《政治经济学经典导读 Comparative Political Economy》课程教学资源（阅读资料）The Evolution of Cooperation

II The Emergence of Cooperation

II The Emergence of Cooperation

CHAPTER 2 The Success of TIT FOR TAT in Computer Tournaments SINCE the Prisoner's Dilemma is so common in every- thing 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 chap- ter 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 Dilem- ma for useful advice.Fortunately,a great deal of research has been done in this area. Psychologists using experimental subjects have found 27

CHAPTER 2 The Success of TIT FOR TAT in Computer Tournaments SINCE the Prisoner's Dilemma is so common in every￾thing 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 chap￾ter 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 Dilem￾ma for useful advice. Fortunately, a great deal of research has been done in this area. Psychologists using experimental subjects have found 27

The Emergence of Cooperation that,in the iterated Prisoner's Dilemma,the amount of cooperation attainedand the specific pattern for attaining it-depend on a wide variety of factors relating to the con- text 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 Ber- ger 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 Dilemmacited in PsychologicalAbstracts.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 foun- dation for models of important social processes.Richard- son'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 (Richard- son 1960;Zinnes 1976,pp.330-40).Oligopolistic compe- tition can also be modeled as a Prisoner's Dilemma(Sam- uelson 1973,pp.503-5).The ubiquitous problems of collective action to produce a collective good are analyz- able 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 Dilem- 28

The Emergence of Cooperation 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 con￾text 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 Ber￾ger 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 foun￾dation for models of important social processes. Richard￾son'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 (Richard￾son 1960; Zinnes 1976, pp. 330-40). Oligopolistic compe￾tition can also be modeled as a Prisoner's Dilemma (Sam￾uelson 1973, pp. 503-5). The ubiquitous problems of collective action to produce a collective good are analyz￾able 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 Dilem- 28

ComputerTournaments ma.This literature goes beyond the empirical questions of the laboratory or the real world,and instead uses the ab- stract 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 (Schel- ling 1973),and cooperation without enforcement (Taylor 1976). Unfortunately,none of these three literatures on the Prisoner's Dilemma reveals very much about how to play the game well.The experimental literature is not much help,because virtually all of it is based on analyzing the choices made by players who are seeing the formal game for the first time.Their appreciation of the strategic subtle- ties is bound to be restricted.Although the experimental subjects may have plenty of experience with everyday oc- currences of the Prisoner's Dilemma,their ability to call on this experience in a formal setting may be limited.The choices of experienced economic and political elites in nat- ural settings are studied in some of the applied literature of Prisoner's Dilemma,but the evidence is of limited help because of the relatively slow pace of most high-level inter- actions and the difficulty of controlling for changing cir- cumstances.All together,no more than a few dozen choices have been identified and analyzed this way.Finally, the abstract literature of strategic interaction usually studies variants of the iterated Prisoner's Dilemma designed to eliminate the dilemma itself by introducing changes in the game,such as allowing interdependent choices (Howard 1966;Rapoport 1967),or putting a tax on defection(Tide- man and Tullock 1976;Clarke 1980). To learn more about how to choose effectively in an iterated Prisoner's Dilemma,a new approach is needed. Such an approach would have to draw on people who have 29

Computer Tournaments ma. This literature goes beyond the empirical questions of the laboratory or the real world, and instead uses the ab￾stract 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 (Schel￾ling 1973), and cooperation without enforcement (Taylor 1976). Unfortunately, none of these three literatures on the Prisoner's Dilemma reveals very much about how to play the game well. The experimental literature is not much help, because virtually all of it is based on analyzing the choices made by players who are seeing the formal game for the first time. Their appreciation of the strategic subtle￾ties is bound to be restricted. Although the experimental subjects may have plenty of experience with everyday oc￾currences of the Prisoner's Dilemma, their ability to call on this experience in a formal setting may be limited. The choices of experienced economic and political elites in nat￾ural settings are studied in some of the applied literature of Prisoner's Dilemma, but the evidence is of limited help because of the relatively slow pace of most high-level inter￾actions and the difficulty of controlling for changing cir￾cumstances. All together, no more than a few dozen choices have been identified and analyzed this way. Finally, the abstract literature of strategic interaction usually studies variants of the iterated Prisoner's Dilemma designed to eliminate the dilemma itself by introducing changes in the game, such as allowing interdependent choices (Howard 1966; Rapoport 1967), or putting a tax on defection (Tide￾man and Tullock 1976; Clarke 1980). To learn more about how to choose effectively in an iterated Prisoner's Dilemma, a new approach is needed. Such an approach would have to draw on people who have 29

The Emergence of Cooperation a rich understanding of the strategic possibilities inherent in a non-zero-sum setting,a situation in which the interests of the participants partially coincide and partially conflict. Two important facts about non-zero-sum settings would have to be taken into account.First,the proposition of the previous chapter demonstrates that what is effective de- pends not only upon the characteristics of a particular strat- egy,but also upon the nature of the other strategies with which it must interact.The second point follows directly from the first.An effective strategy must be able at any point to take into account the history of the interaction as it has developed so far. A computer tournament for the study of effective choice in the iterated Prisoner's Dilemma meets these needs.In a computer tournament,each entrant writes a program that embodies a rule to select the cooperative or noncooperative choice on each move.The program has available to it the history of the game so far,and may use this history in making a choice.If the participants are recruited primarily from those who are familiar with the Prisoner's Dilemma, the entrants can be assured that their decision rule will be facing rules of other informed entrants.Such recruitment would also guarantee that the state of the art is represented in the tournament. Wanting to find out what would happen,I invited pro- fessional game theorists to send in entries to just such a computer tournament.It was structured as a round robin, meaning that each entry was paired with each other entry. As announced in the rules of the tournament,each entry was also paired with its own twin and with RANDOM,a program that randomly cooperates and defects with equal probability.Each game consisted of exactly two hundred moves.'The payoff matrix for each move was the familiar 30

The Emergence of Cooperation a rich understanding of the strategic possibilities inherent in a non-zero-sum setting, a situation in which the interests of the participants partially coincide and partially conflict. Two important facts about non-zero-sum settings would have to be taken into account. First, the proposition of the previous chapter demonstrates that what is effective de￾pends not only upon the characteristics of a particular strat￾egy, but also upon the nature of the other strategies with which it must interact. The second point follows directly from the first. An effective strategy must be able at any point to take into account the history of the interaction as it has developed so far. A computer tournament for the study of effective choice in the iterated Prisoner's Dilemma meets these needs. In a computer tournament, each entrant writes a program that embodies a rule to select the cooperative or noncooperative choice on each move. The program has available to it the history of the game so far, and may use this history in making a choice. If the participants are recruited primarily from those who are familiar with the Prisoner's Dilemma, the entrants can be assured that their decision rule will be facing rules of other informed entrants. Such recruitment would also guarantee that the state of the art is represented in the tournament. Wanting to find out what would happen, I invited pro￾fessional game theorists to send in entries to just such a computer tournament. It was structured as a round robin, meaning that each entry was paired with each other entry. As announced in the rules of the tournament, each entry was also paired with its own twin and with RANDOM, a program that randomly cooperates and defects with equal probability. Each game consisted of exactly two hundred moves.1 The payoff matrix for each move was the familiar 30