540 THE EVOLUTION OF LIFR 



most of the other attributes. If those members of the 

 species which have but ordinary shares of it, nevertheless 

 survive by virtue of other superiorities which they severally 

 possess; then it is not easy to see how this particular attri- 

 bute can be developed by natural selection in subsequent 

 generations. The probability seems rather to be that, by 

 gamogenesis, this extra endowment will, on the average, be 

 diminished in posterity — just serving in the long run to 

 make up for the deficient endowments of those whose special 

 powers lie in other directions; and so to keep up the normal 

 structure of the species. As fast as the number of bodily 

 and mental faculties increases, and as fast as maintenance of 

 life comes to depend less on the amount of any one and more 

 on the combined actions of all; so fast does the production 

 of specialities of character b}'' natural selection alone, become 

 difficult. Particularly does this seem to be so with a species 

 so multitudinous in its powers as mankind; and above all 

 does it seem to be so with such of the human powers as have 

 but minor shares in aiding the struggle for life — the aesthetic 

 faculties, for example. 



It by no means follows, however, that in cases of this kind, 

 and cases of the preceding kind, natural selection plays no 

 part. Wherever it is not the chief agent in working organic 

 changes, it is still, very generally, a secondary agent. The 

 survival of the fittest must nearly always further the produc- 

 tion of modifications which produce fitness, whether they be 

 incidental modifications, or modifications caused by direct 

 adaptation. Evidently, those individuals whose constitu- 

 tions have facilitated the production in them of any struc- 

 tural change consequent on any functional change demanded 

 by some new external condition, will be the individuals most 

 likely to live and to leave descendants. There must be a 

 natural selection of functionally-acquired peculiarities, as 

 well as of spontaneously-acquired peculiarities; and hence 

 such structural changes in a species as result from changes of 

 habit necessitated by changed circumstances, natural selec- 

 tion will render more rapid than they would otherwise be. 



