Social Consequences of Heredity. 383 



be spent on the business of life, and growth of mental life would 

 not take place. Difficulty in getting a living is alike the incentive 

 to a higher education of childaen, and to a more intense and 

 long-continued application in adults. In the mother it induces 

 foresight, economy, and skilful house-keeping; in the father, 

 laborious days and constant self-denial. Nothing but necessity 

 could make men submit to this discipline ; and nothing but this 

 discipline could produce a continued progression. 



' In this case, as in many others, nature secures each step in 

 advance by a succession of trials, which are perpetually repeated, 

 and cannot fail to be repeated, until success is achieved. . . . 



' 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 evolution, 

 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 accompanied 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 complexity, 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 intensifying competition of social life, is, other 

 things equal, the correlative of larger brain. Those higher feelings 

 pre-supposed 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 feeling and thought, in a brain thus augmented in 

 size and developed in structure, is, other things equal, the correla- 

 tive of a greater wear of nervous tissue and greater consumption of 

 materials to repair it. So that, both in original cost of construction 

 and in subsequent cost of working, the nervous system must become 



