Scientists have found that differences in skin color are most highly related to geographic latitude and average dose of UV radiation (UV-R), allowing for selection of dark skin in equatorial regions of the world and light skin at the poles.1 Darker, eumelanin-rich skin endowed a crucial reproductive success by protecting the body’s folate stores from UV light, thereby preventing neural tube defects. Competing theories, such as protection from skin cancer or predation avoidance in low light, as drivers of dark skin held little significance in comparison to the birth advantage of folate.1 Studies have shown that the melanocortin 1 receptor (MC1R) gene shows close to zero genetic variation among modern Africans, making it possible for melanocytes to produce large amounts of eumelanin.1 Its counterpart MC1R gene varies greatly outside of Africa, allowing for lighter skin.1 Light skin was selected for at greater latitudes most notably to maximize UV-R based conversion of 7-dehydrocholesterol to cholecalciferol, or vitamin D3, in the summer months.1 Adequate vitamin D contributed to stronger immune systems, protection from certain cancers, and reduced female pelvic deformities, which had complicated childbirth. Nature molded us into our fittest selves, or so it thought.1
Trivedi A, Gandhi J. The Evolution of Human Skin Color. JAMA Dermatol. 2017;153(11):1165. doi:10.1001/jamadermatol.2017.3695
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