《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

The Problem ofCooperation well by getting the reward,R,for mutual cooperation or both can do poorly by getting the punishment,P,for mu- tual defection.Using the assumption that the other player will always make the move you fear most will lead you to expect that the other will never cooperate,which in turn will lead you to defect,causing unending punishment.So unlike chess,in the Prisoner's Dilemma it is not safe to assume that the other player is out to get you. In fact,in the Prisoner's Dilemma,the strategy that works best depends directly on what strategy the other player is using and,in particular,on whether this strategy leaves room for the development of mutual cooperation. This principle is based on the weight of the next move relative to the current move being sufficiently large to make the future important.In other words,the discount parameter,w,must be large enough to make the future loom large in the calculation of total payoffs.After all,if you are unlikely to meet the other person again,or if you care little about future payoffs,then you might as well defect now and not worry about the consequences for the future. This leads to the first formal proposition.It is the sad news that if the future is important,there is no one best strategy. Proposition 1.If the discount parameter,w,is sufficient- ly high,there is no best strategy independent of the strate- gy used by the other player. The proof itself is not hard.Suppose that the other play- er is using ALL D,the strategy of always defecting.If the other player will never cooperate,the best you can do is always to defect yourself:Now suppose,on the other hand, that the other player is using a strategy of "permanent re- taliation."This is the strategy of cooperating until you de- 15

The Problem of Cooperation well by getting the reward, R, for mutual cooperation or both can do poorly by getting the punishment, P, for mu￾tual defection. Using the assumption that the other player will always make the move you fear most will lead you to expect that the other will never cooperate, which in turn will lead you to defect, causing unending punishment. So unlike chess, in the Prisoner's Dilemma it is not safe to assume that the other player is out to get you. In fact, in the Prisoner's Dilemma, the strategy that works best depends directly on what strategy the other player is using and, in particular, on whether this strategy leaves room for the development of mutual cooperation. This principle is based on the weight of the next move relative to the current move being sufficiently large to make the future important. In other words, the discount parameter, w, must be large enough to make the future loom large in the calculation of total payoffs. After all, if you are unlikely to meet the other person again, or if you care little about future payoffs, then you might as well defect now and not worry about the consequences for the future. This leads to the first formal proposition. It is the sad news that if the future is important, there is no one best strategy. Proposition 1. If the discount parameter, w, is sufficient￾ly high, there is no best strategy independent of the strate￾gy used by the other player. The proof itself is not hard. Suppose that the other play￾er is using ALL D, the strategy of always defecting. If the other player will never cooperate, the best you can do is always to defect yourself. Now suppose, on the other hand, that the other player is using a strategy of "permanent re￾taliation." This is the strategy of cooperating until you de- 15

Introduction feet and then always defecting after that.In that case,your best strategy is never to defect,provided that the tempta- tion to defect on the first move will eventually be more than compensated for by the long-term disadvantage of getting nothing but the punishment,P,rather than the reward,R,on future moves.This will be true whenever the discount parameter,w,is sufficiently great.Thus, whether or not you should cooperate,even on the first move,depends on the strategy being used by the other player.Therefore,if w is sufficiently large,there is no one best strategy. In the case of a legislature such as the U.S.Senate,this proposition says that if there is a large enough chance that a member of the legislature will interact again with another member,there is no one best strategy to use independently of the strategy being used by the other person.It would be best to cooperate with someone who will reciprocate that cooperation in the future,but not with someone whose future behavior will not be very much affected by this in- teraction (see,for example,Hinckley 1972).The very pos- sibility of achieving stable mutual cooperation depends upon there being a good chance of a continuing interac- tion,as measured by the magnitude of w.As it happens,in the case of Congress,the chance of two members having a continuing interaction has increased dramatically as the bi- ennial turnover rates have fallen from about 40 percent in the first forty years of the republic to about 20 percent or less in recent years (Young 1966,pp.87-90;Polsby 1968; Jones 1977,p.154;Patterson 1978,pp.143-44). However,saying that a continuing chance of interaction is necessary for the development of cooperation is not the same as saying that it is sufficient.The demonstration that there is not a single best strategy leaves open the question 16

