'O 



r^ ORGANIC EVOLUTION 



upon man, the "new phrenology" is far more complete 

 as regards the simian than as regards the human 

 brain. But whenever Nature, by means of disease, 

 makes an experiment upon the human brain, and 

 whenever the surgeon has occasion to open the 

 cranium, and whenever an accident, such as frac- 

 ture of the skull, causes pressure upon an area of 

 the brain, it is found that the physiological corre- 

 spondence between the brain of man and that of 

 the anthropoid is as complete as is the anatomical 

 correspondence. This fact has a practical as well 

 as a theoretical bearing, for it repeatedly enables 

 the surgeon, by making the safe assumption that 

 what has been observed in the simian is true of 

 the human brain, to perform operations which save 

 life or relieve pain. Such and such facts having 

 been experimentally observed as true of the brain 

 of the chimpanzee, the cranial surgeon knows where 

 to open the human skull and in which direction 

 to incise the brain so as to reach a tumour, let us 

 say, which, token found, it is no very difficult matter 

 to remove. 



Having observed, then, these facts of correspond- 

 ence, we are now prepared to consider the facts of 

 difference between the brain of man and the brain 

 of the anthropoid. It has already been stated that 

 the difference is essentially one of brain-proportion. 

 This is true in three senses. 



In the first place, it is true as regards the pro- 

 portion of brain-weight to body- weight. This pro- 

 portion is much higher in man — and also in woman, 

 though the difference is less — than in the ape. 

 Students have naturally sought to explain this 



