The Making of Species 



"It does not seem possible to maintain the 

 contention that these various species are the 

 products of natural selection, for that would 

 mean if the black of the head of the Punjab 

 species extended further into the neck the bird 

 could not live in that country." 



Thus, natural selection clearly is unable to 

 explain some cases of divergence of character 

 due to geographical isolation. 



There remains the third explanation, that the 

 divergence is the result of the simple fact of 

 isolation. 



We have already shown how insuperable are 

 the objections to the view held by Romanes and 

 Gulick. 



It seems to us that explanation must lie in the 

 fact that mutations occur every now and again in 

 some species. If two portions of a species are 

 separated and a mutation occurs in one portion 

 and not in the other, and if the mutating form 

 succeeds in supplanting the parent form in that 

 isolated portion of the species in which it has 

 appeared, we should have the phenomenon of 

 two races or species differing in appearance 

 although subjected to what appear to be identical 

 environment. 



This, of course, is pure conjecture. All that 

 can be said of it at present is that it is not 

 opposed to observed facts. That mutations do 

 occur must be admitted. At present we are 



380 