Introduction feet and then always defecting after that. In that case, your best strategy is never to defect, provided that the tempta￾tion to defect on the first move will eventually be more than compensated for by the long-term disadvantage of getting nothing but the punishment, P, rather than the reward, R, on future moves. This will be true whenever the discount parameter, w, is sufficiently great.5 Thus, whether or not you should cooperate, even on the first move, depends on the strategy being used by the other player. Therefore, if w is sufficiently large, there is no one best strategy. In the case of a legislature such as the U.S. Senate, this proposition says that if there is a large enough chance that a member of the legislature will interact again with another member, there is no one best strategy to use independently of the strategy being used by the other person. It would be best to cooperate with someone who will reciprocate that cooperation in the future, but not with someone whose future behavior will not be very much affected by this in￾teraction (see, for example, Hinckley 1972). The very pos￾sibility of achieving stable mutual cooperation depends upon there being a good chance of a continuing interac￾tion, as measured by the magnitude of w. As it happens, in the case of Congress, the chance of two members having a continuing interaction has increased dramatically as the bi￾ennial turnover rates have fallen from about 40 percent in the first forty years of the republic to about 20 percent or less in recent years (Young 1966, pp. 87-90; Polsby 1968; Jones 1977, p. 154; Patterson 1978, pp. 143-44). However, saying that a continuing chance of interaction is necessary for the development of cooperation is not the same as saying that it is sufficient. The demonstration that there is not a single best strategy leaves open the question 16

The Problem ofCooperation of what patterns of behavior can be expected to emerge when there actually is a sufficiently high probability of continuing interaction between two individuals. Before going on to study the behavior that can be ex- pected to emerge,it is a good idea to take a closer look at which features of reality the Prisoner's Dilemma frame- work is,and is not,able to encompass.Fortunately,the very simplicity of the framework makes it possible to avoid many restrictive assumptions that would otherwise limit the analysis: 1.The payoffs of the players need not be comparable at all.For example,a journalist might get rewarded with an- other inside story,while the cooperating bureaucrat might be rewarded with a chance to have a policy argument pre- sented in a favorable light. 2.The payoffs certainly do not have to be symmetric.It is a convenience to think of the interaction as exactly equivalent from the perspective of the two players,but this is not necessary.One does not have to assume,for example, that the reward for mutual cooperation,or any of the other three payoff parameters,have the same magnitude for both players.As mentioned earlier,one does not even have to assume that they are measured in comparable units.The only thing that has to be assumed is that,for each player, the four payoffs are ordered as required for the definition of the Prisoner's Dilemma. 3.The payoffs of a player do not have to be measured on an absolute scale.They need only be measured relative to each other. 4.Cooperation need not be considered desirable from the point of view of the rest of the world.There are times when one wants to retard,rather than foster,cooperation between players.Collusive business practices are good for 17

The Problem of Cooperation of what patterns of behavior can be expected to emerge when there actually is a sufficiently high probability of continuing interaction between two individuals. Before going on to study the behavior that can be ex￾pected to emerge, it is a good idea to take a closer look at which features of reality the Prisoner's Dilemma frame￾work is, and is not, able to encompass. Fortunately, the very simplicity of the framework makes it possible to avoid many restrictive assumptions that would otherwise limit the analysis: 1. The payoffs of the players need not be comparable at all. For example, a journalist might get rewarded with an￾other inside story, while the cooperating bureaucrat might be rewarded with a chance to have a policy argument pre￾sented in a favorable light. 2. The payoffs certainly do not have to be symmetric. It is a convenience to think of the interaction as exactly equivalent from the perspective of the two players, but this is not necessary. One does not have to assume, for example, that the reward for mutual cooperation, or any of the other three payoff parameters, have the same magnitude for both players. As mentioned earlier, one does not even have to assume that they are measured in comparable units. The only thing that has to be assumed is that, for each player, the four payoffs are ordered as required for the definition of the Prisoner's Dilemma. 3. The payoffs of a player do not have to be measured on an absolute scale. They need only be measured relative to each other.6 4. Cooperation need not be considered desirable from the point of view of the rest of the world. There are times when one wants to retard, rather than foster, cooperation between players. Collusive business practices are good for 17

Introduction the businesses involved but not so good for the rest of soci- ety.In fact,most forms of corruption are welcome in- stances of cooperation for the participants but are unwel- come to everyone else.So,on occasion,the theory will be used in reverse to show how to prevent,rather than to promote,cooperation. 5.There is no need to assume that the players are ration- al.They need not be trying to maximize their rewards. Their strategies may simply reflect standard operating pro- cedures,rules of thumb,instincts,habits,or imitation (Si- mon 1955;Cyert and March 1963). 6.The actions that players take are not necessarily even conscious choices.A person who sometimes returns a favor, and sometimes does not,may not think about what strategy is being used.There is no need to assume deliberate choice at all.? The framework is broad enough to encompass not only people but also nations and bacteria.Nations certainly take actions which can be interpreted as choices in a Prisoner's Dilemma-as in the raising or lowering of tariffs.It is not necessary to assume that such actions are rational or are the outcome of a unified actor pursuing a single goal.On the contrary,they might well be the result of an incredibly complex bureaucratic politics involving complicated infor- mation processing and shifting political coalitions(Allison 1971). Likewise,at the other extreme,an organism does not need a brain to play a game.Bacteria,for example,are highly responsive to selected aspects of their chemical envi- ronment.They can therefore respond differentially to what other organisms are doing,and these conditional strategies of behavior can be inherited.Moreover,the behavior of a bacterium can affect the fitness of other organisms around 18

