DNA analysis indicates that all humans descended from a single ancestral group of Africans. Despite the fact that all humans came from the same place, there is still a large variety in the types of skin color, and almost no two skin colors are the same. Scientists have recently done research on the genetics of skin color and how it is passed on from generation to generation. They have determined that it is an incomplete codominant trait, and the color of your skin is affected by the amount of melanin in your body. Light-skinned people have smaller amounts of melanin and dark-skinned people have larger amounts of melanin. The gene that controls the amount of melanin has at least three alleles. Relating skin color back to geography, the worldwide pattern of human skin color is the product of natural selection to regulate the effects of the suns UV radiation in different regions on key nutrients crucial to reproductive success.
One environmental factor that affects skin color is the place you live. If the area receives a lot of sunlight, you will have darker skin (in order to absorb the UV rays) but if your region receives very little sunlight you will have lighter skin. Scientists believe that this is why people living near the tropics tend to be darker skinned then people living near the poles. But if we all were descended from the same area, why are our skin colors so different? The reason for this is migration and natural selection. As humans left Africa and traveled to the poles and reproduced, their offspring did not need to produce as much melanin, because there was not very much sunlight for the melanin to absorb. Another important factor of skin color is vitamin D absorption. A person with very dark skin is able to handle UV rays very well, but if their skin is too dark they will not be able to create vitamin d. Likewise, light skinned people do not handle UV rays well but they are able to produce vitamin D easily.
To read a very interesting article about skin color and the genetics and DNA involved click here
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