432 V. THE NATURE OF EVOLUTION 



tibility to their primitive structure. Sometimes it is regarded as a 

 type of virus diseases. Now, it is a noteworthy fact that cancer is 

 prevailing extensively among civilized nations. For example, in the 

 United States present cancer mortality is over 200,000 per year and it 

 is increasing at the rate of approximately 3 per cent or about 5,000 per 

 year. Specifically, 207,721 deaths from cancer and leucaemia were 

 reported in 1948. If cancer will continue to increase at this rate, in 

 only a few hundred years it will so happen that all the people in 

 United States are doomed to die of cancer. This fact strongly sug- 

 gests that the decreasing process of the structural rigidity in human 

 genes is rapidly proceeding in civilized people, presumably because of 

 hypohysis increasing in its function. Moon et at. (119) have actually 

 confirmed that hypophysectomy does exhibit inhibitory effect upon 

 cancer of the rat induced by methylcholanthrene. Moreover, the 

 significance of pituitary function in neoplastic diseases including cancer 

 is indicated by the many and diverse tumours that develop in the rat 

 following the prolonged administration of growth hormone (120). 



During pregnancy, as was already pointed out, a remarkable hyper- 

 trophy is observed in hypophysis ; at the same time, attention is paid 

 on the increased incidence of poliomyelitis during pregnancy. Domestic 

 animals and cultivated plants have been highly specialized probably 

 by the lessening in the rigidity of the genes. Their character highly 

 susceptible to viruses must be based upon this ; as is well known the 

 more specialized, the more susceptible they are to viruses. Civilized 

 people showing the tendency to increase in stature and becoming more 

 and more resistant to tuberculosis may be regarded, as highly specialized 

 species. At the same time, they are very susceptible to some virus 

 diseases including cancer as seen above, whereas among small uncivilized 

 people inclined to be severely afflicted by tuberculosis, the incidence of 

 virus diseases including cancer appears to be much fewer than among 

 civilized. 



Poliomyelitis is extensively prevalent among civilized nations es- 

 pecially in United States and Canada, whereas low incidence of the 

 paralytic disease, even among children, of the tropics and subtropics, 

 such as Africa or Far East, has been reported (121). In Japan, recent- 

 ly poliomyelitis is becoming not a rare disease, while the decrease in 

 tuberculosis has become conspicuous. In 1916 there was an explosive 

 outbreak of poliomyelites in America, and in was then impressed by 

 the fact that patients so often were of the same physical type, usually 

 large, overgrown children (122). 



On the other hand, many experimental results suggesting that the 

 hyperfunction of hypophysis is disavantageous to virus infection have 

 been recently accumulated. Thus, adrenal cortex hormone (cortisone) 



