166 Darwin, and after Darwin. 



general theory of descent. Starting from an erroneous 

 definition of the theorj' of natural selection as primarily 

 a theory of the origin of species, both friends and 

 foes oif the theory have concluded that the principle 

 of utility must by hypothesis be of universal occur- 

 rence so far as species are concerned ; whereas, if once 

 these naturalists were to perceive that their definition 

 of the theory is erroneous, they would likewise 

 perceive that their conclusion cannot follow deduc- 

 tively from the theory itself. If such a conclusion is 

 to be established at all. it can only be by other 

 and independent evidence of the inductive kind to 

 wit, by actual observation. 



Hence we see the importance of starting with an 

 accurate definition of the theory before proceeding 

 to examine the doctrine of utility as of universal 

 application to species a doctrine which, as just 

 stated, has been habitually and expressly deduced 

 from the theory. This doctrine occurs in two forms ; 

 or, more correctly, there are with reference to this 

 subject two distinct doctrines, which partly coincide 

 and partly exclude one another. First, it is held by 

 some naturalists that all species must necessarily owe 

 their origin to natural selection. And secondly, it is 

 held by other naturalists, that not only all species, 

 but likewise all specific characters must necessarily 

 do the same. Let us consider these two doctrines 

 separately. 



The first, and less extensive doctrine, rests on the 

 deduction that every species must owe its differentiation 

 as a species to the evolution of at least one adaptive 

 character, which is peculiar to that species. Although, 

 when thus originated, a species may come to present 



