Appendix II. 309 



sumption — that all species have been originated by natural 

 selection; but why? Only because natural selection has origin- 

 ated t/iose particular adaptive features in virtue of which {by the 

 hypothesis) species exist as species. It is only in virtue of having 

 created these features that natural selection has created the 

 species presenting them — ^just as it has created genera, families, 

 orders, &c., in virtue of other adaptive features extending through 

 progressively wider areas of taxonomic division. Everywhere 

 and equally this principle has been " primarily " engaged in the 

 evolution of adaptations, and if one result of its work has 

 been that of enabling the systematist to trace lines of genetic 

 descent under his divisions of species, genera, and the rest, 

 such a result is but "secondary" or "incidental." 



In short, it is ^'■primarily" a theory of adaptations wher- 

 ever these occur, and only becomes ^^ also'^ or ^^ incidentally^' 

 a theory of species in cases where adaptations happen to be 

 restricted in their occurrence to organic types of a certain order 

 of taxonomic division. 



II. Hitherto, for the sake of argument, I have conceded 

 that, in the words of my critic, " it is a necessary consequence 

 of the theory of selection that every species must have some 

 one or more structural or functional peculiarities " of an 

 adaptive kind. But now I will endeavour to show that this 

 statement does not " follow as a necessary consequence " 

 from "the theory o( selection." 



Most obviously "it follows" from the theory of selection that 

 " every variety which is selected into a species is favoured and 

 preserved in consequence of being, in some one or more 

 respects, better adapted to its surroundings than its rivals." 

 This, in fact, is no more than a re-statement of the theory 

 itself. But it does not follow that " every species which exists, 

 exists in virtue of adaptation" peculiar to that species; i.e. 

 that every species which exists, exists in vittue of having 

 been ^^ selected." This may or may not be true as a matter 

 of fact : as a matter of logic, the inference is not deducible 

 from the selection theory. Every variety which is ^'■selected 

 into" a species must, indeed, present some such peculiar 

 advantage ; but this is by no means equivalent to saying, "in 

 other words," that every variety which becomes a species 



