Study: Detecting Cheats Is an Ancient Skill

By JOAN MAGRUDER

Humans have a mechanism in their brains to detect when individuals "violate the terms of social contracts"--in other words, cheat--say researchers at UC Santa Barbara in a report in the Proceedings of the National Academy of Science.

Evolutionary psychologists John Tooby and Leda Cosmides and their colleagues have produced neurological and anthropological evidence in support of their theory that detecting social cheaters requires specialized neural circuitry.

"Social exchange--also known in biology as reciprocal altruism--is an ancient, pervasive, and central part of human social life," according to Cosmides. "This mutual provisioning of benefits, each conditional on the others' compliance, is rare in the animal kingdom. Some species, including humans and baboons, engage is this very useful form of mutual help."

Because the ability to understand social exchanges makes the reciprocation of favors possible, it provides a cognitive foundation for human economic activity and several other forms of cooperation, said the researchers, who are co-directors of the Center for Evolutionary Psychology at UCSB.

In a study of a patient (R.M.) with damage to the limbic system--a brain region critical for processing emotional and social information--the researchers found that while R.M. did well on some reasoning tests, he did poorly on tests that required him to determine who might be breaking a social contract (i.e. not holding up his or her end of the bargain).

"The patient's pattern of spared and impaired reasoning could not occur if cheater detection was caused by more general reasoning abilities, such as circuits that embody logical or other general purpose rational rules," said Cosmides.

In a related study, which tested the prediction that complex evolved adaptations must be universal in humans, the researchers gave oral and pictorial versions of the same tasks to the Shiwiar, nonliterate hunter-horticulturalists who live in a remote region of the Ecuadorian Amazon. The results were compared to a previous study of Harvard undergraduates.

"As predicted, the ability of the Shiwiar to identify potential cheaters on this complex reasoning task was virtually identical to that of the Harvard students," Tooby said. "That this brain mechanism reliably develops even in disparate cultural contexts suggests that it is a universal feature of human nature."

For further information, go to the center's Web site at <www.psych.ucsb.edu/research/cep>.