Sexual orientation is associated with 2D:4D finger length ratios in both sexes: an updated and expanded meta-analysis.
Level 3 - non-randomized controlled study
Meta-analysis of observational studies
PubMed 40351575 · doi:10.3389/fpsyg.2025.1559158
What was done
An expanded meta-analysis evaluated the association between the 2nd-to-4th finger length ratio (2D:4D) and sexual orientation across 51 studies (44 male and 34 female datasets, including 17 newly published and 11 unpublished datasets; total n = 227,648). The analysis examined differences between heterosexual, homosexual, and bisexual or non-exclusive individuals in both sexes and used trim-and-fill and leave-one-out robustness tests to address publication bias.
What was found
Homosexual women showed significantly lower (more male-typical) digit ratios than heterosexual women (adjusted right hand g = 0.26, left hand g = 0.16). Homosexual men showed significantly higher (more female-typical) digit ratios than heterosexual men (adjusted right hand g = -0.17, left hand g = -0.20). No significant differences were observed between bisexual and heterosexual individuals of either sex. Moderator analyses found evidence of publication bias for male datasets (positive findings favored) but not female datasets; male results remained robust after trim-and-fill adjustments.
Why it matters
By incorporating unpublished datasets and analyzing bisexual individuals separately, this study provides large-scale evidence that atypical digit ratios are linked to homosexuality in both sexes, supporting theories that prenatal androgen and estrogen exposure influence sexual orientation.
Limits
The underlying studies are observational and rely on 2D:4D as a putative, indirect proxy rather than direct measurement of prenatal hormone levels. Effect sizes are small (|g| = 0.16 to 0.26). Publication bias was detected in the male literature, and potential heterogeneity across measurement methods or study populations was not detailed in the abstract.