The natural selection hypothesis suggests that lighter skin colour evolved to optimise vitamin D production. Some authors question if vitamin D deficiency leads to sufficient health problems to act as a selection pressure. This paper reviews the numerous effects of vitamin D deficiency on human health and argues that vitamin D deficiency is sufficient to pose as a potent selection pressure for lighter skin colour. Vitamin D deficiency manifesting as rickets and osteomalacia are sufficient to impair reproductive success, but additionally, animal studies and some clinical observations suggest that vitamin D may have more direct impact on human fertility. Vitamin D deficiency may lead to a whole host of clinical conditions which impair health and increase mortality rates: increase susceptibility to bacterial and viral infections; rickets, osteomalacia and osteoporosis, with increased risk of falls and fractures; increased risk of cancers; hypertension and cardiovascular disease; maturity onset diabetes; autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease and Type 1 diabetes; and gum disease. We submit that at higher latitudes, lighter skin colour evolved to facilitate vitamin D production under conditions of low ultra-violet B radiation in order to avoid a plethora of ill health, reproductive difficulties and early mortality.
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