The Indians of South America, though all fundamentally of the same ethnic stock, are variously acclimated to the warm, damp, forested plains of the Amazon; to the hot, dry, treeless coasts of Peru; and to the cold, arid heights of the Andes. The habitat that bred them tends to hold them, by restricting the range of climate which they can endure. In the zone of the Andean slope lying between 4,000 and 6,000 feet of altitude, which produces the best flavored coffee and which must be cultivated, the imported Indians from the high plateaus and from the low Amazon plains alike sicken and die after a short time; so that they take employment on these coffee plantations for only three or five months, and then return to their own homes. Labor becomes nomadic on these slopes, and in the intervals these farm lands of intensive agriculture show the anomaly of a sparse population only of resident managers.[51] Similarly in the high, dry Himalayan valley of the upper Indus, over 10,000 feet above sea level, the natives of Ladak are restricted to a habitat that yields them little margin of food for natural growth of population but forbids them to emigrate in search of more,—applies at the same time the lash to drive and the leash to hold, for these highlanders soon die when they reach the plains.[52] Here are two antagonistic geographic influences at work from the same environment, one physical and the other social-economic. The Ladaki have reached an interesting resolution of these two forces by the institution of polyandry, which keeps population practically stationary.
Pigmentation and climate.
The relation of pigmentation to climate has long interested geographers as a question of environment; but their speculations on the subject have been barren, because the preliminary investigations of the physiologist, physicist and chemist are still incomplete. The general fact of increasing nigrescence from temperate towards equatorial regions is conspicuous enough, despite some irregularity of the shading.[53] This fact points strongly to some direct relation between climate and pigmentation, but gives no hint how the pigmental processes are affected. The physiologist finds that in the case of the negro, the dark skin is associated with a dense cuticle, diminished perspiration, smaller chests and less respiratory power, a lower temperature and more rapid pulse,[54] all which variations may enter into the problem of the negroes coloring. The question is therefore by no means simple.
Yet it is generally conceded by scientists that pigment is a protective device of nature. The negro's skin is comparatively insensitive to a sun heat that blisters a white man. Livingstone found the bodies of albino negroes in Bechuana Land always blistered on exposure to the sun,[55] and a like effect has been observed among albino Polynesians, and Melanesians of Fiji.[56] Paul Ehrenreich finds that the degree of coloration depends less upon annual temperature than upon the direct effect of the sun's rays; and that therefore a people dwelling in a cool, dry climate, but exposed to the sun may be darker than another in a hot, moist climate but living in a dense forest. The forest-dwelling Botokudos of the upper San Francisco River in Brazil are fairer than the kindred Kayapo tribe, who inhabit the open campos; and the Arawak of the Purus River forests are lighter than their fellows in the central Matto Grosso.[57] Sea-faring coast folk, who are constantly exposed to the sun, especially in the Tropics, show a deeper pigmentation than their kindred of the wooded interior.[58] The coast Moros of western Mindanao are darker than the Subanos, their Malay brethren of the back country, the lightness of whose color can be explained by their forest life.[59] So the Duallas of the Kamerun coast of Africa are darker than the Bakwiri inhabiting the forested mountains just behind them, though both tribes belong to the Bantu group of people.[60] Here light, in contradistinction to heat, appears the dominant factor in pigmentation. A recent theory, advanced by von Schmaedel in 1895, rests upon the chemical power of light. It holds that the black pigment renders the negro skin insensitive to the luminous or actinic effects of solar radiation, which are far more destructive to living protoplasm than the merely calorific effects.[61]
Pigmentation and altitude
Coloration responds to other more obscure influences of environment. A close connection between pigmentation and elevation above sea level has been established: a high altitude operates like a high latitude. Blondness increases appreciably on the higher slopes of the Black Forest, Vosges Mountains, and Swiss Alps, though these isolated highlands are the stronghold of the brunette Alpine race.[62] Livi, in his treatise on military anthropometry, deduced a special action of mountains upon pigmentation on observing a prevailing increase of blondness in Italy above the four-hundred meter line, a phenomenon which came out as strongly in Basilicata and Calabria provinces of the south as in Piedmont and Lombardy in the north.[63] The dark Hamitic Berbers of northern Africa have developed an unmistakable blond variant in high valleys of the Atlas range, which in a sub-tropical region rises to the height of 12,000 feet. Here among the Kabyles the population is fair; grey, blue or green eyes are frequent, as is also reddish blond or chestnut hair.[64] Waitz long ago affirmed this tendency of mountaineers to lighter coloring from his study of primitive peoples.[65] The modification can not be attributed wholly to climatic contrast between mountain and plain. Some other factor, like the economic poverty of the environment and the poor food-supply, as Livi suggests, has had a hand in the result; but just what it is or how it has operated cannot yet be defined.[66]
Difficulty of Generalization