Monkeys, like humans, will take the time and effort to punish others who get more than their fair share, according to a study conducted at Yale. In fact, they can act downright spiteful.
Capuchin monkeys will yank on a rope to collapse a table that is holding a partner monkey's food. While chimpanzees collapse their partner's table only after direct personal affronts like theft, capuchins punish more often, even in cases where the other monkey merely had more food, according to a study published online in the journal Evolution and Human Behavior.
"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" said Laurie Santos, Yale psychologist and senior author of the study. "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."
Santos and her colleagues Kristin Leimgruber and Alexandra Rosati, now both at Harvard University, wanted to know if a distantly related primate species would punish the beneficiaries of social inequalities. Like chimpanzees, capuchins did collapse tables to punish monkeys that stole food. But they also punished beneficiaries of windfalls as well.
"Our study provides the first evidence of a non-human primate choosing to punish others simply because they have more," said Leimgruber, first author of the paper. "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."
"Our findings suggest that the psychological roots of human-like punishment motivations may extend deeper into our evolutionary history than previously thought." Santos said.
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Kristin L. Leimgruber et al. Capuchin monkeys punish those who have more, Evolution and Human Behavior (2015). DOI: 10.1016/j.evolhumbehav.2015.12.002