Generosity Drives Success in Evolution: How Cooperation Works

Generosity and cooperation may just have their roots in evolution. With new insights into the classical game theory match-up known as the "Prisoner's Dilemma," researchers have shown how these two traits succeeded in nature.

Last year, researchers identified a new class of strategies for succeeding in the Prisoner's Dilemma. This particular scenario is a way of studying how individuals choose whether or not to cooperate. In the game, if both players cooperate then they both receive a payoff. If one cooperates and the other does not, the cooperating player receives the smallest possible payoff and the defective player receives the largest. If both do not cooperate, they receive a payoff. However, that payoff is less than what they would gain if both had cooperated. In other words, it pays to cooperate, but it can pay more to be selfish.

"Ever since Darwin, biologists have been puzzled about why there is so much apparent cooperation, and even flat-out generosity and altruism, in nature," said Joshua B. Plotkin, one of the researchers, in a news release. "The literature on game theory has worked to explain why generosity arises. Our paper provides such an explanation for why we see so much generosity in front of us."

In the previous research, scientists found a class of approaches called "zero determinant" strategies. The score of one player was related linearly to the other. In addition, if a player employed an extortion strategy against an unwitting opponent, that player could force the opponent into receiving a lower score or payoff. Yet this latest study seems to reveal that these extortion strategies don't succeed in large, evolving populations.

In generous strategies, players tend to cooperate with their opponents. But if they don't, they suffer more than their opponents do over the long term. In addition, "forgiveness" is a feature of these strategies. A player who encounters a defector, for example, may punish the defector a bit but after a time, may cooperate with the defector again. The scientists found that after simulating these generous strategies, the strategy succeeded in the evolutionary version of the Prisoner's Dilemma. In fact, these methods are the only approaches that resist defectors over the long term.

"Our paper shows that no selfish strategies will succeed in evolution," said Plotkin in a news release. "The only strategies that are evolutionary robust are generous ones."

The findings are published in the Proceedings of the National Academy of Sciences.