n the Iterated Prisoner's Dilemma, two players repeatedly face off against one another and can employ different strategies to beat their opponent. In 2012, Press and Dyson "shocked the world of game theory," Plotkin said, by identifying a group of strategies for playing this version of the game. They called this class of approaches "zero determinant" strategies because the score of one player is related linearly to the other. What's more, they focused on a subset of zero determinant approaches they deemed to be extortion strategies. If a player employed an extortion strategy against an unwitting opponent, that player could force the opponent into receiving a lower score or payoff.
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.
"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 doPage: 1 2 3 Related biology news :1
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