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Game Theory in Evolutionary Biology


Author Emily Singer presents the difficult resolution between game theory tactics and cooperation in nature. The optimal strategy in the prisoner’s dilemma, which points to the “generous” strategy of both not confessing, has been used to explain why cooperation occurs in nature. However, physicist Freeman Dyson and computer scientist William Press have challenged this idea by claiming that the best strategies were ones that were more “selfish,” that encouraged extortion. This would be analogous to having one prisoner confessing and receiving a much lighter sentence than the other prisoner who does not confess.

Joshua Plotkin, a theoretical biologist at the University of Pennsylvania, tested this claim in the context of ecological interactions. Plotkin was puzzled by the idea of the optimal strategy being extortion because of several cooperative dynamics that still persist in communities today: Vampire bats donate some of their blood meal to members of the community that were unable to feed – at the expense of not intaking all of the blood that they collected. Also, the vervet monkey screams to alert its community of a predatorial presence – at the cost of potentially bringing the predator’s attention to itself. Plotkin found that variations in the context of the biological games can determine which strategy – cooperation or extortion – is better than the other. In addition to the ideas posited by Dyson and Press, Plotkin determined that extortion is good if there is only one opponent: It would be an optimal strategy if a vampire bat does not share its blood meal with one who has not fed because it would stay full while the other dies. However, in an evolutionarily more realistic setting with a larger population, an extortioner will pair with another extortioner, and both will defect with a lower payoff. It is then better to cooperate: A player that gains the highest payoff in each encounter will pass on their strategies and payoffs to their offspring; the generous strategy will spread through the population, and ultimately, the population will convert from extortion to cooperation as the best strategy. For example, a vampire bat that chooses to cooperate and share its meal may encourage other members to be generous; therefore, in a tit-for-tat strategy, that vampire bat may later benefit from another member who shares its blood meal.

In the Prisoner’s Dilemma, the pure strategy Nash equilibrium is for both prisoners not to confess, which is the more generous option, as opposed to the more selfish option of a prisoner confessing on the other. Just as how this model does not always hold in reality, in which variable factors, including personal incentives and temperaments, may drastically change the game, the same can be said about the very fine line that exists between generosity and extortion as the best strategy when the Prisoner’s Dilemma is projected onto cooperative biological interactions. However, considering that evolution is the change of large populations over generations, it seems plausible to posit – at least for the time being – that the “generous option” is a good basic explanation for cooperative behaviors that have evolved within species.


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