566 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1912. 



If the erect attitude is to explain all, why did not the gibbon 

 become a man in Miocene times? The whole of my argument has 

 aimed at demonstrating that the steady growth and specialization 

 of the brain has been the fundamental factor in leading man's ances- 

 tors step by step right upward from the lowly insectivore status, nay, 

 further, through every earher phase in the evolution of mammals — for 

 man's brain represents the consummation of precisely those factors 

 which throughout the vertebrata have brought their possessors to 

 the crest of the wave of progress. But such advances as the assump- 

 tion of the erect attitude are brought about simply because the brain 

 has made skilled movements of the hands possible and of definite use 

 in the struggle for existence; yet once such a stage has been attained 

 the very act of Hberating the hands for the performance of more 

 deUcate movements opens the way for a further advance in brain 

 development to make the most of the more favorable conditions and 

 the greater potentiahties of the hands. 



It is a fact beyond dispute that the divergent speciahzation of the 

 human limbs, one pair for progression, and the other for prehension 

 and the more delicately adjusted skilled action, has played a large 

 part in preparing the way for the emergence of the distinctly human 

 characteristics : but it would be a fatal mistake unduly to magnify the 

 influence of these developments. The most primitive hving primate, 

 the spectral tarsier, frequently assumes the erect attitude, and uses 

 its hands for prehension rather than progression in many of its acts, 

 and many other lemurs, such as the Indrisinse of Madagascar, can and 

 do walk erect. 



In the remote Oligocene, a catarrhine ape, nearly akin to the 

 ancestors of the Indian sacred monkey, Semnopithecus, became 

 definitely speciahzed in structure in adaptation for the assumption 

 of the erect attitude ; and this type of early anthropoid has persisted 

 with relatively slight modifications in the gibbon of the present day. 

 But if the earhest gibbons were already able to walk upright, how is 

 it, one might ask, that they did not begin to use their hands, thus 

 freed from the work of progression on the earth, for skilled work, and 

 at once before men? The obvious reason is that the brain had not 

 yet attained a sufficiently high stage of development to provide a 

 sufficient amount of useful skilled work, apart from the tree cHmbing, 

 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 neopaUium 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 undoubtedly possesses. What is implied 



