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 differences 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 comparatively insignificant. Studies of the effects of diseases or injury upon the brain has shown that damage to these particular 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
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