Possible Evolution in Man 223 



reason for the sluggishness of organic evolution in 

 mankind. 



The probability is that some improvements in 

 adaptation, such as a shortening of the food-canal 

 and immunity to certain diseases, are in slow prog- 

 ress in mankind ; but even if this be so, there must be 

 put on the other side of the account the likelihood 

 that disadvantageous changes, such as short sight 

 and neurasthenia, are taking racial grip because of 

 the inadequacy of the sifting processes that remain 

 at work. 



Two lines of possible evolution seem to be particu- 

 larly promising. The first is an increase in the com- 

 plexity of the inter-relations amongst the 9200 mil- 

 lions of nerve-cells in the cerebral cortex. The size of 

 the brain has not increased since the days of the Cro- 

 Magnon men, who lived some 20,000 years ago, but 

 without increase of size there might be increase in 

 complexity; and that would mean the improvement 

 of intelligence. The second possibility is an extension 

 of the youthful period and an abbreviation of the 

 time of senescence. This might come about by varia- 

 tions in the endocrinal or regulative system of the 

 body. 



Man stands apart in his reason and language and 

 morality, but also in the degree to which he en- 

 registers the gains of the past in the social heritage. 

 This is only incipient among animals, as in the per- 

 manent ant-hill or the beaver village ; it means half of 

 evolution to man. To the enrichment and increased 

 utilization of the social heritage no limits can be set. 



