212 Changing Human Nature 



It is not assumed that the actual body form o£ an in- 

 dividual is determined by a single factor. In the matter of 

 human stature alone, at least four factors are involved (see 



Fig. 54)- 



In any given population we may find the different body 



types distributed in some relation to social or economic classes. 

 Thus, the slender type, which is present in a comparatively 

 small proportion of the Japanese population, occurs five 

 times as frequently among the official classes as among the 

 laborers; Whereas the short stocky type, which constitutes 

 more than half the population, occurs nine times as fre- 

 quently among the laborers as among the officials. 



Glands and Types 



The existence of these varied types has been attributed 

 to environmental conditions. It has been assumed, for ex- 

 ample, that the development of the stocky type is due to a 

 diet relatively poor in iodin, since this element has been found 

 essential to the normal activity of the thyroid gland, and 

 this in turn has been found essential to development. There 

 is indeed a very close connection between the distribution 

 of iodin in the soil and waters of a given region, and the 

 prevalence of simple goiter. We have in our own country 

 large areas around the Great Lakes and in the northwest that 

 have been practically depleted of iodin in the course of past 

 ages. In these areas today there appears an excessive pro- 

 portion of young people, especially girls, with enlarged thy- 

 roids. Domestic animals often show striking effects of the 

 privation of iodin, such as hairlessness in pigs and enlarged 

 head in calves and sheep. Furthermore, it has been estab- 

 lished that this deficiency and the accompanying disorders 

 can be adequately overcome by supplying the children iodin 

 compounds in small amounts. Parallel to these facts is the 



In such a way that the recessives remain " pure," whereas the dominants, 

 although appearing to be aUke, are one-third pure and two-thirds hybrid 

 hke their hybrid parents. 



