Generosity Leads to Evolutionary Success, Say Researchers

A new finding has implications for human evolution.

Here is another clue for scientists engaged in figuring out how human evolution worked: Just like in the movies, researchers are finding that the good guys always win in the end.

This is the message from results of a recent study published in the Proceedings of the National Academy of Sciences during the week of September 2, 2013. The study was conducted by a duo of University of Pennsylvania biologists. Postdoctoral researcher Alexander J. Stewart and associate professor Joshua B. Plotkin analyzed the outcome of the Prisoner’s Dilemma game, as played continuously by a large, evolving population of players.

The Prisoner’s Dilemma is a game that shows why two individuals might not cooperate, even if it appears that it is in their collective best interests to do so. In the game, if both players cooperate, they both receive a payoff. If one cooperates and the other does not, the cooperating player receives the smallest possible payoff, and the defecting player the largest. If both players do not cooperate, they receive a payoff, but it is less than what they would gain if both had cooperated. In other words, it pays to cooperate, but it can pay even more to be selfish.

The significance of the research is that, while previous researchers have suggested that cooperative strategies can be successful, for the first time, Stewart and Plotkin offer mathematical proof that the only strategies that succeed in the long term are generous ones. It flies in the face of the principle of “survival of the fittest”, which has traditionally underpinned the Darwinian concept of biological evolution. 

“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.”

The research differed from previous studies in another way. Instead of a one-on-one 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.

“The fact that there are extortion strategies immediately suggests that, at the other end of the scale, there might also be generous strategies,” Stewart said. “You might think being generous would be a stupid thing to do, and it is if there are only two players in the game, but, if there are many players and they all play generously, they all benefit from each other’s generosity.”

In generous strategies, which are essentially the opposite of extortion strategies, players tend to cooperate with their opponents, but, if they don’t, they suffer more than their opponents do over the long term. “Forgiveness” is also a feature of these strategies. A player who encounters a defector may punish the defector a bit but after a time may cooperate with the defector again.

After simulating how some generous strategies would fare in an evolving population, Stewart and Plotkin crafted a mathematical proof showing that, not only can generous strategies succeed in the evolutionary version of the Prisoner’s Dilemma, in fact these are the only approaches that resist defectors over the long term.

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

The discovery, while abstract, helps explain the presence of generosity in nature, an inclination that can sometimes seem counter to the Darwinian notion of survival of the fittest.

“When people act generously they feel it is almost instinctual, and indeed a large literature in evolutionary psychology shows that people derive happiness from being generous,” Plotkin said. “It’s not just in humans. Of course social insects behave this way, but even bacteria and viruses share gene products and behave in ways that can’t be described as anything but generous.”

“We find that in evolution, a population that encourages cooperation does well,” Stewart said. “To maintain cooperation over the long term, it is best to be generous.”


Source: Adapted and edited from a University of Pennsylvania press release.

Cover Photo, Top Left: Allegorical personification of Charity (Generosity) as a mother with three infants by Anthony van Dyck.  Wikimedia Commons


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