SELECTION 149 



Except in being less uniform than natural 

 species, in often differing more widely in a 

 single part, and in being fertile when crossed, 

 there are no well -marked distinctions between 

 our domestic races and the so-called true 

 species of a genus. The many breeds of 

 dogs and cattle may have arisen from more 

 than one species ; but probably those of horses 

 and fowls, and clearly those of rabbits, ducks 

 and pigeons, are each descended from a 

 single wild species. At least a score of varie- 

 ties of pigeon might be chosen which differ 

 so thoroughly, internally as well as externally, 

 that an ornithologist, treating them as wild 

 birds, would be compelled to grant them 

 specific, and even distinct generic rank. Yet, 

 since all these have indisputably arisen from 

 the wild rock-dove, it is clear that naturalists 

 who admit a unity to such domestic races, 

 which professed breeders have often laughed 

 to scorn, should in turn be cautious before 

 deriding the unity of wild ones. 



ARTIFICIAL SELECTION. How, then, have 

 domestic races been produced ? By external 

 conditions or habits alone ? One of their 

 tell-tale features is in exhibiting adaptations, 

 not to their own good, but to man's use or 

 fancy. We know that all the breeds were 

 not produced in their present state of per- 



