Human sexual differences in the use of social ostracism as a competitive tactic

An aspect of social systems that is similar between chimpanzees and humans is that males form larger groups than females do. Both chimpanzee and human studies suggest that large groups are costlier for females than for males, so females attempt to reduce group size. Social ostracism of female group members occurs in both species and may serve as a mechanism for group size reduction. We formed groups of female and male children to examine directly whether human females would be more likely than males to employ social ostracism. We asked 7 female and 7 male groups of 10-yr-old children to compose and perform a play about a topic of interest to them. Female groups engaged in social ostracism more than male groups did. Further, within female groups, cortisol levels remained higher for female perpetrators of social ostracism than for their victims, suggesting that social ostracism is costly. In contrast, more frequent 1:1 conflictual behavior occurred in male than in female groups, but cortisol was unrelated to frequencies of 1:1 conflicts. Our results support the theory that human females find groups aversive and seek to reduce their size via social ostracism. Coalitions minimize the risk of retaliation but may induce costs.