|MadSci Network: Evolution|
Dear questioner: First of all, most modern day biological anthropologists do not find that the concept of 'race' is useful when applied to humans. Human biological variation is better viewed in terms of 'clines,' in other words gradual changes in the frequency of specific traits over space. You are right that humans were basically one skin color (darkly pigmented) when they all lived in equatorial Africa. Within the past several hundred thousand years, as humans spread out to the north and south of the equator this particular phenotypical trait can be seen in terms of a gradual gradient reflecting lighter skin color the further north or south from the equator that humans settled. This gradation in skin color is usually understood as involving the risk/benefit of ultraviolet radiation vs. intake of vitamin D. Biological Anthropologists have found many clines for numerous human biological traits some fairly simple and others very complicated. I recommend for further reading that you take a look at Stephen Jay Gould's book "The Mismeasure of Man" and a good textbook of biological anthropology such as Weiss and Mann's "Human Biology and Behavior." Dr. Smerken
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