Is white skin an adaptation to the cereal diet that Europeans have been consuming for the past five to seven thousand years?
When early Europeans switched from hunting and gathering to cereal agriculture, the new diet may have provided less vitamin D (i.e., from fatty fish), which the body needs to metabolize calcium and create strong bones. There would thus have been stronger selection for endogenous production of vitamin D in the skin’s tissues. Since such production requires UV-B light and since melanin blocks UV, this selection may have favored a lighter skin color (Sweet, 2002). In addition, cereals seem to increase vitamin D requirements by decreasing calcium absorption and by shortening the half-life of the main blood metabolite of vitamin D (Pettifor, 1994; see Paleodiet).
Undoubtedly, lighter skin allows more UV-B into the skin. As Robins (1991, pp. 60-61) notes, black African skin transmits three to five times less UV than does European skin. But is this a serious constraint on vitamin D production? Apparently not. Blood metabolites of vitamin D show similar increases in Asian, Caucasoid, and Negroid subjects when their skin is either artificially irradiated with UV-B or exposed to natural sunlight from March to October in Birmingham, England (Brazerol et al., 1988; Ellis et al., 1977; Lo et al., 1986; Stamp, 1975; also see discussion in Robins, 1991, pp. 204-205).
The vitamin D hypothesis also implies that European skin turned white almost at the dawn of human history. Cereal agriculture did not reach northern Europe until some 5,000 years ago and, presumably, the whitening of northern European skin would not have been complete until well into the historical period. Is this a realistic assumption, given the depictions of white-skinned Europeans in early Egyptian art?
Brazerol, W.F., McPhee, A.J., Mimouni, F., Specker, B.L., & Tsang, R.C. (1988). Serial ultraviolet B exposure and serum 25 hydroxyvitamin D response in young adult American blacks and whites: no racial differences. Journal of the American College of Nutrition, 7, 111-118.
Ellis, G., Woodhead, J.S., & Cooke, W.T. (1977). Serum-25-hydroxyvitamin-D concentrations in adolescent boys. Lancet, 1, 825-828.
Lo, C.W., Paris, P.W., & Holick, M.F. (1986). Indian and Pakistani immigrants have the capacity as Caucasians to produce vitamin D in response to ultraviolet radiation. American Journal of Clinical Nutrition, 44, 683-685.
Pettifor, J.M. (1994). Privational rickets: a modern perspective. Journal of the Royal Society of Medicine, 87, 723-725.
Robins, A.H. (1991). Biological perspectives on human pigmentation. Cambridge Studies in Biological Anthropology, Cambridge: Cambridge University Press.
Stamp, T.C. (1975). Factors in human vitamin D nutrition and in the production and cure of classical rickets. Proceedings of the Nutrition Society, 34, 119-130.
Sweet, F.W. (2002). The paleo-etiology of human skin tone. Backintyme Essays.