It's a heartwarming story, but is "paying it forward" really worth the effort?
Well, new research, published Sept. 2 in the Proceedings of the National Academy of Sciences, shows that generosity really does pay off in the long run — for everyone.
"Ever since Darwin," study researcher Joshua Plotkin of the University of Pennsylvania 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."
Building from previous studies on the "Prisoner's Dilemma" and "Game Theory," or the study of decision-making, Plotkin and co-author Alexander Stewart claim they've found mathematical proof that evolution favors selfless strategies.
The "Prisoner's Dilemma"
The Prisoner's Dilemma works like this: Two "players" commit a crime and how they behave during questioning determines their punishment. When a player "defects," he or she betrays his or her partner. "Cooperating" means keeping quiet.
If X testifies (defects) against Y, X avoids jail altogether while Y gets three years behind bars — bad for one and very good for the other. If both criminals defect, they each receive a two-year sentence. Lastly, if both keep quiet, they'll each spend only one year in jail, the largest mutual payoff.
The question is — do you trust your partner in crime to keep quiet?
According to the Nash Equilibrium, named after Nobel Prize recipient John Nash (of "A Beautiful Mind" fame) in reality, most people do squeal on their partners. People simply don't trust each other to keep quiet. But statistically, when both players stay silent, they reap the best mutual outcome.
When the game goes on for multiple rounds, players can employ different strategies to achieve the greatest benefit. As players learn more about how their partner behaves, they'll alter their approaches — one player's outcome therefore directly affects the other's.
A Species-Wide View
Previous research has only tested how these approaches change for a single set of players. But in the new study, Stewart and Plotkin analyzed the approaches of a large population over time. They crafted a mathematical proof showing that evolution favors everyone cooperating.
"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," Stewart said in a press release.
Remember X and Y? Well, imagine they go through multiple rounds of questioning with numerous other offenders. If X and Y both keep quiet, they're more likely to trust others to do the same in the future. As this "generosity" spreads, fewer criminals defect on each other, and everyone gets less jail time.
But if X and Y face each other and one defects, the other carries that cynicism into the next match — domino-ing through the population, resulting in everyone getting more jail time.
Stewart's and Plotkin's research also begins to explain the overwhelming, albeit confusing, presence of altruism in nature. Darwin's classic theory of natural selection seems to favor selfishness, yet animals will send out warning cries to their comrades even if it gives away their location to a predator, and bacteria share genetic information that gives them resistance to drugs even though that means more competition for resources in the long run.
"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."
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