No sex differences in the origins of covariation between social and physical aggression.

Abstract

Prior work has indicated both theoretical and empirical overlap between social and physical aggression. The extent to which their covariance can be explained by the same underlying genetic or environmental factors, however, remains unclear. It is also uncertain whether or how the origins of their covariance might vary across sex. The current study sought to fill these gaps in the literature. We examined maternal and teacher reports of youth physical and social aggression in over 1000 6-10 years old (mean age = 8.02 years) twin pairs from the Michigan State University Twin Registry. We made use of the bivariate correlated factors model to clarify the origins of their association. We further tested both sex difference and no-sex difference versions of that model to determine whether there are sex differences in the association between social and physical aggression, as often assumed. The covariation between social and physical aggression was due to overlapping genetic factors and common environmental conditions. Specifically, 50-57% of the genetic factors, 74-100% of the shared environmental factors, and 28-40% of the unique environmental factors influencing physical aggression also influenced social aggression according to both mother and teacher reports. These shared etiological factors did not differ across sex. These findings argue against the common assumption that social aggression is the 'female version' of male physical aggression, and instead suggest that social aggression may be best conceptualized as a form of antisocial behavior that shares developmental pathways with other manifestations of externalizing pathology.