Bacteria Use Chat to Play the ‘Prisoner’s Dilemma’ Game in Deciding Their Fate. When faced with life-or-death situations, bacteria — and maybe even human cells — use an extremely sophisticated version of “game theory” to consider their options and decide upon the best course of action, scientists reported in San Diego March 27. In a presentation at the 243rd National Meeting & Exposition of the American Chemical Society (ACS), they said microbes “play” a version of the classic “Prisoner’s Dilemma” game.
José Onuchic, Ph.D., who headed the research team, said these and other new insights into the “chat” sessions that bacteria use to communicate among themselves — information about cell stress, the colony density (quorum-sensing peptides) and the stress status and inclinations of neighboring cells (peptide pheromones) — could have far-reaching medical applications.
“Just as in the classic Prisoner’s Dilemma game, the bacteria have to weigh the pros and cons of their decisions,” said Onuchic. “The bacteria make a decision based not only on what it knows about its own stress and environment, but it also has to think about what the other bacteria might do. So this is like the Prisoner’s Dilemma being played with 1 trillion cells in a colony instead of just two people.”
Though I’m not really a game theory or philosophy buff, one problem I’ve always found fascinating is the Prisoner’s Dilemma. The basic version goes like this:
Two suspects are arrested by the police. The police have insufficient evidence for a conviction, and, having separated the prisoners, visit each of them to offer the same deal. If one testifies for the prosecution against the other (defects) and the other remains silent (cooperates), the defector goes free and the silent accomplice receives the full 10-year sentence. If both remain silent, both prisoners are sentenced to only six months in jail for a minor charge. If each betrays the other, each receives a five-year sentence. Each prisoner must choose to betray the other or to remain silent. Each one is assured that the other would not know about the betrayal before the end of the investigation. How should the prisoners act?
If you only play the game once, the only rational response is defection. But the more interesting mechanic is iterated prisoner’s dilemma; that is, playing it over and over for a set number of games. There are a number of strategies that I won’t go into here, but in a continuous IPD game, the most effective strategy is called “tit-for-tat”. Basically, the person using that strategy remains silent for the first turn, and after that they do whatever the other prisoner did on the previous turn.
On a whole, altruistic strategies almost always fared better than aggressive or greedy strategies, even when judged solely on what would be in the best self-interest (basically, they add up the amount of time spent in prison over the course of the 200 or however many games).
This fact has been used to explain the evolution of altruistic behavior, when one would think that if we’re all competing to survive, we’d want to be aggressive and greedy and take what we want…it’s actually re-defined evolution from purely Darwinian (“strictly competitive”)/Malthusian (“struggle to survive”) standpoint to one that can explain why and how “morality” and Social Darwinism work for humans.
Fascinating stuff, really. Read Robert Axelrod’s “The Evolution of Cooperation” to learn more about it…it’s a good book and really easy to understand.