Tit for Tat

Tit for Tat is a highly-effective strategy in game theory for the iterated prisoner's dilemma. It was first introduced by Anatol Rapoport in Robert Axelrod's 1984 tournament. Based on the English saying meaning "equivalent retaliation" ("tip for tap"), an agent using this strategy will initially cooperate, then respond in kind to a previous opponent's action. If the opponent previously was cooperative, the agent is cooperative. If not, the agent is not.

Implications

The success of the strategy, which is largely cooperative, took many by surprise. In successive competitions various teams produced complex strategies which attempted to "cheat" in a variety of cunning ways, but Tit for Tat eventually prevailed in every competition.

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Some theorists believe this result may give insight into how groups of animals (and particularly human societies) have come to live in largely (or entirely) cooperative societies, rather than the individualistic "red in tooth and claw" way that might be expected from individual engaged in a Darwinian struggle. This, and particularly its application to human society and politics, is the subject of Robert Axelrod's book The Evolution of Cooperation.

Related Topics:
Robert Axelrod - The Evolution of Cooperation

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