We experimentally investigate the effect of imperfect separation of groups on group selection and cooperation in a standard prisoner¿s dilemma environment. Subjects can repeatedly choose between two groups, where in one of them an institutionalized norm fosters cooperation. The degree of...

We study experimentally how players learn to make decisions if they face many different (normal-form) games. Games are generated randomly from a uniform distribution in each of 100 rounds. We find that agents do extrapolate between games but learn to play strategically equivalent games in the...

We experimentally investigate the effect of population viscosity (an increased probability to interact with others of one's type or group) on cooperation in a standard prisoner's dilemma environment. Subjects can repeatedly choose between two groups that differ in the defector gain in the...