonia a great genus of shells in the secondary formations survive
in the Australian seas and a few members of the great and almost
extinct group of Ganoid fishes still inhabit our fresh waters
Therefore the utter extinction of a group is generally as we have
seen a slower process than its production

With respect to the apparently sudden extermination of whole families or
orders as of Trilobites at the close of the palaeozoic period and of
Ammonites at the close of the secondary period we must remember what
has been already said on the probable wide intervals of time between our
consecutive formations and in these intervals there may have been
much slow extermination Moreover when by sudden immigration or by
unusually rapid development many species of a new group have taken
possession of an area many of the older species will have been
exterminated in a correspondingly rapid manner and the forms which thus
yield their places will commonly be allied for they will partake of the
same inferiority in common

Thus as it seems to me the manner in which single species and whole
groups of species become extinct accords well with the theory of natural
selection We need not marvel at extinction if we must marvel let it
be at our presumption in imagining for a moment that we understand
the many complex contingencies on which the existence of each species
depends If we forget for an instant that each species tends to increase
inordinately and that some check is always in action yet seldom
perceived by us the whole economy of nature will be utterly obscured
Whenever we can precisely say why this species is more abundant
in individuals than that why this species and not another can be
naturalised in a given country then and not until then we may justly
feel surprise why we cannot account for the extinction of any particular
species or group of species

ON THE FORMS OF LIFE CHANGING ALMOST SIMULTANEOUSLY THROUGHOUT THE
WORLD

Scarcely any palaeontological discovery is more striking than the fact
that the forms of life change almost simultaneously throughout the
world Thus our European Chalk formation can be recognised in many
distant regions under the most different climates where not a fragment
of the mineral chalk itself can be found namely in North America in
equatorial South America in Tierra del Fuego at the Cape of Good Hope
and in the peninsula of India For at these distant points the organic
remains in certain beds present an unmistakable resemblance to those
of the Chalk It is not that the same species are met with for in some
cases not one species is identically the same but they belong to
the same families genera and sections of genera and sometimes are
similarly characterised in such trifling points as mere superficial
sculpture Moreover other forms which are not found in the Chalk of
Europe but which occur in the formations either above or below occur
in the same order at these distant points of the world In the several
successive palaeozoic formations of Russia Western Europe and North
America a similar parallelism in the forms of life has been observed
by several authors so it is according to Lyell with the European and
North American tertiary deposits Even if the few fossil species which
are common to the Old and New Worlds were kept wholly out of view the
general parallelism in the successive forms of life in the palaeozoic
and tertiary stages would still be manifest and the several formations
could be easily correlated

These observations however relate to the marine inhabitants of the
world we have not sufficient data to judge whether the productions
of the land and of fresh water at distant points change in the same
parallel manner We may doubt whether they have thus changed if the
Megatherium Mylodon Macrauchenia and Toxodon had been brought
to Europe from La Plata without any information in regard to their
geological position no one would have suspected that they had
coexisted with seashells all still living but as these anomalous
monsters coexisted with the Mastodon and Horse it might at least
have been inferred that they had lived during one of the later tertiary
stages

When the marine forms of life are spoken of as having changed
simultaneously throughout the world it must not be supposed that this
expression relates to the same year or even to the same century or
even that it has a very strict geological sense for if all the marine
animals now living in Europe and all those that lived in Europe during
the pleistocene period a very remote period as measured by years
including the whole glacial epoch were compared with those now existing
in South America or in Australia the most skilful naturalist would
hardly be able to say whether the present or the pleistocene inhabitants
of Europe resembled most closely those of the southern hemisphere So
again several highly competent observers maintain that the existing
productions of the United States are more closely related to those which
lived in Europe during certain late tertiary stages than to the
present inhabitants of Europe and if this be so it is evident that
fossiliferous beds now deposited on the shores of North America would
hereafter be liable to be classed with somewhat older European beds
Nevertheless looking to a remotely future epoch there can be little
doubt that all the more modern MARINE formations namely the upper
pliocene the pleistocene and strictly modern beds of Europe North and
South America and Australia from containing fossil remains in some
degree allied and from not including those forms which are found
only in the older underlying deposits would be correctly ranked as
simultaneous in a geological sense

The fact of the forms of life changing simultaneously in the above large
sense at distant parts of the world has greatly struck those admirable
observers MM de Verneuil and dArchiac After referring to the
parallelism of the palaeozoic forms of life in various parts of Europe
they add If struck by this strange sequence we turn our attention to
North America and there discover a series of analogous phenomena
it will appear certain that all these modifications of species their
extinction and the introduction of new ones cannot be owing to mere
changes in marine currents or other causes more or less local and
temporary but depend on general laws which govern the whole animal
kingdom M Barrande has made forcible remarks to precisely the same
effect It is indeed quite futile to look to changes of currents
climate or other physical conditions as the cause of these great
mutations in the forms of life throughout the world under the most
different climates We must as Barrande has remarked look to some
special law We shall see this more clearly when we treat of the present
distribution of organic beings and find how slight is the relation
between the physical conditions of various countries and the nature of
their inhabitants

This great fact of the parallel succession of the forms of life
throughout the world is explicable on the theory of natural selection
New species are formed by having some advantage over older forms and
the forms which are already dominant or have some advantage over the
other forms in their own country give birth to the greatest number of
new varieties or incipient species We have distinct evidence on this
head in the plants which are dominant that is which are commonest and
most widely diffused producing the greatest number of new varieties
It is also natural that the dominant varying and farspreading species
which have already invaded to a certain extent the territories of
other species should be those which would have the best chance of
spreading still further and of giving rise in new countries to other
new varieties and species The process of diffusion would often be
very slow depending on climatal and geographical changes on strange
accidents and on the gradual acclimatization of new species to the
various climates through which they might have to pass but in the
course of time the dominant forms would generally succeed in spreading
and would ultimately prevail The diffusion would it is probable be
slower with the terrestrial inhabitants of distinct continents than with
the marine inhabitants of the continuous sea We might therefore expect
to find as we do find a less strict degree of parallelism in the
succession of the productions of the land than with those of the sea

Thus as it seems to me the parallel and taken in a large sense
simultaneous succession of the same forms of life throughout the world
accords well with the principle of new species having been formed by
dominant species spreading widely and varying the new species thus
produced being themselves dominant owing to their having had some
advantage over their already dominant parents as well as over other
species and again spreading varying and producing new forms The
old forms which are beaten and which yield their places to the new and
victorious forms will generally be allied in groups from inheriting
some inferiority in common and therefore as new and improved groups
spread throughout the world old groups disappear from the world and
the succession of forms everywhere tends to correspond both in their
first appearance and final disappearance

There is one other remark connected with this subject worth making I
have given my reasons for believing that most of our great formations
rich in fossils were deposited during periods of subsidence and that
blank intervals of vast duration as far as fossils are concerned
occurred during the periods when the bed of the sea was either
stationary or rising and likewise when sediment was not thrown down
quickly enough to embed and preserve organic remains During these
long and blank intervals I suppose that the inhabitants of each region
underwent a considerable amount of modification and extinction and
that there was much migration from other parts of the world As we have
reason to believe that large areas are affected by the same movement
it is probable that strictly contemporaneous formations have often been
accumulated over very wide spaces in the same quarter of the world
but we are very far from having any right to conclude that this has
invariably been the case and that large areas have invariably been
affected by the same movements When two formations have been deposited
in two regions during nearly but not exactly the same period
we should find in both from the causes explained in the foregoing
paragraphs the same general succession in the forms of life but the
species would not exactly correspond for there will have been a
little more time in the one region than in the other for modification
extinction and immigration

I suspect that cases of this nature occur in Europe Mr Prestwich in
his admirable Memoirs on the eocene deposits of England and France is
able to draw a close general parallelism between the successive stages
in the two countries but when he compares certain stages in England
with those in France although he finds in both a curious accordance in
the numbers of the species belonging to the same genera yet the species
themselves differ in a manner very difficult to account for considering
the proximity of the two areas unless indeed it be assumed that an
isthmus separated two seas inhabited by distinct but contemporaneous
faunas Lyell has made similar observations on some of the later
tertiary formations Barrande also shows that there is a striking
general parallelism in the successive Silurian deposits of Bohemia and
Scandinavia nevertheless he finds a surprising amount of difference in
the species If the several formations in these regions have not been
deposited during the same exact periods a formation in one region often
corresponding with a blank interval in the other and if in both regions
the species have gone on slowly changing during the accumulation of the
several formations and during the long intervals of time between them
in this case the several formations in the two regions could be arranged
in the same order in accordance with the general succession of the
forms of life and the order would falsely appear to be strictly
parallel nevertheless the species would not all be the same in the
apparently corresponding stages in the two regions

ON THE AFFINITIES OF EXTINCT SPECIES TO EACH OTHER AND TO LIVING FORMS

Let us now look to the mutual affinities of extinct and living species
All fall into a few grand classes and this fact is at once explained on
the principle of descent The more ancient any form is the more as a
general rule it differs from living forms But as Buckland long ago
remarked extinct species can all be classed either in still existing
groups or between them That the extinct forms of life help to fill
up the intervals between existing genera families and orders is
certainly true but as this statement has often been ignored or even
denied it may be well to make some remarks on this subject and to give
some instances If we confine our attention either to the living or to
the extinct species of the same class the series is far less perfect
than if we combine both into one general system In the writings of
Professor Owen we continually meet with the expression of generalised
forms as applied to extinct animals and in the writings of Agassiz of
prophetic or synthetic types and these terms imply that such forms
are in fact intermediate or connecting links Another distinguished
palaeontologist M Gaudry has shown in the most striking manner that
many of the fossil mammals discovered by him in Attica serve to break
down the intervals between existing genera Cuvier ranked the Ruminants
and Pachyderms as two of the most distinct orders of mammals but so
many fossil links have been disentombed that Owen has had to alter the
whole classification and has placed certain Pachyderms in the same
suborder with ruminants for example he dissolves by gradations the
apparently wide interval between the pig and the camel The Ungulata
or hoofed quadrupeds are now divided into the eventoed or oddtoed
divisions but the Macrauchenia of South America connects to a certain
extent these two grand divisions No one will deny that the Hipparion
is intermediate between the existing horse and certain other ungulate
forms What a wonderful connecting link in the chain of mammals is the
Typotherium from South America as the name given to it by Professor
Gervais expresses and which cannot be placed in any existing order The
Sirenia form a very distinct group of the mammals and one of the most
remarkable peculiarities in existing dugong and lamentin is the entire
absence of hind limbs without even a rudiment being left but the
extinct Halitherium had according to Professor Flower an ossified
thighbone articulated to a welldefined acetabulum in the pelvis and
it thus makes some approach to ordinary hoofed quadrupeds to which the
Sirenia are in other respects allied The cetaceans or whales are
widely different from all other mammals but the tertiary Zeuglodon and
Squalodon which have been placed by some naturalists in an order
by themselves are considered by Professor Huxley to be undoubtedly
cetaceans and to constitute connecting links with the aquatic
carnivora

Even the wide interval between birds and reptiles has been shown by
the naturalist just quoted to be partially bridged over in the
most unexpected manner on the one hand by the ostrich and extinct
Archeopteryx and on the other hand by the Compsognathus one of
the Dinosaurians that group which includes the most gigantic of all
terrestrial reptiles Turning to the Invertebrata Barrande asserts a
higher authority could not be named that he is every day taught that
although palaeozoic animals can certainly be classed under existing
groups yet that at this ancient period the groups were not so
distinctly separated from each other as they now are

