 To get an idea of why cooperative behavior might spread in this and similar frameworks, consider two agents on either side of a frontier between cooperating and non-cooperating subpopulations. The cooperative agent sees a cooperative neighbor whose four neighbors all cooperate, and who therefore gets four times the reward payoff after playing them all. So he will imitate this neighbor's strategy and remain cooperative. The non-cooperating agent, on the other hand, sees his cooperative counterpart, who gets three reward payoffs from his cooperative neighbors and one sucker payoff. He compares this to the payoffs of his non-cooperatiave neighbors. The best these can do is to get three punishments and a temptation. So, as long as \(3R+S\) exceeds \(3P+T\), the non-coperative agent on the frontier will adopt the strategy of his cooperative neighbor. Axelrod's payoffs of 5, 3, 1 and 0 for \(T\), \(R\), \(P\), and \(S\), do meet this condition.