The conscious psychological motive for this behavior, regardless of its effect, is typically not deterrence but what some psychologists call just-deserts retribution. In a landmark 2002 study, psychologists at Princeton University had more than 1,000 participants evaluate vignettes describing various crimes and misdemeanors, and give sentencing recommendations. The psychologists found that people very carefully tailored their recommended sentences to the details of the infraction, its brutality and the record of the perpetrator. That is, people valued punishment for its own sake, as a measured consequence for behavior, not as a deterrent.

In a study published last year, University of Pennsylvania psychologists demonstrated how easy it was to influence how often, or how intensely, people acted on such urges to punish. The researchers had students participate in several variations of the investment game. Afterward, another group of students entered the laboratory, examined the results of earlier games and had the option to punish players who they thought deserved it.

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A striking pattern emerged among these judges. When allowed to mete out their punishments anonymously, they docked players’ earnings very little  about one dollar on average, or 10 percent of the allowed maximum. But when being watched by the researchers and other participants, the judges’ fines tripled in value. “This suggests that when given the opportunity to punish third parties, people don’t do it much,” said Robert Kurzban, who conducted the study with Peter DeScioli and Erin O’Brien. “They may be happy to see others do it, but they don’t like to do it themselves.”

The sense of betrayal Americans feel toward Wall Street, and the financial tumult’s effects on 401(k) accounts and small businesses, has certainly made many people less laissez-faire in their attitudes toward punishment, Dr. Kurzban said. And there is nothing anonymous about the debates over the economic rescue plan, whether in Congress or at the water cooler: people are stating their views to an audience, and the collective fairness instinct is stoked to high heat.

Fortunately for the economy, researchers say, a strong countervailing psychological force is also at work: the instinct to forgive, and to cooperate. Punishments are balanced by peace offerings, and in fact researchers have come close to calculating the rough ratio most people employ.

Running thousands of computer variations of the investment game, scientists have found that the strategies that pay off the most are tipped toward cooperation.