Digit Ratio (2D:4D) in Homosexual and Heterosexual Men from Austria

@article{Voracek2005DigitR,
  title={Digit Ratio (2D:4D) in Homosexual and Heterosexual Men from Austria},
  author={Martin Voracek and John T. Manning and Ivo Ponocny},
  journal={Archives of Sexual Behavior},
  year={2005},
  volume={34},
  pages={335-340}
}
Neurohormonal theories of sexual orientation emphasize the organizational effects of testosterone on the developing brain. A recent suggestion, that the ratio of the length of the 2nd and 4th digits (2D:4D) is negatively correlated with prenatal testosterone, has led to a number of studies of 2D:4D in homosexual and heterosexual men and women. The results have been mixed. In comparison to heterosexual men, mean 2D:4D in gay men has been reported to be hypermasculinized (lower 2D:4D… 
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Digit Ratio (2D:4D) in Twins: Heritability Estimates and Evidence for a Masculinized Trait Expression in Women from opposite-Sex Pairs
TLDR
Investigation of the 2D:4D ratio of 44 men and 70 women from 36 identical and 21 fraternal twin pairs suggested that the trait is substantially heritable, consistent with a prediction from sex-hormone transfer theory.
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