What are desirable and undesirable matings?  The general law followed by nature in her helterskelter way seems to be the production of the greatest number of hybrids and variations possible, whether for good or evil does not matter.  Certain endocrine types appear to be specially attracted to others belonging to the same group.  Thus thymus-centered types frequently marry.  The ante-pituitary type of male, the strongly masculine, mates often with the post-pituitary type of female, the markedly feminine.  The children exhibit the lineaments of the pituitary-centered type.  The general trend seems to be the establishment of a better balanced, equilibrated type.  Yet the children often are apt to segregate into pituitary dominants or pituitary deficients.  Happiness and unhappiness in marriage should be examined from the standpoint of endocrine compatibility or incompatibility.  Likewise those divorced or about to be divorced.

The correction of endocrine defects, disturbances, imbalances and instabilities, before mating, presents another field.  It remains to be seen whether we shall thereby, in one generation, be able to affect at all the germplasm, hitherto revered by all pious biologists as an environment-proof holy of holies.  No one can deny, in the face of the multitude of evidence available, that internal secretion disturbances occur in the mother, which, when grave, offer in the infant gross proof of their significance, and therefore when slight must more subtly work upon it.  Endocrine disturbances in infancy have been traced to endocrine disturbances in the mother during pregnancy.  Pregnant animals fed on thyroid give birth to young with large thymus glands.  The diet of the mother has been proved conclusively to influence the development and constitution of the child.  As the internal secretions influence the history of the food in the body, they affect development in the womb indirectly as well as directly.  Certainly, whether or no we learn how to change the nature of germplasm within a short time, we have in the endocrines the means at hand for affecting the whole individual that is born and sees the light of day.

THE CONTROL OF MUTATIONS

The true physical and intellectual evolution of man depends upon the production of mutations of a desirable kind that can survive.  The information furnished by the study of the endocrines concerning the genesis of personality provides the foundations for a positive eugenics, a eugenics of the encouragement of desirable matings, with the proper legal and social procedures.  Selective breeding for the production of the best endocrine types should become practicable.