Tit for Tat

Tit for tat is an English expression meaning equivalent retaliation, descended from the earlier phrase tip for tap, or blow for blow, first recorded in 1558. In game theory it names a strategy in which an agent first cooperates and then simply repeats the opponent's previous move, a pattern that mirrors reciprocal altruism found in biological systems. The strategy became prominent through the political scientist Robert Axelrod's study of the iterated prisoner's dilemma around 1980, where tit for tat proved to be both the simplest strategy entered and the most successful in direct competition in his tournaments, a result that surprised researchers because it showed that largely cooperative behavior, particularly among humans, could emerge from a competitive setting, and it has since informed research on conflict resolution across the social sciences. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/