The Second to Fourth Digit Ratio (2D:4D) in a Japanese Twin Sample: Heritability, Prenatal Hormone Transfer, and Association with Sexual Orientation

  title={The Second to Fourth Digit Ratio (2D:4D) in a Japanese Twin Sample: Heritability, Prenatal Hormone Transfer, and Association with Sexual Orientation},
  author={Kai Hiraishi and Shoko Sasaki and Chizuru Shikishima and Juko Ando},
  journal={Archives of Sexual Behavior},
The second to fourth digit ratio has been argued to reflect prenatal hormonal influences and is reportedly associated with various psychological and behavioral traits, such as sexual orientation, cognitive abilities, and personality. We examined genetic and environmental influences on the second to fourth digit ratio (2D:4D) using a Japanese twin sample (N = 300). The genetic analysis showed substantial additive genetic influences for both right and left hand 2D:4D. The rest of the variance was… 
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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
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.
Heritability of the Second to Fourth Digit Ratio (2d:4d): A Twin Study
A substantial genetic contribution is suggested to the determination of this hormonally related skeletal ratio in women, which could be more influential than the effects of common prenatal environmental factors.
Brief communication: Familial resemblance in digit ratio (2D:4D).
Familial resemblance in the second-to-fourth digit ratio (2D:4D), a proxy for prenatal androgen action, was studied in 1,260 individuals from 235 Austrian families and heritability estimates based on parent-child and full-sib dyad similarity indicated substantial genetic contributions to trait expression.
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Multivariate modeling of the left- and right-hand measurements revealed significant genetic and environmental covariation between hands, suggesting that X-linked effects (such as the previously identified association with the Androgen receptor) are likely to be small.
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Differences in 2D:4D ratio suggest that MZ twins share virtually the same genes, and lower ratio in lesbians is a result of differences in prenatal environment.
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Low values of 2D:4D were associated with large family size in men and the situation was less clear in women but on balance there was evidence to support a relationship between high values of two to fourth digit ratio and large family sizes.