1504 THE STORY OF THE UNIVERSE 



come rarer and rarer, and finally extinct. The forms 

 which stand in closest competition with those under- 

 going 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 spe- 

 cies of the same genus or of related genera which, 

 from having nearly the same structure, constitution, 

 and habits, generally come into the severest compe- 

 tition 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 extermination among our domesticated 

 productions, through the selection of improved forms 

 by man. Many curious instances could be given 

 snowing 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 his- 

 torically 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 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 of 

 how to rank them yet certainly differ far less from 

 each other than do good and distinct species. Never- 

 theless, according to my view, varieties are species 



