In support of 2D:4D: More data exploring its conflicting results on handedness, sexual orientation and sex differences

Abstract

In the last few years, several studies have questioned the value of the second-to-fourth digit ratio (2D:4D) as a measure of exposure to sex hormones before birth. Controversy has also extended to the 2D:4D association with individual features previously related to this exposure such as handedness and sexual orientation. Given that it has been argued that sex differences in 2D:4D could be a consequence of body-size differences, we have tested in a large sample the allometric relationship between finger lengths and body size. Our results show that the association is either allometric or isometric, depending on the analyses performed. In any case, the deviation from isometry is not large enough to explain the typically observed sex difference in this trait. We have also tested the association between sexual orientation and 2D:4D, finding a relationship between 2D:4D and sexual orientation in men but not in women. We attribute this discordance with previously published meta-analysis to differences in genetic background, a variable that has gained relevance in recent years in studies involving 2D:4D. Finally, we did not find any relationship between 2D:4D and handedness, evaluated through self-reported preference and hand performance. Our main conclusion is that 2D:4D shows differences between sexes beyond their disparity in body size. In our opinion, 2D:4D can be used cautiously as an indicator of intrauterine exposure to sex hormones taking into account some considerations, such as analysing a very large sample and taking careful measurements of the ethnicity of the sample.

The associations between digit ratio (2D:4D and right – left 2D:4D), maximal oxygen consumption and ventilatory thresholds in professional male football players

“…Manning, 2002aManning, , 2002b has suggested that 2D:4D is a highly conserved trait that is linked to the early emergence of tetrapods from an aquatic to a terrestrial existence. Since this suggestion, there have been some 30 reports concerning 2D:4D sexual dimorphism in amphibians, reptiles, birds, artiodactyls, rodents, and primates (Lupu et al, 2023). The findings suggest a pattern of sex differences of moderate effect, with some species showing male 2D:4D lower than female 2D:4D and other species having the reverse pattern.…”