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There may also be significant within-caucasian differences in concentration of prenatal testosterone. Testosterone, vitamin-D, and melanin compete for the same precursor cholestero (Bell et all.1980). In areas with low levels of sunlight the synthesis of vitamin D is reduced. It may then be adaptive to reduce melanin production and therefore increase the synthesis of vitamin D. Reducing the production of melanin could also lead to increase in the production of testosterone. There is indirect evidence that blond hair may be linked with high prenatal testosterone. Geschwind and Galaburda (1985a) have argued that the frequency of non-right-handedness is increased by high level of in utero testosterone (see chapter 4 for evidence of an association between 2D:4D and left hand preference.) They found that in sample of 986 nonblonds 76% were right-handed, 12% were ambidextrious, and 12 % were left-handed. The corresponding figures for 131 blond-haired subjects were 56%, 28% and 16% respectively. These observations are consistent with the possibility of high prenatal testosterone and low digit ratios in people of northern latitudes.
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