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Table 1 Payoffs for a generic two-by-two game, a typical Prisoner's Dilemma game payoff matrix and a typical Mutualism game payoff matrix.

From: Individual variation evades the Prisoner's Dilemma

  Generic Prisoner's
  C D C D C D
C R S 3 0 5 1
D T P 5 1 3 0
  1. C denotes cooperation and D denotes a defection by both row and column player. Payoffs in the generic game denote the temptation to defect (T), the reward for mutual cooperation (R), punishment for mutual defection (P), and the sucker's payoff (S). In Prisoner's Dilemma, T is the best option against R, which is in turn better than P, with the worst payoff coming from S – cooperating when the opponent defects. Mutual defection is the Nash equilibrium since it is better to defect regardless of which strategy the opponent plays. In Mutualism, R is the highest payoff and S approaches T, so cooperation is always the best option regardless of your opponent's move. Mutual cooperation is a strong Nash equilibrium as all other options are less profitable.