But the biologist should be able to go farther.  If the eugenist is to limit himself to the method of the animal breeder he will have to rest satisfied with the characters or hereditary factors given, that turn up spontaneously in an individual.  But with the internal secretions as the controllable controllers of mutations, the outlook changes.  It should become possible to produce new mutations, good and bad, to speed up their production at any rate.  The feeding of thyroid to a gifted father before procreation might enhance immeasurably the chances of transmission of his gift as well as of its intensification in his offspring.  A field of investigation is opened that would embrace in due time the deliberate control of human evolution.

All the physical traits, stature, color, muscle function, and so on, offer themselves for improvement, as well as brain size, and the intellectual and emotional factors which have dominated man’s social evolution.  The general prevalence of nervous disorders in civilized countries, visible even in the nervous infants the specialist in children’s diseases is called upon to treat, shows that the nervous system of the better part of mankind is in a state of unstable equilibrium.  It may be another example of the curious coincidences that have been called the Fitness of the Environment that the investigation of the endocrines promises to put into our hands the instruments of the control of the future of the nervous system.  In general, meanwhile, the eugenist should strive for raising the level of the endocrine potential, and discourage its lowering.  That means the encouragement of matings in which all the internal secretion activities are reinforced.  On the other hand, those internal secretion combinations, generally leading to a deficiency of all of them which produce types of mental defectives, delinquency and crime should not be allowed to occur.

THE INFLUENCE OF ENVIRONMENT

What suggestions now are there for the euthenist who would control the influence of environment upon child culture.  There are certain pertinent facts and leads that are worth considering.

In analyzing environment, one must distinguish sharply in the jungle, the non-living factors from the living.  For while the nonliving act upon the endocrines directly, the living act upon the vegetative system, as a whole.  The non-living factors are those with the intimate scrutiny of which physics and chemistry have busied themselves:  food, water, air, light, heat, electricity, magnetism.  The living are the animals that prowl all over the planet, the predatories spreading the gospel of fear.

The dietetic habits of a person, for instance, are known to have an influence upon the glands of internal secretion.  Meat-eating produces a greater call upon the thyroid than any other form of food.  In time this ought to produce a degree of hyperthyroidism in the carniverous populations.  Pre-war statistics concerning meat-eating in different countries show the greatest meat-eating among the English-speaking groups, who all in all must be admitted the most energetic.