16 VAKIATION Chap. I. 



the same species, also, often have a somewhat monstrous 

 character; by which I mean, that, although differing 

 from each other, and from the other species of the same 

 genus, in several trifling respects, they often differ in an 

 extreme degree in some one part, both when compared 

 one with another, and more especially when compared 

 with all the species in nature to which they are nearest 

 allied. With these exceptions (and with that of the 

 perfect fertility of varieties when crossed, — a subject 

 hereafter to be discussed), domestic races of the same 

 species differ from each other in the same manner as, 

 only in most cases in a lesser degree than, do closely- 

 allied species of the same genus in a state of nature. I 

 think this must be admitted, when we find that there are 

 hardly any domestic races, either amongst animals or 

 plants, which have not been ranked by some competent 

 judges as mere varieties, and by other competent judges 

 as the descendants of aboriginally distinct species. If 

 any marked distinction existed between domestic races 

 and species, this source of doubt could not so perpetu- 

 ally recur. It has often been stated that domestic races 

 do not differ from each other in characters of generic 

 value. I think it could be shown that this statement is 

 hardly correct; but naturalists differ most widely in 

 determining what characters are of generic value ; all 

 such valuations being at present empirical. Moreover, 

 on the view of the origin of genera which I shall pre- 

 sently give, we have no right to expect often to meet 

 with generic differences in our domesticated productions. 

 When we attempt to estimate the amount of structural 

 difference between the domestic races of the same species, 

 we are soon involved in doubt, from not knowing whether 

 they have descended from one or several parent-species. 

 This point, if it could be cleared up, would be interest- 

 ing ; if, for instance, it could be shown that the grey- 



