Distinctive features of sub-species (races [1] or groups) of humans have
evolved as adaptations to particular environmental conditions. These
include:
* depth of skin colour (due to production of melanin) is related to
amount of UV radiation; dark skinned indigenous peoples in Africa and
Australia have a lower incidence of skin cancer [2] than light skinned
people;
* light skin is an adaptation [3] to reduced UV in far northern areas; a
certain amount of UV is necessary for vitamin D production which reduces
the incidence of rickets;
* Inuits of Alaska and far N America are dark skinned but the fish they
eat is high in Vitamin D; dark skinned immigrants to N Europe have a higher
incidence of rickets than light skinned people;
* epicanthic fold (fatty tissue) above the eyelid reduces the chance of
damage to the eye from frost, cold winds, UV and severe climatic conditions
of higher altitudes;
* the relationship between build and temperature (related to distance
from the Equator); the closer to the Equator the greater the height/weight
ratio; think in terms of surface area to volume ratio and heat loss;
* the shape and size of the nose varies according to climate; broad, flat
noses are common to populations [4] in hot, dry climates and smallest in
cold regions of the Arctic, Central Asia Plateaux; the difference is
evident in the range of size in N American Indians from the tip of S
America (very small), through Central and SW America (largest) to Alaska
and Canada (very small);
* high cheekbones are common to Asians;
* temperature tolerance varies; many groups of aboriginal Australians can
tolerate large daily ranges in temperature and the Indians of Tierra del
Fuego can tolerate extremely low temperatures;
* the colour, texture and curliness of hair can also be related to
geographic distribution and the climatic conditions experienced.
With increased immigration and emigration between distinct groups of
humans which evolved differently due to geographic isolation, there is
greater gene flow. The characteristics which could identify people as
coming from different parts of the world are slowly merging.
