Explaining human cooperation in large groups of non-kin is a major challenge to both rational choice theory and the theory of evolution. Recent research suggests that group cooperation can be explained by positing that cooperators can punish non-cooperators or cheaters. The experimental evidence...

According to Adam Smith (1790), human selfishness can be restrained by introspection. We test the effect of introspection on people’s willingness to cooperate in a public good game. Drawing on the concept of identity utility (George A. Akerlof and Rachel E. Kranton, 2000), we show...