Colossium Magazine March Issue_2019 | Page 72

skin pigmentation, which acted as a mech- anism of natural selection against folate depletion, and to a lesser extent, DNA dam- age. The primary factor contributing to the evolution of dark skin pigmentation was the breakdown of folate in reaction to ultraviolet radiation; the relationship between folate breakdown induced by ultraviolet radiation and reduced fitness as a failure of normal embryogenesis and spermatogenesis led to the selection of dark skin pigmentation. By the time modern Homo sapiens evolved, all humans were dark-skinned. Humans with dark skin pigmentation have skin naturally rich in melanin (especially eu- melanin), and have more melanosomes which provide a superior protection against the del- eterious effects of ultraviolet radiation. This helps the body to retain its folate reserves and protects against damage to the DNA. D ark-skinned people who live in high latitudes with mild sunlight are at an increased risk – espe- cially in the winter – of vitamin D defi- ciency. As a conse- quence of vitamin D deficiency, they are at a higher risk of de- veloping rickets, and numerous types of cancers, and possibly car- diovascular disease and low immune system activity. However, some recent studies have questioned if the thresholds indicating Vita- min D deficiency in light-skinned individuals are relevant for dark-skinned individuals, as they found that, on average, dark-skinned in- dividuals have higher bone density and lower risk of fractures than lighter-skinned individ- uals with the same levels of Vitamin D. This is attributed as, possibly, due to lower presence of Vitamin D binding agents (and thus higher 72 | Colossium . March 2019 bioavailability) in dark-skinned individuals. The global distribution of generally dark- skinned populations is strongly correlated with the high ultraviolet radiation levels of the regions inhabited by them. These popula- tions, almost-exclusively, live near the equa- tor, in tropical areas with intense sunlight: Australia, Melanesia, New Guinea, South Asia and, Africa. Studies into these popula- tions indicates dark skin is a retention of the pre-existing high UV adapted state of modern humans before the out of Africa migration and not a later evo- lutionary adaptation. Due to mass migration and increased mobility of people between geographical regions in the re- cent past, dark- skinned popula- tions today are found all over the world.