Digit ratio (2D:4D), physical strength, and aggression in Turkish young adults: A biobehavioral analysis

This study aimed to examine the associations between digit ratio (2D:4D), handgrip strength (HGS), and aggression in young adults, proposing a biobehavioral model to elucidate the biological foundations of aggressive behavior. Sex differences in these associations were also explored.

A total of 410 Turkish university students (208 males, 202 females) aged 18-25 participated in the study. Sociodemographic data were collected, and aggression was measured using the Buss-Perry Aggression Questionnaire (BPAQ). The lengths of the second and fourth digits were measured bilaterally using a digital caliper, and handgrip strength was assessed with a Camry EH101 digital dynamometer following standardized procedures. Analyses included sex-stratified correlations, multiple regressions, and group comparisons across HGS tertiles.

Males showed significantly lower right-hand 2D:4D ratios (0.931 vs. 0.963; p < .001), higher handgrip strength (47.3 kg vs. 27.6 kg; p < .001), and elevated aggression scores (76.9 vs. 65.3; p < .001) compared to females. Right-hand 2D:4D was negatively correlated with both HGS (r = -0.32, p < .01) and aggression (r = -0.26, p < .01), while HGS was positively associated with aggression (r = +0.18, p < .05). In simple regression, right-hand 2D:4D significantly predicted aggression (β = -0.29, R² = 0.045, p < .001). A multiple regression including 2D:4D, sex, HGS, and age explained 27 % of the variance in aggression (R² = 0.27, F(4,405) = 25.41, p < .001), with HGS remaining a significant predictor (β = +0.10, p = .023). Aggression also varied across HGS tertiles (F(2,407) = 12.7, p < .001), with higher aggression scores observed in the highest-strength group. Notably, the negative association between 2D:4D and aggression was stronger in males and non-significant in females, indicating potential sex-specific biological pathways.

These findings support a biobehavioral framework in which both digit ratio and physical strength are linked to aggression, particularly in males. The results align with formidability-based models of aggression, emphasizing the role of prenatal androgen exposure and musculoskeletal capacity in shaping behavioral tendencies. Integrating anatomical and functional traits offers valuable insight into the biological underpinnings of aggression.