Introduction the businesses involved but not so good for the rest of soci￾ety. In fact, most forms of corruption are welcome in￾stances of cooperation for the participants but are unwel￾come to everyone else. So, on occasion, the theory will be used in reverse to show how to prevent, rather than to promote, cooperation. 5. There is no need to assume that the players are ration￾al. They need not be trying to maximize their rewards. Their strategies may simply reflect standard operating pro￾cedures, rules of thumb, instincts, habits, or imitation (Si￾mon 1955; Cyert and March 1963). 6. The actions that players take are not necessarily even conscious choices. A person who sometimes returns a favor, and sometimes does not, may not think about what strategy is being used. There is no need to assume deliberate choice at all.7 The framework is broad enough to encompass not only people but also nations and bacteria. Nations certainly take actions which can be interpreted as choices in a Prisoner's Dilemma—as in the raising or lowering of tariffs. It is not necessary to assume that such actions are rational or are the outcome of a unified actor pursuing a single goal. On the contrary, they might well be the result of an incredibly complex bureaucratic politics involving complicated infor￾mation processing and shifting political coalitions (Allison 1971). Likewise, at the other extreme, an organism does not need a brain to play a game. Bacteria, for example, are highly responsive to selected aspects of their chemical envi￾ronment. They can therefore respond differentially to what other organisms are doing, and these conditional strategies of behavior can be inherited. Moreover, the behavior of a bacterium can affect the fitness of other organisms around 18

The Problem ofCooperation it,just as the behavior of other organisms can affect the fitness of a bacterium.But biological applications are best saved for chapter 5. For now the main interest will be in people and organi- zations.Therefore,it is good to know that for the sake of generality,it is not necessary to assume very much about how deliberate and insightful people are.Nor is it neces- sary to assume,as the sociobiologists do,that important aspects of human behavior are guided by one's genes.The approach here is strategic rather than genetic. Of course,the abstract formulation of the problem of cooperation as a Prisoner's Dilemma puts aside many vital features that make any actual interaction unique.Examples of what is left out by this formal abstraction include the possibility of verbal communication,the direct influence of third parties,the problems of implementing a choice,and the uncertainty about what the other player actually did on the preceding move.In chapter 8 some of these complicat- ing factors are added to the basic model.It is clear that the list of potentially relevant factors that have been left out could be extended almost indefinitely.Certainly,no intel- ligent person should make an important choice without trying to take such complicating factors into account.The value of an analysis without them is that it can help to clarify some of the subtle features of the interaction-fea- tures which might otherwise be lost in the maze of com- plexities of the highly particular circumstances in which choice must actually be made.It is the very complexity of reality which makes the analysis of an abstract interaction so helpful as an aid to understanding. The next chapter explores the emergence of cooperation through a study of what is a good strategy to employ if 19

The Problem of Cooperation it, just as the behavior of other organisms can affect the fitness of a bacterium. But biological applications are best saved for chapter 5. For now the main interest will be in people and organi￾zations. Therefore, it is good to know that for the sake of generality, it is not necessary to assume very much about how deliberate and insightful people are. Nor is it neces￾sary to assume, as the sociobiologists do, that important aspects of human behavior are guided by one's genes. The approach here is strategic rather than genetic. Of course, the abstract formulation of the problem of cooperation as a Prisoner's Dilemma puts aside many vital features that make any actual interaction unique. Examples of what is left out by this formal abstraction include the possibility of verbal communication, the direct influence of third parties, the problems of implementing a choice, and the uncertainty about what the other player actually did on the preceding move. In chapter 8 some of these complicat￾ing factors are added to the basic model. It is clear that the list of potentially relevant factors that have been left out could be extended almost indefinitely. Certainly, no intel￾ligent person should make an important choice without trying to take such complicating factors into account. The value of an analysis without them is that it can help to clarify some of the subtle features of the interaction—fea￾tures which might otherwise be lost in the maze of com￾plexities of the highly particular circumstances in which choice must actually be made. It is the very complexity of reality which makes the analysis of an abstract interaction so helpful as an aid to understanding. The next chapter explores the emergence of cooperation through a study of what is a good strategy to employ if 19