Microsoft researchers bring computer power to social science

It’s called the prisoner’s dilemma and it goes like this: You and a fellow gang member are in jail. One of you committed a heinous crime, but the prosecutor doesn’t know who. Instead, you are both booked on a lesser charge and serving a one-year sentence in solitary confinement.

But here’s the deal: The prosecutor has given you both an opportunity to rat. If you betray your fellow gang member but are not ratted on, you walk free while your buddy serves a three-year term. If you both rat, you both serve two years. The prosecutor knocks on your cell door. What do you do?

For decades, social scientists have studied how cooperation among humans evolves by observing people play multiple games of prisoner’s dilemma, each game lasting for a fixed number of rounds. Over the course of these games, the players balance the benefit of cooperation with the risk of exploitation and the temptation to rat with the risk of retaliation in subsequent games.

Findings from these prisoner’s dilemma studies suggest that players at first are likely to cooperate for several rounds, but eventually rat, hoping to get out of jail before they are exploited. What’s more, as players learn the game, they realize that the rational choice is to rat, which they do in earlier and earlier rounds in each subsequent game.