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Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts
Michael E W Varnum1, Amanda P Kirsch1, Daniel J Beal2
1Department of Psychology, Arizona State University, Tempe, AZ 85282-1104, USA.
PNAS Nexus
|August 28, 2025
Summary
Human sex differences in aggression are not universal. While males are typically more aggressive toward non-relatives, females report equal or greater aggression toward siblings, challenging established generalizations.
Area of Science:
- Evolutionary Psychology
- Human Behavior
- Social Psychology
Background:
- Generalizations about sex differences in human aggression often stem from studies of non-kin interactions.
- Previous research consistently indicates higher male aggression compared to female aggression.
Purpose of the Study:
- To investigate whether the typical sex difference in aggression extends to sibling relationships.
- To examine sex differences in aggression within families across diverse cultural contexts.
Main Methods:
- Retrospective self-report data collected from 4,013 individuals across 24 societies.
- Analysis of both direct and indirect aggression reported by participants towards their siblings.
Main Results:
- The generalization of higher male aggression did not hold true for sibling relationships.
- Females reported being as aggressive as, or more aggressive than, males toward their siblings.
- This pattern was consistent for direct and indirect aggression, and across childhood and adulthood.
Conclusions:
- Aggression dynamics within family relationships differ significantly from those between non-kin.
- Context and target are crucial factors in understanding sex differences in aggressive tendencies.
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