Through a glass, darkly: Human digit ratios reflect prenatal androgens, imperfectly

AbstractAmong non-human mammals, exposure to androgens during critical periods of development leads to gynephilia (attraction to females), whereas the absence or low levels of prenatal androgens leads to androphilia (attraction to males). However, in humans, retrospective markers of prenatal androgens have only been associated with gynephilia among women, but not with androphilia among men. Here, we asked whether an indirect indication of prenatal androgen exposure, 2D:4D, differs between subsets of gay men delineated by anal sex role (ASR). ASR was used as a proxy for subgroups because ASR groups tend to differ in other measures affected by brain sexual differentiation, such as gender conformity. First, we replicated the finding that gay men with a receptive ASR preference (bottoms) report greater gender nonconformity (GNC) compared to gay men with an insertive ASR preference (tops). We then found that Tops have a lower (male-typical) average right-hand digit ratio than Bottoms, and that among all gay men the right-hand 2D:4D correlated with GNC, indicating that a higher (female-typical) 2D:4D is associated with increased GNC. Differences were found between non-exclusive and exclusive same-sex attraction and GNC, and ASR group differences on digit ratios do not reach significance when all non-heterosexual men are included in the analyses, suggesting greater heterogeneity in the development of non-exclusive same-sex sexual orientations. Overall, results support a role for prenatal androgens, as approximated by digit ratios, in influencing the sexual orientation and GNC of a subset of gay men.

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Digit Ratios (2D:4D and other) and Relative Thumb Length: A Test of Developmental Stability

Perceptual and Motor Skills ◽

10.2466/pms.105.1.143-152 ◽

2007 ◽

Vol 105 (1) ◽

pp. 143-152 ◽

Cited By ~ 22

Author(s):

Martin Voracek ◽

Denise Offenmuller

Keyword(s):

Young Adults ◽

Sex Differences ◽

Developmental Stability ◽

Digit Ratio ◽

Childhood And Adolescence ◽

Finger Length ◽

Digit Ratios ◽

Fourth Digit ◽

Prenatal Androgens ◽

Length Measurements

Sex and side differences in relative thumb length of children and adolescents have been reported by prior researchers. These findings mirror those reported for the second-to-fourth digit ratio (2D:4D), a likely biomarker for the organizational (permanent) effects of prenatal androgens on the human brain and body. The present study investigated relative thumb length, in particular, its associations with all possible digit ratios (2D:3D, 2D:4D, 2D:5D, 3D:4D, 3D:5D, and 4D:5D), in a sample of young adults (60 men and 64 women). Relative thumb length was less precisely measurable than direct or image-based finger-length measurements, as used in digit ratio research. There were no significant sex or side differences in relative thumb length. Contrary to expectation, thumb size was not positively correlated with any digit ratios. Relative thumb length appears to be developmentally unstable (decreases during childhood and adolescence). Additional findings, such as the magnitude ranking of sex differences in digit ratios and the comparability of direct versus image-based finger-length measurements, are also discussed.

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Minireview: Organizational Hypothesis: Instances of the Fingerpost

Endocrinology ◽

10.1210/en.2010-0041 ◽

2010 ◽

Vol 151 (9) ◽

pp. 4116-4122 ◽

Cited By ~ 139

Author(s):

S. Marc Breedlove

Keyword(s):

Attention Deficit Disorder ◽

Receptor Gene ◽

Androgen Receptor Gene ◽

Androgen Insensitivity Syndrome ◽

Fetal Life ◽

Human Behaviors ◽

Digit Ratios ◽

Prenatal Androgens ◽

Valid Test ◽

Prenatal Androgen

There is now compelling evidence that the ratio of the length of the second digit divided by the length of the fourth digit (2D:4D) is affected by prenatal androgens in humans. This ratio is greater in females than males from fetal life through adulthood, correlates with polymorphism in the androgen receptor gene in men, is feminine in XY androgen insensitivity syndrome, and masculinized in congenital adrenal hyperplasia. Using 2D:4D as a correlate, researchers have found evidence that prenatal androgens affect many sexually differentiated human behaviors, including sexual orientation in women (but not in men), attention deficit disorder, autism, eating disorders, aggression, and risk-taking. In each case, lower 2D:4D, indicative of greater prenatal androgen stimulation, is associated with behavior more commonly displayed by males than females. The correlation between 2D:4D and prenatal androgen stimulation is too imperfect to accurately predict the phenotype of a particular individual, even in terms of sex. However, digit ratio is the best available retrospective marker of average differences in prenatal androgen stimulation between groups of people, and/or correlations of prenatal androgen stimulation with particular behaviors and characteristics within a group. Thus digit ratios offer a valid test of the organizational hypothesis that androgens act early in life to masculinize various human behaviors.

