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Vitamin D affects bone growth, and, without a sufficient amount, the disease known as rickets would have been devastating to early human groups trying to survive in the cold, wintry weather of the north. As these groups adapted to northern climates with limited sunlight, natural selection brought about the gradual loss of melanin in favour of skin tones that enabled some individuals to better synthesize vitamin D.


https://archive.ph/d7nKz



The low incidence of skin cancers in darker skinned groups is primarily a result of photo-protection provided by increased epidermal melanin, which filters twice as much ultraviolet (UV) radiation as does that in the epidermis of Caucasians (Montagna and Carlisle, 1991).


https://archive.ph/2RynK