Punishment Not a Succesful Play

Revenge may be more satisfying, but according to Harvard mathematical biologist Martin A. Nowak, turning the other cheek is ultimately sweeter.

A study published in the science journal Nature last month and co-authored by Nowak and several other Harvard researchers suggests that costly punishment is not an effective strategy in a modified version of the prisoner’s dilemma.

The prisoner’s dilemma is a classic game theory experiment in which two players choose whether to cooperate or compete against each other. Cooperation is mutually beneficial, and in the modified version, players also have the option to punish their partners while incurring a cost to themselves.

In the experiment, conducted at Harvard Business School’s Computer Lab for Experimental Research, a participant played multiple rounds of the Prisoner’s Dilemma with each of his or her partners. Points were tallied over the course of an hour to determine the relative success of each participant’s strategies.

While many researchers have proposed that punishing selfishness forces people to cooperate, Nowak’s study suggests otherwise: the most successful players used the punish option the least, indicating that punishment may not be the driving force behind the development of cooperative societies.

“The big question we asked is, ‘If the other person chose to be selfish, how would you respond?’,” said David G. Rand, a doctoral candidate who collaborated on the study as a part of his dissertation research.

The most successful subjects in the study employed a “tit-for-tat” strategy, responding to cooperation with cooperation and competition with competition and never choosing to punish.

Participants who reacted “spitefully” to their partners’ defection tended to be the least successful after an hour of playing the game. Although exacting punishment can be satisfying in the short term, the researchers concluded, such behavior causes even more selfish behavior in the long run—and that leaves both participants worse off.

“Often when people punish, the other person responds by punishing back, and you get this downward spiral of escalation,” Rand said.

Although real life adds many levels of complexity, Rand said that he believed the study was generalizable, assuming that the players begin on an equal standing.

“I think that it is indicative and fits with a lot of work in psychology, and at least my own personal experience of the world,” he said.

The study may also explain why cooperative societies developed.

“The evolution of cooperation is one of the big topics in evolutionary biology—how cooperation can evolve in spite of the cost of being generous,” said Pat Barclay, a neurobiology professor at Cornell.

—Staff writer Athena Y. Jiang can be reached at ajiang@fas.harvard.edu.

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