360 THE GROWTH OF THE BRAIN. 



be remembered that, as a rule, our latent capacities as 

 individuals are far beyond our regular achievements, 

 and that the stimuli which shall bring these powers into 

 action may be of very different sorts. An isolated 

 race may apparently have progressed but little, when 

 suddenly an earthquake, an invasion by a neighbour, or 

 the birth of a more generously endowed member of the 

 community, serves to give them an impulse which may 

 not be exhausted for many generations. 



Striking indeed are the different ways in which such 

 communities respond to the new influences brought to 

 bear upon them from without, grappling at one and the 

 same moment with novel activities, ideals, and diseases. 

 Wallace, in all his journeyings through the Malay 

 Archipelago, was impressed by the differences in the 

 degree with which communities, apparently similar, 

 responded to European influences. Thus far, however, 

 it has been impossible to state the anthropological 

 peculiarities of those who have supported such a trial, 

 as contrasted with the characters of those who have 

 succumbed to it. Further, the question is still to be 

 answered, whether the exercise of the nervous system 

 demanded in highly civilised societies really causes an 

 enlargement, as the exercise of glands and muscles can 

 be shown to do. 



The comparison here suggested must be made with 

 caution ; glands and muscles are of slow growth, in one 

 sense of slower growth than the central system. They 

 shrink when the body is starved, and expand when it is 

 well nourished. The central nervous system seems 

 more stable, and starvation at least appears to produce 

 little or no change in its bulk. Such powers of resist- 

 ance probably have their shadow side, and the system 

 which is thus but little affected in its bulk by unfavour- 

 able conditions may be equally resistant to improve- 



