Finger length ratio (2D:4D) and sex differences in aggression during a simulated war game

We tested the association between a biomarker of early sex differentiation, the second-to-fourth finger length ratio (2D:4D), and unprovoked attack during a simulated war game (n = 176). We also investigated whether 2D:4D mediated the tendency for men to attack more than women and whether personality dimensions previously associated with sex differences in aggression or hostility (social dominance orientation, narcissism, perceived stress, and self-esteem) mediated either relationship. We found that sex and lower, more male-typical, 2D:4D predicted unprovoked attack independently. In men, high levels of narcissism predicted greater than 10 times greater odds of attacking. We also found non-monotonic effects of social dominance orientation and of perceived stress on unprovoked attack, which were not as predicted. However, we saw no evidence that effects of sex or 2D:4D were mediated by the personality dimensions we measured.