Races of man / by Sonia Cole.

  • Sonia Mary Cole
Date:
1965
Catalogue details
    33/150 page 28
    natural selection, on the other hand, favours types able to withstand change— such as extreme seasonal ranges of temperature or times of famine—but it does not encourage the formation of new genotypes. The Effects of Climate Through natural selection, the effects of climate may encourage some characters and discourage others. In cold climates, adaptations are favoured which minimize heat lossj in hot climates, those which facilitate body cooling are favoured. Such adaptations take place in response to both latitude and altitude. Adaptation to climate in animals in general is governed by three rules. Glo- ger's rule states that pigmentation is greatest in warm and humid areas. The association of black skins with heat applies broadly in the case of man; the fact that desert dwellers have brown rather than black skins can be accounted for by the absence of humidity. In the dry atmosphere of the tropical deserts evaporation takes place readily, so that there is less discomfort than in a damp atmosphere. Also, in many cases the lighter-skinned desert people are comparatively recent arrivals; the Tuareg, for instance, have probably lived in the Sahara for only about 1,500 years. In some areas of extreme cold, brown skins are also found. It has been suggested that the Eskimo are such relatively recent arrivals that they have not had enough time to lose their pigmentation; to some extent, also, their brown skins may serve as a protection against sun glare. There is no reason to suppose that brown skin is ^advantageous in cold areas (as it would be in the case of animals needing camouflage in the snow, thus encouraging selection for white fur or feathers), so there is no apparent reason why it should be eliminated by selection. Bergman's rule states that animals are smaller in warmer than in cooler climates. This does not apply to stature so much as body build. In human popula tions, both the shortest—pygmies—and the tallest—Nuer, Dinka, Tutsi—people on earth live near the equator, but their build is slender. All people living round the Arctic circle are short, but they are thick-set with broad chests and padded with fat. They present the least possible surface in proportion to their volume and weight and are built to radiate as little heat as possible. The third of these rules, Allen's rule, states that the extremities of the body are shorter in cold climates; the extremities include limbs, ears, nose, and tail in the case of animals. The Eskimos have very short legs, toes, fingers and noses. Desert dwellers, on the other hand, have long slender limbs and often prominent noses (which would soon get frozen in Siberia or Greenland).
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