Human skin color

Human skin color can range from almost black to pinkish white. Skin color has sometimes been used in an attempt to define human races. In general, people with recent ancestors in sunny regions have darker skin then people with recent ancestors in regions that lack much sun light.

Skin color is determined by the amount and type of the pigment melanin in the skin. Melanin comes in two types: phenomelanin (red to yellow) and eumelanin (dark brown to black). This in turn is determined by 4-6 genes which operate under incomplete dominance. One copy of each of those genes is inherited from the father and one from the mother. Each gene comes in several alleles, resulting in a variety of different skin colors.

Dark skin protects against skin cancer, mutations in the skin induced by ultraviolet light. Light skinned persons have about a tenfold risk of dying from skin cancer under equal sun conditions. The advantage of light skin is that it lets more sunlight through, which leads to increased vitamin D₃ production necessary for calcium absorbtion and bone growth. People in sun-poor regions often lack vitamin D₃ and light skin is therefore an advantage for them. People in sun-rich regions typically have an overabundance of vitamin D₃.