It has been known for many years that 2D:4D varies according to sex, such that males tend to have longer fourth digits relative to second digits (low 2D:4D) than females. We discuss this refinement of the 2D:4D paradigm in relation to the links between 2D:4D and sports performance, and aggression.ĭigit ratio (or 2D:4D) is the relative lengths of the second digit (the “index” finger) and the fourth digit (the “ring” finger). We argue that this is particularly evident in “challenging” conditions such as aggressive and sexual encounters, in which individuals show increased levels of T. In particular, we hypothesize that 2D:4D correlates with organizing effects on the endocrine system that moderate activating effects in adulthood. Here, we suggest that in order to understand the link between 2D:4D and sex hormones, one must consider both fetal organizing and adult activating effects of T and E. In contrast, the relationships between 2D:4D and levels of sex steroids in adults are less clear, as many correlational studies of 2D:4D and adult sex steroids have concluded that this association is statistically non-significant. Evidence for this assertion is derived from direct and indirect measures of prenatal hormonal exposure (in experimental animals, via amniotic fluid samples and in the study of sex-typical traits) in relation to 2D:4D.
This ratio is considered to be a biomarker of the balance between fetal testosterone (T) and estrogen (E) in a narrow window of early ontogeny. 5Department of Biological Personality Psychology and Assessment, University of Göttingen, Göttingen, Germanyĭigit ratio (2D:4D) denotes the relative length of the second and fourth digits.4Hamlyn Centre, Imperial College, London, UK.
3School of Sport, Health and Exercise Science, Bangor University, Gwynedd, UK.2Applied Sports Technology, Exercise and Medicine Research Centre, Swansea University, Swansea, UK.1Department of Psychology, Northumbria University, Newcastle upon Tyne, UK.John Manning 1* Liam Kilduff 2 Christian Cook 3 Blair Crewther 4 Bernhard Fink 5
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