The Evolution of Cooperation by Robert Axelrod

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In The Evolution of Cooperation, Robert Axelrod studies the evolution and nature of cooperation through his two computer tournaments of prisoner's dilemma. In both of his tournaments, the winning program employs the tit for tat strategy, and he attributes the success to:

• Being nice: it always cooperates unless the opponent defects
• Provocable: one provoked (being defected), it is quick to defect on the next turn. Thus it is not exploitable.
• Forgiving: it forgives the opponent for defecting as soon as the opponent switches to cooperating. This makes it easy for the two sides to restore to mutual cooperation
• Clarity: its strategy is very clear, allowing the opponent to know that it is best to cooperate with it

In the book, the author also discusses how this might come in play in many situations, the "stability" of such a strategy, as well as how to encourage or discourage cooperation.