The Iterated Prisoner's Dilemma Has Become the E. coli of Social Psychology; the Prisoner's Dilemma Is Used to Model Arms Races, Oligopolistic Competition, Collective Action Problems, Vote Trading, etc.

Since the Prisoner's Dilemma is so common in everything from personal relations to international relations, it would be useful to know how best to act when in this type of setting. However, the proposition of the previous chapter demonstrates that there is no one best strategy to use. What is best depends in part on what the other player is likely to be doing. Further, what the other is likely to be doing may well depend on what the player expects you to do.

To get out of this tangle, help can be sought by combing the research already done concerning the Prisoner's Dilemma for useful advice. Fortunately, a great deal of research has been done in this area.

Psychologists using experimental subjects have found that, in the iterated Prisoner's Dilemma, the amount of cooperation attained—and the specific pattern for attaining it—depend on a wide variety of factors relating to the context of the game, the attributes of the individual players, and the relationship between the players. Since behavior in the game reflects so many important factors about people, it has become a standard way to explore questions in social psychology, from the effects of westernization in Central Africa (Bethlehem 1975) to the existence (or nonexistence) of aggression in career-oriented women (Baefsky and Berger 1974), and to the differential consequences of abstract versus concrete thinking styles (Nydegger 1974). In the last fifteen years, there have been hundreds of articles on the Prisoner's Dilemma cited in Psychological Abstracts. The iterated Prisoner's Dilemma has become the E. coli of social psychology.

Just as important as its use as an experimental test bed is the use of the Prisoner's Dilemma as the conceptual foundation for models of important social processes. Richardson's model of the arms race is based on an interaction which is essentially a Prisoner's Dilemma, played once a year with the budgets of the competing nations (Richardson 1960; Zinnes 1976, pp. 330-40). Oligopolistic competition can also be modeled as a Prisoner's Dilemma (Samuelson 1973, pp. 503-5). The ubiquitous problems of collective action to produce a collective good are analyzable as Prisoner's Dilemmas with many players (G. Hardin 1982). Even vote trading has been modeled as a Prisoner's Dilemma (Riker and Brams 1973). In fact, many of the best-developed models of important political, social, and economic processes have the Prisoner's Dilemma as their foundation.

There is yet a third literature about the Prisoner's Dilemma. This literature goes beyond the empirical questions of the laboratory or the real world, and instead uses the abstract game to analyze the features of some fundamental strategic issues, such as the meaning of rationality (Luce and Raiffa 1957), choices which affect other people (Schelling 1973), and cooperation without enforcement (Taylor 1976).

--Robert Axelrod, The Evolution of Cooperation, rev. ed. (New York: Basic Books, 2006), 27-29.