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Sexual Orientation, Sexual Arousal, and Finger Length Ratios in Women

Archives of Sexual Behavior ◽

10.1007/s10508-021-02095-5 ◽

2021 ◽

Author(s):

Luke Holmes ◽

Tuesday M. Watts-Overall ◽

Erlend Slettevold ◽

Dragos C. Gruia ◽

Jamie Raines ◽

...

Keyword(s):

Sexual Orientation ◽

Sexual Arousal ◽

Ring Finger ◽

Prenatal Development ◽

Behavioral Traits ◽

Sexual Stimuli ◽

Digit Ratios ◽

Heterosexual Women ◽

Prenatal Androgens ◽

Sexual Responses

AbstractIn general, women show physiological sexual arousal to both sexes. However, compared with heterosexual women, homosexual women are more aroused to their preferred sex, a pattern typically found in men. We hypothesized that homosexual women’s male-typical arousal is due to their sex-atypical masculinization during prenatal development. We measured the sexual responses of 199 women (including 67 homosexual women) via their genital arousal and pupil dilation to female and male sexual stimuli. Our main marker of masculinization was the ratio of the index to ring finger, which we expected to be lower (a masculine pattern) in homosexual women due to increased levels of prenatal androgens. We further measured observer- and self-ratings of psychological masculinity–femininity as possible proxies of prenatal androgenization. Homosexual women responded more strongly to female stimuli than male stimuli and therefore had more male-typical sexual responses than heterosexual women. However, they did not have more male-typical digit ratios, even though this difference became stronger if analyses were restricted to white participants. Still, variation in women's digit ratios did not account for the link between their sexual orientation and their male-typical sexual responses. Furthermore, homosexual women reported and displayed more masculinity than heterosexual women, but their masculinity was not associated with their male-typical sexual arousal. Thus, women’s sexual and behavioral traits, and potential anatomical traits, are possibly masculinized at different stages of gestation.

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Faculty Opinions recommendation of Effects on gender identity of prenatal androgens and genital appearance: evidence from girls with congenital adrenal hyperplasia.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.724097312.793508341 ◽

2015 ◽

Author(s):

Phyllis Speiser

Keyword(s):

Gender Identity ◽

Congenital Adrenal Hyperplasia ◽

Adrenal Hyperplasia ◽

Prenatal Androgens

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Masculine (Low) Digit Ratios Predict Masculine Food Choices in Hungry Consumers

Food Quality and Preference ◽

10.1016/j.foodqual.2020.104168 ◽

2020 ◽

pp. 104168

Author(s):

Tobias Otterbring ◽

Christian T. Elbæk ◽

Chaoren Lu

Keyword(s):

Food Choices ◽

Digit Ratios

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Investigating the reliability and sex differences of digit lengths, ratios, and hand measures in infants

Scientific Reports ◽

10.1038/s41598-021-89590-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Luisa Ernsten ◽

Lisa M. Körner ◽

Martin Heil ◽

Gareth Richards ◽

Nora K. Schaal

Keyword(s):

Sex Differences ◽

Measurement Techniques ◽

Directional Asymmetry ◽

Computer Assisted ◽

Sexually Dimorphic ◽

Digit Ratios ◽

Androgen Exposure ◽

Prenatal Androgen Exposure ◽

Test Retest Reliability ◽

Prenatal Androgen

AbstractHands and digits tend to be sexually dimorphic and may reflect prenatal androgen exposure. In the past years, the literature introduced several hand and digit measures, but there is a lack of studies in prepubertal cohorts. The available literature reports more heterogeneous findings in prepubertal compared to postpubertal cohorts. The comparability of the available studies is further limited by the study design and different measurement techniques. The present study compared the reliability and sex differences of available hand and digit measures, namely digit lengths of 2D, 3D, 4D, 5D, digit ratios 2D:4D, 2D:5D, 3D:4D, 3D:5D, 4D:5D, relative digit lengths rel2, rel3, rel4, rel5, directional asymmetry of right and left 2D:4D (Dr-l), hand width, length, and index of 399 male and 364 female 6-month-old German infants within one study using only indirect and computer-assisted measurements. The inter-examiner reliability was excellent while the test-retest reliability of hand scans was only moderate to high. Boys exhibited longer digits as well as wider and longer hands than girls, but smaller digit ratios, with ratios comprising the fifth digit revealing the largest effect sizes. Other hand and digit ratios revealed sex differences to some extent. The findings promote the assumption of sexual dimorphic hand and digit measures. However, by comparing the results of the available literature, there remains an uncertainty regarding the underlying hypothesis. Specifically in prepubertal cohorts, i.e. before the influence of fluctuating hormones, significant effects should be expected. It seems like other factors than the influence of prenatal androgens contribute to the sexual dimorphism in hand and digit lengths.

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