EVOLUTION OF THE PRIMATES AND MAN 473 



and serially traced through the Catarrhine, the ape (Gorilla), 

 Australopithecus, Pithecanthropus, Eoanthropus, Homo rhode- 

 siensis, Homo neanderthalensis to Homo sapiens. There is 

 further the very interesting fact that in human develop- 

 ment, the regions of the neopallium which are the last to be 

 formed are precisely these parietal, prefrontal and temporal 

 areas. 



There is therefore good reason to believe that the per- 

 fection of these areas of the cerebral cortex and of the functions 

 with which they are associated played the major part in the 

 evolution of man. The brain developed first, and other 

 features such as the reduction of the face and assumption of 

 the erect attitude followed. It is to be noted that the perfec- 

 tion of the parietal and prefrontal areas is directly or indirectly 

 concerned with the function of vision, so that it may be said 

 that sight was of capital importance in the evolution of man. 

 In this connexion, mention may be made of some other aspects 

 of the bearing of sight on evolution. 



In the first place, it will be remembered that the eyes are 

 " distance-receptors, " and that the responses which they evoke 

 on the part of the animal are anticipatory rather than con- 

 summatory movements. Next, there is the fact that in man, 

 the number of nerve-fibres entering the brain from one eye 

 vastly exceeds the number of all the other afferent nerve- 

 fibres of one side put together. From the physiological side, 

 it is found that in the higher Primates including the monkeys, 

 apes, and man, the eyes assume great importance in regulating 

 the posture of the organism, a regulation which in lower forms 

 is principally dependent on the semicircular canals of the ear. 

 Lastly, from the psychological point of view, experiments on 

 the behaviour of chimpanzees when confronted with problems 

 shows that the eyes play a very important part in solving the 

 problem. Cases of great interest are those in which there 

 lies close at hand some instrument, such as a stick, and by 

 using which the ape would be able to solve its problem 

 easily. Unless the instrument to be used is seen by the ape 

 in the same field of vision as the object or goal for which it is 

 to be used, it pays no attention to it. Without this optic 



