Editing Tit for tat (section)

==Tit for two tats==
Tit for two tats is similar to tit for tat, but allows the opponent to defect from the agreed upon strategy twice before the player retaliates.  This aspect makes the player using the tit for tat strategy appear more "forgiving" to the opponent.

In a tit for tat strategy, once an opponent defects, the tit for tat player immediately responds by defecting on the next move.  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.  If the opponent defects twice in a row, the tit for two tats player will respond by defecting.

This strategy was put forward by [[Robert Axelrod (political scientist)|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.  As a result, he himself entered it with high expectations in the second tournament.  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.<ref>{{cite book
  | last = Axelrod
  | first = Robert
  | title = The Evolution of Cooperation
  | url = https://archive.org/details/evolutionofcoop000axel
  | url-access = registration
  | publisher = Basic Books
  | year = 1984
  | isbn = 978-0-465-02121-5}}</ref>