HUMAN POPULATION IN THE FUTURE. 529 



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 evolution so brought about, itself 

 necessitates a decline in his fertility. 



All future progress in civilization which the never- 

 ceasing pressure of population must produce, will be accom 

 panied 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 compli 

 cated, must have for its concomitant an increase of the great 

 nervous centres in mass, in complexity, in activity. That 

 larger body of emotion needed as a fountain of energy for 

 men who have to hold their places and rear their families 

 under the intensifying 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 requisite for successful life as 

 society advances. And the genesis of this larger quantity of 



gone on most favourably. In the second place, there is no trace of the idea 

 that natural selection may by co-operation with the cause assigned, or with 

 other causes, produce divergences of structure ; and of course, in the absence 

 of this idea, there is no implication that natural selection has anything to do 

 with the origin of species. And in the third place, the all-important factor 

 of variation &quot; spontaneous,&quot; 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 Mr. Darwin supposes though, w:hile pur 

 suing 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. B^arwin 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 pass 

 ing recognition 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. 

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