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From NPR News, this is ALL THINGS CONSIDERED. I'm Melissa Block.


And I'm Michele Norris.

No one likes a freeloader, but what can you do about them? Scientists seem to have found an answer. It involves evolution, altruism, and punishment.

NPR's Jon Hamilton explains.

JON HAMILTON reporting:

It's certainly tempting to let someone else do most of the work. And James Fowler, a political scientist at UC Davis, says it makes sense from an individual's point of view.

Mr. JAMES FOWLER (University of California, Davis): You and your neighbor want to build a dam. You're best off if your neighbor builds the dam for you and you get to do other things. If evolution favors those individuals then it's sort of puzzling why we might cooperate.

HAMILTON: Yet we do cooperate. And scientists in England and Germany wanted to know why. So, they conducted an economic game. The goal was for each person to make as much money as possible. But to be really successful, people had to cooperate by pooling their funds. People in the game could join one of two teams or institutions. The first depended on voluntary cooperation. The second allowed members to sanction those who didn't chip in.

Bernd Irlenbusch, of the London School of Economics, says students' behavior changed dramatically over time.

Ms. BERND IRLENBUSCH (London School of Economics): In the beginning, participants were very reluctant to join the sanctioning institution.

HAMILTON: But the sanctioning group made more money, because more people contributed. There were fewer freeloaders. After every round, more students switched to the sanctioning group, even though you had to pay money if you wanted to sanction someone. Irlenbusch says eventually the freeloaders in the first group switched to the second.

Ms. IRLENBUSCH: What was even more surprising, they also adopted the punishment norms. So, they punished other free riders.

HAMILTON: The result may explain a lot about how one culture evolves to dominate another.

Rob Boyd is an anthropologist at UCLA. He says one example of this sort of cultural evolution is the decline of paganism in ancient Rome.

Mr. ROB BOYD (University of California, Los Angeles): Pagan Rome didn't have much of a social support network, so when people got sick or when there was a plague or things got too bad, they were just out of luck.

HAMILTON: By contrast, the Christians expected members to take care of each other.

Mr. BOYD: This was a very attractive situation, and so people gradually switched.

HAMILTON: Boyd says only humans appear to have this capacity to create competing cultures within the species. He says it may give humans an edge because they can evolve quickly, through cultural changes rather than physical ones.

The study, which appears in this week's issue of the journal Science, also helps explain why some individuals choose to punish rather than ignore behavior that's bad for their group. James Fowler, from UC Davis, says he sees it all the time in California.

Mr. FOWLER: So you can imagine, for example, someone doing something really rude on the highway in L.A., and it makes you really angry, and you say something to them. You're taking a risk.

HAMILTON: That's great for the group, but that sort of altruism doesn't make sense for the individual, at least in the era of road rage. There's evidence that our brains are wired to reward us for punishing freeloaders.

Mr. FOWLER: That might be why we see individuals having an emotional, and even sort of a brain response, to punishing, where they actually feel pleasure when they punish other people for violating a social norm.

HAMILTON: And Fowler says just a few of these punishers in a group can change the behavior of a lot of freeloaders.

Jon Hamilton, NPR News.

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