134 DIVBKGEjSTCE op character. [Chap. In- 



formed through natural selection, others will become 

 rarer and rarer, and finally extinct. The forms which 

 stand in closest competition with those undergoing 

 modification and improvement will naturally suffer 

 most. And we have seen in the chapter on the Struggle 

 for Existence that it is the most closely-allied forms, — 

 varieties of the same species, and species of the same 

 genus or of related genera, — which, from having nearly 

 the same structure, constitution, and habits, generally 

 come into the severest competition with each other; 

 consequently, each new variety or species, during the 

 progress of its formation, will generally press hardest on 

 its nearest kindred, and tend to exterminate them. We 

 see the same process of extermination amongst our do- 

 mesticated productions, through the selection of im- 

 proved forms by man. Many curious instances could 

 be given showing how quickly new breeds of cattle, 

 sheep, and other animals, and varieties of flowers, take 

 the place of older and inferior kinds. In Yorkshire, 

 it is historically known that the ancient black cattle 

 were displaced by the long-horns, and that these " were 

 swept away by the short-horns " (I quote the words of an 

 agricultural writer) "as if by some murderous pestilence." 



Divergence of Character. 



The principle, which I have designated by this term, 

 is of high importance, and explains, as I believe, several 

 important facts. In the first place, varieties, even 

 strongly-marked ones, though having somewhat of the 

 character of species — as is shown by the hopeless doubts 

 in many cases how to rank them — yet certainly differ 

 far less from each other than do good and distinct species. 



