The Selfish Gene

by Richard Dawkins

Since there are 2 × 2 cards, there are four possible outcomes. For each outcome, our winnings are as follows (quoted in dollars in deference to the North American origins of the game): Outcome I: We have both played COOPERATE. The banker pays each of us $300. This respectable sum is called the Reward for mutual cooperation. Outcome II: We have both played DEFECT. The banker fines each of us $10. This is called the Punishment for mutual defection. Outcome III: You have played COOPERATE; I have played DEFECT. The banker pays me $500 (the Temptation to defect) and fines you (the Sucker) $100. Outcome IV: You have played DEFECT; I have played COOPERATE. The banker pays you the Temptation payoff of $500 and fines me, the Sucker, $100. Outcomes III and IV are obviously mirror images: one player does very well and the other does very badly. In outcomes I and 11 we do as well as one another, but I is better for both of us than II. The exact quantities of money don’t matter. It doesn’t even matter how many of them are positive (payments) and how many of them, if any, are negative (fines). What matters, for the game to qualify as a true Prisoner’s Dilemma, is their rank order. The Temptation to defect must be better than the Reward for mutual cooperation, which must be better than the Punishment for mutual defection, which must be better than the Sucker’s payoff. (Strictly speaking, there is one further condition for the game to qualify as a true Prisoner’s Dilemma: the average of t...