By Roger Highfield, Science Editor
19 Mar 2008
David Rand, Anna Dreber and Martin Nowak who were part of the research team
Taking the law into your own hands is ineffective. Nor is it true that sparing the rod spoils the child, according to a study that shows people who resort to punishment are losers.
These are not the ravings of someone who has been penalised once too often but the conclusion of an eminent group of biologists, economists and mathematicians at Harvard University, led by Prof Martin Nowak.
Earlier work suggested that punishment helps people to cooperate but was only based on people playing one off games, not having to deal with each other again and again.
When a long term relationship is taken into account, "the kind of punishment by people who 'take the law into their own hands' is now proven to be ineffective," says Prof Nowak.
But he adds that the new work focuses on peer punishment, not that meted out by the state. "Sanctioning institutions (such as the state enforcing law) is a different type of punishment, which still needs to be investigated from an evolutionary perspective."
The team bases its conclusions on a mathematical analysis of strategic games. In these games, people are given the choice of making a fair contribution or free loading.
Over the years, some earlier experiments seemed to suggest that cooperation founders without punishment. These observations lead to the bleak conclusion that cooperative societies need peer punishment.
But the new study published in the journal Nature, concludes that the people who engage in costly punishment do not benefit from their behaviour.
Working with the Harvard Business School, Prof Nowak asked 104 college students to take part in a variant of a classic game, called the Prisoner's Dilemma.
In this game people have a choice between cooperation and defection. Cooperation means paying $1 for the other person to receive $3.
Defection means taking away $1 from the other person. In the extended version of the game there is a third option: costly punishment, which means paying $1 for the other person to lose $4.
The study found that those who punished lost out overall, and that punishment bestows no benefit on the group as a whole.
The five top-ranked players never used costly punishment. More successful players would use tit for tat, while players who earned the lowest payoffs punished most often. "Put simply, winners don't punish," says co-author David Rand.
Punishment is to do with telling someone who is boss, or to defend a possession, and not part of the fabric of a society where people cooperate, as was previously thought.
"Punishment can lead to a downward spiral of retaliation, with destructive outcomes for everybody involved. The people with the highest total payoffs do not use costly punishment."
"Costly punishment," the punitive behaviour studied by Prof Nowak and his colleagues, refers to situations where a punisher is willing to incur a cost - whether a financial one or to his reputation - in order to penalise someone else.
Importantly, most real world punishment is costly in one way or another. Punishers are typically driven by anger and not by altruistic motives.
The reason the findings overturn textbook wisdom is that earlier work has "not been on situations where individuals use punishment in the context of ongoing interactions," says co-author Anna Dreber.
"We make the setting more realistic by having subjects play repeated games and introducing costly punishment as one of several options."
The new study shows that punishment is not an effective way to promote cooperation, the glue that holds society together, but probably evolved for other reasons such as establishing dominance and defend ownership.
"Punishment may be a tool for forcing another person to do what you want," Dreber says. "It might have been for those kinds of dominance situations that the use of punishment has evolved."
"Our finding has a very positive message: in an extremely competitive setting, the winners are those who resist the temptation to escalate conflicts, while the losers punish and perish," says Prof Nowak.
This study was supported by the John Templeton Foundation, the National Science Foundation, the National Institutes of Health, the Jan Wallander Foundation, and billionaire philanthropist Jeffrey Epstein.