Some writers have objected to any extinct species or group of species
being considered as intermediate between any two living species or
groups of species If by this term it is meant that an extinct form is
directly intermediate in all its characters between two living forms or
groups the objection is probably valid But in a natural classification
many fossil species certainly stand between living species and some
extinct genera between living genera even between genera belonging to
distinct families The most common case especially with respect to very
distinct groups such as fish and reptiles seems to be that supposing
them to be distinguished at the present day by a score of characters
the ancient members are separated by a somewhat lesser number of
characters so that the two groups formerly made a somewhat nearer
approach to each other than they now do

It is a common belief that the more ancient a form is by so much the
more it tends to connect by some of its characters groups now widely
separated from each other This remark no doubt must be restricted
to those groups which have undergone much change in the course of
geological ages and it would be difficult to prove the truth of
the proposition for every now and then even a living animal as the
Lepidosiren is discovered having affinities directed towards very
distinct groups Yet if we compare the older Reptiles and Batrachians
the older Fish the older Cephalopods and the eocene Mammals with the
recent members of the same classes we must admit that there is truth in
the remark

Let us see how far these several facts and inferences accord with the
theory of descent with modification As the subject is somewhat complex
I must request the reader to turn to the diagram in the fourth chapter
We may suppose that the numbered letters in italics represent genera
and the dotted lines diverging from them the species in each genus The
diagram is much too simple too few genera and too few species being
given but this is unimportant for us The horizontal lines may
represent successive geological formations and all the forms beneath
the uppermost line may be considered as extinct The three existing
genera a14 q14 p14 will form a small family b14 and f14 a closely
allied family or subfamily and o14 i14 m14 a third family These
three families together with the many extinct genera on the several
lines of descent diverging from the parent form A will form an order
for all will have inherited something in common from their ancient
progenitor On the principle of the continued tendency to divergence
of character which was formerly illustrated by this diagram the more
recent any form is the more it will generally differ from its ancient
progenitor Hence we can understand the rule that the most ancient
fossils differ most from existing forms We must not however assume
that divergence of character is a necessary contingency it depends
solely on the descendants from a species being thus enabled to seize
on many and different places in the economy of nature Therefore it is
quite possible as we have seen in the case of some Silurian forms
that a species might go on being slightly modified in relation to its
slightly altered conditions of life and yet retain throughout a vast
period the same general characteristics This is represented in the
diagram by the letter F14

All the many forms extinct and recent descended from A make as
before remarked one order and this order from the continued effects
of extinction and divergence of character has become divided into
several subfamilies and families some of which are supposed to have
perished at different periods and some to have endured to the present
day

By looking at the diagram we can see that if many of the extinct forms
supposed to be embedded in the successive formations were discovered
at several points low down in the series the three existing families on
the uppermost line would be rendered less distinct from each other If
for instance the genera a1 a5 a10 f8 m3 m6 m9 were disinterred
these three families would be so closely linked together that they
probably would have to be united into one great family in nearly the
same manner as has occurred with ruminants and certain pachyderms Yet
he who objected to consider as intermediate the extinct genera which
thus link together the living genera of three families would be partly
justified for they are intermediate not directly but only by a long
and circuitous course through many widely different forms If many
extinct forms were to be discovered above one of the middle horizontal
lines or geological formations for instance above No VI but none
from beneath this line then only two of the families those on the left
hand a14 etc and b14 etc would have to be united into one and
there would remain two families which would be less distinct from each
other than they were before the discovery of the fossils So again if
the three families formed of eight genera a14 to m14 on the uppermost
line be supposed to differ from each other by halfadozen important
characters then the families which existed at a period marked VI would
certainly have differed from each other by a less number of characters
for they would at this early stage of descent have diverged in a less
degree from their common progenitor Thus it comes that ancient and
extinct genera are often in a greater or less degree intermediate
in character between their modified descendants or between their
collateral relations

Under nature the process will be far more complicated than is
represented in the diagram for the groups will have been more numerous
they will have endured for extremely unequal lengths of time and will
have been modified in various degrees As we possess only the last
volume of the geological record and that in a very broken condition
we have no right to expect except in rare cases to fill up the wide
intervals in the natural system and thus to unite distinct families or
orders All that we have a right to expect is that those groups which
have within known geological periods undergone much modification
should in the older formations make some slight approach to each other
so that the older members should differ less from each other in some of
their characters than do the existing members of the same groups
and this by the concurrent evidence of our best palaeontologists is
frequently the case

Thus on the theory of descent with modification the main facts with
respect to the mutual affinities of the extinct forms of life to each
other and to living forms are explained in a satisfactory manner And
they are wholly inexplicable on any other view

On this same theory it is evident that the fauna during any one great
period in the earths history will be intermediate in general character
between that which preceded and that which succeeded it Thus the
species which lived at the sixth great stage of descent in the diagram
are the modified offspring of those which lived at the fifth stage and
are the parents of those which became still more modified at the
seventh stage hence they could hardly fail to be nearly intermediate in
character between the forms of life above and below We must however
allow for the entire extinction of some preceding forms and in any one
region for the immigration of new forms from other regions and for a
large amount of modification during the long and blank intervals between
the successive formations Subject to these allowances the fauna of
each geological period undoubtedly is intermediate in character between
the preceding and succeeding faunas I need give only one instance
namely the manner in which the fossils of the Devonian system
when this system was first discovered were at once recognised by
palaeontologists as intermediate in character between those of the
overlying carboniferous and underlying Silurian systems But each fauna
is not necessarily exactly intermediate as unequal intervals of time
have elapsed between consecutive formations

It is no real objection to the truth of the statement that the fauna of
each period as a whole is nearly intermediate in character between the
preceding and succeeding faunas that certain genera offer exceptions
to the rule For instance the species of mastodons and elephants when
arranged by Dr Falconer in two series in the first place according
to their mutual affinities and in the second place according to their
periods of existence do not accord in arrangement The species extreme
in character are not the oldest or the most recent nor are those which
are intermediate in character intermediate in age But supposing for
an instant in this and other such cases that the record of the first
appearance and disappearance of the species was complete which is far
from the case we have no reason to believe that forms successively
produced necessarily endure for corresponding lengths of time A very
ancient form may occasionally have lasted much longer than a form
elsewhere subsequently produced especially in the case of terrestrial
productions inhabiting separated districts To compare small things with
great if the principal living and extinct races of the domestic pigeon
were arranged in serial affinity this arrangement would not closely
accord with the order in time of their production and even less with
the order of their disappearance for the parent rockpigeon still
lives and many varieties between the rockpigeon and the carrier
have become extinct and carriers which are extreme in the important
character of length of beak originated earlier than shortbeaked
tumblers which are at the opposite end of the series in this respect

Closely connected with the statement that the organic remains from an
intermediate formation are in some degree intermediate in character
is the fact insisted on by all palaeontologists that fossils from two
consecutive formations are far more closely related to each other than
are the fossils from two remote formations Pictet gives as a wellknown
instance the general resemblance of the organic remains from the
several stages of the Chalk formation though the species are distinct
in each stage This fact alone from its generality seems to have
shaken Professor Pictet in his belief in the immutability of species
He who is acquainted with the distribution of existing species over the
globe will not attempt to account for the close resemblance of distinct
species in closely consecutive formations by the physical conditions of
the ancient areas having remained nearly the same Let it be remembered
that the forms of life at least those inhabiting the sea have changed
almost simultaneously throughout the world and therefore under the most
different climates and conditions Consider the prodigious vicissitudes
of climate during the pleistocene period which includes the whole
glacial epoch and note how little the specific forms of the inhabitants
of the sea have been affected

On the theory of descent the full meaning of the fossil remains from
closely consecutive formations being closely related though ranked as
distinct species is obvious As the accumulation of each formation
has often been interrupted and as long blank intervals have intervened
between successive formations we ought not to expect to find as
I attempted to show in the last chapter in any one or in any two
formations all the intermediate varieties between the species which
appeared at the commencement and close of these periods but we ought
to find after intervals very long as measured by years but only
moderately long as measured geologically closely allied forms or as
they have been called by some authors representative species and these
assuredly we do find We find in short such evidence of the slow and
scarcely sensible mutations of specific forms as we have the right to
expect

ON THE STATE OF DEVELOPMENT OF ANCIENT COMPARED WITH LIVING FORMS

We have seen in the fourth chapter that the degree of differentiation
and specialisation of the parts in organic beings when arrived at
maturity is the best standard as yet suggested of their degree of
perfection or highness We have also seen that as the specialisation of
parts is an advantage to each being so natural selection will tend to
render the organisation of each being more specialised and perfect
and in this sense higher not but that it may leave many creatures with
simple and unimproved structures fitted for simple conditions of life
and in some cases will even degrade or simplify the organisation yet
leaving such degraded beings better fitted for their new walks of life
In another and more general manner new species become superior to their
predecessors for they have to beat in the struggle for life all
the older forms with which they come into close competition We may
therefore conclude that if under a nearly similar climate the eocene
inhabitants of the world could be put into competition with the existing
inhabitants the former would be beaten and exterminated by the
latter as would the secondary by the eocene and the palaeozoic by
the secondary forms So that by this fundamental test of victory in the
battle for life as well as by the standard of the specialisation of
organs modern forms ought on the theory of natural selection to
stand higher than ancient forms Is this the case A large majority of
palaeontologists would answer in the affirmative and it seems that this
answer must be admitted as true though difficult of proof

It is no valid objection to this conclusion that certain Brachiopods
have been but slightly modified from an extremely remote geological
epoch and that certain land and freshwater shells have remained nearly
the same from the time when as far as is known they first appeared
It is not an insuperable difficulty that Foraminifera have not as
insisted on by Dr Carpenter progressed in organisation since even the
Laurentian epoch for some organisms would have to remain fitted for
simple conditions of life and what could be better fitted for this end
than these lowly organised Protozoa Such objections as the above
would be fatal to my view if it included advance in organisation as
a necessary contingent They would likewise be fatal if the above
Foraminifera for instance could be proved to have first come into
existence during the Laurentian epoch or the above Brachiopods during
the Cambrian formation for in this case there would not have been time
sufficient for the development of these organisms up to the standard
which they had then reached When advanced up to any given point there
is no necessity on the theory of natural selection for their further
continued process though they will during each successive age have to
be slightly modified so as to hold their places in relation to slight
changes in their conditions The foregoing objections hinge on the
question whether we really know how old the world is and at what period
the various forms of life first appeared and this may well be disputed

The problem whether organisation on the whole has advanced is in
many ways excessively intricate The geological record at all times
imperfect does not extend far enough back to show with unmistakable
clearness that within the known history of the world organisation has
largely advanced Even at the present day looking to members of the
same class naturalists are not unanimous which forms ought to be ranked
as highest thus some look at the selaceans or sharks from their
approach in some important points of structure to reptiles as the
highest fish others look at the teleosteans as the highest The ganoids
stand intermediate between the selaceans and teleosteans the latter
at the present day are largely preponderant in number but formerly
selaceans and ganoids alone existed and in this case according to
the standard of highness chosen so will it be said that fishes have
advanced or retrograded in organisation To attempt to compare members
of distinct types in the scale of highness seems hopeless who will
decide whether a cuttlefish be higher than a bee that insect which
the great Von Baer believed to be in fact more highly organised than a
fish although upon another type In the complex struggle for life it
is quite credible that crustaceans not very high in their own class
might beat cephalopods the highest molluscs and such crustaceans
though not highly developed would stand very high in the scale of
invertebrate animals if judged by the most decisive of all trials the
law of battle Beside these inherent difficulties in deciding which
forms are the most advanced in organisation we ought not solely to
compare the highest members of a class at any two periods though
undoubtedly this is one and perhaps the most important element in
striking a balance but we ought to compare all the members high
and low at two periods At an ancient epoch the highest and lowest
molluscoidal animals namely cephalopods and brachiopods swarmed in
numbers at the present time both groups are greatly reduced
while others intermediate in organisation have largely increased
consequently some naturalists maintain that molluscs were formerly more
highly developed than at present but a stronger case can be made out on
the opposite side by considering the vast reduction of brachiopods and
the fact that our existing cephalopods though few in number are more
highly organised than their ancient representatives We ought also to
compare the relative proportional numbers at any two periods of the
high and low classes throughout the world if for instance at the
present day fifty thousand kinds of vertebrate animals exist and if
we knew that at some former period only ten thousand kinds existed we
ought to look at this increase in number in the highest class which
implies a great displacement of lower forms as a decided advance in the
organisation of the world We thus see how hopelessly difficult it is to
compare with perfect fairness under such extremely complex relations
the standard of organisation of the imperfectlyknown faunas of
successive periods

