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.
Meat per Day per Countries Capita in Grams
Australia 306
U.S. of America 149
Great Britain 130
France 92
Belgium and Holland 86
Austria-Hungary 79
Russia 59
Spain 61
Italy 29
Japan 25
Sea-water contains iodine. People living in contact with sea-water would be apt to get more iodine in their systems, and so a greater degree of thyroid activity. On the other hand, certain bodies and sources of inland water hold something deleterious to the thyroid, so that whole populations in Europe, Asia and America drinking such water have become goitrous and cretinous, and a large percentage straight imbeciles. Endemic cretinism is the name given to the condition. In parts of Switzerland, Savoy, Tyrol and the Pyrenees, in America around some of the Great Lakes, there are still such foci. Marco Polo described similar areas he encountered in his travels through Asia.
Certain foods with aphrodisiac qualities may act by stimulating the internal secretion of the sex glands. A type of pituitocentric has an almost uncontrollable craving for sweets. Alcohol and the endocrines remain to be studied.
Light, heat and humidity stand in some special relation to the adrenals. Pigment deposit in the skin as protection against light is controlled by the adrenal cortex. The reaction of the skin blood vessels to heat and humidity is regulated by the adrenal medulla. A change in the adrenal as a response to changes of temperature and humidity in an environment would result in a number of concomitant transformations throughout the body. So variation and adaptation are probably connected. Most Europeans living for a sufficiently long time in the tropics suffer from a combination of symptoms spoken of as "Punjab head" or "Bengal head." The condition is probably the result of excessive adrenal stimulation by the excessive heat and light of the tropical sun, followed by a reaction of exhaustion and failure, with the consequent phenomena of a form of neurasthenia. In the section on the pineal gland there was mentioned the relation between light and the pineal gland in growing animals, and how it serves to keep in check the sex-stimulating action of light. The earlier puberty and menstruation of the warmer climates may be explained as due to an earlier regression of the pineal under the pressure of a great amount of light playing upon the skin.
All these, and many more could be cited, are instances of the direct influence of environmental factors upon one or more of the endocrines, and so upon the organism as a whole. Indeed, stimuli may be considered to modify an organism only in so far as they modify the glands of internal secretion. Consequently, climatic factors will tend to make a population possess certain points of resemblance in common.
Varieties of the human race exist as do varieties of dogs. The pekingese and the fox terrier are as different as the Slav and Latin are different: because of differences in internal secretion make-up. The Slav peasant is definitely subthyroid in his general effect: round head, coarse features, stubby hands, and his stolid, brooding intellectual and emotional reaction. The Latin shows a pronounced adrenal streak in his coloration, his emotivity, his susceptibility to neurosis and psychosis. H. Laing Gordon, a Scot physician, reported that of 700 cases he studied, more than twice as many of duplex eyed individuals (brown or black, i.e., adrenal-centered most often), were susceptible to the mental disturbances of war as the simplex (blue or gray-eyed, i.e., thyroid-centered most often). He also pointed out that such individuals tend to have a narrow and abnormally arched palate. The Anglo-Saxon tends to be more sharply pituitarized, his features are more clean-cut, his mentality more stable. The Frenchman is rather a cross between the Anglo-Saxon pituitary-centered and the Italian or Spanish adrenal-centered.
So national resemblances, traceable to climatic influences being repeated from generation to generation upon the endocrines, may be explained physiologically. The physiologic interpretation of history will indeed be found the broadest, including as complementary Buckle's climatic theory, Hegel's ideas on the influence of ideas, and Marx's on the superiority of the economic motives and forces.