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Thread: Black-White Differences in Digit Ratio During Prenatal Development

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    Black-White Differences in Digit Ratio During Prenatal Development

    An exhibit from the 1921 second international congress of eugenics shows black-white 2d:4d differences established by the third month of gestation [1].

    While this bit of evidence does not definitively rule out involvement of androgens in the black-white divergence in digit ratio, it certainly does nothing to quell my doubts about the meaningfulness of cross-racial comparisons of digit ratio for inferring cross-racial differences in prenatal testosterone exposure. The critical windows of androgen exposure for developing males seem to come with mid-gestational and postnatal surges of testosterone to near-adult levels [2]. I'm inclined to believe, rather, black-white differences in digit ratio are due largely if not entirely to genetic factors unconnected to prenatal androgenization. On an entirely unrelated note, a caption above reads:
    The hand is relatively broader and slightly shorter and the thumb relatively longer in the white fetus than in the negro fetus
    Coincidentally, according to the second source I cite above (a review article from 2006):
    Non-human apes and brachiating monkeys have shorter thumbs and longer fingers, and also lower 2D:4D.
    Other differences reported in the 1921 study include smaller brain case and higher frequency of evolution toe in black fetuses (continue reading).

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    But within a population digit ratio (2d:4d) is a stable marker for androphiles and gynophiles, in both sexes. Common sense says there are other factors involved. But gays are womanish and lesbians are mannish. At the same time other suggestions that digit ratio demonstrates risk of heart disease or schizophrenia, remain unverified.

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