Preschoolers' group bias in punishing selfishness in the Ultimatum Game.

Previous studies have shown that both adults and children tend to favor members of their own group and expect reciprocity of such in-group privilege. If a person is treated unfairly by an in-group member, a conflict arises between the tendency of in-group favoritism and the desire to punish violators of in-group norms. How do children solve the conflict at different points in development? We compared how preschoolers punished in-group and out-group members (marked by color preference) for selfishness in the Ultimatum Game. We found that (a) 3- to 6-year-old Chinese children rejected selfish allocations more often than fair ones, showing a robust preference for fairness; (b) 3- and 4-year-olds showed no group differences in their punishment behavior, suggesting that second-party punishment of selfishness is not biased during early childhood; (c) 5- and 6-year-old girls were more likely to punish selfishness of in-groups than of out-groups, illuminating an early sign of maintaining group-based fairness norms even at a personal cost; and (d) 5- and 6-year-old boys, however, punished in-groups and out-groups equally often and punished out-groups more often than did girls. These age and gender differences in children's punishment imply that socialization may play an important role in showing group bias when enforcing fairness norms.