502 LAWS OV MULTIPLICATION. 



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 correlative of a greater wear of nerv- 

 ous tissue and greater consumption of materials to repair it. 

 So that both in original cost of construction and in subse- 

 quent cost of working, the nervous system must become a 

 heavier tax on the organism. Already the brain of the civi- 

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

 of the savage. Already, too, it presents an increased hetero- 

 geneity — especially in the distribution of its convolutions. 

 And further changes like these which have taken place 

 under the discipline of civilized life, we infer will continue 

 to take place. But everywhere and always, evolu- 



tion is antagonistic to procreative dissolution. Whether it 

 be in greater growth of the organs which subserve self-main- 

 tenance, whether it be in their added complexity of structure, 

 or whether it be in their higher activity, the abstraction of 

 the required materials, implies a diminished reserve of ma- 

 terials for race- maintenance. And we have seen reason to 

 believe that this antagonism between Individuation and 

 Genesis, becomes unusually marked where the nervous sys- 

 tem is concerned, because of the costliness of nervous struc- 

 ture and function. In § 346 was pointed out the apparent 

 connexion between high cerebral development and pro- 

 longed delay of sexual maturity ; and in § § 366, 367, 

 the evidence went to show that where exceptional fer- 

 tility 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. 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 higher nervous development and greater expenditure 

 m nervous action, here described as indirectly brought about 



