,84 Heredity. 



a heavier task on the organism. Already the brain of the civilized 

 man is larger by nearly thirty per cent, than the brain of the 

 savage. Already, too, it presents an increased heterogeneity, 

 especially in the distribution of its convolutions. And further 

 changes like these which have taken place under the discipline of 

 life we infer will continue to take place. 



* But, everywhere and always, evolution is antagonistic to pro- 

 creative dissolution. . . . And we have seen reason to believe 

 that this antagonism between individuation and genesis becomes 

 unusually marked where the nervous system is concerned, because 

 of the costliness of nervous structure and function. In another 

 place was pointed out the apparent connection between high 

 cerebral development and prolonged decay of sexual maturity, 

 the evidence going to show that where exceptional fertility exists 

 there is sluggishness of mind, and that where there has been 

 during education excessive expenditure in mental action, there 

 frequently follows a complete or partial infertility. 1 Hence, the 

 particular kind of further evolution which man is hereafter to 

 undergo is one which, more than any other, may be expected 

 to cause a decline in his power of reproduction. . . . 



* The necessary antagonism between individuation and genesis 

 not only, then, fulfils with precision the a priori law of main- 

 tenance of race, from the monad up to man, but ensures final 

 attainment of the highest form of this maintenance a form in 

 which the amount of life shall be the greatest possible, and the 

 births and deaths the fewest possible. This antagonism could 

 not fail to work out the results we see it working out. The 

 excess of fertility has itself rendered the process of civilization 

 inevitable; and the process of civilization must inevitably di- 

 minish fertility, and at last destroy its excess. From the beginning, 

 pressure of population Has been the proximate cause of progress. 

 It produced the original diffusion of the race. It compelled men 

 to abandon predatory habits and take to agriculture. It led to 

 the clearing of the earth's surface. It forced men into the social 

 state; made social organization inevitable, and has developed the 

 social sentiments. It has stimulated to progressive improvements 



1 For details see Spencer's Biology, 346, 366, and 367. 



