Preschoolers’ in-group bias promotes altruistic sharing and reduces second-party punishment: The role of theory of mind

This study examines how in-group bias affects altruistic sharing and second-party punishment in preschoolers and the role of theory of mind (ToM) in in-group bias. Preschoolers aged 4 to 7 years (N = 309; 160 girls) were asked to share resources with an in-group member and an out-group member (Dictator Game) and to reject or accept an unequal allocation proposed by an in-group member and an out-group member (Ultimatum Game). The results showed that preschoolers shared more resources with, and tolerated more unfair behaviors from, in-group members. ToM influenced the in-group bias in both altruistic sharing and second-party punishment. Notably, children’s degree of in-group favoritism in altruistic sharing was positively related to the second-party punishment children imposed on out-group members. However, this pattern was found only among children who had acquired first-order ToM. This study reveals the developmental patterns of preschoolers’ in-group bias in altruistic sharing and second-party punishment and the effects of ToM on in-group bias.