DIVERGENCE OF CHARACTER. 95 



We have seen that the species which are most numerous 

 in individuals have the best chance of producing favorable 

 variations within any given period. We have evidence of 

 this, in the facts stated in the second chapter, showing that 

 it is the common and diffused or dominant species which 

 offer the greatest number of recorded varieties. Hence, rare 

 species will be less quickly modified or improved within any 

 given period ; they will consequently be beaten in the race 

 for life by the modified and improved descendants of the 

 commoner species. 



From these several considerations I think it inevitably 

 follows, that as new species in the course of time are 

 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 related 

 genera — which, from having nearly the same structure, 

 constitution, and habits, generally come into the severest 

 competition with each other ; consequently, each new vari- 

 ety 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 extermina- 

 tion among our domesticated productions, through the 

 selection of improved forms by man. Many curious in- 

 stances 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 agricul- 

 tural 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 im- 

 portant 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. Nevertheless, 



