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Assortative mating and digit ratio (2D:4D): A pre-registered empirical study and meta-analysis

Lookup NU author(s): Dr Gareth RichardsORCiD



This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND).


Background: It has been hypothesised that the ratio of length between the second and fourth fingers (2D:4D), commonly employed as an indicator of foetal sex hormone exposure, may be positively correlated between heterosexual partners.Aims: As previous evidence has been conflicting, our study aimed to determine whether intra-couple correlations exist for digit ratio variables, and if so, to estimate the size and direction of these effects.Study design: We present a preregistered ( correlational study and quantitative meta-analysis of the available literature, and attempted to locate further published and unpublished data (i.e. ‘grey literature’) by contacting n=244 researchers in the 2D:4D and related fields.Subjects: n=58 heterosexual dating couples from the UK took part in our empirical study, and the meta-analysis included data from k=11 samples.Outcome measures: We measured digit ratio for the right hand (R2D:4D), left hand (L2D:4D), and average of both hands (M2D:4D), as well as the right-left-difference (D[R-L]).Results: We found no evidence of significant positive intra-couple correlations in our own data, but a significant (positive) meta-analytic effect size estimate emerged for R2D:4D (r=0.072, p=0.014). The meta-analytic effects for L2D:4D (r=0.043, p=0.303), M2D:4D (r=0.070, p=0.225), and D[R-L] (r=0.028, p=0.649) were all in the same direction but not statistically significant. However, if the sample from Klimek et al. (2014, 2016) were omitted, meta-analysis would also yield a significant positive correlation for M2D:4D (r=0.128, p=0.001).Conclusions: Although our findings are based on a fairly small range of studies, which themselves provide a relatively small sample of participants, they do imply the intriguing possibility of small effects of positive assortment in relation to characteristics associated with the prenatal hormonal environment.

Publication metadata

Author(s): Richards G, Baron-Cohen S, van Steen T, Galvin J

Publication type: Article

Publication status: Published

Journal: Early Human Development

Year: 2020

Volume: 151

Print publication date: 01/12/2020

Online publication date: 20/08/2020

Acceptance date: 18/08/2020

Date deposited: 24/08/2020

ISSN (print): 0378-3782

ISSN (electronic): 1872-6232

Publisher: Elsevier Ireland Ltd


DOI: 10.1016/j.earlhumdev.2020.105159


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