HUMAN POPULATION IN THE FUTURE. 501 



§ 374. The proposition at which we have thus arrived, is 

 then, that excess of fertility, through the changes it is ever 

 working in Man's environment, is itself the cause of Man's 

 further evolution ; and the obvious corollary here to be 

 drawn, is, that Man's further evolutioD so brought about, 

 itself necessitates a decline in his fertility. 



That future progress of civilization which the never- 

 ceasing pressure of population must produce, will be ac 

 companied by an enhanced cost of Individuation, both in 

 structure and function ; and more especially in nervous 

 structure and function. The peaceful struggle for existence 

 in societies ever growing more crowded and more complicated, 

 must have for its concomitant an increase of the great nervous 

 centres in mass, in complexit}^, in activity. The larger body 

 of emotion needed as a fountain of energy for men who have 

 to hold their places and rear their families under the inten- 

 sifying competition of social life, is, other things equal, the 

 correlative of larger brain. Those higher feelings presupposed 

 by the better self-regulation which, in a better society, can 

 alone enable the individual to leave a persistent posterity, are, 

 other things equal, the correlatives of a, more complex brain ; 

 as are also those more numerous, more varied, more general, 

 and more abstract ideas, which must also become increasingly 



of structure ; and of course, in the absence of this idea, there is no im- 

 plication, even, that natural selection has anything to do with the origin of 

 species. And in the third place, the all- important factor of variation — 

 " spontaneous," or incidental as we may otherwise call it — is wholly ignored. 

 Though use and disuse are, I think, much more potent causes of organic 

 modification than Mi. Darwin supposes — though, while pursuing the inquiry 

 in detail, I have been led to believe that direct equilibration has played a 

 more active part even than I had myself at one time thought ; yet I hold 

 Mr. Darwin to have shown beyond question, that a great part of the facts— 

 perhaps the greater part — are explicable only as resulting from the survival of 

 individuals which have deviated in some indirectly-caused way from the 

 ancestral type. Thus, the above paragraph contains merely a passing recogni- 

 tion of the selective process ; and indicates no suspicion of the enormous 

 range of its effects, or of the conditions under which a large part of its effects 

 are produced. 



