In hypothetical scenarios involving two groups (nations or groups of workers), subjects voted on three proposals: one helped group A (their group), one helped B, and one helped both groups, more than the average of the first two but less than their maximum. When subjects voted for one proposal,...

People often sacrifice their self-interest for a group to which they belong, even when outsiders are harmed so that the sacrifice has no net benefit. Two experiments (conducted on the World Wide Web) suggest that people do this, in part, because they think that cooperation on behalf of the group...