We shall appreciate this difficulty more clearly by looking to certain
existing faunas and floras From the extraordinary manner in which
European productions have recently spread over New Zealand and have
seized on places which must have been previously occupied by the
indigenes we must believe that if all the animals and plants of Great
Britain were set free in New Zealand a multitude of British forms would
in the course of time become thoroughly naturalized there and would
exterminate many of the natives On the other hand from the fact that
hardly a single inhabitant of the southern hemisphere has become wild in
any part of Europe we may well doubt whether if all the productions
of New Zealand were set free in Great Britain any considerable number
would be enabled to seize on places now occupied by our native plants
and animals Under this point of view the productions of Great Britain
stand much higher in the scale than those of New Zealand Yet the
most skilful naturalist from an examination of the species of the two
countries could not have foreseen this result

Agassiz and several other highly competent judges insist that ancient
animals resemble to a certain extent the embryos of recent animals
belonging to the same classes and that the geological succession of
extinct forms is nearly parallel with the embryological development of
existing forms This view accords admirably well with our theory In a
future chapter I shall attempt to show that the adult differs from its
embryo owing to variations having supervened at a not early age and
having been inherited at a corresponding age This process whilst it
leaves the embryo almost unaltered continually adds in the course of
successive generations more and more difference to the adult Thus the
embryo comes to be left as a sort of picture preserved by nature of
the former and less modified condition of the species This view may be
true and yet may never be capable of proof Seeing for instance that
the oldest known mammals reptiles and fishes strictly belong to their
proper classes though some of these old forms are in a slight degree
less distinct from each other than are the typical members of the same
groups at the present day it would be vain to look for animals having
the common embryological character of the Vertebrata until beds rich
in fossils are discovered far beneath the lowest Cambrian strata a
discovery of which the chance is small

ON THE SUCCESSION OF THE SAME TYPES WITHIN THE SAME AREAS DURING THE
LATER TERTIARY PERIODS

Mr Clift many years ago showed that the fossil mammals from the
Australian caves were closely allied to the living marsupials of that
continent In South America a similar relationship is manifest even to
an uneducated eye in the gigantic pieces of armour like those of the
armadillo found in several parts of La Plata and Professor Owen has
shown in the most striking manner that most of the fossil mammals
buried there in such numbers are related to South American types This
relationship is even more clearly seen in the wonderful collection of
fossil bones made by MM Lund and Clausen in the caves of Brazil I was
so much impressed with these facts that I strongly insisted in 1839
and 1845 on this law of the succession of types on this wonderful
relationship in the same continent between the dead and the living
Professor Owen has subsequently extended the same generalisation to
the mammals of the Old World We see the same law in this authors
restorations of the extinct and gigantic birds of New Zealand We see
it also in the birds of the caves of Brazil Mr Woodward has shown that
the same law holds good with seashells but from the wide distribution
of most molluscs it is not well displayed by them Other cases could
be added as the relation between the extinct and living landshells of
Madeira and between the extinct and living brackish watershells of the
AraloCaspian Sea

Now what does this remarkable law of the succession of the same types
within the same areas mean He would be a bold man who after comparing
the present climate of Australia and of parts of South America under
the same latitude would attempt to account on the one hand through
dissimilar physical conditions for the dissimilarity of the inhabitants
of these two continents and on the other hand through similarity
of conditions for the uniformity of the same types in each continent
during the later tertiary periods Nor can it be pretended that it is
an immutable law that marsupials should have been chiefly or solely
produced in Australia or that Edentata and other American types should
have been solely produced in South America For we know that Europe in
ancient times was peopled by numerous marsupials and I have shown
in the publications above alluded to that in America the law of
distribution of terrestrial mammals was formerly different from what it
now is North America formerly partook strongly of the present character
of the southern half of the continent and the southern half was
formerly more closely allied than it is at present to the northern
half In a similar manner we know from Falconer and Cautleys
discoveries that Northern India was formerly more closely related in
its mammals to Africa than it is at the present time Analogous facts
could be given in relation to the distribution of marine animals

On the theory of descent with modification the great law of the long
enduring but not immutable succession of the same types within the
same areas is at once explained for the inhabitants of each quarter of
the world will obviously tend to leave in that quarter during the next
succeeding period of time closely allied though in some degree modified
descendants If the inhabitants of one continent formerly differed
greatly from those of another continent so will their modified
descendants still differ in nearly the same manner and degree But
after very long intervals of time and after great geographical changes
permitting much intermigration the feebler will yield to the more
dominant forms and there will be nothing immutable in the distribution
of organic beings

It may be asked in ridicule whether I suppose that the megatherium and
other allied huge monsters which formerly lived in South America have
left behind them the sloth armadillo and anteater as their degenerate
descendants This cannot for an instant be admitted These huge animals
have become wholly extinct and have left no progeny But in the caves
of Brazil there are many extinct species which are closely allied in
size and in all other characters to the species still living in South
America and some of these fossils may have been the actual progenitors
of the living species It must not be forgotten that on our theory all
the species of the same genus are the descendants of some one species
so that if six genera each having eight species be found in one
geological formation and in a succeeding formation there be six other
allied or representative genera each with the same number of species
then we may conclude that generally only one species of each of the
older genera has left modified descendants which constitute the new
genera containing the several species the other seven species of each
old genus having died out and left no progeny Or and this will be a
far commoner case two or three species in two or three alone of the six
older genera will be the parents of the new genera the other species
and the other old genera having become utterly extinct In failing
orders with the genera and species decreasing in numbers as is the case
with the Edentata of South America still fewer genera and species will
leave modified blooddescendants

SUMMARY OF THE PRECEDING AND PRESENT CHAPTERS

I have attempted to show that the geological record is extremely
imperfect that only a small portion of the globe has been geologically
explored with care that only certain classes of organic beings have
been largely preserved in a fossil state that the number both of
specimens and of species preserved in our museums is absolutely as
nothing compared with the number of generations which must have passed
away even during a single formation that owing to subsidence being
almost necessary for the accumulation of deposits rich in fossil species
of many kinds and thick enough to outlast future degradation great
intervals of time must have elapsed between most of our successive
formations that there has probably been more extinction during
the periods of subsidence and more variation during the periods
of elevation and during the latter the record will have been least
perfectly kept that each single formation has not been continuously
deposited that the duration of each formation is probably short
compared with the average duration of specific forms that migration has
played an important part in the first appearance of new forms in any
one area and formation that widely ranging species are those which have
varied most frequently and have oftenest given rise to new species
that varieties have at first been local and lastly although each
species must have passed through numerous transitional stages it is
probable that the periods during which each underwent modification
though many and long as measured by years have been short in comparison
with the periods during which each remained in an unchanged condition
These causes taken conjointly will to a large extent explain
why though we do find many links we do not find interminable
varieties connecting together all extinct and existing forms by the
finest graduated steps It should also be constantly borne in mind that
any linking variety between two forms which might be found would be
ranked unless the whole chain could be perfectly restored as a new
and distinct species for it is not pretended that we have any sure
criterion by which species and varieties can be discriminated

He who rejects this view of the imperfection of the geological record
will rightly reject the whole theory For he may ask in vain where are
the numberless transitional links which must formerly have connected the
closely allied or representative species found in the successive stages
of the same great formation He may disbelieve in the immense intervals
of time which must have elapsed between our consecutive formations
he may overlook how important a part migration has played when the
formations of any one great region as those of Europe are considered
he may urge the apparent but often falsely apparent sudden coming in
of whole groups of species He may ask where are the remains of those
infinitely numerous organisms which must have existed long before the
Cambrian system was deposited We now know that at least one animal did
then exist but I can answer this last question only by supposing that
where our oceans now extend they have extended for an enormous period
and where our oscillating continents now stand they have stood since the
commencement of the Cambrian system but that long before that epoch
the world presented a widely different aspect and that the older
continents formed of formations older than any known to us exist now
only as remnants in a metamorphosed condition or lie still buried under
the ocean

Passing from these difficulties the other great leading facts
in palaeontology agree admirably with the theory of descent with
modification through variation and natural selection We can thus
understand how it is that new species come in slowly and successively
how species of different classes do not necessarily change together or
at the same rate or in the same degree yet in the long run that all
undergo modification to some extent The extinction of old forms is the
almost inevitable consequence of the production of new forms We can
understand why when a species has once disappeared it never reappears
Groups of species increase in numbers slowly and endure for unequal
periods of time for the process of modification is necessarily
slow and depends on many complex contingencies The dominant species
belonging to large and dominant groups tend to leave many modified
descendants which form new subgroups and groups As these are
formed the species of the less vigorous groups from their inferiority
inherited from a common progenitor tend to become extinct together and
to leave no modified offspring on the face of the earth But the
utter extinction of a whole group of species has sometimes been a slow
process from the survival of a few descendants lingering in protected
and isolated situations When a group has once wholly disappeared it
does not reappear for the link of generation has been broken

We can understand how it is that dominant forms which spread widely and
yield the greatest number of varieties tend to people the world with
allied but modified descendants and these will generally succeed
in displacing the groups which are their inferiors in the struggle for
existence Hence after long intervals of time the productions of the
world appear to have changed simultaneously

We can understand how it is that all the forms of life ancient and
recent make together a few grand classes We can understand from the
continued tendency to divergence of character why the more ancient
a form is the more it generally differs from those now living Why
ancient and extinct forms often tend to fill up gaps between existing
forms sometimes blending two groups previously classed as distinct
into one but more commonly bringing them only a little closer together
The more ancient a form is the more often it stands in some degree
intermediate between groups now distinct for the more ancient a form
is the more nearly it will be related to and consequently resemble
the common progenitor of groups since become widely divergent Extinct
forms are seldom directly intermediate between existing forms but are
intermediate only by a long and circuitous course through other extinct
and different forms We can clearly see why the organic remains of
closely consecutive formations are closely allied for they are closely
linked together by generation We can clearly see why the remains of an
intermediate formation are intermediate in character

The inhabitants of the world at each successive period in its history
have beaten their predecessors in the race for life and are in so
far higher in the scale and their structure has generally become more
specialised and this may account for the common belief held by so many
palaeontologists that organisation on the whole has progressed Extinct
and ancient animals resemble to a certain extent the embryos of the more
recent animals belonging to the same classes and this wonderful fact
receives a simple explanation according to our views The succession
of the same types of structure within the same areas during the later
geological periods ceases to be mysterious and is intelligible on the
principle of inheritance

