Does Cooperation Beat Cheating After All?

This is the question at the heart of the so-called prisoner’s dilemma, one of the most famous ideas in game theory. Suppose that two suspects are arrested for the same crime, and then separated and offered a plea deal. They can either “cooperate” by staying silent, or “cheat”—betraying the other and taking the deal. If both of them stay silent, they both get short sentences. If one stays silent and the other rats him out, one gets the maximum sentence and the other walks free. But what often happens is that they both cheat instead. Fearing betrayal, each suspect acts in their own self-interest, takes the plea, and spends years rotting in prison. (This outcome is known as the Nash equilibrium, for Nobel-prize winning mathematician John Nash, and was dramatized in the film A Beautiful Mind.)

The prisoner’s dilemma has long been used to understand everything from the behavior of competing microbes in a petri dish to human societies seeking to head off nuclear war.  But the model has always confounded scientists: Cooperation is essential for the survival of biological life, but how can cooperation emerge if cheating always offers the biggest payoff?

Now, a new study led by Rutgers University physicist Alexandre Morozov suggests cooperation can emerge naturally as long as we assume people are neither heroes nor villains, but something in between: They cooperate with some individuals and cheat with others, and they change their behavior based on who their opponents are.