September 22, 1923J 



NATURE 



443 



cipline can be developed to justify the creation of a 

 real science of man. 



The full recognition of the mechanism of the diffusion 

 of culture involves a new orientation in psychological 

 investigation, for it points the way to the true explana- 

 tion of the origin of folk-lore and myth and of custom 

 and belief ; and it throws a new light upon the springs 

 of human action and upon the problems of social and 

 political organisation and of education. The outcome 

 of this new movement in ethnology will be to effect a 

 closer bond of union with real psychology and through 

 psychology with the biological sciences that are 

 essential for the full appreciation of the meaning of 

 mental evolution. 



It is too often forgotten by students of man's evolu- 

 tion that the fundamental distinctive feature of the 

 human family is the nature and range of the powers of 

 mind, which differentiate it from all other living 

 creatures. The chief aim of the interpreter of this 

 evolution should be to offer some explanation of how 

 these distinctively human attributes were acquired. 



With his usual facility of expression Sir James Frazer 

 puts this view with great force. It is all the more 

 welcome because he, who so freely uses the theory of 

 the independent evolution of belief, reproves another 

 ethnologist for too exclusive a devotion to biological 

 methods of interpretation and for forgetting " the part 

 that human thought and will have played in moulding 

 human destiny." He says that some of his colleagues 

 " would write the history of man without taking into 

 account the things that make him a man and dis- 

 criminate him from the lower animals. To do this, to 

 adopt a common Comparison, is to write the play of 

 ' Hamlet ' without the Prince of Denmark. It is to 

 attempt the solution of a complex problem while ignor- 

 ing the principal factor which ought to come into the 

 calculations. It is, as I have already said, not science 

 but a bastard imitation of it. For true science reckons 

 with all the elements of the problem which it sets out 

 to solve. ... In particular, the science which deals 

 with human society will not, if it is truly scientific, omit 

 to reckon with the qualities which distinguish man from 

 the beasts." * 



It should, then, be the fundamental aim of any move- 

 ment to integrate the forces of anthropological inquiry 

 to provide an explanation of how man acquired his 

 distinctive position and how precisely his behaviour 

 was modified by the attainment of such heightened 

 powers of discrimination and ability to profit from his 

 experience. 



The Evolution of the Human Brain. 



Intensive research in comparative anatomy and em- 

 br>-oIogy and discoveries in paleontology have made it 

 possible for us to reconstruct man's pedigree with a 

 confidence that hitherto would not have been justifi- 

 able. Using this scheme as a foundation, we can deter- 

 mine precisely what structural changes, especially in 

 the brain, were effected at each stage of the progress of 

 the Primates toward man's estate ; and in the light of 

 the information afforded by physiology and clinical 

 medicine we are able in some measure to interpret the 

 meaning of each of the stages in the attainment of the 

 distinctively human attributes of mind. 



• " Totemism and Exogamy," 1910, p. 98. 

 NO. 2812, VOL. 112] 



In an address delivered at the Dundee meeting of the 

 British Association eleven years ago, and elsewhere on 

 several occasions since then, I have discussed this 

 problem : but I make no apology for returning to its 

 consideration again. For, as I have said already, it is 

 the fundamental question in the study of man ; and 

 recent research has cleared up many difficult points 

 since I last spoke on the subject. 



Even before the beginning of the Tertiary period the 

 trend had already been determined for that particular 

 line of brain development, the continuation of which 

 eventually led to the emergence of man's distinctive 

 attributes. Moreover, man, as I said in 191 2, is " the 

 ultimate product of that line of ancestry which was 

 never compelled to turn aside and adopt protective 

 specialisations, either of structure or mode of life, which 

 would be fatal to its plasticity and power of further 

 development." 



Vision the Foundation of Man's Mental 

 Powers. 



The first step was taken when in a very primitive and 

 unspecialised arboreal mammal vision became the 

 dominant sense, by which its movements were guided 

 and its behaviour so largely determined. One of the 

 immediate results of the enhancement of the import- 

 ance of vision was to awaken the animal's curiosity 

 concerning the things it saw around it. Hence it was 

 prompted to handle them, and its hands were guided by 

 visual control in doing so. This brought about not 

 merely increased skill in movement, but also the culti- 

 vation of the tactile and kinaesthetic senses, and the 

 building up of an empirical knowledge of the world 

 around it by a correlation of the information obtained 

 experimentally by vision, touch, and movement. The 

 acquisition of greater skill affected not merely the hands 

 but also the cerebral mechanisms that regulate all move- 

 ments ; and one of the ways in which this was expressed 

 was in the attainment of a wider range and an increased 

 precision of the conjugate movements of the eyes, and 

 especially of a more accurate control of convergence. 

 This did not occur, however, until the flattening of the 

 face (reduction of the snout) allowed the eyes to come 

 to the front of the head and look forward so that the 

 visual fields overlapped. Moreover, a very complicated 

 mechanism had to be developed in the brain before 

 these delicate associated movements of the eyes could 

 be effected. The building-up of the instrument for 

 regulating these eye-movements was the fundamental 

 factor in the evolution of man's ancestors, which 

 opened the way for the wider vision and the power of 

 looking forward that are so pre-eminently distinctive 

 of the human intellect. Our common speech is per- 

 meated with the symbolism that proclaims the influence 

 of vision in our intellectual life. 



The first stage in this process seems to have been the 

 expansion of the prefrontal cortex and the acquisition 

 of the power of voluntarily extending the range of 

 conjugate movements of the eyes and focussing them 

 upon any object. Then came the laborious process of 

 building up in the mid-brain the instrument for effecting 

 these complex adjustments automatically,'^ so that the 

 animal was then able to fix its gaze upon an object and 



' John I. Hunter, "The Oculomotor Nucleus in Tarsiusand Nycticebus," 

 Brain, 1923. 



