Ruby Array include? vs index

gistfile1.txt

require 'benchmark'

total_times = 30000
items1 = []
items2 = []
items3 = []
Benchmark.bm do |x|
  
  x.report("include?") {
    total_times.times do |i|
      items1 << i if !items1.include?(i)
    end
    
    puts " #{items1.size}"
  }
  x.report("index") {
    total_times.times do |i|
      items2 << i if items2.index(i) == nil
    end
    
    puts " #{items2.size}"
  }
end

gistfile2.txt

       user     system      total        real
include? 30000
 18.460000   0.050000  18.510000 ( 18.587449)
index 30000
  2.940000   0.000000   2.940000 (  2.947624)

   user     system      total        real

include? 30000
30000
73.700000 0.040000 73.740000 ( 73.940654)
index 30000
58.830000 0.010000 58.840000 ( 59.140464)
好长时间啊,难道是我的电脑太次吗?

   user     system      total        real

include? 30000
16.080000 0.000000 16.080000 ( 16.135302)
index 30000
15.940000 0.000000 15.940000 ( 15.953061)
=> [ 16.080000 0.000000 16.080000 ( 16.135302)
, 15.940000 0.000000 15.940000 ( 15.953061)

什么情况, 为什么我这里 include? 和 index 相差不大.
我是 ruby 1.9.3

$ ruby -v
ruby 2.1.1p76 (2014-02-24 revision 45161) [x86_64-darwin13.0]

$ ruby -v
ruby 2.1.0p0 (2013-12-25 revision 44422) [x86_64-linux]

$ ruby test.rb
user system total real
include? 30000
21.650000 0.000000 21.650000 ( 21.662378)
index 30000
3.930000 0.000000 3.930000 ( 3.931389)