Generosity leads to evolutionary success, biologists show

With new insights into the classical game theory match-up known as the "Prisoner's Dilemma," University of Pennsylvania biologists offer a mathematically based explanation for why cooperation and generosity have evolved in nature.

Their work builds upon the seminal findings of economist John Nash, who advanced the field of game theory in the 1950s, as well as those of computational biologist William Press and physicist-mathematician Freeman Dyson, who last year identified a new class of strategies for succeeding in the Prisoner's Dilemma.

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"Ever since Darwin," Plotkin said, "biologists have been puzzled about why there is so much apparent cooperation, and even flat-out generosity and altruism, in nature. 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."

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Stewart and Plotkin became intrigued with this finding, and last year wrote a commentary in PNAS about the Press and Dyson work. They began to explore a different approach to the Prisoner's Dilemma. Instead of a head-to-head competition, they envisioned a population of players matching up against one another, as might occur in a human or animal society in nature. The most successful players would get to "reproduce" more, passing on their strategies to the next generation of players.

It quickly became clear to the Penn biologists that extortion strategies wouldn't do well if played within a large, evolving population because an extortion strategy doesn't succeed if played against itself.

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

Generosity leads to evolutionary success, biologists show