424 V. THE NATURE OF EVOLUTION 



followed by the demonstrable acromagaly or gigantism, that is, enlarge- 

 ment of hands and feet, and the thickening of the lips and nose, 

 probably due to the hypersecretion of growth hormone, whereas the 

 gonadotrophic content of the pituitary is found to be reduced (102). 



It may be concluded, therefore, that the absence of stimulating 

 climate makes a precocious, small man tending to Addisonism, ownng 

 to the hyperfunction of both gonadotrophic and thyrotrophic hormones 

 together with the insufficiency of growth hormone and ACTH, accompa- 

 nying the dysfunction of adrenal cortex. This is the feature of man, 

 common in tropical regions. A similar phenomenon may be observable 

 also in animals. Thus, each group of garter snakes is found to show 

 independently dwarfing as the distance increases from the center of 

 dispersal in the Mexican plateau, no matter whether the group is 

 pushing into the tropics or temperate regions (30). This may be 

 ascribed to the degree of deficiency in climatic or other factors, which 

 can stimulate the secretion of growth hormone in the snake, resulting 

 in the hyperfunction of thyroid gland. 



As we have seen above, our genes possess rigid structure with 

 strong elasticity, so that they can show a resistance to environmental 

 factors which are able to induce a change in them. If any change 

 is induced, usually repulsive force will become stronger as the change 

 proceeds, so that the progress of the change may come to be very 

 slow, if not stopped, a consequence which may not issue when the 

 genes have weak structures with feeble elasticity. A loss of the 

 rigidity in genes, therefore, may lead to a rapid, unceasing change 

 of the characters of the organism having the genes. In such a case 

 the organism under a climate or other environments that stimulate 

 the hypophysis will become continuously bigger to attain a gigantic 

 figure which may result in its extinction. As is known as Cope's 

 law, overspecialized animals usually would become extinct with gigan- 

 tism. The extensive specialization results from a rapid change of 

 a gene, which would be in turn a result of a loss of the structural 

 rigidity in a gene. 



Here a very remarkable fact should be pointed out that a fearful 

 tendency to this gigantism is most manifestly being revealed in 

 mankind. The statistics indicating the increase in stature of man go 

 back a century and a half in Switzerland and fifty years or so in 

 many other places. Among European countries data covering one or 

 two generations are available for Norway, Sweden, Denmark, Germany, 

 the Netherlands, Italy, and Spain. People in the United States also 

 share this trend. Japanese date from 1878 onwards are partcularly 

 significant because they show that an Asiatic people is undergoing 

 the same lengthening process as those of European extraction. The 



