If you’re an optimist, you probably believe that humanity is inherently cooperative and willing to sacrifice for the greater good of all. If you’re a pessimist, chances are you believe that, in the end, people will always do what is in their own interests.
But if you’re Martin Nowak, you believe that the truth is: It’s a matter of context.
A professor of mathematics and of biology and director of the Program for Evolutionary Dynamics, Nowak is the senior author of a new study that finds, across repeated interactions, the environment that individuals find themselves in can affect whether they act as partners or rivals. The study is described in a recently published paper in the journal Nature Human Behavior.
“Direct reciprocity is one of the main theories to explain cooperation among humans,” Nowak said. “It’s been studied for at least 50 or 60 years, but work over the last six years has allowed for a completely new look at this idea.
“What we’re studying here is the emergence of so-called partner and rival strategies,” he continued. “If you consider all strategies of direct reciprocity, a very small subset of them are either partners or rivals, but evolution always leads to one or the other.”
To understand how different strategies can emerge, Nowak and colleagues Christian Hilbe and Krishnendu Chatterjee, both from the Institute of Science and Technology in Austria, began with a classic paradigm from game theory, namely the prisoner’s dilemma.
The game works like this: When faced with the chance to interact, two individuals must decide whether to cooperate or defect. If both cooperate, both receive a reward. If one person defects while the other chooses to cooperate, the defector collects a larger reward, while the other person gets nothing. If both defect, both receive a reward, albeit one that is smaller than the reward for cooperation. If players behave in a purely logical fashion, the best strategy is to defect, because it is in their self-interest to try to maximize their reward.
“If you play the game once, there’s no easy way to reach cooperation, because people, if they’re rational, will always defect,” Nowak said. “But if you play the game multiple times, there is a possibility of cooperation. If you defect against me in the first round, then I might defect against you in the next round, so you might realize that it’s better to cooperate.”