THE EFFECT UPON HUMAN EVOLUTION 279 



2. An increased or decreased appropriation by them of 



the hormone controlling their function. 



3. A corresponding increase or decrease in function of 



the gland of internal secretion and so, 



4. An increased or decreased representation of it in the 



reproductive sex cells in the gonads. 



To take a classic illustration, the long neck of the giraffe. 

 The neck of certain animals living in a district populated by- 

 trees with high branches would be in state of instability. If at 

 the same time the pituitary, for some reason, was unstable and 

 reacted with an extra supply of its secretion, it would stimulate 

 the neck cells to reproduce themselves. In turn the pituitary 

 would become stabilized in the direction of increased secretion, 

 and hand on the component of increased secretion to the sex cells. 

 That component, in conjunction with other factors, would there- 

 fore determine the emergence of a definite species character. In 

 other words, the glands of internal secretion, as intermediaries 

 between the environment and body, and between the body and 

 the reproductive sex cells or germplasm, tender the clue to a 

 phase of the puzzle of heredity, adaptation and evolution. It is 

 only a dotted outline of an explanation to be sure, but one cer- 

 tainly capable of being filled in. 



The Bearing on Breeding 



Since the endocrine glands are so subtly sensitive and respon- 

 sive to environment, and are at the same time so intimately con- 

 cerned in the process of inheritance — a law which sums up their 

 influence upon resemblance and variation in animals — there is 

 no need to stress their importance for the practical science and 

 art of good breeding, eugenics. Another mode of approach to its 

 problems is opened up, and fresh enthusiasm instilled into its 

 hopes and aspirations. A method of analysis of the factors in- 

 volved, together with rules for the prediction of the outcome of 

 certain matings, when finally worked out, will elevate its pro- 

 cedure to the level of the more exact sciences. 



A man's chief gift to his children is his internal secretion com- 

 position. The endocrines are truly the matter of breeding as 

 they are of growth. They are the material carriers of the in- 

 herited physical and psychic dispositions, powers, abilities and 

 disabilities from the soma to the germplasm and back from the 

 germplasm to the soma. All kinds of questions arise as soon as 



