Evolution of Cooperation - Subsequent Work

Subsequent Work

In 1984 Axelrod estimated that there were "hundreds of articles on the Prisoner's Dilemma cited in Psychological Abstracts", and estimated that citations to The Evolution of Cooperation alone were "growing at the rate of over 300 per year". To fully review this literature is infeasible. What follows are therefore only a few selected highlights.

Axelrod has a subsequent book, The Complexity of Cooperation, which he considers a sequel to The Evolution of Cooperation. Other work on the evolution of cooperation has expanded to cover prosocial behavior generally, and in religion, other mechanisms for generating cooperation, the IPD under different conditions and assumptions, and the use of other games such as the Public Goods and Ultimatum games to explore deep-seated notions of fairness and fair play. It has also been used to challenge the rational and self-regarding "economic man" model of economics, and as a basis for replacing Darwinian sexual selection theory with a theory of social selection.

Nice strategies are better able to invade if they have social structures or other means of increasing their interactions. Axelrod discusses this in chapter 8; in a later paper he and Rick Riolo and Michael Cohen use computer simulations to show cooperation rising among agents who have negligible chance of future encounters but can recognize similarity of an arbitrary characteristic (such as a green beard).

When an IPD tournament introduces noise (errors or misunderstandings) TFT strategies can get trapped into a long string of retaliatory defections, thereby depressing their score. TFT also tolerates "ALL C" (always cooperate) strategies, which then give an opening to exploiters. In 1992 Martin Nowak and Karl Sigmund demonstrated a strategy called Pavlov (or "win–stay, lose–shift") that does better in these circumstances. Pavlov looks at its own prior move as well as the other player's move. If the payoff was R or P (see "Prisoner's Dilemma", above) it cooperates; if S or T it defects.

In a 2006 paper Nowak listed five mechanisms by which natural selection can lead to cooperation. In addition to kin selection and direct reciprocity, he shows that:

• Indirect reciprocity is based on knowing the other player's reputation, which is the player's history with other players. Cooperation depends on a reliable history being projected from past partners to future partners.

• Network reciprocity relies on geographical or social factors to increase the interactions with nearer neighbors; it is essentially a virtual group.

• Group selection assumes that groups with cooperators (even altruists) will be more successful as a whole, and this will tend to benefit all members.

The payoffs in the Prisoner's Dilemma game are fixed, but in real life defectors are often punished by cooperators. Where punishment is costly there is a second-order dilemma amongst cooperators between those who pay the cost of enforcement and those who do not. Other work has shown that while individuals given a choice between joining a group that punishes free-riders and one that does not initially prefer the sanction-free group, yet after several rounds they will join the sanctioning group, seeing that sanctions secure a better payoff.

In small populations or groups there is the possibility that indirect reciprocity (reputation) can interact with direct reciprocity (e.g. tit for tat) with neither strategy dominating the other. The interactions between these strategies can give rise to dynamic social networks which exhibit some of the properties observed in empirical networks

And there is the very intriguing paper "The Coevolution of Parochial Altruism and War" by Jung-Kyoo Choi and Samuel Bowles. From their summary:

Altruism—benefiting fellow group members at a cost to oneself —and parochialism—hostility towards individuals not of one's own ethnic, racial, or other group—are common human behaviors. The intersection of the two—which we term "parochial altruism"—is puzzling from an evolutionary perspective because altruistic or parochial behavior reduces one's payoffs by comparison to what one would gain from eschewing these behaviors. But parochial altruism could have evolved if parochialism promoted intergroup hostilities and the combination of altruism and parochialism contributed to success in these conflicts.... would have been viable singly, but by promoting group conflict they could have evolved jointly.

They do not claim that humans have actually evolved in this way, but that computer simulations show how war could be promoted by the interaction of these behaviors.