The new convergence of biology and economy has been helped by a common methodology — game theory. John Maynard Smith, a professor of biology at the University of Sussex, in Britain, was the first to effectively apply the economist’s habit of playing a “game” with competing strategies to evolutionary mysteries. The only difference is that the economic games reward winners with money while evolutionary games reward winners with chance to survive and breed. One game in particular has proved especially informative in both disciplines: the prisoner’s dilemma.
A dramatized version of the game runs as follows: two guilty accomplices are held in separate cells and interrogated by the police. Each is faced with a dilemma. If they both confess (or “defect”), they will both go to jail for three years. If they both stay silent (or “cooperate”), they will both go to jail for a year on a lesser charge that the police can prove. But if one confesses and the other does not, the former will walk free on an agreement, while the cooperator, who stayed silent, will get a five-year sentence.
Assuming that they have not discussed the dilemma before they were arrested, can each trust his accomplice to stay silent? If not, he should defect and reduce his sentence from five to three years. But even if he can rely on his partner to cooperate, he is still better off if he defects, because that reduces his sentence from three years to none at all. So each will reason that the right thing to do is to defect, which results in three years for each of them. In the language of game theorists, individually rational strategies result in a collectively irrational outcome.
Biologists were interested in the prisoner’s dilemma as a model for the evolution of cooperation. Under what conditions, they wanted to know, would it pay an animal to evolve a strategy based on cooperation rather than defection? They discovered that the bleak message of the prisoner’s dilemma need not obtain if the game is only one in a long series — played by students, researchers, or computers, for points rather than years in jail. Under these circumstances the best strategy is to cooperate on the first trial and then do whatever the other guy did last time. This strategy became known as tit-for-tat. The threat of retaliation makes defection much less likely to pay.
Robert Alfred, a political scientist, and William Hamilton, a biologist, both at the University of Michigan, discovered by public tournament that there seems to be no strategy that beats tit-for-tat. Tit-for-two-tats — that is, cooperate even if the other defects once, but not if he defects twice — comes close to beating it, but of hundreds of strategies that have been tried, none works better.
1.What is game theory?
2.The two guilty accomplices mentioned in Para. 2 are （ ）.
3.For the worst situation, what is the total year of the two accomplices’ sentence?
4.What are the biologists’ findings for the cooperation strategy?
5.What does tit-for-two-tats mean?
