ver the last couple of weeks, as the Enron fiasco has played itself out like a louche fusion of Shakespeare and the old "Dewey, Cheatum & Howe" routine, Americans have been transfixed by the story, united in a nearly seamless sense of outrage.

Regardless of whether any laws were broken in the spectacular collapse of one of the nation's largest companies, citizens of all political pipings have voiced disgust at accounts of top Enron executives selling off their stock in time to enrich themselves handsomely, while ordinary Enron employees were later forced to sit by in impotent desperation as their retirement savings evaporated.

In the ferocity of the public outcry, and the demand from even those with no personal stake in the Enron collapse that "justice" be done, some scientists see a vivid example of humanity's evolved and deep-seated hatred of the Cheat. The Cheat is the transgressor of fair play, the violator of accepted norms, the sneak who smiles with Chiclet teeth while ladling from the community till.

Human beings are elaborately, ineluctably social creatures, scientists say, and are more willing than any other species to work for the common good — to cooperate with nonkin and to help out strangers, sometimes at great cost to oneself, as the death of hundreds of rescue workers at the World Trade Center only too sadly showed.

Such a readiness to trust others, to behave civilly in a crowd, to share and empathize, to play the occasional Samaritan — all the behaviors that we laud and endorse and vow to cultivate more fully in ourselves — could not have evolved without a corresponding readiness to catch, and to punish, the Cheat.

Only recently have researchers realized that a willingness, even eagerness, to punish transgressors of the social compact is at least as important to the maintenance of social harmony as are regular displays of common human decency. And while the punitive urge may seem like a lowly and unsavory impulse, scientists point out that the effort to penalize cheaters is very often a selfless act.

In an article titled "Altruistic Punishment in Humans," which appears in the Jan. 10 issue of the journal Nature, Dr. Ernst Fehr of the University of Zurich and Dr. Simon Gachter of the University of St. Gallen in Switzerland offer evidence that people will seek to punish a cheat even when the punishment is costly to them and offers no material benefit — the very definition of altruism. The researchers propose that the threat of such punishment may have been crucial to the evolution of human civilization and all its concomitant achievements.

"It's a very important force for establishing large-scale cooperation," Dr. Fehr said in a telephone interview. "Every citizen is a little policeman in a sense. There are so many social norms that we follow almost unconsciously, and they are enforced by the moral outrage we expect if we were to violate them."

Dr. David Sloan Wilson, an evolutionary biologist at the State University of New York at Binghamton, said, "People are used to thinking of social control and moralistic aggression as forms of selfishness, and that you must be punishing someone for your own benefit. But if you look at the sort of punishment that promotes altruistic behavior, you see that it is itself a form of altruism."

In their new work, Dr. Fehr and Dr. Gachter put 240 students through a series of "public goods" experiments with real monetary stakes, always a good incentive for cash- strapped young scholars.

Each participant was given an initial lump sum of 20 "monetary units" and allowed to play a series of games with rotating groups of three other participants. By the rules of the game, the members of each group independently decided how much of their sum to contribute to a community project, which in turn determined how much would be divvied up to participants in the end. The more generous each contributor, the better the group did as a whole, but there was always the risk of a participant's trying to freeload off the contributions of others.

From one round to the next, students were kept apprised of the investment decisions by others in their group. In some cases, there was nothing they could do about their teammates' behavior. In other cases, though, participants were allowed to "punish" freeloaders and skinflints after the round was through: one monetary unit from them would cost the shirker three monetary units. Hence, cooperators had to pay out of their own pocket to express their disgust at another's selfish behavior.

The outcome of the study was striking on two fronts. One was the popularity of punishment when it was permitted: 84 percent punished defectors at least once, 34.3 percent took punitive action five times or more and almost 10 percent punished the stingy 10 times or more. And all this, remember, involved the doling out of mad money from people who really needed it.

The second significant result was that when the game was carried out under no-punishment conditions, cooperation among group members quickly broke down, and participants contributed progressively less to the public kitty as the rounds went on. But when the opportunity to punish and be punished was applied, individual contributions to the collective fund jumped sharply, and cooperation among group members grew stronger rather than weaker from round to round.

The researchers also asked participants to describe their feelings toward free-riders on a seven-point scale, from "no big deal" to "very angry," and about 84 percent ranked themselves a five or higher. A sense of emotional outrage is very easily evoked, said Dr. Fehr, and sometimes it feels almost good to indulge and stoke it.

Perhaps part of the reason it feels good to rail against the sinner is that not to do so seems irresponsible, if not cowardly. "Once you think of punishment as a form of altruism, then the kind of person who doesn't punish emerges as a kind of freeloader too," said Dr. Wilson, author with Dr. Elliott Sober of "Unto Others: The Evolution and Psychology of Unselfish Behavior."

The emotional palette behind the effectiveness of social control is a rich one, composed not only of a sharp sense of moral indignation and a fear of being punished, but embarrassment and shame when one violates social norms.

Dr. Wilson said that when he and his children, nonbowlers all, recently went bowling, they were mortified when others gently scolded them for failing to observe common bowling etiquette, like taking turns with bowlers in neighboring lanes. "My ears were burning with shame, and we fled as soon as we could," he said.

And sometimes the severity of the emotion far outstrips that of the transgression. Dr. Fehr cited a case during the oil crisis of the 1970's that led to long waits at gas stations, when one motorist shot another to death for attempting to butt into line. Some of the most odious of human behaviors, including torture, public stonings and lynchings, may all be examples of the meting out of altruistic punishment run amok.

The drive to punish selfish transgressors seems to be a basic human predilection. Paradoxically, it stems from something normally associated with rosy-eyed utopianism: according to most anthropological evidence, traditional hunter-gatherer societies have always been highly egalitarian.

In such cultures, there are no kings or commanders, and the bounty of a good hunt or forage is generally shared with the entire community. If one person doesn't like or trust another, the person may walk away, or articulate that distrust with the tip of a spear.

"Hunter-gatherer societies are scrupulously egalitarian, but not harmoniously so," said Dr. Herbert Gintis of the University of Massachusetts, a co-author on a commentary that appears with the current Nature research report. "They're violently egalitarian."

Despite its antiquity, the strength and expression of the urge to scourge is clearly shaped by culture. Anthropological studies by Dr. Fehr, Dr. Gintis and others have shown considerable cross-cultural variation in the ardor with which people seek to punish shifty noncooperators. As a rule, said Dr. Fehr, the more closely a society's economy is based on market rather than kinship ties, the more prevalent the use of altruistic punishment to bring others into line.

In other words, the more likely a person is to be negotiating with nonrelatives, and hence the higher the chances that selfish freeloaders will seek to infiltrate the system, the more important it becomes that everybody play by the rules. Or else.