Humans 'programmed to spot cheats'

There is a specific part of the brain that concentrates on "social exchange" which is not part of the general reasoning area.

Scientists have found the same results Westerners, and in a tribe from the remote Ecuadorian Amazon.

Studies have suggested the "cheat-detector" lies within the limbic system, a part of the brain used for processing emotional and social information.

They believe the trait developed in humans and apes as social behaviour became more complex.

Researchers from the University of California at Santa Barbara looked at one patient, known as R.M. who damaged this area of his brain in a cycling accident in 1974.

He was able to successfully perform tasks which asked him to assess whether someone might be breaking a precautionary rule - the rule was "if you engage in hazardous activity X, you must take precaution Y".

But he fared less well in tests which used the same kind of logical thought process which were to do with assessing if an individual might be cheating on a social contract - going by the rule "if you receive benefit X, you must fulfil requirement Y".

The researchers said if R.M.'s general reasoning was poor, he would have performed badly in both tasks.

Evolution

The team then gave modified versions of the same tests to undergraduates from Harvard University and to members of the Shiwiar, who live in a remote region on the Ecuadorian Amazon almost entirely cut off from civilisation, to see if they had the same responses.

The Shiwiar's ability to detect cheats was as good as that of the undergraduates, leading the scientists to conclude "cheat dectecting" was an evolutionary trait rather than a skill linked to complex social environments.

Both studies were published in the journal Proceedings of the National Academy of Sciences.

Writing in the journal, the researchers led by Leda Cosmides from the Center for Evolutionary Psychology at the University of California, Santa Barbara, said: "R.M.'s differential impairment indicates that being able to detect potential cheaters may be a separable component of the human mind."

"Knowing how to engage in social exchange is an important aspect of human social intelligence.

"It is difficult to imagine two populations that differ more than Shiwiar villagers and Harvard students in their exposure to Western-style schooling, word problems, the institution of science, or the concept of an experimental situation - factors that are known to affect performance in cross-cultural studies of cognition."