Deceitful dilemma

A theory developed to study chess and poker offers an insight into why some animals cheat

Published: Thursday 15 June 1995

Crowing about skulduggery: the IMAGINE this: 2 prisoners are charged with a crime which they allegedly committed together. If neither confesses - that is, they agree to 'cooperate' - each will serve a term, say 1 year. If one honours the pact between the 2 prisoners to cooperate, while the other 'defects', blaming the first prisoner for the crime, the defector goes free while the cooperator serves 10 years in"Prison. If both defect, both serve 4 years in jail.

Each prisoner reasons that defection will ensure a shorter prison term (being turned free against serving I year and a 4-year prison term against a 10-year one). So both defect, and consequently, both are sentenccd,to a 4-year prison term. Also known as the Prisoner's Dilemma, this is,'in fact, a traditional model of the game theory, which says that the 'best' strategy adopted by a person is guided by the actions of another.

Evolutionary biologists now say that applying the game theory to study animal behaviour could provide an answer to questions such as why organisms choose cooperation as the most-favoured or the least-favoured strategy in different situations - from spiders fighting over web sites to cooperation amon@ fish. Such studies, apart from providing an opportunity to verify, game theory predictions, could also help in understanding a wide range of animal and even human behaviour, they argue (Science, Vol 267, No 5204).

For instance, Stephen and Melinda Pruett-Jones of the University of Chicago, say that bowerbirds resort to cheating for mating advantage. The scientists say that male bowerbirds build elaborate bowers - structures of twigs, leaves and other objects - to attract females, but some of them also indulge in damaging the bowers of other male birds in their absence. The 'marauders' increase their chances of success with the females at the expense of their non-marauding rivals, making cooperation a losing strategy.

But cooperation can become a viable strategy if the players interact again and again in an 'iterated Prisoner's Dilemma', so that they know w@'ho are cooperating and who are not. If somebody does not cooperate, a tit-for-tat strategy could be adopted towards that player subsequently. But could a tit-for-tat strategy work in a real world?

Manfred Milinski of the University of Bern, Switzerland, suggests that one place to look for an answer is among small fish, which face an 'iterated Prisoners Dilemma' naturally.

When a large fish ventures near a shoal of small fish, one or more of the school approaches the big one to see how dangerous it is. This predator inspection, says Milinski, is risky for the scouts, but the information can benefit them as well as the rest - if the big fish is not a predator or is not hungry, the smaller ones need not scatter.

The group of scouts approaching a prospective predator is playing out a Prisoner's Dilemma, argues Milmski. "Each has a strong urge to defect and let others take all the chances, but if all defect they learn nothing about the big fish. Full cooperation, on the other hand, minimises risks because the predator becomes confused if it cannot focus on a single target," he adds.

Milinski claims to have tested this idea in sticklebacks, and found that the fish indeed use tit-for-tat strategy for predator inspection. If a scout fails to make a move forward when its turn comes, the other would also hold back. "This model makes some new and very interesting predictions about evolution of cooperation," says Lee Dugatkin of University of Missouri, Colombia.

Robert Axelrod, a political scientist at the University of Michigan, even suggests that the evolutionary game theory may help in predicting the strategies politicians employ during elections.

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