The Making of Species 



plumes growing from the back, it cannot be said 

 that the short tail of the vast majority of the 

 waders is due to the fact that these birds would 

 be at a disadvantage were their caudal feathers 

 long. 



ISOLATION 



Isolation is a most important factor in the 

 making of species. It is a factor to which 

 Darwin failed to attach sufficient importance, 

 and one which has been to a large extent 

 neglected by Wallaceians. 



We have seen how a species can be improved 

 or changed by natural selection. All those in- 

 dividuals which have varied in a favourable 

 direction have been preserved, and allowed to 

 leave behind them offspring that inherit their 

 peculiarities, while those which have not so 

 varied have perished without leaving behind 

 any descendants. Thus the nature of the species 

 has changed. The old type has given place to 

 a new one. Instead of species A, species B 

 exists. This is what Romanes has called mono- 

 typic evolution the transformation of one species 

 into another species. But any theory of the 

 origin of species must be able to answer the 

 question, Why have species multiplied ? How is 

 it that species A has given rise to species B, C, 

 and D, or, while itself continuing to exist, has 

 thrown off sister species B and C ? How is it 



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