36 THE THEORY OF EVOLUTION 



leads to a similar conclusion. Under the conditions 

 of domestication, these creatures have been so pro- 

 foundly modified that, in many instances, the orig- 

 inal, wild progenitor of the race or breed cannot be 

 determined. The various breeds of horses, cattle, 

 sheep, pigeons, fowls, not to mention the garden and 

 field-plants, differ among themselves far more than 

 do many wild species from each other. Were the 

 pointer, terrier and spaniel dogs, the fan-tail, pouter 

 and tumbler pigeons found in a state of nature, no 

 zoologist would hesitate for a moment to recognize 

 them as well-defined species, yet we know that all the 

 breeds of pigeons have been derived from a single 

 wild form. Dogs are all domesticated wolves, but 

 the history of the various breeds has not been pre- 

 served and it is not known whether all the familiar 

 races are descended from a single wild species or 

 from several, or what that wild progenitor or pro- 

 genitors were. All this diversity has been produced 

 by human agency, acting sometimes with intelligent 

 and conscious purpose, sometimes with no definite 

 end in view, by taking advantage of variability and 

 individual differences. If man can accomplish such 

 results in a relatively short time, it is difficult to see 

 why nature, with illimitable aeons at her disposal, 

 should not bring about correspondingly greater trans- 

 formations. The phenomena of domestication make 

 the dogma of the fixity and immutability of species 

 seem very ill-founded and improbable. This is a 

 very large subject and it has been necessary, on ac- 



