Races of man / by Sonia Cole.

  • Sonia Mary Cole
Date:
1965
Catalogue details
    25/150 page 20
    skins were 'eliminated' when their ancestors passed through the 'cold filter' after crossing the Bering Straits and no subsequent mutations for this character have arisen since the American Indians became isolated. Since there is no evidence of genes for black skins having been present in their Mongoloid ancestors, however, perhaps 'eliminated' is not the right word. It seems most likely that early man had a brownish skin and that mutations took place both in the direction of lighter and darker skins. Mutations involving increased pigmentation would be advantageous in the tropics and were therefore encouraged by natural selection. Mutations towards blondness would seem to offer an advantage in relation to vitamin D formation in higher latitudes, sunlight being absorbed more readily through lighter skins. Hair Form and Colour Hair has been classified as follows: Leiotrichous (straight, as in the Mongoloids) Cynotrichous (straight, wavy or curly, as in Caucasoids) Helicotrichous (helical, or spiral, as in Negroids) Tightly curled hair occurs in two forms—helical, in which the loops are of constant diameter, and spiral, in which the loops diminish in diameter outwards from the scalp. The extreme form of spiral hair is known as 'peppercorn', in which there are open spaces between the clusters of hair. The greatest centre of helical hair is in Africa, with another centre in Mela nesia and with islands of spiral-haired Negritos in between. Helical hair, as seen for instance in Sudanese Negroes and Melanesians, grows in a tight mat and might have a protective value in areas of strong sunlight where there is little shade. The centres of spiral hair follow the belt of tropical rain forests, a belt which was probably wider at various times in the past. This form of hair seems to be of ancient origin and has spread further afield than its companion black skin. Peppercorn hair might be an advantage in the hot, damp conditions of forests since the open spaces between the clusters of hair would allow sweat from the scalp to evaporate. Peppercorn hair is typical of Bushmen, who now live in the desert ; but they undoubtedly had a wider distribution in the past and may have had a common origin with the pygmies, who also have peppercorn hair but to a lesser extent. This peculiar form of hair is also found among the Andaman Islanders.
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