Finger-Length Ratios in Female Monozygotic Twins Discordant for Sexual Orientation

@article{Hall2003FingerLengthRI,
  title={Finger-Length Ratios in Female Monozygotic Twins Discordant for Sexual Orientation},
  author={Lynn S. Hall and Craig T. Love},
  journal={Archives of Sexual Behavior},
  year={2003},
  volume={32},
  pages={23-28}
}
The second to fourth finger digit ratio (2D:4D ratio) is a sex-dimorphic characteristic in humans that may reflect relative levels of first trimester prenatal sex hormones. Low interdigital ratio has been associated with high levels of androgens. It has been reported in unrelated women that low 2D:4D ratio is associated with lesbian sexual orientation, but because of the nature of those samples, it was not possible to conclude whether lower ratio (and hypothetically, higher androgen levels) in… 

Finger Length Ratios of Identical Twins with Discordant Sexual Orientations

TLDR
Examination of patterns in identical twins with discordant sexual orientations found males had more masculinized 2D:4D ratios than females, and this sex difference did not vary by sexual orientation.

Prenatal Influences on Sexual Orientation: Digit Ratio (2D:4D) and Number of Older Siblings

Prenatal androgen levels are suggested to influence sexual orientation in both sexes. The 2D:4D digit ratio has been found to associate with sexual orientation, but published findings have often been

Sexual orientation and the second to fourth finger length ratio: a meta-analysis in men and women.

TLDR
It is found that heterosexual women had higher (more feminine) left- and right-hand 2D:4D than did lesbians, but there was no difference between heterosexual and gay men.

Genetic and Environmental Influences on 2D:4D Finger Length Ratios: A Study of Monozygotic and Dizygotic Male and Female Twins

TLDR
Biometric model-fitting analyses indicated significant additive genetic and nonshared environmental influences on digit ratios in twins, and suggest greater similarity between 2D:4D ratios in MZ relative to DZ twins that can be accounted for by genetic and nontraditional environmental factors.

Intrauterine Position Effects on Anogenital Distance and Digit Ratio in Male and Female Mice

TLDR
The lack of correlation between 2D:4D and AGDs in this mouse strain suggests that these two measures do not reflect a common influence of androgen exposure, and the possible roles of temporal and localized effects of masculinization are discussed.

Sex dimorphism in digital formulae of children.

TLDR
Test for a sex difference in the relative lengths of the finger bones, including the second-to-fourth digit ratio (2D:4D), using left-hand radiographs taken in young children indicate that relative digit lengths are sex-dimorphic in children, and suggests that 3D: 4D may be a better marker of perinatal sex differentiation.

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

TLDR
The existence of non-shared environmental influences that affect both 2D:4D and sexual orientation are suggested, which are in the predicted direction according to the prenatal hormone transfer hypothesis.
...

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