As architects of human qualities the endocrines must be involved in the Mendelian unit factors. Moreover, they seem to act upon a particular locale in different degrees, which is the strongest argument against the resolution of a number of structural traits into Mendelian unit characters. Most characters, somatic or psychic, are the products not of the action of one internal secretion alone, but of the interlinked activities of all of them. The amount of fat deposited under the skin, for instance, is influenced by the pituitary, the thyroid, the pancreas, the liver, the adrenals and the sex glands. Other qualities, likewise, are resultants of a compromise between all the endocrine factors comprising the equation of the individual. If we are to look for unit factors at all in endocrine heredity, we must look more deeply into constitution, and measure the hormone potentials and their mobilization or suppression.
It will, in all probability, be found that the stability or instability of an endocrine will have a good deal to do with the part played by it in inheritance as well as in the life of the individual An unstable pituitocentric marrying another unstable pituitocentric will have children either exceptionally small or tall, or abnormally bright or stupid. The instability tends to right itself in the next generation, or that following. Genius as a sport, as well as sudden degeneration of family stock, the whole problem of mutation, may be closely connected with this tendency.
It has been noted that the extinction of species has been preceded by a great increase in their size, for example, the case of the great reptilia of prehistoric time. That possibly represented pituitary stabilization, and so an abeyance of the ability to vary, necessary for fresh adaptation to a changing environment. Indeed, endocrine instability appears the fundamental condition of the tendency to vary, endocrine stability the opposite.
Certain endocrine facts in relation to heredity should be mentioned. The daughters of mothers who menstruated early, themselves menstruate early. Animals fed upon thyroid during pregnancy, comparable to the thyrocentric, give birth to offspring with a very large thymus, comparable to the thymocentric. Women with partial thyroid deficiency, or myxedema, bear cretins. These are suggestive of what the internal secretions may do to an individual in inheritance and development. Inherited endocrine potential is the maximum reaction of which a gland is capable. This matter of potential is comparable to the factor of reserve power or margin of safety demonstrated up to the hilt for such organs as the heart and kidney as varying from individual to individual. A low potential, like instability of an internal secretion gland, may be latent, and not made manifest until the proper stimulus, the maximum amount of stress and strain, like accident, disease, shock or war, arrives.
When the individual is tested the effects may be purely local because there is always in the organism a point of least resistance. Physical changes alone may be prominent. Or because somatic changes are minor, the psychic will dominate the picture. An attack of the "blues," unaccompanied by any demonstrable transformation of the bodily processes, may be the sole symptom of an endocrine failure somewhere in the chain due to hereditary weakness or low potential.
So we may account for family trends and streaks, for varieties and strains among individuals, upon more precise lines based upon endocrine analysis. Family disturbances of the internal secretions of the extreme sort denominated disease are well known. Indeed, a number of family diseases or predispositions to diseases, have been traced to them. Predisposition in any direction will probably be shown to be caused by them, within limits. Research here has its opportunity.
THE IMPROVEMENT OF RACIAL STOCK
A vast new territory of inquiry and achievement, as yet totally unexplored, is opened by the endocrines to the eugenists, and those idealists whose most earnest aspiration is the improvement of racial stock as a necessary preliminary to improvement of racial life. Beginning with Galton, they have brought to light a great collection of data to prove that human traits and faculties, good and bad, are inherited. Ability has been shown to run in certain families and degeneracy in others. Yet all of the practical net result has been summed up in the term "negative eugenics," the eugenics of prohibition and warning.
Now the concept of personality, as woven around a system of chemical reflexes, handed on from generation to generation, is bound to change all that, and to create a structure of positive eugenics. It has been said that what radium is to chemistry, the internal secretions are to physiology. Just as radium enlightens the chemist about the history of matter, and the integrations and disintegrations constituting the life of an element—the internal secretions illuminate the history of the individual as part of the life of the race, and of its integrations and disintegrations. Seeing the individual as a system of chemical substances interacting will assist enormously to predict the nature, character and constitution of his descendants, which is essentially what the eugenist is after.
The study of matings, the heart of the matter, will concern itself with the investigation and comparison of the kind of endocrine personalities that mate, the internal secretion predominances that cross, and the consequent endocrine personality of the offspring. Data bearing upon physique and physiognomy, details of anatomy and function, mind and behaviour will so be co-ordinated as no eugenist has hitherto succeeded in doing. Laws of endocrine inheritance will emerge that will bring the control of heredity within measurable distance. Standards and norms of a new kind would be obtained.