Skip to content

Instantly share code, notes, and snippets.

@WinstonCampeau

WinstonCampeau/oos.txt

Last active Jul 12, 2019
Embed
What would you like to do?
Convert Origin of Species to Noise
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")
This file has been truncated, but you can view the full file.
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 th