Evolution of Cooperation – Robert Axelrod – Summary


The Evolution of Cooperation

By Robert Axelrod

Under what conditions will cooperation emerge in a world of egoists without central authority? This question has intrigued people for a long time.

A good example of the fundamental problem of cooperation is the case where two industrial nations have erected trade barriers to each other’s exports. Because of the mutual advantages of free trade, both countries would be better off if these barriers were eliminated. But if either country were to eliminate its barriers unilaterally, it would find itself facing terms of trade that hurt its own economy. In fact, whatever one country does, the other country is better off retaining its own trade barriers. Therefore, the problem is that each country has an incentive to retain trade barriers, leading to a worse outcome than would have been possible had both countries cooperated with each other.

A. Lessons from “the Prisoners’ dilema”

This basic problem occurs when the pursuit of self-interest by each leads to a poor outcome for all.

This maybe illustrated with a game is called the Prisoner’s Dilemma because in its original form two prisoners face the choice of informing on each other (defecting) or remaining silent (cooperating). Each must make the choice without knowing what the other will do.

The rewards are: If both players defect: Both players get $1. If both players cooperate: Both players get $3. If one player defects while the other player cooperates: The defector gets $5 and the cooperator gets zero.

One can see that no matter what the other player does, defection yields a higher payoff than cooperation.

The winner was the simplest of all candidates submitted. This was a strategy of simple reciprocity which cooperates on the first move and then does whatever the other player did on the previous move.

The analysis of the data from these tournaments reveals four properties which tend to make a strategy successful:

  1. avoidance of unnecessary conflict by cooperating as long as the other player does ,
  2. provocability in the face of an uncalled-for defection by the other,
  3. forgiveness after responding to a provocation, and
  4. clarity of behavior so that the other player can recognize and adapt to your pattern of action.

In summary, the best strategy is: Don’t be envious, don’t be the first to defect, reciprocate both cooperation and defection, and don’t be too clever.

B. Lessons from World War I: Live and Let Live

This System emerged during the trench warfare of the western front in World War I. In the midst of this bitter conflict, the frontline soldiers often refrained from shooting to kill – provided their restraint was reciprocated by the soldiers on the other side.

C. Conditions for Stable Cooperation

1. The individuals involved do not have to be rational: The evolutionary process allows successful strategies to thrive, even if the players do not know why or how.

2. Nor do they have to exchange messages or commitments: They do not need words, because their deeds speak for them.

3. Likewise, there is no need to assume trust between the players: The use of reciprocity can be enough to make defection unproductive.

4. Altruism is not needed: Successful strategies can elicit cooperation even from an egoist.

5. Finally, no central authority is needed: Cooperation based on reciprocity can be self-policing.

6. For cooperation to emerge, the interaction must extend over an indefinite (or at least an unknown) number of moves. For cooperation to prove stable, the future must have a sufficiently large shadow. This means that the importance of the next encounter between the same two individuals must be great enough to make defection an unprofitable strategy.

7. In order for cooperation to get started in the first place, there must be some clustering of individuals who use strategies with two properties: The strategy cooperates on the first move, and discriminates between those who respond to the cooperation and those who do not.

D. How Cooperation Evolves

Cooperation can begin with small clusters. It can thrive with strategies that are “nice” (that is, never the first to defect), provocable, and somewhat forgiving. Once established in a population, individuals using such discriminating strategies can protect themselves from invasion. The overall level of cooperation tends to go up and not down.

The foundation of cooperation is not really trust, but the durability of the relationship. When the conditions are right, the players can come to cooperate with each other through trial-and-error learning about possibilities for mutual rewards, through imitation of other successful players, or even through a blind process of selection of the more successful strategies with a weeding out of the less successful ones.

E. The Value of Provocability

One of my biggest surprises in working on this project has been the value of provocability and that it is important to respond sooner, rather than later. I came to this project believing one should be slow to anger. The results of the computer tournament for the Prisoner’s Dilemma demonstrate that it is actually better to respond quickly to a provocation.

F. A Self-Reinforcing Ratchet Effect

Once the word gets out that reciprocity works – among nations or among individuals – it becomes the thing to do. If you expect others to reciprocate your defections as well as your cooperations, you will be wise to avoid starting any trouble.

The establishment of stable cooperation can take a long time if it is based upon blind forces of evolution, or it can happen rather quickly if its operation can be appreciated by intelligent players.

There is a lesson in the fact that simple reciprocity succeeds without doing better than anyone with whom it interacts. It succeeds by eliciting cooperation from others, not by defeating them. We are used to thinking about competitions in which there is only one winner, competitions such as football or chess. But the world is rarely like that. In a vast range of situations, mutual cooperation can be better for both sides than mutual defection. The key to doing well lies not in overcoming others, but in eliciting their cooperation.

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