Evidence suggests that males are, on average, more aggressive than females, but it is not completely clear why that is the case. By analysing social network data from more than 11,000 children attending nearly 600 schools, Ralf Wölfer and Miles Hewstone were able to build "aggression networks" that mapped the agressive relations among pupils. They then used these networks (see example) to abitrate among competing theories explain this sex difference on the basis of intermale competition (sexual selection theory; Darwin, 1871) or the traditional division of labor (social role theory; Eagly, 1987).
With the help of aggression networks (see Figure), the researchers were able to precisely differentiate intrasex aggression (males aggress males or females aggress females) and intersex aggression (males aggress females or females aggress males). They found that males are more aggressive to same-sex and other-sex individuals, while sexual selection theory predicted sex differences in intrasex aggression and social role theory predicted sex differences in intersex aggression. These findings suggest the value of a dual-theory framework that considers both biological and social factors for explaining aggressive behavior.
The paper has been published in the journal Psychological Science.
The figure shows an aggression network (black circles = boys, white triangles = girls, lines = aggression nominations)