XII. THE EVOLUTION OF MANKIND AND ITS FUTURE 439 



comparable to the present and live a considerably high civilized life 

 in the old stone age. nearly 20,000 years ago. Their cranial capacity 

 appears to have been even somewhat greater than that of modern 

 Europeans. Their extinction might be caused by the loss of structural 

 rigidity in the genes, followed by the prevalence of some severe virus 

 diseases. In their days, the ancestors of the present Europeans must 

 have been only a barbarous, insignificant existence, but now they are 

 the representative of mankind and apparently are going to follow in 

 the steps of Cro-Magnon. 



How fatal are some viruses to overspecialized people may be 

 understood if one remembers the dreadful prevalence of influenza which 

 outbroke during the 1st War ; the victims of the disease were far 

 greater than those of the War. Human being have presumably achieved 

 since then a great advance in their specialization by losing remarkably 

 the rigidity of genes ; who can warrant you there is no chance of out- 

 break of an influenza or other virus diseases so severe that almost all 

 the civilized people will be sacrificed to it ? 



However, the writer's forecast concerning the future of man thus 

 far described will be failed if his theories are accepted generally and 

 counter-measures are taken against the human orthogenesis. Not only 

 the prevention of human extinction as a race but also as an individual 

 may be not utterly impossible. Since the individual development is 

 raised by hormones, administration of a proper hormone or hormones 

 may be able to stop or retard the advancement ; even to accomplish 

 the rejuvenescence may be not imppossible as seen in the production of 

 germ cells. As already stated, thyroid hormones will promote matura- 

 tion leading to premature decay, while certain pituitary horm.ones 

 appear to be involved in prolonging the life span. Carlson and Hoelzel 

 (136) compared the effects of omnivorous and herbivorous diets upon 

 the life of rats, and confirmed a favourable influence of the diet rich 

 in meat. This may be accounted for by the positive effect of the 

 protein rich diet upon the pituitary function. Moreover, in most ex- 

 periments recorded in the literature the female of a species such as 

 the rat lives longer than the male, a phenomenon which has long been 

 recognized also in the case of man. This must be attributed to the 

 difference of hormones due to the difference of sex. 



