A new study offers hints about how societies correct the behavior of freeloaders. The answer involves evolution, altruism -- and punishment.
Scientists say the explanation is important because individuals have so many incentives to let others in a group do most of the work. James Fowler, a political scientist at the University of California, Davis, uses the example of two neighbors who want to build a dam.
"You're best off if your neighbor builds the dam for you and you get to do other things," he says. "If evolution favors those individuals, it's puzzling why we might cooperate."
Yet we do cooperate.
To help understand why, scientists in England and Germany conducted an economic game. The goal was for each player 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. 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.
"In the beginning participants were very reluctant to join the sanctioning institution," she says.
But they soon figured out that people in the sanctioning group were making more money because more people contributed. There were fewer freeloaders.
After every round, Irlenbusch says, more students switched to the sanctioning group, even though members had to pay money if they wanted to sanction someone.
She says eventually even the freeloaders in the first group switched to the second group and changed their ways. And they began punishing anyone else who didn't cooperate.
The results of the study, which appear in this week's issue of the journal Science, may explain a lot about how one culture evolves to dominate another.
Rob Boyd, an anthropologist at University of California, Los Angeles, says one example of this sort of cultural evolution is the decline of paganism in ancient Rome.
"Pagan Rome didn't have much a social support network," Boyd says. "So when people got sick, or when there was a plague, or things got bad, they were just out of luck."
By contrast, the Christians expected members to take care of each other. That gave them a competitive edge, he says, and led Romans to gradually switch to Christianity.
Boyd says humans appear unique in their ability to create competing cultures. He says that may give humans an edge because we can evolve quickly through cultural changes rather than physical ones.
The study may also help explain why some people choose to punish, rather than ignore, behavior that's bad for their group. Fowler says he sees examples of this behavior all the time in California.
"You can imagine, for example, someone doing something really rude on the highway in Los Angeles. And it makes you really angry and you say something to them," he says. "You're taking a risk."
That's great for the group. But this sort of altruism doesn't make sense for an individual in the era of road rage.
Fowler says the explanation for altruistic behavior may be that our brains are wired to reward us for punishing freeloaders.
"That might be why we see individuals having an emotional and even sort of a brain response to punishing," he says. "They actually feel pleasure when they punish people for violating a social norm."
And Fowler says it takes just a few punishers to change the behavior of a lot of freeloaders.