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 therefore 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 certainly capable of being filled in.

THE BEARING ON BREEDING

Since the endocrine glands are so subtly sensitive and responsive to environment, and are at the same time so intimately concerned 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 involved, together with rules for the prediction of the outcome of certain matings, when finally worked out, will elevate its procedure to the level of the more exact sciences.

A man’s chief gift to his children is his internal secretion composition.  The endocrines are truly the matter of breeding as they are of growth.  They are the material carriers of the inherited 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 one attempts to consider the bearing of this underlying principle upon concrete situations.  What happens, say, when a pituitocentric mates with a thyrocentric?  Or when a pituitocentric marries a pituitocentric?  Is there a reinforcement or a cancellation of the dominant endocrine?  Is there a quantitative addition of internal glandular tendencies in the germplasm, or a more complex rearrangement dependent upon reactions between all the internal secretions?