266 Darwin, and after Darwin. 



obsolete. But against these assumptions there lies 

 the following fact. The callosities in question are 

 not similarly distributed through all existing species 

 of the genus. The horse has them upon all 

 his four legs, while other species have them only 

 upon two. Therefore, if all specific characters are 

 necessarily due to natural selection, it is manifest 

 that these callosities are not now vestigial : on the 

 contrary, they must stiW be— or, at best, have recently 

 been — ^of so much importance to all existing species 

 of the genus, that not only is it a matter of selection- 

 value to all these species that they should possess 

 these callosities ; but it is even a matter of selection- 

 value to a horse that he should possess four of 

 them, while it is equally a matter of selection-value 

 to the ass that he should possess only two. Here, 

 it seems to me, we have once more the doctrine of 

 the necessary utility of specific characters reduced 

 to an ab.surdity ; while at the same time we display 

 the incoherency of the distinction, between specific 

 characters and generic characters in respect of this 

 doctrine. For the distinction in such a case amounts 

 to saying that a generic character, if evenly distributed 

 among all the species, need not be an adaptive 

 character ; whereas, if any one of the species presents 

 it in a slightly different form, the character must 

 be, on this account, necessarily adaptive. In other 

 words, the uniformity with which a generic character 

 occurs among the species of the genus is taken to 

 remove that character from the necessarily useful 

 class, while the absence of such uniformity is taken 

 as proof that the character must be placed within 

 the necessarily useful class. Which is surely no less 



