Behavioral Aggression Is Associated with the 2D:4D Ratio in Men but Not in Women

Abstract

Abstract. Numerous studies have investigated the relationship between testosterone (T) and aggression but yielded inconsistent findings in healthy subjects. One possible reason for this might be the measurement of actual T-levels, ignoring that its role in neurodevelopment seems to be of predominant importance. The aim of our study was to further elucidate the effects of T availability during early phases of gestation, operationalized by the measurement of the 2nd to 4th digit ratio (2D:4D), on behavioral aggression in healthy volunteers. A low 2D:4D (indicating a long ring finger relative to the index finger) relates to high levels of prenatal T. A total number of 171 healthy subjects (98 men, 73 women) ranging in age from 20 to 30 years were tested. Participants were subjected to a modified version of a competitive reaction-time task, a commonly used and well-established tool to elicit and measure aggression (Taylor paradigm). They also completed self-report scales on trait aggression. Ventral surface scans of both hands were used to determine the 2D:4D ratio. As expected, the 2D:4D was lower in men as compared to women for both hands. Moreover, in contrast to questionnaire data, men reveal higher levels of aggression in the computer task compared to women. Finally, a negative correlation between 2D:4D and aggression was found in males but not in females. Results are discussed with respect to the usefulness of the 2D:4D construct as well as to sex differences in organizational effects of T.