EVOLUTION AND SIGNIFICANCE OF CEREBRAL CORTEX 315 



blind impulse of the innate nature and the acquired intellectual, 

 esthetic, and moral control. 



And herein lies the solution of the problem of human freedom, 

 so far as this rests within our own control. The limits of one's 

 powers and the range within which his freedom of action is cir- 

 cumscribed are in part determined by his hereditary endowments 

 and by environmental influences over which he has no control. 

 These are decreed to him by his fate, and the innate organization 

 of the nervous system is the chief instrument of this fate. But 

 man differs from the brute creation chiefly in that he can more 

 completely control his own environment and thereby to that 

 extent take his fate into his own hands; in other words, he can 

 enrich his own experience along lines of his own selection. To 

 some extent each individual can do this for himself through self- 

 culture; but to ensure the best results of such efforts there must 

 be a social control of the environment as a whole by concerted 

 community action. Individual freedom of action can, therefore, 

 attain its highest efficiency only through a certain amount of 

 voluntary renunciation of the selfish interests where these con- 

 flict with community welfare. Ethical ideals and altruism are 

 as truly evolutionary factors in human societies as are the ele- 

 mental laws of self-preservation and propagation of the species. 1 



To return now to the developing nervous system, we note that 

 the educational period is limited to the age during which the 

 association centers, whose form is not predetermined in heredity, 

 remain plastic and capable of modification under environmental 

 influence. Ultimately even the cerebral cortex matures and 

 loses its power of reacting except in fixed modes. Its unspecial- 

 ized tissue originally a diffuse and equipotential nervous mesh- 

 work becomes differentiated along definite lines and the funda- 

 mental pattern becomes more or less rigid. The docile period is 

 past, and though the man may continue to improve in the 

 technic of his performance, he can no longer do creative work. 

 He is apt to say, "The dog is too old to learn new tricks." 



1 In this connection reference may be made to two very interesting ad- 

 dresses recently delivered before the American Society of Naturalists: 



JENNINGS, H. S. 1911. Heredity and Personality, Science, N. S., vol. 

 xxxiv, pp. 902-910. 



CONKLIN, EDWIN G. 1913. Heredity and Responsibility, Science, N. S., 

 vol. xxxvii, pp. 46-54. 



