THE EVOLUTION OF THE BRAIN 



there is any homology. Bearing in mind these profound 

 differences in pattern it comes as something akin to a shock 

 to discover that the general pattern of the brain of a gorilla 

 (Fig. 2) is essentially identical with that of the brain of a 

 man (Fig. 3). In spite of the fact that the exceptionally 

 small and very primitive human brain represented in Fig. 3 

 is double the bulk of the ape's (1,000 grammes and 500 

 grammes, respectively), the form and pattern of the 

 gorilla's brain so closely reproduce those of the human brain 

 that it is easy to recognise corresponding areas in the two. 

 By comparing these areas the further fact emerges that the 

 parts that receive the impulses of vision, hearing, and touch 

 are almost, if not quite, as extensive in the brain of the ape 

 as in the brain of man. In fact, the only noteworthy dif- 

 ferences are due to the enormous expansion in the human 

 brain of three areas, the representatives of which in the 

 gorilla's brain (distinguished by stars in Fig. 2) are com- 

 paratively insignificant. Studies of the effects of diseases or 

 injury upon the brain has shown that damage to these par- 

 ticular areas of man's brain has the most profound effects 

 upon intelligence and personality. Moreover, one who 

 studies the microscopic structure of these areas that we know 

 to be concerned with the expression of man's highest mental 

 powers, the instruments of his distinctive intelligence and 

 personality, can detect no difference in structure or quality 

 between them and their diminutive representatives in the 

 brain of the ape. 



The accompanying diagrams show the profound contrast 

 between the patterns of the brains of the lion and the gorilla 

 and throw into relief the remarkable identity of structure of 

 the brains of the gorilla and of man, although the human 

 brain is double the volume of the gorilla's. The human 

 brain chosen for this purpose is exceptionally small (about 



[319] 



