This paper offers a new and robust model of the emergence and persistence of cooperation when interactions are anonymous, the population is well-mixed, and the evolutionary process selects strategies according to material payoffs. The model has a Prisoner’s Dilemma structure, but with an...

Cooperation in real-world dilemmas takes many forms. We introduce a class of two-player games that permits two distinct ways to cooperate in the repeated game. One way to cooperate is to play cutoff strategies, which rely solely on a player's private value to defection. The second cooperative...

We introduce a class of two-player cooperation games where each player faces a binary decision, enter or exit. These games have a unique Nash equilibrium of entry. However, entry imposes a large enough negative externality on the other player such that the unique social optimum involves the...