If then the geological record be as imperfect as many believe and
it may at least be asserted that the record cannot be proved to be much
more perfect the main objections to the theory of natural selection are
greatly diminished or disappear On the other hand all the chief laws
of palaeontology plainly proclaim as it seems to me that species have
been produced by ordinary generation old forms having been supplanted
by new and improved forms of life the products of variation and the
survival of the fittest




CHAPTER XII GEOGRAPHICAL DISTRIBUTION

 Present distribution cannot be accounted for by differences in physical
 conditions Importance of barriers Affinity of the productions of the
 same continent Centres of creation Means of dispersal by changes of
 climate and of the level of the land and by occasional means Dispersal
 during the Glacial period Alternate Glacial periods in the North and
 South


In considering the distribution of organic beings over the face of
the globe the first great fact which strikes us is that neither the
similarity nor the dissimilarity of the inhabitants of various regions
can be wholly accounted for by climatal and other physical conditions
Of late almost every author who has studied the subject has come to
this conclusion The case of America alone would almost suffice to prove
its truth for if we exclude the arctic and northern temperate parts
all authors agree that one of the most fundamental divisions in
geographical distribution is that between the New and Old Worlds yet
if we travel over the vast American continent from the central parts of
the United States to its extreme southern point we meet with the most
diversified conditions humid districts arid deserts lofty mountains
grassy plains forests marshes lakes and great rivers under almost
every temperature There is hardly a climate or condition in the Old
World which cannot be paralleled in the New at least so closely as the
same species generally require No doubt small areas can be pointed out
in the Old World hotter than any in the New World but these are not
inhabited by a fauna different from that of the surrounding districts
for it is rare to find a group of organisms confined to a small area
of which the conditions are peculiar in only a slight degree
Notwithstanding this general parallelism in the conditions of Old and
New Worlds how widely different are their living productions 

In the southern hemisphere if we compare large tracts of land in
Australia South Africa and western South America between latitudes
25 and 35 degrees we shall find parts extremely similar in all their
conditions yet it would not be possible to point out three faunas
and floras more utterly dissimilar Or again we may compare the
productions of South America south of latitude 35 degrees with those
north of 25 degrees which consequently are separated by a space of
ten degrees of latitude and are exposed to considerably different
conditions yet they are incomparably more closely related to each other
than they are to the productions of Australia or Africa under nearly
the same climate Analogous facts could be given with respect to the
inhabitants of the sea

A second great fact which strikes us in our general review is that
barriers of any kind or obstacles to free migration are related in a
close and important manner to the differences between the productions of
various regions We see this in the great difference in nearly all the
terrestrial productions of the New and Old Worlds excepting in the
northern parts where the land almost joins and where under a slightly
different climate there might have been free migration for the northern
temperate forms as there now is for the strictly arctic productions
We see the same fact in the great difference between the inhabitants of
Australia Africa and South America under the same latitude for these
countries are almost as much isolated from each other as is possible On
each continent also we see the same fact for on the opposite sides of
lofty and continuous mountainranges and of great deserts and even of
large rivers we find different productions though as mountain chains
deserts etc are not as impassable or likely to have endured so long
as the oceans separating continents the differences are very inferior
in degree to those characteristic of distinct continents

Turning to the sea we find the same law The marine inhabitants of
the eastern and western shores of South America are very distinct with
extremely few shells crustacea or echinodermata in common but Dr
Gunther has recently shown that about thirty per cent of the fishes are
the same on the opposite sides of the isthmus of Panama and this fact
has led naturalists to believe that the isthmus was formerly open
Westward of the shores of America a wide space of open ocean extends
with not an island as a haltingplace for emigrants here we have a
barrier of another kind and as soon as this is passed we meet in the
eastern islands of the Pacific with another and totally distinct fauna
So that three marine faunas range northward and southward in parallel
lines not far from each other under corresponding climate but from
being separated from each other by impassable barriers either of
land or open sea they are almost wholly distinct On the other hand
proceeding still further westward from the eastern islands of the
tropical parts of the Pacific we encounter no impassable barriers and
we have innumerable islands as haltingplaces or continuous coasts
until after travelling over a hemisphere we come to the shores of
Africa and over this vast space we meet with no welldefined and
distinct marine faunas Although so few marine animals are common to the
abovenamed three approximate faunas of Eastern and Western America and
the eastern Pacific islands yet many fishes range from the Pacific into
the Indian Ocean and many shells are common to the eastern islands of
the Pacific and the eastern shores of Africa on almost exactly opposite
meridians of longitude

A third great fact partly included in the foregoing statement is the
affinity of the productions of the same continent or of the same sea
though the species themselves are distinct at different points and
stations It is a law of the widest generality and every continent
offers innumerable instances Nevertheless the naturalist in
travelling for instance from north to south never fails to be
struck by the manner in which successive groups of beings specifically
distinct though nearly related replace each other He hears from
closely allied yet distinct kinds of birds notes nearly similar and
sees their nests similarly constructed but not quite alike with eggs
coloured in nearly the same manner The plains near the Straits of
Magellan are inhabited by one species of Rhea American ostrich and
northward the plains of La Plata by another species of the same genus
and not by a true ostrich or emu like those inhabiting Africa and
Australia under the same latitude On these same plains of La Plata we
see the agouti and bizcacha animals having nearly the same habits as
our hares and rabbits and belonging to the same order of Rodents but
they plainly display an American type of structure We ascend the lofty
peaks of the Cordillera and we find an alpine species of bizcacha we
look to the waters and we do not find the beaver or muskrat but the
coypu and capybara rodents of the South American type Innumerable
other instances could be given If we look to the islands off the
American shore however much they may differ in geological structure
the inhabitants are essentially American though they may be all
peculiar species We may look back to past ages as shown in the last
chapter and we find American types then prevailing on the American
continent and in the American seas We see in these facts some deep
organic bond throughout space and time over the same areas of land and
water independently of physical conditions The naturalist must be dull
who is not led to inquire what this bond is

The bond is simply inheritance that cause which alone as far as we
positively know produces organisms quite like each other or as we
see in the case of varieties nearly alike The dissimilarity of the
inhabitants of different regions may be attributed to modification
through variation and natural selection and probably in a subordinate
degree to the definite influence of different physical conditions
The degrees of dissimilarity will depend on the migration of the more
dominant forms of life from one region into another having been more
or less effectually prevented at periods more or less remote on the
nature and number of the former immigrants and on the action of the
inhabitants on each other in leading to the preservation of different
modifications the relation of organism to organism in the struggle for
life being as I have already often remarked the most important of
all relations Thus the high importance of barriers comes into play by
checking migration as does time for the slow process of modification
through natural selection Widelyranging species abounding in
individuals which have already triumphed over many competitors in their
own widelyextended homes will have the best chance of seizing on new
places when they spread out into new countries In their new homes they
will be exposed to new conditions and will frequently undergo further
modification and improvement and thus they will become still further
victorious and will produce groups of modified descendants On this
principle of inheritance with modification we can understand how it is
that sections of genera whole genera and even families are confined
to the same areas as is so commonly and notoriously the case

There is no evidence as was remarked in the last chapter of the
existence of any law of necessary development As the variability of
each species is an independent property and will be taken advantage of
by natural selection only so far as it profits each individual in its
complex struggle for life so the amount of modification in different
species will be no uniform quantity If a number of species after
having long competed with each other in their old home were to migrate
in a body into a new and afterwards isolated country they would be
little liable to modification for neither migration nor isolation in
themselves effect anything These principles come into play only by
bringing organisms into new relations with each other and in a lesser
degree with the surrounding physical conditions As we have seen in the
last chapter that some forms have retained nearly the same character
from an enormously remote geological period so certain species have
migrated over vast spaces and have not become greatly or at all
modified

According to these views it is obvious that the several species of the
same genus though inhabiting the most distant quarters of the world
must originally have proceeded from the same source as they are
descended from the same progenitor In the case of those species which
have undergone during whole geological periods little modification
there is not much difficulty in believing that they have migrated from
the same region for during the vast geographical and climatical
changes which have supervened since ancient times almost any amount of
migration is possible But in many other cases in which we have
reason to believe that the species of a genus have been produced within
comparatively recent times there is great difficulty on this head It
is also obvious that the individuals of the same species though now
inhabiting distant and isolated regions must have proceeded from
one spot where their parents were first produced for as has been
explained it is incredible that individuals identically the same should
have been produced from parents specifically distinct

SINGLE CENTRES OF SUPPOSED CREATION

We are thus brought to the question which has been largely discussed by
naturalists namely whether species have been created at one or more
points of the earths surface Undoubtedly there are many cases of
extreme difficulty in understanding how the same species could possibly
have migrated from some one point to the several distant and isolated
points where now found Nevertheless the simplicity of the view that
each species was first produced within a single region captivates the
mind He who rejects it rejects the vera causa of ordinary generation
with subsequent migration and calls in the agency of a miracle It is
universally admitted that in most cases the area inhabited by a species
is continuous and that when a plant or animal inhabits two points so
distant from each other or with an interval of such a nature that the
space could not have been easily passed over by migration the fact
is given as something remarkable and exceptional The incapacity of
migrating across a wide sea is more clear in the case of terrestrial
mammals than perhaps with any other organic beings and accordingly
we find no inexplicable instances of the same mammals inhabiting distant
points of the world No geologist feels any difficulty in Great Britain
possessing the same quadrupeds with the rest of Europe for they were
no doubt once united But if the same species can be produced at two
separate points why do we not find a single mammal common to Europe and
Australia or South America The conditions of life are nearly the
same so that a multitude of European animals and plants have become
naturalised in America and Australia and some of the aboriginal plants
are identically the same at these distant points of the northern and
southern hemispheres The answer as I believe is that mammals have
not been able to migrate whereas some plants from their varied means
of dispersal have migrated across the wide and broken interspaces The
great and striking influence of barriers of all kinds is intelligible
only on the view that the great majority of species have been produced
on one side and have not been able to migrate to the opposite side
Some few families many subfamilies very many genera a still greater
number of sections of genera are confined to a single region and it
has been observed by several naturalists that the most natural genera
or those genera in which the species are most closely related to each
other are generally confined to the same country or if they have a
wide range that their range is continuous What a strange anomaly it
would be if a directly opposite rule were to prevail when we go down one
step lower in the series namely to the individuals of the same species
and these had not been at least at first confined to some one region 

Hence it seems to me as it has to many other naturalists that the
view of each species having been produced in one area alone and having
subsequently migrated from that area as far as its powers of migration
and subsistence under past and present conditions permitted is the most
probable Undoubtedly many cases occur in which we cannot explain how
the same species could have passed from one point to the other But the
geographical and climatical changes which have certainly occurred within
recent geological times must have rendered discontinuous the formerly
continuous range of many species So that we are reduced to consider
whether the exceptions to continuity of range are so numerous and of so
grave a nature that we ought to give up the belief rendered probable
by general considerations that each species has been produced within
one area and has migrated thence as far as it could It would be
hopelessly tedious to discuss all the exceptional cases of the same
species now living at distant and separated points nor do I for a
moment pretend that any explanation could be offered of many instances
But after some preliminary remarks I will discuss a few of the most
striking classes of facts namely the existence of the same species
on the summits of distant mountain ranges and at distant points in the
Arctic and Antarctic regions and secondly in the following chapter
the wide distribution of fresh water productions and thirdly the
occurrence of the same terrestrial species on islands and on the nearest
mainland though separated by hundreds of miles of open sea If the
existence of the same species at distant and isolated points of the
earths surface can in many instances be explained on the view of each
species having migrated from a single birthplace then considering our
ignorance with respect to former climatical and geographical changes
and to the various occasional means of transport the belief that a
single birthplace is the law seems to me incomparably the safest

