XII. THE EVOLUTION OF MANKIND AND ITS FUTURE 



429 



related connection between hormones and temperament ; hormones 

 effect the latter, while the latter effects the development of endocrine 

 glands. Such a relation is especially obvious in the relation between 

 thyroid gland and temperament, and general irritability goes parallel 

 to the increased function of the gland. Therefore, an uncivilized life 

 requesting beastly tenseness and nervousness may lead to the develop- 

 ment of thyroid gland, or hyperfunction of thyrotrophic hormone of 

 the pituitary gland, which in turn exerts antagonistic influence upon 

 the function of adrenocorticotrophic hormone and probably also on 

 growth hormone, thus reducing the stimulating action of climate. On 

 the other hand, civilized life makes man feel at ease resulting in the 

 loss of the beastly strain, contributing to the effect of climate, and 

 may thus promote the loss of the rigidity. Environmental factors 

 are considered to affect hormonal glands mainly through autonomous 

 nervous system, and hence it may be a matter of course that psychic 

 conditions such as irritability and nervous tenseness are capable of 

 exerting a similar effect through the nervous system. 



In this connection, it shoud be mentioned that adrenal cortex ex- 

 hibits the function of releasing the nervous irritability in contrast to 

 thyroid. Also in this respect these two hormonal glands act antago- 

 nistically with each other. Thus, it has been reported that adrenal 

 extract produced improvement in some cases of pathological irritabi- 



+0.20 - 



+0.15 



t> +0.10- 



-0.05 



-0.05 



-a.io - 



Number of children 



Fig. 39. Excess of stature over averge stature for families of various 

 sizes. Reproduced from Boas : Race. Language and Cul- 

 tures, New York. 1949. 



