156 THE LESSON OF EVOLUTION 



of divergence. Nevertheless it is true that natural 

 selection cannot make one species divide into two, 

 but actually prevents such a thing from coming 

 about. Natural selection hinders variation except 

 in that direction which is the one most profitable to 

 the whole of the individuals ; and, when the external 

 conditions remain the same for a long time, it en- 

 tirely destroys all new variations. 



Darwin, when discussing the question of diver- 

 gent evolution, says : "As has always been my 

 practice, let us seek light on this head from our 

 domestic productions." After stating that fanciers 

 of pigeons choose different characters, he asks, 

 "Can any analogous principle apply in nature?" and 

 he answers, " I believe it can and does apply most 

 efficiently, from the simple circumstance that the 

 more diversified the descendants from any one 

 species become in structure, constitution, and habits, 

 by so much will they be the better enabled to seize 

 on many diversified places in the polity of nature, 

 and thus increase in numbers." 40 



But Mr. Darwin here forgets that the pigeon 

 fancier not only selects his birds, but he isolates 

 them from each other ; while natural selection does 

 not isolate a few individuals from others of the same 

 group. In another place he truly says, " inter- 

 -crossing plays a very important part in nature, by 

 keeping individuals of the same species, or of the 

 same variety, true and uniform in character;" and 

 he evidently overlooked the fact that this will pre- 

 vent a species branching off and occupying diversified 



""Origin of Species," 1st edition, p. 112. 



