All for one, or in it for yourself? That depends on how you were brought up, according to a new study involving the prisoner's dilemma, perhaps the most famous scenario in game theory. In the game, you can either cooperate or betray your partner. And adult males who were exposed as children to violence, crime, conflict, and neglect turn on their partners earlier and more often in the game than males who grew up in more stable environments, the study finds.
Imagine that you're a thief, and you and your partner have been nabbed by the police. If you both stay silent, you both get a month in jail. But if you rat out your partner, or "defect," while he stays silent, he gets 2 years and you go free. Alas, if you both snitch, you both get a year. Dreamed up decades ago, the prisoner's dilemma has now become a staple of social psychology experiments. "It's really an assay for how your mind is built to tradeoff between different ways of living in the world," says psychologist Michael McCullough of the University of Miami in Coral Gables, Florida. "Are you going to be tempted by short-term payoffs or are you going to invest again and again to try to get long-term benefits?"
McCullough and colleagues wanted to explore how these choices might vary based on a person's background. The researchers recruited 244 male and female undergraduate students to participate in multiple iterations of the prisoner's dilemma game in which points—later converted into real money—were won in each round depending on the choices made. Each student was told they were playing at least 20 rounds of the game via a computer. They were told their opponents were human—but instead the computer was programmed to take a "tit for tat" strategy: The computer repeats the moves made by the player in the previous round.
After their play on the computer, the participants completed questionnaires (on scales of one to five or one to seven) about the environment they grew up in, including socioeconomic status and whether they were exposed to family neglect, violence, and conflict, or to neighborhood violence and crime. They were also questioned about whether they believed in a "code of honor"—for example, endorsing statements such as: "Sometimes, you have to fight to uphold your honor."
Among women, the researchers found no link between childhood exposure to violence or socioeconomic status and their choice of strategy in the game. However, men with childhood exposure to violence and conflict, whether familial or in their neighborhoods, were more likely to endorse a code of honor and also more likely to exploit their opponent —defecting earlier in the game—and to retaliate once their opponent had defected. Overall, for every one-unit increase in scoring on the childhood violence survey, there was a 9.2% greater likelihood of defection and a 4.5% decrease in cooperation with an opponent after they had defected. The males' childhood socioeconomic status, on the other hand, didn't change their playing behavior, the scientists report online today in the Proceedings of the Royal Society B.
McCullough and his colleagues hypothesize that risk-taking behavior and a "live fast, die young" mentality are tied into the link between a harsh childhood and a tendency toward exploitation and retaliation. "If you look at the world in front of you and see cues that your situation isn't stable, you're going to become programmed to take rewards that are right in front of your eyes right now," McCullough says.
Psychologist Ying-yi Hong of Nanyang Technological University in Singapore, who was not involved in the new research, says that the research of McCullough and his team "shows that early experience matters to the extent that it affects someone's tendencies toward cooperation versus competition. That ultimately affects the whole society, because for a society to function, you need people to cooperate."
But Hong, who has studied the effects of Western versus Chinese cultures on the prisoner's dilemma, suggests that it's not just that people who grew up in unstable situations who are programmed to seize rewards; she thinks there may be something else at play. "In my opinion, a more likely explanation for what was seen here is that people who grew up in these environments with more conflict have a lower expectation of other people," Hong says. "And once someone doesn't cooperate with you once, that just backs up your opinion of people."
The researchers hope to continue studying the relationship between environment and exploitation tendencies through more in-depth longitudinal studies that can aim to explain the link more fully.