OLS regression of 2D:4D onto mean fingers length.

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.

近年来，多项研究对第二至第四指长比（2D:4D）作为出生前性激素暴露水平衡量指标的有效性提出了质疑。相关争议还延伸至2D:4D与此前被认为与该类暴露相关的个体特征之间的关联，例如利手性与性取向。鉴于有观点提出，2D:4D的性别差异可能源于体型差异，我们依托大样本检验了指长与体型之间的异速生长关系。研究结果显示，二者的关联模式依所采用的分析方法而定，可呈现异速生长或等速生长特征。无论如何，与等速生长的偏差幅度均不足以解释该特征中普遍观测到的性别差异。我们还检验了性取向与2D:4D之间的关联，结果发现男性群体中2D:4D与性取向存在相关性，而女性群体中未观测到此类关联。我们将这一与既往已发表荟萃分析结果不符的现象归因于遗传背景差异——该变量在近年来涉及2D:4D的相关研究中已愈发受到重视。最后，我们未发现2D:4D与利手性之间存在任何关联，其中利手性通过自我报告的用手偏好与手部表现进行评估。我们的核心结论为：2D:4D的性别差异并非仅由体型差异所导致。我们认为，在兼顾部分注意事项的前提下，2D:4D可谨慎用作宫内性激素暴露的指示指标，例如采用超大样本量开展分析，并对研究样本的种族信息进行精准记录。