Directional asymmetry (right–left differences) in digit ratio (2D:4D) predict indirect aggression in women

A large body of research has revealed that digit length ratios (2D:4D) are influenced by exposure to prenatal androgens. It is thought that higher exposure to prenatal androgens leads to the development of more masculinized (smaller) digit ratios. Low 2D:4D, particularly low right 2D:4D and low right–left 2D:4D (directional asymmetry or DA) has been linked with a number of behavioral traits which are sex-dependent, including performance in sports and exercise, and to some degree, aggression. To date, the focus of digit ratio research has been on physical aggression, however, 2D:4D has never been linked with indirect aggression (also called social or relational aggression), a form of aggression often preferred by women. We measured the 2D:4D of 100 women and compared these scores with responses on indirect and direct aggression questionnaires. Although 2D:4D was not linked to direct aggression in women, we found that low DA predicted indirect aggression. We conclude that higher levels of prenatal testosterone induce higher levels of aggression, and that the link between prenatal testosterone and aggression in women is most strongly seen for indirect aggression.