Human men are typically more aggressive than human women, a finding supported by reams of research. But surveys of 4,136 individuals in 24 countries reveal an exception to the trend: aggression in sibling relationships. Douglas T. Kenrick and Michael E.W. Warnum, along with a team of 49 colleagues, asked participants how often they had acted aggressively towards a sister, a brother, a female friend, a male friend, a female acquaintance, or a male acquaintance—both when they were children and when they were adults. Aggressive actions included both direct aggression, such as hitting/slapping or yelling, as well as reputational aggression, such as sharing harmful gossip, or reporting someone’s behavior to an authority—“telling” in a childhood context. In terms of direct aggression, girls and women were slightly more aggressive towards their siblings than were boys and men. Men and boys, by contrast, were more likely to be directly aggressive with non-siblings. Women and girls were also just as likely to be indirectly aggressive to siblings as men and boys were, both in childhood and adulthood. Patterns of sibling aggression by sex were not correlated with country-level gender equality indicators. The trend held in wealthier and poorer countries and in Western and Non-Western cultures, suggesting to the authors that the contextual effect of sibling relationships on female aggression may well be universal. According to the authors, a more nuanced understanding of the relationship between sex and aggression should include the social context in which it occurs.
PNAS Nexus
Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts
26-Aug-2025