C O O P E R A T I O N   5

How Tit for Tat Works

Axelrod concluded that Tit for Tat succeeded not by trying to do the absolute best for itself in every transaction, but by trying to maximize the sum of its own and the other player's reward in all transactions combined. In other words, Tit for Tat did well for itself because the effect of its strategy was to allow every player with whom it interacted to do well.

An intriguing aspect of this is found in the raw scores of the various Prisoner's Dilemma tournaments. Looking at the numbers, it quickly becomes obvious that in individual encounters Tit for Tat never did better than strategies which were more "aggressive" (i.e., defected more often) or--interestingly--strategies which were more "forgiving" (i.e., didn't always respond immediately to a defection with a defection of its own). In individual transactions, Tit for Tat's numbers were solidly middle-of-the-road.

But over iterated transactions the consequences of defection began to outweigh the benefits. As more players started to resemble Tit for Tat, which always retaliated immediately to a defection but was always open to cooperation, the long-term payoff for defection dropped. Soon there were no players who could be taken advantage of by a defecting strategy. Meanwhile, the Tit for Tat-like cooperating strategies were busy cooperating. Their long-term payoffs were never outstanding... just better than those of the defectors.

Next:

The Principles of Tit for Tat

How Tit for Tat Works

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