CAPACITY AND ACQUIREMENT 421 



his immediate surroundings in a much greater degree than his 

 body. 



693. Sometimes it is asked if nature or nurture plays the more 

 important part in the mental development of the human being. 

 As a fact this question is nonsensical. It is as if we asked whether 

 the locomotive or the steam played the greater part in transporting 

 the train. The truth is that nature has rendered man trans- 

 cendently responsive to the nurture of use and experience. The 

 question should be "To what extent has nature rendered man 

 responsive to the stimulus of nutriment and to what extent to that 

 of use and experience?" Nature has rendered all living beings 

 equally responsive to nurture. The caterpillar is responsive to 

 the nurture of nutriment. Man differs from the caterpillar in that 

 nature has rendered him responsive in addition to the nurture of 

 use and experience. He differs from other animals in that he is 

 immensely the most responsive of all to this kind of nurture. It 

 is the one peculiarity which strongly differentiates him. Mental 

 experience is, after all, only a form of use. We use our minds 

 when we store experiences; or rather, if mind is a function of 

 brain, we use our brains. When, for example, we acquire a new 

 manual dexterity, our brains acquire a new function ; through use 

 they learn to do a new thing. Doubtless the acquirement is 

 accompanied by actual growth of brain, which however, especially 

 in adult life when gains are being balanced by losses, need not 

 imply an increase in bulk, but only a relative increase in certain 

 of the brain constituents such as nerve cells or connections 

 between nerve cells. In youth, when man is making the great 

 mass of his mental acquirements including the more important of 

 his * physical ' and mental dexterities (e.g. walking and reasoning), 

 there is rapid growth in the bulk of the brain, which is most rapid 

 just when the acquirements are being most rapidly made. In old 

 age, though the individual may still be making mental acquire- 

 ments, he is usually losing more than he acquires. Then, while 

 the total mass of his brain does not decrease, the nervous elements 

 tend to be replaced by fibrous tissue. 



694. If we wish to avoid hopeless confusion it is necessary 

 to distinguish sharply between two entirely different things ; 

 between, on the one hand, capacity to make mental acquirements, 

 and, on the other, the mental acquirements themselves, between 

 the memory and the things that are stored in the memory. The 

 capacity is an * innate,' a nutritional character ; the acquirements 

 arise under the stimulus of experience. Thus a man may have 



