Page:Popular Science Monthly Volume 50.djvu/782

760 we are warranted in dismissing them from further consideration in this place.

Anthropologists have endeavored for a long time to find the cause of these differences in the color of the skin. Some have asserted that they were the direct effects of heat; but our map shows that the American stock, for example, is in no wise affected by it. A consideration of all the races of the earth in general shows no correspondence whatever of the color of the skin with the isothermal lines. The Chinese are the same color at Singapore as at Pekin and at Kamchatka. Failing in this explanation, scientists have endeavored to connect pigmentation of the skin with humidity, or with heat and humidity combined; but in Africa, as we saw, the only really black negroes are in the dry region near the Sahara Desert, while the Congo basin, one of the most humid regions on the globe, is distinctly lighter in tint. Others have attempted to prove that this color, again, might be due to the influence of the tropical sun, or perhaps to oxygenation taking place under the stimulation of exposure to solar rays. This has at first sight a measure of probability, since the color which appears in tanning or freckles is not to be distinguished physiologically from the pigment which forms in the main body of the skin of the darker races. The objection to this hypothesis is that the covered portions of the body are equally dark with the exposed ones, and that certain groups of men whose lives are peculiarly sedentary, such as the Jews, who have spent much of their time for centuries within doors, are distinctly darker than other races whose occupations keep them continually in the open air. This holds true whether in the tropics or in the northern part of Europe. This local coloration in tanning, moreover, due to the direct influence of the sun is not hereditary, as far as we can determine. Sailors' children are not darker than those of the merchant, even after generations of men have followed the same profession. Each of these theories seems to fail as a sole explanation. The best working hypothesis is, nevertheless, that this coloration is due to the combined influences of a great number of factors of environment working through physiological processes, none of which can be isolated from the others. One point is certain, whatever the cause may be—that this characteristic has been very slowly acquired, and has to-day become exceedingly persistent in the several races.

Study of the color of the skin alone has nothing further to interest us in this inquiry than the very general conclusions we have just outlined. We are compelled to turn to an allied