Scientists Used Game Theory To Prove That Being Selfish Pays Off In Nature


As cynical as it sounds, the selfish find success in life.


So concludes a new study published Monday in the Proceedings of the National Academy of Sciences. Building on other studies of the "prisoner's dilemma" and "game theory," or the study of decision-making, the researchers, Joshua Plotkin and Alexander Stewart from the University of Pennsylvania, found that self-interest pays off. While the study focuses on the theoretical mathematics behind general evolution, the same trends could apply to human thinking.

Last year, Plotkin and Stewart conducted similar research, determining that evolution actually favors altruism. The new study, however, adds a twist. The model not only allows "players" to alter their strategies, but also their rewards. The results showed the exact opposite - that in the long-run, cooperation tends to collapse.

"It's a somewhat depressing evolutionary outcome, but it makes intuitive sense." said Plotkin, a professor of biology in the School of Arts & Sciences.

How It Works

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 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 two-year sentences. Lastly, if both cooperate, they'll each spend only one year in jail, the largest mutual payoff.

According to the Nash Equilibrium, named after Nobel Prize recipient John Nash (of "A Beautiful Mind" fame) in reality, most people do snitch on their partners. People simply don't trust each other to keep quiet.

When the game continues for multiple rounds, players can employ different strategies to achieve the greatest benefit. As they learn more about how their partners behave, players can alter their approaches to achieve the greatest payoff in the end. Therefore, players' decisions greatly affect other players' future strategies.

While organisms in nature don't necessarily make decisions the way prisoner's facing interrogation would, the natural world still includes trade-offs. For example, a smaller, weaker male in a species could somehow help a larger, stronger male breed with a female, ensuring the next generation has the best chance of survival. Or the less advanced male could try and mate with the female himself, furthering his line while potentially harming the overall species.

New Findings

Plotkin and Stewart's original study explained how these principles of generosity and cooperation would have evolved in nature. When costs increased, cooperation did as well - a linear relationship. When the researchers upped the variables, however, the benefits of a more selfish mindset became apparent.


While the prevalence of cooperation quickly arises in populations with the power to determine how frequently to cooperate, that sentiment soon collapses when players can also determine to what extent they work together. Plotkin and Stewart found a mathematical tipping point, where the hypothetical players favored defection, time and again.

"When cooperative strategies predominate, payoffs will rise as well," Stewart said. "With higher and higher payoffs at stake, the temptation to defect also rises. In a sense the cooperators are paving the way for their own demise."

As a next step, the marine bacteria Vibrionaceae could provide a real-world example to back this theory up. This species cooperates by sharing a protein they release which allows them to metabolize iron. The bacteria, however, sometimes mutate to alter whether they generate it and how much - a "natural experiment" for Stewart and Plotkin's theory.

While this creates a bit of a depressing view of evolution, it also makes more sense in nature, according to the researchers.