We analyse interethnic cooperation in an infinitely repeated prisoner's dilemma when members of one group are unable to target punishment towards individual defectors from the other group. We first show that indiscriminate outgroup punishment may sustain cooperation in this setting. Our main...

Markov perfection has become the usual solution concept to determine the non-cooperative equilibrium in a dynamic game. However, Markov perfection is a stronger solution concept than subgame perfection: Markov perfection rules out any cooperation in a repeated prisoners' dilemma game because the...

We calculate the equilibrium fraction of cooperators in a population in which payoffs accrue from playing a single-shot prisoner's dilemma game. Individuals who are hardwired as cooperators or defectors are randomly matched into pairs, and cooperators are able to perfectly find out the type of a...

We offer a game-theoretic proof of Hamilton's rule for the spread of altruism. For a simple case of siblings, we show that the rule can be derived as the outcome of a one-shot prisoner's dilemma game between siblings.

The paper shows that being able to forecast another player's actual cooperation better than pure chance can change players' strategic incentives in a one-shot simultaneous PD-situation. In particular, it is shown that if both players have such ability (to forecast each others' actual choices...

We study the individual behavior of students and workers in an experiment where they repeatedly face the same cooperative task. The data show that clerical workers differ from college students in overall cooperation rates, strategy adoption and use of punishment opportunities. Students cooperate...

We analyse interethnic cooperation in an infinitely repeated prisoner’s dilemma when members of one group are unable to target punishment towards individual defectors from the other group. We first show that indiscriminate outgroup punishment may sustain cooperation in this setting. Our main...

Social norms of cooperation are studied under several forms of communication. In an experiment, strangers could make public statements before playing a prisoner’s dilemma. The interaction was repeated indefinitely, which generated multiple equilibria. Communication could be used as a tool to...