We conduct a public good experiment with high school teenagers. Some groups exclusively consist of students that we know to be friends. Other groups exclusively consist of students that we know not to be friends, and that are mere classmates. We find that 'friends' contribute more to the public...

Explaining the evolution and maintenance of cooperation among unrelated individuals is one of the fundamental problems in biology and the social sciences. Recent experimental evidence suggests that altruistic punishment is an important mechanism to maintain cooperation among humans. In this...

Economic and social interaction takes place between individuals with heterogeneous characteristics. We investigate experimentally the emergence and informal enforcement of different contribution norms to a public good in homogeneous and different heterogeneous groups. When punishment is not...