In discussing this subject we shall be enabled at the same time to
consider a point equally important for us namely whether the several
species of a genus which must on our theory all be descended from a
common progenitor can have migrated undergoing modification during
their migration from some one area If when most of the species
inhabiting one region are different from those of another region though
closely allied to them it can be shown that migration from the one
region to the other has probably occurred at some former period our
general view will be much strengthened for the explanation is obvious
on the principle of descent with modification A volcanic island for
instance upheaved and formed at the distance of a few hundreds of miles
from a continent would probably receive from it in the course of time
a few colonists and their descendants though modified would still be
related by inheritance to the inhabitants of that continent Cases of
this nature are common and are as we shall hereafter see inexplicable
on the theory of independent creation This view of the relation of the
species of one region to those of another does not differ much from
that advanced by Mr Wallace who concludes that every species has come
into existence coincident both in space and time with a preexisting
closely allied species And it is now well known that he attributes
this coincidence to descent with modification

The question of single or multiple centres of creation differs from
another though allied question namely whether all the individuals
of the same species are descended from a single pair or single
hermaphrodite or whether as some authors suppose from many
individuals simultaneously created With organic beings which never
intercross if such exist each species must be descended from a
succession of modified varieties that have supplanted each other
but have never blended with other individuals or varieties of the same
species so that at each successive stage of modification all the
individuals of the same form will be descended from a single parent
But in the great majority of cases namely with all organisms which
habitually unite for each birth or which occasionally intercross the
individuals of the same species inhabiting the same area will be kept
nearly uniform by intercrossing so that many individuals will go on
simultaneously changing and the whole amount of modification at each
stage will not be due to descent from a single parent To illustrate
what I mean our English racehorses differ from the horses of every
other breed but they do not owe their difference and superiority to
descent from any single pair but to continued care in the selecting and
training of many individuals during each generation

Before discussing the three classes of facts which I have selected as
presenting the greatest amount of difficulty on the theory of single
centres of creation I must say a few words on the means of dispersal

MEANS OF DISPERSAL

Sir C Lyell and other authors have ably treated this subject I can
give here only the briefest abstract of the more important facts Change
of climate must have had a powerful influence on migration A region now
impassable to certain organisms from the nature of its climate might
have been a high road for migration when the climate was different I
shall however presently have to discuss this branch of the subject
in some detail Changes of level in the land must also have been highly
influential a narrow isthmus now separates two marine faunas submerge
it or let it formerly have been submerged and the two faunas will now
blend together or may formerly have blended Where the sea now extends
land may at a former period have connected islands or possibly even
continents together and thus have allowed terrestrial productions to
pass from one to the other No geologist disputes that great mutations
of level have occurred within the period of existing organisms Edward
Forbes insisted that all the islands in the Atlantic must have been
recently connected with Europe or Africa and Europe likewise with
America Other authors have thus hypothetically bridged over every
ocean and united almost every island with some mainland If indeed
the arguments used by Forbes are to be trusted it must be admitted that
scarcely a single island exists which has not recently been united to
some continent This view cuts the Gordian knot of the dispersal of the
same species to the most distant points and removes many a difficulty
but to the best of my judgment we are not authorized in admitting such
enormous geographical changes within the period of existing species It
seems to me that we have abundant evidence of great oscillations in the
level of the land or sea but not of such vast changes in the position
and extension of our continents as to have united them within the
recent period to each other and to the several intervening oceanic
islands I freely admit the former existence of many islands now buried
beneath the sea which may have served as halting places for plants and
for many animals during their migration In the coralproducing oceans
such sunken islands are now marked by rings of coral or atolls standing
over them Whenever it is fully admitted as it will some day be that
each species has proceeded from a single birthplace and when in
the course of time we know something definite about the means of
distribution we shall be enabled to speculate with security on the
former extension of the land But I do not believe that it will ever be
proved that within the recent period most of our continents which now
stand quite separate have been continuously or almost continuously
united with each other and with the many existing oceanic islands
Several facts in distribution such as the great difference in the
marine faunas on the opposite sides of almost every continent the close
relation of the tertiary inhabitants of several lands and even seas to
their present inhabitants the degree of affinity between the mammals
inhabiting islands with those of the nearest continent being in part
determined as we shall hereafter see by the depth of the intervening
ocean these and other such facts are opposed to the admission of such
prodigious geographical revolutions within the recent period as are
necessary on the view advanced by Forbes and admitted by his followers
The nature and relative proportions of the inhabitants of oceanic
islands are likewise opposed to the belief of their former continuity of
continents Nor does the almost universally volcanic composition of
such islands favour the admission that they are the wrecks of sunken
continents if they had originally existed as continental mountain
ranges some at least of the islands would have been formed like other
mountain summits of granite metamorphic schists old fossiliferous and
other rocks instead of consisting of mere piles of volcanic matter

I must now say a few words on what are called accidental means but
which more properly should be called occasional means of distribution
I shall here confine myself to plants In botanical works this or that
plant is often stated to be ill adapted for wide dissemination but the
greater or less facilities for transport across the sea may be said to
be almost wholly unknown Until I tried with Mr Berkeleys aid a
few experiments it was not even known how far seeds could resist
the injurious action of seawater To my surprise I found that out
of eightyseven kinds sixtyfour germinated after an immersion of
twentyeight days and a few survived an immersion of 137 days It
deserves notice that certain orders were far more injured than others
nine Leguminosae were tried and with one exception they resisted the
saltwater badly seven species of the allied orders Hydrophyllaceae
and Polemoniaceae were all killed by a months immersion For
convenience sake I chiefly tried small seeds without the capsules or
fruit and as all of these sank in a few days they could not have been
floated across wide spaces of the sea whether or not they were injured
by salt water Afterwards I tried some larger fruits capsules etc
and some of these floated for a long time It is well known what a
difference there is in the buoyancy of green and seasoned timber and it
occurred to me that floods would often wash into the sea dried plants or
branches with seedcapsules or fruit attached to them Hence I was led
to dry the stems and branches of ninetyfour plants with ripe fruit and
to place them on seawater The majority sank quickly but some which
whilst green floated for a very short time when dried floated much
longer for instance ripe hazelnuts sank immediately but when dried
they floated for ninety days and afterwards when planted germinated
an asparagus plant with ripe berries floated for twentythree days
when dried it floated for eightyfive days and the seeds afterwards
germinated the ripe seeds of Helosciadium sank in two days when
dried they floated for above ninety days and afterwards germinated
Altogether out of the ninetyfour dried plants eighteen floated for
above twentyeight days and some of the eighteen floated for a very
much longer period So that as 64/87 kinds of seeds germinated after an
immersion of twentyeight days and as 18/94 distinct species with ripe
fruit but not all the same species as in the foregoing experiment
floated after being dried for above twentyeight days we may
conclude as far as anything can be inferred from these scanty facts
that the seeds of 14/100 kinds of plants of any country might be floated
by seacurrents during twentyeight days and would retain their power
of germination In Johnstons Physical Atlas the average rate of the
several Atlantic currents is thirtythree miles per diem some currents
running at the rate of sixty miles per diem on this average the seeds
of 14/100 plants belonging to one country might be floated across 924
miles of sea to another country and when stranded if blown by an
inland gale to a favourable spot would germinate

Subsequently to my experiments M Martens tried similar ones but in a
much better manner for he placed the seeds in a box in the actual sea
so that they were alternately wet and exposed to the air like really
floating plants He tried ninetyeight seeds mostly different from
mine but he chose many large fruits and likewise seeds from plants
which live near the sea and this would have favoured both the average
length of their flotation and their resistance to the injurious action
of the saltwater On the other hand he did not previously dry the
plants or branches with the fruit and this as we have seen would have
caused some of them to have floated much longer The result was that
18/98 of his seeds of different kinds floated for fortytwo days and
were then capable of germination But I do not doubt that plants exposed
to the waves would float for a less time than those protected from
violent movement as in our experiments Therefore it would perhaps be
safer to assume that the seeds of about 10/100 plants of a flora after
having been dried could be floated across a space of sea 900 miles in
width and would then germinate The fact of the larger fruits often
floating longer than the small is interesting as plants with large
seeds or fruit which as Alph de Candolle has shown generally have
restricted ranges could hardly be transported by any other means

Seeds may be occasionally transported in another manner Drift timber
is thrown up on most islands even on those in the midst of the widest
oceans and the natives of the coral islands in the Pacific procure
stones for their tools solely from the roots of drifted trees these
stones being a valuable royal tax I find that when irregularly shaped
stones are embedded in the roots of trees small parcels of earth
are very frequently enclosed in their interstices and behind them so
perfectly that not a particle could be washed away during the longest
transport out of one small portion of earth thus COMPLETELY enclosed by
the roots of an oak about fifty years old three dicotyledonous plants
germinated I am certain of the accuracy of this observation Again
I can show that the carcasses of birds when floating on the sea
sometimes escape being immediately devoured and many kinds of seeds
in the crops of floating birds long retain their vitality peas and
vetches for instance are killed by even a few days immersion in
seawater but some taken out of the crop of a pigeon which had floated
on artificial seawater for thirty days to my surprise nearly all
germinated

Living birds can hardly fail to be highly effective agents in the
transportation of seeds I could give many facts showing how frequently
birds of many kinds are blown by gales to vast distances across the
ocean We may safely assume that under such circumstances their rate of
flight would often be thirtyfive miles an hour and some authors have
given a far higher estimate I have never seen an instance of nutritious
seeds passing through the intestines of a bird but hard seeds of fruit
pass uninjured through even the digestive organs of a turkey In the
course of two months I picked up in my garden twelve kinds of seeds
out of the excrement of small birds and these seemed perfect and some
of them which were tried germinated But the following fact is more
important the crops of birds do not secrete gastric juice and do not
as I know by trial injure in the least the germination of seeds
now after a bird has found and devoured a large supply of food it is
positively asserted that all the grains do not pass into the gizzard for
twelve or even eighteen hours A bird in this interval might easily be
blown to the distance of five hundred miles and hawks are known to look
out for tired birds and the contents of their torn crops might thus
readily get scattered Some hawks and owls bolt their prey whole and
after an interval of from twelve to twenty hours disgorge pellets
which as I know from experiments made in the Zoological Gardens
include seeds capable of germination Some seeds of the oat wheat
millet canary hemp clover and beet germinated after having been from
twelve to twentyone hours in the stomachs of different birds of prey
and two seeds of beet grew after having been thus retained for two days
and fourteen hours Freshwater fish I find eat seeds of many land and
water plants fish are frequently devoured by birds and thus the seeds
might be transported from place to place I forced many kinds of
seeds into the stomachs of dead fish and then gave their bodies to
fishingeagles storks and pelicans these birds after an interval of
many hours either rejected the seeds in pellets or passed them in their
excrement and several of these seeds retained the power of germination
Certain seeds however were always killed by this process

Locusts are sometimes blown to great distances from the land I myself
caught one 370 miles from the coast of Africa and have heard of others
caught at greater distances The Rev RT Lowe informed Sir C Lyell
that in November 1844 swarms of locusts visited the island of Madeira
They were in countless numbers as thick as the flakes of snow in the
heaviest snowstorm and extended upward as far as could be seen with a
telescope During two or three days they slowly careered round and round
in an immense ellipse at least five or six miles in diameter and at
night alighted on the taller trees which were completely coated with
them They then disappeared over the sea as suddenly as they had
appeared and have not since visited the island Now in parts of Natal
it is believed by some farmers though on insufficient evidence that
injurious seeds are introduced into their grassland in the dung left
by the great flights of locusts which often visit that country In
consequence of this belief Mr Weale sent me in a letter a small packet
of the dried pellets out of which I extracted under the microscope
several seeds and raised from them seven grass plants belonging to
two species of two genera Hence a swarm of locusts such as that which
visited Madeira might readily be the means of introducing several kinds
of plants into an island lying far from the mainland

