Exposure to fetal testosterone, aggression, and violent behavior: A meta-analysis of the 2D:4D digit ratio

The search for reliable risk factors is a staple among both scholars and policymakers concerned with structuring interventions designed to reduce aggressive and violent behavior. Within this line of work, strong claims have recently been made regarding the predictive capacity of a potential physical biomarker of criminogenic risk: the 2D:4D digit ratio, a purported indirect indicator of exposure to fetal testosterone. The results of studies assessing the link between the digit ratio and problematic behavior are, however, mixed. Accordingly, in the present study we subject this literature (N = 32 studies; 361 effect size estimates) to a meta-analysis using multilevel modeling techniques. Our results reveal that the overall mean effect size of the 2D:4D digit ratio to measures of aggressive and violent behavior is weak but statistically significant (mean r = 0.036, p < 0.05). Moderator analyses confirm that these weak effects are generally consistent (and often non-significant) across a variety of methodological conditions (e.g., different outcome measures, different kinds of samples). We conclude with a call for caution against placing emphasis on the 2D:4D digit ratio as a reliable risk factor for aggressive and violent behavior.