124 



NATURE 



[September 26, 1912 



obvious reason is that the brain had not yel attained 

 a sufficiently high stage of development to provide a 

 sufficient amount of useful skilled work, apart from 

 the Iree-climbing, for these competent hands to do. 



The ape is tied down absolutely to his experience, 

 and has only a very limited ability to anticipate the 

 results even of relatively simple actions, because so 

 large a proportion of his neopallium is under the 

 dominating influence of the senses. 



Without a fuller appreciation of the consequences of 

 its actions than the gibbon is capable of, the animal 

 is not competent to make the fullest use of the skill 

 it undoubtedlv possesses. What is implied in acquir- 

 ing this fuller appreciation of the meaning of events 

 taking place around the animal? The state of con- 

 sciousness awakened by a simple sensory stimulation 

 is not merely an appreciation of the physical proper- 

 ties of the object that supplies the stimulus : the 

 object simply serves to bring to consciousness the 

 results of experience of similar or contrasted stimu- 

 lations in the past, as well as the feelings aroused 

 by or associated with them, and the acts such feelings 

 excited. This mental enrichment of a mere sensation 

 so that it acquires a very precise and complex mean- 

 ing is possible only because the individual has this 

 extensive experience to fall back upon ; and the 

 faculty of acquiring such experience implies the 

 possession of large neopallial areas for recording, so 

 to speak, these sensation-factors and the feelings asso- 

 ciated with them. The "meaning" which each 

 creature can attach to a sensory impression presum- 

 ably depends, not on its experience only, but more 

 especially upon the neopallial provision in its brain 

 for recording the fruits of such experience. 



Judged by this standard, the human brain bears 

 ample witness, in the expansion of the great temporo- 

 parietal area, which .so obviously has been evolved 

 from the regions into which visual, auditory, and 

 tactile impulses are poured, to the perfection of the 

 physical counterpart of the enrichment of mental 

 structure, which is the fundamental characteristic of 

 the human mind. 



The second factor that came into operation in the 

 evolution of the human brain is merely the culmina- 

 tion of a process which has been steadily advancing 

 throughout the primates : I refer to the high state 

 of perfection of the cortical regulation of skilled move- 

 n\ents, many of which are acquired bv each indi- 

 vidual in response to a compelling instinct that forces 

 every normal human being to work out his own salva- 

 tion by perpetually striving to acquire such manual 

 dexterity. 



This brings us to the consideration of the nature 

 of the factors that have led to the wide differ- 

 entiation of man from the gorilla. Why is it that 

 these two primates, structurally so similar and derived 

 simultaneously from common parents, should have 

 become separated bv such an enormous chasm, so far 

 as their mental abilities are concerned? 



There can be no doubt that this nrocess of dif- 

 ferentiation is of the same nature as those which led 

 one branch of the Eocene tarsioids to become 

 monkeys while the other remained prosimiae ; 

 advanced one Erroup of primitive monkeys to the 

 ratarrhine status, while the rest remained platvr- 

 ihine : and converted one division of the Old 

 World apes into anthropoids, while the others retained 

 llieir old status. Put into this form as an obvious 

 (r'lism, the conclusion is suggested that the changes 

 which have taken place in the brain to convert an 

 ape into man are of the same nature as, and may 

 be looked upon merelv as a continuation of, those 

 processes of evolution which we have been examining 

 in the lowlier members of the nrimate series. It was 



NO. 2 2;?Q, VOL. qo"l 



not the adoption of the erect attitude or the invention 

 of articulate language that made man from an ape, 

 but the gradual perfecting of the brain and the slow 

 upbuilding of the mental structure, of which erect- 

 ness of carriage and speech are some of the incidental 

 manifestations. 



The ability to perform skilled movements is con- 

 ducive to a marked enrichment of the mind's struc- 

 ture and the high development of the neopallium, 

 which is the material e.xpression of that enrichment. 

 There are several reasons why this should be so. 

 The mere process of learning to execute any act of 

 skill necessarily involves the cultivation, not only of 

 the muscles which produce the movement, and the 

 cortical area which excites the actions of these 

 muscles, but in even greater measure the sensorv 

 mechanisms in the neopallium which are receiving 

 impressions from the skin, the muscles, and the eyes, 

 to control the movements at the moment, and inci- 

 dentally are educating these cortical areas, stimu- 

 lating their growth, and enriching the mental struc- 

 ture with new elements of experience. Out of the 

 e.xperience gained in constantly performing acts of 

 skill, the k-iowledge of cause and effect is eventually 

 acquired. Thus the high specialisation of the motor 

 area, which made complicated actions possible, and 

 the great expansion of the temporo-parietal area, 

 which enabled the ape-man to realise the "meaning" 

 of events occurring around it, reacted one upon the 

 other, so that the creature came to understand that 

 a particular act would entail certain consequences. 

 In other words, it gradually acquired the faculty of 

 shaping its conduct in anticipation of results. 



Long ages ago, possiblv in the Miocene, the ances- 

 tors common to man, the gorilla, and the chimpanzee 

 became separated into groups, and the different con- 

 ditions to which thev became exposed after they 

 parted company were in the main responsible for the 

 contrasts in their fate. In one group the distinctively 

 primate process of growth and specialisation of the 

 brain, which had been going on in their ancestors 

 for many thousands, even millions, of years, reached 

 a stage when the more venturesome members of the 

 group, stimulated perhaps by some local failure of 

 the customary food, or maybe led forth by a 

 curiosity bred of their growing realisation of the 

 possibilities of the unknown world beyond the trees 

 which hitherto had been their home, were impelled 

 to issue forth from their forests, and seek new 

 sources of food and new surroundings on hill and 

 plain, wherever thev could obtain the sustenance they 

 needed. The other group, perhaps because they 

 happened to be more favourably situated or attuned 

 to their surroundings, living in a land of plenty which 

 encouraged indolence in habit and stagnation of effort 

 and growth, were free from this glorious unrest, and 

 remained apes, continuing to lead very much the 

 same kind of life fas gorillas and chimpanzees) as 

 their ancestors had been living since the Miocene 

 or even earlier times. That both of these unenter- 

 prisinc relati\-es of man happen to live in the forests 

 of tropical .Africa has alwavs seemed to me to be a 

 strong argument in favour of Darwin's view that 

 Africa was the original home of the first creatures 

 definitely committed to the human career ; for while 

 man was evolved amidst the strife with adverse con- 

 ditions, the ancestors of the gorilla and chimpanzee 

 gave up the struggle for mental supremacy simply 

 because thev were satisfied with their circumstances; 

 I and it is more likely than not that they did not 

 change their habitat. 



The erect attitude, infinitely more ancient than man 

 himself, is not the real cause of man's emergence 

 from the simian stage ; but it is one of the factors 