Although the beaks and feet of birds are generally clean earth
sometimes adheres to them in one case I removed sixtyone grains and
in another case twentytwo grains of dry argillaceous earth from the
foot of a partridge and in the earth there was a pebble as large as the
seed of a vetch Here is a better case the leg of a woodcock was sent
to me by a friend with a little cake of dry earth attached to the
shank weighing only nine grains and this contained a seed of
the toadrush Juncus bufonius which germinated and flowered Mr
Swaysland of Brighton who during the last forty years has paid close
attention to our migratory birds informs me that he has often shot
wagtails Motacillae wheatears and whinchats Saxicolae on their
first arrival on our shores before they had alighted and he has
several times noticed little cakes of earth attached to their feet Many
facts could be given showing how generally soil is charged with seeds
For instance Professor Newton sent me the leg of a redlegged partridge
Caccabis rufa which had been wounded and could not fly with a ball of
hard earth adhering to it and weighing six and a half ounces The earth
had been kept for three years but when broken watered and placed
under a bell glass no less than eightytwo plants sprung from it these
consisted of twelve monocotyledons including the common oat and at
least one kind of grass and of seventy dicotyledons which consisted
judging from the young leaves of at least three distinct species
With such facts before us can we doubt that the many birds which are
annually blown by gales across great spaces of ocean and which
annually migrate for instance the millions of quails across the
Mediterranean must occasionally transport a few seeds embedded in
dirt adhering to their feet or beaks But I shall have to recur to this
subject

As icebergs are known to be sometimes loaded with earth and stones and
have even carried brushwood bones and the nest of a landbird it can
hardly be doubted that they must occasionally as suggested by Lyell
have transported seeds from one part to another of the arctic and
antarctic regions and during the Glacial period from one part of the
now temperate regions to another In the Azores from the large number
of plants common to Europe in comparison with the species on the other
islands of the Atlantic which stand nearer to the mainland and as
remarked by Mr HC Watson from their somewhat northern character in
comparison with the latitude I suspected that these islands had been
partly stocked by iceborne seeds during the Glacial epoch At my
request Sir C Lyell wrote to M Hartung to inquire whether he had
observed erratic boulders on these islands and he answered that he had
found large fragments of granite and other rocks which do not occur in
the archipelago Hence we may safely infer that icebergs formerly landed
their rocky burdens on the shores of these midocean islands and it
is at least possible that they may have brought thither the seeds of
northern plants

Considering that these several means of transport and that other means
which without doubt remain to be discovered have been in action year
after year for tens of thousands of years it would I think be a
marvellous fact if many plants had not thus become widely transported
These means of transport are sometimes called accidental but this is
not strictly correct the currents of the sea are not accidental nor
is the direction of prevalent gales of wind It should be observed
that scarcely any means of transport would carry seeds for very great
distances for seeds do not retain their vitality when exposed for a
great length of time to the action of sea water nor could they be long
carried in the crops or intestines of birds These means however would
suffice for occasional transport across tracts of sea some hundred
miles in breadth or from island to island or from a continent to a
neighbouring island but not from one distant continent to another The
floras of distant continents would not by such means become mingled
but would remain as distinct as they now are The currents from their
course would never bring seeds from North America to Britain though
they might and do bring seeds from the West Indies to our western
shores where if not killed by their very long immersion in salt
water they could not endure our climate Almost every year one or two
landbirds are blown across the whole Atlantic Ocean from North
America to the western shores of Ireland and England but seeds could be
transported by these rare wanderers only by one means namely by dirt
adhering to their feet or beaks which is in itself a rare accident
Even in this case how small would be the chance of a seed falling on
favourable soil and coming to maturity  But it would be a great error
to argue that because a wellstocked island like Great Britain has
not as far as is known and it would be very difficult to prove this
received within the last few centuries through occasional means
of transport immigrants from Europe or any other continent that a
poorlystocked island though standing more remote from the mainland
would not receive colonists by similar means Out of a hundred kinds of
seeds or animals transported to an island even if far less wellstocked
than Britain perhaps not more than one would be so well fitted to
its new home as to become naturalised But this is no valid argument
against what would be effected by occasional means of transport during
the long lapse of geological time whilst the island was being upheaved
and before it had become fully stocked with inhabitants On almost bare
land with few or no destructive insects or birds living there nearly
every seed which chanced to arrive if fitted for the climate would
germinate and survive

DISPERSAL DURING THE GLACIAL PERIOD

The identity of many plants and animals on mountainsummits separated
from each other by hundreds of miles of lowlands where Alpine species
could not possibly exist is one of the most striking cases known of the
same species living at distant points without the apparent possibility
of their having migrated from one point to the other It is indeed a
remarkable fact to see so many plants of the same species living on the
snowy regions of the Alps or Pyrenees and in the extreme northern parts
of Europe but it is far more remarkable that the plants on the White
Mountains in the United States of America are all the same with those
of Labrador and nearly all the same as we hear from Asa Gray with
those on the loftiest mountains of Europe Even as long ago as 1747
such facts led Gmelin to conclude that the same species must have
been independently created at many distinct points and we might have
remained in this same belief had not Agassiz and others called vivid
attention to the Glacial period which as we shall immediately see
affords a simple explanation of these facts We have evidence of almost
every conceivable kind organic and inorganic that within a very
recent geological period central Europe and North America suffered
under an Arctic climate The ruins of a house burnt by fire do not tell
their tale more plainly than do the mountains of Scotland and Wales
with their scored flanks polished surfaces and perched boulders of
the icy streams with which their valleys were lately filled So greatly
has the climate of Europe changed that in Northern Italy gigantic
moraines left by old glaciers are now clothed by the vine and maize
Throughout a large part of the United States erratic boulders and
scored rocks plainly reveal a former cold period

The former influence of the glacial climate on the distribution of the
inhabitants of Europe as explained by Edward Forbes is substantially
as follows But we shall follow the changes more readily by supposing
a new glacial period slowly to come on and then pass away as formerly
occurred As the cold came on and as each more southern zone became
fitted for the inhabitants of the north these would take the places of
the former inhabitants of the temperate regions The latter at the
same time would travel further and further southward unless they were
stopped by barriers in which case they would perish The mountains
would become covered with snow and ice and their former Alpine
inhabitants would descend to the plains By the time that the cold had
reached its maximum we should have an arctic fauna and flora covering
the central parts of Europe as far south as the Alps and Pyrenees
and even stretching into Spain The now temperate regions of the United
States would likewise be covered by arctic plants and animals and
these would be nearly the same with those of Europe for the present
circumpolar inhabitants which we suppose to have everywhere travelled
southward are remarkably uniform round the world

As the warmth returned the arctic forms would retreat northward
closely followed up in their retreat by the productions of the more
temperate regions And as the snow melted from the bases of the
mountains the arctic forms would seize on the cleared and thawed
ground always ascending as the warmth increased and the snow still
further disappeared higher and higher whilst their brethren were
pursuing their northern journey Hence when the warmth had fully
returned the same species which had lately lived together on the
European and North American lowlands would again be found in the arctic
regions of the Old and New Worlds and on many isolated mountainsummits
far distant from each other

Thus we can understand the identity of many plants at points so
immensely remote as the mountains of the United States and those of
Europe We can thus also understand the fact that the Alpine plants
of each mountainrange are more especially related to the arctic forms
living due north or nearly due north of them for the first migration
when the cold came on and the remigration on the returning warmth
would generally have been due south and north The Alpine plants for
example of Scotland as remarked by Mr HC Watson and those of
the Pyrenees as remarked by Ramond are more especially allied to the
plants of northern Scandinavia those of the United States to Labrador
those of the mountains of Siberia to the arctic regions of that country
These views grounded as they are on the perfectly wellascertained
occurrence of a former Glacial period seem to me to explain in so
satisfactory a manner the present distribution of the Alpine and Arctic
productions of Europe and America that when in other regions we find
the same species on distant mountainsummits we may almost conclude
without other evidence that a colder climate formerly permitted their
migration across the intervening lowlands now become too warm for their
existence

As the arctic forms moved first southward and afterwards backward to
the north in unison with the changing climate they will not have
been exposed during their long migrations to any great diversity of
temperature and as they all migrated in a body together their mutual
relations will not have been much disturbed Hence in accordance with
the principles inculcated in this volume these forms will not have
been liable to much modification But with the Alpine productions left
isolated from the moment of the returning warmth first at the bases
and ultimately on the summits of the mountains the case will have
been somewhat different for it is not likely that all the same arctic
species will have been left on mountain ranges far distant from each
other and have survived there ever since they will also in all
probability have become mingled with ancient Alpine species which must
have existed on the mountains before the commencement of the Glacial
epoch and which during the coldest period will have been temporarily
driven down to the plains they will also have been subsequently
exposed to somewhat different climatical influences Their mutual
relations will thus have been in some degree disturbed consequently
they will have been liable to modification and they have been modified
for if we compare the present Alpine plants and animals of the several
great European mountain ranges one with another though many of the
species remain identically the same some exist as varieties some as
doubtful forms or subspecies and some as distinct yet closely allied
species representing each other on the several ranges

In the foregoing illustration I have assumed that at the commencement
of our imaginary Glacial period the arctic productions were as uniform
round the polar regions as they are at the present day But it is also
necessary to assume that many subarctic and some few temperate forms
were the same round the world for some of the species which now exist
on the lower mountain slopes and on the plains of North America and
Europe are the same and it may be asked how I account for this degree
of uniformity of the subarctic and temperate forms round the world
at the commencement of the real Glacial period At the present day the
subarctic and northern temperate productions of the Old and New Worlds
are separated from each other by the whole Atlantic Ocean and by the
northern part of the Pacific During the Glacial period when the
inhabitants of the Old and New Worlds lived further southwards than they
do at present they must have been still more completely separated from
each other by wider spaces of ocean so that it may well be asked
how the same species could then or previously have entered the two
continents The explanation I believe lies in the nature of the
climate before the commencement of the Glacial period At this the
newer Pliocene period the majority of the inhabitants of the world were
specifically the same as now and we have good reason to believe that
the climate was warmer than at the present day Hence we may suppose
that the organisms which now live under latitude 60 degrees lived
during the Pliocene period further north under the Polar Circle in
latitude 6667 degrees and that the present arctic productions then
lived on the broken land still nearer to the pole Now if we look at
a terrestrial globe we see under the Polar Circle that there is almost
continuous land from western Europe through Siberia to eastern America
And this continuity of the circumpolar land with the consequent freedom
under a more favourable climate for intermigration will account for the
supposed uniformity of the subarctic and temperate productions of the
Old and New Worlds at a period anterior to the Glacial epoch

Believing from reasons before alluded to that our continents have long
remained in nearly the same relative position though subjected to great
oscillations of level I am strongly inclined to extend the above view
and to infer that during some earlier and still warmer period such as
the older Pliocene period a large number of the same plants and animals
inhabited the almost continuous circumpolar land and that these plants
and animals both in the Old and New Worlds began slowly to migrate
southwards as the climate became less warm long before the commencement
of the Glacial period We now see as I believe their descendants
mostly in a modified condition in the central parts of Europe and the
United States On this view we can understand the relationship with very
little identity between the productions of North America and Europe a
relationship which is highly remarkable considering the distance of
the two areas and their separation by the whole Atlantic Ocean We can
further understand the singular fact remarked on by several observers
that the productions of Europe and America during the later tertiary
stages were more closely related to each other than they are at the
present time for during these warmer periods the northern parts of the
Old and New Worlds will have been almost continuously united by
land serving as a bridge since rendered impassable by cold for the
intermigration of their inhabitants

