Capuchin Monkeys Demonstrate Evolutionary Root of Spiteful Behavior, Researchers Say

Capuchin monkeys will pull a partner's plate right out from under them if they have "more than their fair share," according to a new study. This spiteful behavior was recently observed by researchers from Yale University, who were interested to see if jealous tendencies could be found among our distant primate relatives. 

"One hallmark of the human species is the fact that we're willing to make a special effort to punish those who violate social norms," Laurie Santos, Yale psychologist and senior author of the study, said in a news release. "We punish those who take resources unfairly and those who intend to do mean things to others. Many researchers have wondered whether this motivation is unique to our species."

It turns out it's not. Similar behaviors have also been observed in chimpanzees. In one experiment chimpanzees routinely pulled on a rope to collapse a table holding the food when a partner attempted to snatch the plate.

Capuchin monkeys take it one step further. They punish the greedy more often and will yank on the rope to collapse the table when they notice their partners were given larger portions.   

"Our study provides the first evidence of a non-human primate choosing to punish others simply because they have more," Kristin Leimgruber, first author of the paper, now studying at Harvard University, added. "This sort of 'if I can't have it, no one can' response is consistent with psychological spite, a behavior previously believed unique to humans."

Capuchin monkeys are relatively small, agile animals that live in forests throughout much of Brazil and other parts of Latin America. These monkeys generally feast on fruit, insects, leaves, and small birds. However, they are also surprisingly good at catching frogs and cracking nuts.

"Our findings suggest that the psychological roots of human-like punishment motivations may extend deeper into our evolutionary history than previously thought." Santos concluded.

The study was recently published in the journal Evolution and Human Behavior.

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