Why Skin Comes In Colors

Why Skin Comes In Colors

I have read an article on 'Why skin comes in colors" by Blake Edgar, and he gives a brief analysis of why that is so. According to my research, skin color is largely determined by the amount of melanin the skin produces. Dark-skinned individuals produce more melanin than light-skinned individuals. At least three genes regulate the amount of melanin produced. Each gene has two forms: dark-skin allele (A, B, and C) and light-skin allele (a, b, and c). Neither allele is completely dominant to the other, and heterozygotes exhibit an intermediate phenotype (incomplete dominance). Each dark-skin allele in the genotype adds pigment by increasing melanin production. There are seven different shades of skin color ranging from very light (aabbcc) to very dark (AABBC); most individuals have the intermediate skin color (AaBbCc). A cross between two individuals with intermediate skin color produces offspring with a range of phenotypes (bell-shaped curve). According to the article, some suggest there is a linked between shades of skin color and degrees of exposure to the sun's UV rays. Jablonski was the first to link sun overexposure and neural tube defects as part of a mechanism regulating skin tone.

The mechanism works by adjusting levels of melanin, a dark skin pigment that occurs in all vertebrates and acts as a natural sunblock. The more you have, the better your protection from potentially harmful radiation. As the article discussed, "the dark skin probably became an essential human trait million of years ago, when fossil evidence from Kenya suggests that our ancestors first attained human-like body proportions and perhaps had less body hair, more sweat glands, and lived in more exposed habitats than their predecessors".As an example, consider a group of people who moved to a cold region with little sunlight. Here, the dark-skinned members would not be able to produce enough vitamin D, and thus would be less healthy and have fewer children. Therefore, in time, the light-skinned members would predominate. If several different groups went to such an area, and if one group happened to be carrying few genes for lightness, this particular group in time could die out. Thus, natural selection acts on the characteristics already present, and does not create new ones.

On the other hand, fair-skinned people in very sunny regions could easily be affected by skin cancer. Thus, in these regions dark-skinned people