During the slowly decreasing warmth of the Pliocene period as soon as
the species in common which inhabited the New and Old Worlds migrated
south of the Polar Circle they will have been completely cut off from
each other This separation as far as the more temperate productions
are concerned must have taken place long ages ago As the plants and
animals migrated southward they will have become mingled in the one
great region with the native American productions and would have had to
compete with them and in the other great region with those of the
Old World Consequently we have here everything favourable for
much modification for far more modification than with the Alpine
productions left isolated within a much more recent period on the
several mountain ranges and on the arctic lands of Europe and North
America Hence it has come that when we compare the now living
productions of the temperate regions of the New and Old Worlds we find
very few identical species though Asa Gray has lately shown that more
plants are identical than was formerly supposed but we find in every
great class many forms which some naturalists rank as geographical
races and others as distinct species and a host of closely allied or
representative forms which are ranked by all naturalists as specifically
distinct

As on the land so in the waters of the sea a slow southern migration
of a marine fauna which during the Pliocene or even a somewhat earlier
period was nearly uniform along the continuous shores of the Polar
Circle will account on the theory of modification for many closely
allied forms now living in marine areas completely sundered Thus I
think we can understand the presence of some closely allied still
existing and extinct tertiary forms on the eastern and western shores
of temperate North America and the still more striking fact of many
closely allied crustaceans as described in Danas admirable work some
fish and other marine animals inhabiting the Mediterranean and the seas
of Japan these two areas being now completely separated by the breadth
of a whole continent and by wide spaces of ocean

These cases of close relationship in species either now or formerly
inhabiting the seas on the eastern and western shores of North America
the Mediterranean and Japan and the temperate lands of North America
and Europe are inexplicable on the theory of creation We cannot
maintain that such species have been created alike in correspondence
with the nearly similar physical conditions of the areas for if we
compare for instance certain parts of South America with parts of
South Africa or Australia we see countries closely similar in all their
physical conditions with their inhabitants utterly dissimilar

ALTERNATE GLACIAL PERIODS IN THE NORTH AND SOUTH

But we must return to our more immediate subject I am convinced that
Forbess view may be largely extended In Europe we meet with the
plainest evidence of the Glacial period from the western shores of
Britain to the Ural range and southward to the Pyrenees We may infer
from the frozen mammals and nature of the mountain vegetation that
Siberia was similarly affected In the Lebanon according to Dr Hooker
perpetual snow formerly covered the central axis and fed glaciers which
rolled 4000 feet down the valleys The same observer has recently found
great moraines at a low level on the Atlas range in North Africa Along
the Himalaya at points 900 miles apart glaciers have left the marks of
their former low descent and in Sikkim Dr Hooker saw maize growing
on ancient and gigantic moraines Southward of the Asiatic continent on
the opposite side of the equator we know from the excellent researches
of Dr J Haast and Dr Hector that in New Zealand immense glaciers
formerly descended to a low level and the same plants found by Dr
Hooker on widely separated mountains in this island tell the same story
of a former cold period From facts communicated to me by the Rev WB
Clarke it appears also that there are traces of former glacial action
on the mountains of the southeastern corner of Australia

Looking to America in the northern half iceborne fragments of rock
have been observed on the eastern side of the continent as far south as
latitude 36 and 37 degrees and on the shores of the Pacific where
the climate is now so different as far south as latitude 46 degrees
Erratic boulders have also been noticed on the Rocky Mountains In
the Cordillera of South America nearly under the equator glaciers once
extended far below their present level In central Chile I examined
a vast mound of detritus with great boulders crossing the Portillo
valley which there can hardly be a doubt once formed a huge moraine
and Mr D Forbes informs me that he found in various parts of the
Cordillera from latitude 13 to 30 degrees south at about the height of
12000 feet deeplyfurrowed rocks resembling those with which he was
familiar in Norway and likewise great masses of detritus including
grooved pebbles Along this whole space of the Cordillera true glaciers
do not now exist even at much more considerable heights Further
south on both sides of the continent from latitude 41 degrees to the
southernmost extremity we have the clearest evidence of former glacial
action in numerous immense boulders transported far from their parent
source

From these several facts namely from the glacial action having
extended all round the northern and southern hemispheres from
the period having been in a geological sense recent in both
hemispheres from its having lasted in both during a great length of
time as may be inferred from the amount of work effected and lastly
from glaciers having recently descended to a low level along the whole
line of the Cordillera it at one time appeared to me that we could not
avoid the conclusion that the temperature of the whole world had been
simultaneously lowered during the Glacial period But now Mr Croll
in a series of admirable memoirs has attempted to show that a glacial
condition of climate is the result of various physical causes brought
into operation by an increase in the eccentricity of the earths orbit
All these causes tend towards the same end but the most powerful
appears to be the indirect influence of the eccentricity of the orbit
upon oceanic currents According to Mr Croll cold periods regularly
recur every ten or fifteen thousand years and these at long intervals
are extremely severe owing to certain contingencies of which the most
important as Sir C Lyell has shown is the relative position of the
land and water Mr Croll believes that the last great glacial period
occurred about 240000 years ago and endured with slight alterations
of climate for about 160000 years With respect to more ancient
glacial periods several geologists are convinced from direct evidence
that such occurred during the miocene and eocene formations not to
mention still more ancient formations But the most important result for
us arrived at by Mr Croll is that whenever the northern hemisphere
passes through a cold period the temperature of the southern hemisphere
is actually raised with the winters rendered much milder chiefly
through changes in the direction of the ocean currents So conversely it
will be with the northern hemisphere while the southern passes through
a glacial period This conclusion throws so much light on geographical
distribution that I am strongly inclined to trust in it but I will
first give the facts which demand an explanation

In South America Dr Hooker has shown that besides many closely allied
species between forty and fifty of the flowering plants of Tierra del
Fuego forming no inconsiderable part of its scanty flora are common to
North America and Europe enormously remote as these areas in opposite
hemispheres are from each other On the lofty mountains of equatorial
America a host of peculiar species belonging to European genera occur
On the Organ Mountains of Brazil some few temperate European some
Antarctic and some Andean genera were found by Gardner which do not
exist in the low intervening hot countries On the Silla of Caraccas
the illustrious Humboldt long ago found species belonging to genera
characteristic of the Cordillera

In Africa several forms characteristic of Europe and some few
representatives of the flora of the Cape of Good Hope occur on the
mountains of Abyssinia At the Cape of Good Hope a very few European
species believed not to have been introduced by man and on the
mountains several representative European forms are found which have
not been discovered in the intertropical parts of Africa Dr Hooker has
also lately shown that several of the plants living on the upper parts
of the lofty island of Fernando Po and on the neighbouring Cameroon
Mountains in the Gulf of Guinea are closely related to those on the
mountains of Abyssinia and likewise to those of temperate Europe It
now also appears as I hear from Dr Hooker that some of these same
temperate plants have been discovered by the Rev RT Lowe on the
mountains of the Cape Verde Islands This extension of the same
temperate forms almost under the equator across the whole continent of
Africa and to the mountains of the Cape Verde archipelago is one of the
most astonishing facts ever recorded in the distribution of plants

On the Himalaya and on the isolated mountain ranges of the peninsula of
India on the heights of Ceylon and on the volcanic cones of Java many
plants occur either identically the same or representing each other
and at the same time representing plants of Europe not found in the
intervening hot lowlands A list of the genera of plants collected on
the loftier peaks of Java raises a picture of a collection made on
a hillock in Europe Still more striking is the fact that peculiar
Australian forms are represented by certain plants growing on the
summits of the mountains of Borneo Some of these Australian forms as
I hear from Dr Hooker extend along the heights of the peninsula of
Malacca and are thinly scattered on the one hand over India and on the
other hand as far north as Japan

On the southern mountains of Australia Dr F Muller has discovered
several European species other species not introduced by man occur
on the lowlands and a long list can be given as I am informed by
Dr Hooker of European genera found in Australia but not in the
intermediate torrid regions In the admirable Introduction to the Flora
of New Zealand by Dr Hooker analogous and striking facts are given
in regard to the plants of that large island Hence we see that certain
plants growing on the more lofty mountains of the tropics in all parts
of the world and on the temperate plains of the north and south are
either the same species or varieties of the same species It should
however be observed that these plants are not strictly arctic forms
for as Mr HC Watson has remarked in receding from polar toward
equatorial latitudes the Alpine or mountain flora really become less
and less Arctic Besides these identical and closely allied forms many
species inhabiting the same widely sundered areas belong to genera not
now found in the intermediate tropical lowlands

These brief remarks apply to plants alone but some few analogous facts
could be given in regard to terrestrial animals In marine productions
similar cases likewise occur as an example I may quote a statement
by the highest authority Prof Dana that it is certainly a wonderful
fact that New Zealand should have a closer resemblance in its crustacea
to Great Britain its antipode than to any other part of the world
Sir J Richardson also speaks of the reappearance on the shores of New
Zealand Tasmania etc of northern forms of fish Dr Hooker informs
me that twentyfive species of Algae are common to New Zealand and to
Europe but have not been found in the intermediate tropical seas

From the foregoing facts namely the presence of temperate forms
on the highlands across the whole of equatorial Africa and along the
Peninsula of India to Ceylon and the Malay Archipelago and in a less
wellmarked manner across the wide expanse of tropical South America it
appears almost certain that at some former period no doubt during
the most severe part of a Glacial period the lowlands of these great
continents were everywhere tenanted under the equator by a considerable
number of temperate forms At this period the equatorial climate at the
level of the sea was probably about the same with that now experienced
at the height of from five to six thousand feet under the same latitude
or perhaps even rather cooler During this the coldest period the
lowlands under the equator must have been clothed with a mingled
tropical and temperate vegetation like that described by Hooker as
growing luxuriantly at the height of from four to five thousand feet
on the lower slopes of the Himalaya but with perhaps a still greater
preponderance of temperate forms So again in the mountainous island of
Fernando Po in the Gulf of Guinea Mr Mann found temperate European
forms beginning to appear at the height of about five thousand feet On
the mountains of Panama at the height of only two thousand feet Dr
Seemann found the vegetation like that of Mexico with forms of the
torrid zone harmoniously blended with those of the temperate

Now let us see whether Mr Crolls conclusion that when the northern
hemisphere suffered from the extreme cold of the great Glacial period
the southern hemisphere was actually warmer throws any clear light on
the present apparently inexplicable distribution of various organisms
in the temperate parts of both hemispheres and on the mountains of the
tropics The Glacial period as measured by years must have been very
long and when we remember over what vast spaces some naturalised plants
and animals have spread within a few centuries this period will have
been ample for any amount of migration As the cold became more and more
intense we know that Arctic forms invaded the temperate regions and
from the facts just given there can hardly be a doubt that some of the
more vigorous dominant and widestspreading temperate forms invaded the
equatorial lowlands The inhabitants of these hot lowlands would at the
same time have migrated to the tropical and subtropical regions of the
south for the southern hemisphere was at this period warmer On the
decline of the Glacial period as both hemispheres gradually recovered
their former temperature the northern temperate forms living on the
lowlands under the equator would have been driven to their former homes
or have been destroyed being replaced by the equatorial forms returning
from the south Some however of the northern temperate forms would
almost certainly have ascended any adjoining high land where if
sufficiently lofty they would have long survived like the Arctic
forms on the mountains of Europe They might have survived even if the
climate was not perfectly fitted for them for the change of temperature
must have been very slow and plants undoubtedly possess a certain
capacity for acclimatisation as shown by their transmitting to their
offspring different constitutional powers of resisting heat and cold

