The balance of sex hormones may explain why men have different finger-length proportions than women, according to a new study in the Proceedings of the National Academy of Sciences.

Women usually have an index finger that is longer than their ring finger, while the reverse is true in most men. Scientists have long suspected that sex hormones play a role in this difference, but until now, had no experimental evidence for such a mechanism.

University of Florida researchers examined the developing fingers in female and male mouse embryos. When they tweaked the levels of estrogen and testosterone the mice were exposed to in utero, the finger skeletal precursor cells divided at different rates. The fourth finger grew proportionally longer in response to additional testosterone, while estrogen made the second finger longer. The results suggest that digit length could be used as a marker for early prenatal exposure...

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