Tit for tat
An agent using this strategy will first cooperate, then subsequently replicate an opponent's previous action.
The strategy was first introduced by Anatol Rapoport in Robert Axelrod's two tournaments,[3] held around 1980.
[4] The success of the tit-for-tat strategy, which is largely cooperative despite that its name emphasizes an adversarial nature, took many by surprise.
This result may help explain how groups of animals, especially human societies, have developed to live in mostly or fully cooperative ways, rather than in the fiercely competitive and aggressive manner one might expect from individuals living in a natural state of constant conflict.
This, and particularly its application to human society and politics, is the subject of Robert Axelrod's book The Evolution of Cooperation.
Moreover, the tit-for-tat strategy has been of beneficial use to social psychologists and sociologists in studying effective techniques to reduce conflict.
In the case of conflict resolution, the tit-for-tat strategy is effective for several reasons: the technique is recognized as clear, nice, provocable, and forgiving.
The implications of the tit-for-tat strategy have been of relevance to conflict research, resolution and many aspects of applied social science.
[5] Take for example the following infinitely repeated prisoners dilemma game: The tit-for-tat strategy copies what the other player previously chose.
is the discount factor): a geometric series summing to If a player deviates to defecting (D), then the next round they get punished.
While Axelrod has empirically shown that the strategy is optimal in some cases of direct competition, two agents playing tit for tat remain vulnerable.
This situation frequently arises in real world conflicts, ranging from schoolyard fights to civil and regional wars.
The reason for these issues is that tit for tat is not a subgame perfect equilibrium, except under knife-edge conditions on the discount rate.
[9] "Tit for tat with forgiveness" is a similar attempt to escape the death spiral.
Furthermore, the tit-for-tat strategy is not proved optimal in situations short of total competition.
This has the unfortunate consequence of causing two retaliatory strategies to continuously defect against each other resulting in a poor outcome for both players.
A tit for two tats player will let the first defection go unchallenged as a means to avoid the "death spiral" of the previous example.
This strategy was put forward by Robert Axelrod during his second round of computer simulations at RAND.
After analyzing the results of the first experiment, he determined that had a participant entered the tit for two tats strategy it would have emerged with a higher cumulative score than any other program.
Unfortunately, owing to the more aggressive nature of the programs entered in the second round, which were able to take advantage of its highly forgiving nature, tit for two tats did significantly worse (in the game-theory sense) than tit for tat.
Reciprocal altruism works in animal communities where the cost to the benefactor in any transaction of food, mating rights, nesting or territory is less than the gains to the beneficiary.
[15] This sectarian mentality led to the term "Tit for tat bombings" to enter the common lexicon of Northern Irish society.
