Sibling Kinship, Prosociality, and Norms

This manuscript examines how growing up with a sibling influences prosociality and serves as a behavioral cue, using norm internalization and susceptibility as mechanisms. In a series of experimental games, we found that individuals with siblings were more than twice as likely to cooperate in stag hunt and contribute more in public goods and dictator games, on average, than only children, who acted more aligned with strategic self-interest. In two treatments where sibling status is exogenously revealed, only-child pairs exhibited a negative in-group effect. Subjects’ actions correlate with expected descriptive and perceived injunctive norms, suggesting childhood norm development as a factor in observed behavior. The descriptive norm was far more dominant in only children. We conclude that people without siblings may internalize norms and exercise trust in idiosyncratic ways, leading to an inclination toward passive prosociality.