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Skin Color from WikiPedia:

Human skin color can range from almost black (due to very high concentrations of the dark brown pigment melanin) to nearly colorless (appearing pinkish white due to the blood vessels under the skin) in different people. Skin color is determined primarily by the amount and type of melanin, the pigment in the skin. Variation in skin color is largely due to genetics.

As a general pattern people with ancestors from tropical regions and higher altitudes (hence greater UV light exposure) have darker skin than people with ancestors from subtropical regions. This is far from a hard and fast rule however, because many light skinned groups have managed to survive at the equator by way of social adaptation. The same can be said of dark skinned groups living at subtropical latitudes.

Melanin comes in two types: pheomelanin (red) and eumelanin (very dark brown). Both amount and type are determined by four to six genes which operate under incomplete dominance. One copy of each of those genes is inherited from each parent. Each gene comes in several alleles, resulting in the great variety of different skin tones.

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