In the regular course of events the southern hemisphere would in
its turn be subjected to a severe Glacial period with the northern
hemisphere rendered warmer and then the southern temperate forms would
invade the equatorial lowlands The northern forms which had before been
left on the mountains would now descend and mingle with the southern
forms These latter when the warmth returned would return to their
former homes leaving some few species on the mountains and carrying
southward with them some of the northern temperate forms which had
descended from their mountain fastnesses Thus we should have some
few species identically the same in the northern and southern temperate
zones and on the mountains of the intermediate tropical regions But
the species left during a long time on these mountains or in opposite
hemispheres would have to compete with many new forms and would be
exposed to somewhat different physical conditions hence they would
be eminently liable to modification and would generally now exist as
varieties or as representative species and this is the case We must
also bear in mind the occurrence in both hemispheres of former Glacial
periods for these will account in accordance with the same principles
for the many quite distinct species inhabiting the same widely separated
areas and belonging to genera not now found in the intermediate torrid
zones

It is a remarkable fact strongly insisted on by Hooker in regard to
America and by Alph de Candolle in regard to Australia that many more
identical or slightly modified species have migrated from the north to
the south than in a reversed direction We see however a few southern
forms on the mountains of Borneo and Abyssinia I suspect that this
preponderant migration from the north to the south is due to the greater
extent of land in the north and to the northern forms having existed
in their own homes in greater numbers and having consequently been
advanced through natural selection and competition to a higher stage of
perfection or dominating power than the southern forms And thus when
the two sets became commingled in the equatorial regions during the
alternations of the Glacial periods the northern forms were the more
powerful and were able to hold their places on the mountains and
afterwards migrate southward with the southern forms but not so the
southern in regard to the northern forms In the same manner at the
present day we see that very many European productions cover the ground
in La Plata New Zealand and to a lesser degree in Australia and have
beaten the natives whereas extremely few southern forms have become
naturalised in any part of the northern hemisphere though hides wool
and other objects likely to carry seeds have been largely imported into
Europe during the last two or three centuries from La Plata and during
the last forty or fifty years from Australia The Neilgherrie Mountains
in India however offer a partial exception for here as I hear from
Dr Hooker Australian forms are rapidly sowing themselves and becoming
naturalised Before the last great Glacial period no doubt the
intertropical mountains were stocked with endemic Alpine forms
but these have almost everywhere yielded to the more dominant forms
generated in the larger areas and more efficient workshops of the north
In many islands the native productions are nearly equalled or even
outnumbered by those which have become naturalised and this is the
first stage towards their extinction Mountains are islands on the land
and their inhabitants have yielded to those produced within the larger
areas of the north just in the same way as the inhabitants of real
islands have everywhere yielded and are still yielding to continental
forms naturalised through mans agency

The same principles apply to the distribution of terrestrial animals and
of marine productions in the northern and southern temperate zones and
on the intertropical mountains When during the height of the Glacial
period the oceancurrents were widely different to what they now are
some of the inhabitants of the temperate seas might have reached
the equator of these a few would perhaps at once be able to migrate
southwards by keeping to the cooler currents while others might remain
and survive in the colder depths until the southern hemisphere was in
its turn subjected to a glacial climate and permitted their further
progress in nearly the same manner as according to Forbes isolated
spaces inhabited by Arctic productions exist to the present day in the
deeper parts of the northern temperate seas

I am far from supposing that all the difficulties in regard to the
distribution and affinities of the identical and allied species which
now live so widely separated in the north and south and sometimes on
the intermediate mountain ranges are removed on the views above given
The exact lines of migration cannot be indicated We cannot say why
certain species and not others have migrated why certain species
have been modified and have given rise to new forms while others have
remained unaltered We cannot hope to explain such facts until we can
say why one species and not another becomes naturalised by mans agency
in a foreign land why one species ranges twice or thrice as far and is
twice or thrice as common as another species within their own homes

Various special difficulties also remain to be solved for instance
the occurrence as shown by Dr Hooker of the same plants at points
so enormously remote as Kerguelen Land New Zealand and Fuegia but
icebergs as suggested by Lyell may have been concerned in their
dispersal The existence at these and other distant points of the
southern hemisphere of species which though distinct belong to
genera exclusively confined to the south is a more remarkable case
Some of these species are so distinct that we cannot suppose that there
has been time since the commencement of the last Glacial period for
their migration and subsequent modification to the necessary degree
The facts seem to indicate that distinct species belonging to the same
genera have migrated in radiating lines from a common centre and I am
inclined to look in the southern as in the northern hemisphere to a
former and warmer period before the commencement of the last Glacial
period when the Antarctic lands now covered with ice supported a
highly peculiar and isolated flora It may be suspected that before this
flora was exterminated during the last Glacial epoch a few forms
had been already widely dispersed to various points of the southern
hemisphere by occasional means of transport and by the aid as
haltingplaces of now sunken islands Thus the southern shores of
America Australia and New Zealand may have become slightly tinted by
the same peculiar forms of life

Sir C Lyell in a striking passage has speculated in language almost
identical with mine on the effects of great alternations of climate
throughout the world on geographical distribution And we have now seen
that Mr Crolls conclusion that successive Glacial periods in the one
hemisphere coincide with warmer periods in the opposite hemisphere
together with the admission of the slow modification of species
explains a multitude of facts in the distribution of the same and of the
allied forms of life in all parts of the globe The living waters have
flowed during one period from the north and during another from the
south and in both cases have reached the equator but the stream of
life has flowed with greater force from the north than in the opposite
direction and has consequently more freely inundated the south As the
tide leaves its drift in horizontal lines rising higher on the shores
where the tide rises highest so have the living waters left their
living drift on our mountain summits in a line gently rising from
the Arctic lowlands to a great latitude under the equator The various
beings thus left stranded may be compared with savage races of man
driven up and surviving in the mountain fastnesses of almost every
land which serves as a record full of interest to us of the former
inhabitants of the surrounding lowlands




CHAPTER XIII GEOGRAPHICAL DISTRIBUTION continued

 Distribution of freshwater productions On the inhabitants of oceanic
 islands Absence of Batrachians and of terrestrial Mammals On
 the relation of the inhabitants of islands to those of the nearest
 mainland On colonisation from the nearest source with subsequent
 modification Summary of the last and present chapters


FRESHWATER PRODUCTIONS

As lakes and riversystems are separated from each other by barriers of
land it might have been thought that freshwater productions would not
have ranged widely within the same country and as the sea is apparently
a still more formidable barrier that they would never have extended to
distant countries But the case is exactly the reverse Not only have
many freshwater species belonging to different classes an enormous
range but allied species prevail in a remarkable manner throughout
the world When first collecting in the fresh waters of Brazil I well
remember feeling much surprise at the similarity of the freshwater
insects shells etc and at the dissimilarity of the surrounding
terrestrial beings compared with those of Britain

But the wide ranging power of freshwater productions can I think
in most cases be explained by their having become fitted in a manner
highly useful to them for short and frequent migrations from pond
to pond or from stream to stream within their own countries and
liability to wide dispersal would follow from this capacity as an almost
necessary consequence We can here consider only a few cases of these
some of the most difficult to explain are presented by fish It was
formerly believed that the same freshwater species never existed on
two continents distant from each other But Dr Gunther has lately
shown that the Galaxias attenuatus inhabits Tasmania New Zealand the
Falkland Islands and the mainland of South America This is a wonderful
case and probably indicates dispersal from an Antarctic centre during a
former warm period This case however is rendered in some degree less
surprising by the species of this genus having the power of crossing by
some unknown means considerable spaces of open ocean thus there is
one species common to New Zealand and to the Auckland Islands though
separated by a distance of about 230 miles On the same continent
freshwater fish often range widely and as if capriciously for in two
adjoining river systems some of the species may be the same and some
wholly different

It is probable that they are occasionally transported by what may be
called accidental means Thus fishes still alive are not very rarely
dropped at distant points by whirlwinds and it is known that the ova
retain their vitality for a considerable time after removal from the
water Their dispersal may however be mainly attributed to changes in
the level of the land within the recent period causing rivers to flow
into each other Instances also could be given of this having occurred
during floods without any change of level The wide differences of the
fish on the opposite sides of most mountainranges which are continuous
and consequently must from an early period have completely prevented
the inosculation of the river systems on the two sides leads to the
same conclusion Some freshwater fish belong to very ancient forms
and in such cases there will have been ample time for great geographical
changes and consequently time and means for much migration Moreover
Dr Gunther has recently been led by several considerations to infer
that with fishes the same forms have a long endurance Saltwater
fish can with care be slowly accustomed to live in fresh water and
according to Valenciennes there is hardly a single group of which
all the members are confined to fresh water so that a marine species
belonging to a freshwater group might travel far along the shores
of the sea and could it is probable become adapted without much
difficulty to the fresh waters of a distant land

Some species of freshwater shells have very wide ranges and allied
species which on our theory are descended from a common parent and
must have proceeded from a single source prevail throughout the world
Their distribution at first perplexed me much as their ova are not
likely to be transported by birds and the ova as well as the adults
are immediately killed by seawater I could not even understand
how some naturalised species have spread rapidly throughout the same
country But two facts which I have observed and many others no
doubt will be discovered throw some light on this subject When ducks
suddenly emerge from a pond covered with duckweed I have twice seen
these little plants adhering to their backs and it has happened to me
in removing a little duckweed from one aquarium to another that I have
unintentionally stocked the one with freshwater shells from the other
But another agency is perhaps more effectual I suspended the feet of a
duck in an aquarium where many ova of freshwater shells were hatching
and I found that numbers of the extremely minute and justhatched shells
crawled on the feet and clung to them so firmly that when taken out
of the water they could not be jarred off though at a somewhat more
advanced age they would voluntarily drop off These justhatched
molluscs though aquatic in their nature survived on the ducks feet
in damp air from twelve to twenty hours and in this length of time
a duck or heron might fly at least six or seven hundred miles and
if blown across the sea to an oceanic island or to any other distant
point would be sure to alight on a pool or rivulet Sir Charles Lyell
informs me that a Dyticus has been caught with an Ancylus a freshwater
shell like a limpet firmly adhering to it and a waterbeetle of
the same family a Colymbetes once flew on board the Beagle when
fortyfive miles distant from the nearest land how much farther it
might have been blown by a favouring gale no one can tell

With respect to plants it has long been known what enormous ranges many
freshwater and even marshspecies have both over continents and
to the most remote oceanic islands This is strikingly illustrated
according to Alph de Candolle in those large groups of terrestrial
plants which have very few aquatic members for the latter seem
immediately to acquire as if in consequence a wide range I think
favourable means of dispersal explain this fact I have before mentioned
that earth occasionally adheres in some quantity to the feet and beaks
of birds Wading birds which frequent the muddy edges of ponds if
suddenly flushed would be the most likely to have muddy feet Birds
of this order wander more than those of any other and are occasionally
found on the most remote and barren islands of the open ocean they
would not be likely to alight on the surface of the sea so that any
dirt on their feet would not be washed off and when gaining the land
they would be sure to fly to their natural freshwater haunts I do not
believe that botanists are aware how charged the mud of ponds is with
seeds I have tried several little experiments but will here give only
the most striking case I took in