We experimentally show that current models of reciprocity are in- complete in a systematic way using a new variant of the ultimatum game that provides second-movers with a marginal-cost-free punish- ment option. For a substantial proportion of the population, the de- gree of rst-mover unkindness...

We experimentally show that current models of reciprocity are incomplete in a systematic way using a new variant of the ultimatum game that provides second-movers with a marginal-cost-free punishment option. For a substantial proportion of the population, the degree of first-mover unkindness...

We analyze the interplay between cooperation norms and people's punishment behavior in a social-dilemma game with multiple punishment stages. By combining multiple punishment stages with self- contained episodes of interaction, we are able to disentangle the e ects of retaliation and...