Monkeys Show Sense Of Fairness, Study Says

Sean Markey
National Geographic News
September 17, 2003

If you expect equal pay for equal work, you're not the only species to have a sense of fair play. Blame evolution.

Researchers studying brown capuchin monkeys (Cebus apella) have found that the highly social, cooperative species native to South America show a sense of fairness, the first time such behavior has been documented in a species other than humans.

The question of whether human aversion to unfair treatment—now shown by other primates—is an evolved behavior or the result of the cultural influence of large social institutions like religion, governments, and schools, in the case of humans, has intrigued scientists in recent years.

The new finding suggests evolution may have something to do with it. It also highlights questions about the economic and evolutionary nature of cooperation and its relationship to a species' sense of fairness, while adding yet another chapter to our understanding of primates.

"It looks like this behavior is evolved … it is not simply a cultural construct. There's some good evolutionary reason why we don't like being treated unfairly," said Sarah Brosnan, lead author of the study to be published in tomorrow's issue of the science journal Nature.

Brosnan, a biology Ph. D. candidate schooled in zoology and psychology at the Yerkes National Primate Research Center and Living Links Center at Emory University in Atlanta, Georgia, said her research was inspired, in part, by studies into human cooperation conducted by Swiss economist Ernst Fehr, who found that people inherently reject unfairness.

Monkey Business

To test whether or not such behavior is found in other species, Brosnan designed an experiment for brown capuchin monkeys, a species well-known for strong social bonds and relatively cooperative behavior, particularly in shared food-gathering activities like hunting squirrels and locating fruit trees.

Individuals were drawn from two large, well-established social groups of captive brown capuchins from colonies at the Yerkes National Primate Research Center and paired with a partner. Pairs were placed next to each other and trained to exchange with human handlers a small granite rock within 60 seconds to receive a reward, in most cases, a piece of cucumber.

"That may actually sound simple, but not very many species are willing to relinquish things, especially intentionally," Brosnan said in a telephone interview. (Think of trying to pry a large bone from a dog's mouth.)

Only female capuchins were tested because they most closely monitor equity, or fair treatment, among their peers, Brosnan said.

Partners of capuchins who made the swap either received the same reward (a cucumber slice), or a better reward (a grape, a more desirable food), for the same amount of work or, in some cases, for performing no work at all.

Continued on Next Page >>


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