KACIAL MENTAL DIFFERENCES 293 



general rule the size of the brain varies directly with the 

 intellectual power of the individual. Thus men have greater 

 intellectual powers than lower animals, and the more intel- 

 lectual races of men have usually larger brains than the less 

 intellectual. Reasoning from the analogy of other structures 

 of which man makes a variable amount of use, the size of the 

 brain depends on two separate factors ; first, on the amount 

 of growth which is achieved under the influence of nutrition, 

 a growth that occurs mainly, if not entirely, before birth ; 

 and second, on the amount of growth which results from 

 nutrition plus use, a growth which occurs entirely after birth. 

 Now man may vary innately as regards both factors ; given 

 an equal amount of nutrition, one child may be born with 

 a larger brain than another ; or given an equal amount of use 

 one child's brain may grow more rapidly than another's. If 

 the intellectual powers are proportionate to the size of the 

 brain, as we must suppose they usually are, then the indi- 

 vidual whose brain grows the more rapidly under either kind 

 of stimulus will generally be of greater innate mental capacity 

 than the other. But, while it is probable that the amount of 

 nutrition which is supplied to children in utero is, under 

 normal circumstances, very much the same, the amount of 

 use to which individuals as compared to other individuals, 

 and races as compared to other races, put their brains 

 varies very much. Presumably, therefore, a representative 

 Australian aborigine, educated in England, would have a 

 larger brain than most of his compatriots; whereas an 

 Englishman reared by Blacks would have a smaller brain 

 than most Englishmen. It follows, since brains grow under 

 the influence of use, and since the amount of use varies, we 

 cannot accurately determine the innate mental capacities of 

 the various races by comparing the sizes of their brains. 

 However, since Englishmen long lived and were selected 

 under conditions which more stringently demanded a high 

 degree of intelligence than the conditions under which the 

 Australian Blacks evolved, it is probable that under identical 

 conditions the former would develop larger brains and greater 

 intelligence than the latter, and that the average Chinaman 

 would surpass both. 



467. Yet another factor must be considered when we 

 attempt to estimate the relationship which exists between 



all likelihood it has no more to do with determining mental characters 

 than the bumps on the bony surface have. On the other hand, the size 

 of the skull is probably determined largely by the size of the brain by 

 the amount of growth made by the brain before the sutures close. 



