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Interviewee: Frans de Waal, Yerkes National Primate Research Center
Everybody knows that it feels good to do good. Giving someone a gift can be just as rewarding as getting one yourself. In fact, studies using MRI scans have shown that the part of our brain that stimulates pleasure when
receiving a gift also reacts when giving one.
Until now, scientists believed that such emotional responses were distinctly human traits, but new research indicates monkeys have them too.
Primatologist Frans de Waal, at the Yerkes National Primate Research Center in Atlanta, gave a group of capuchin monkeys a task that involved taking one of two tokens while in the presence of another monkey.
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"One token would give them a reward, and the other token would give them and their partner a reward. So the first token we call a selfish token, because you only work for yourself. This second token we call a pro-social token, because we reward both monkeys at the same time," says de Waal.
The selfish token was colored purple, while the pro-social was green. Once the monkey had chosen, their reward would be a piece of fruit, given to them by the same researcher presenting the tokens.
As de Waal wrote in the Proceedings of The National Academy Of Sciences, if their partner was a stranger, the monkey made the selfish choice. However, if their partner was family or simply familiar to them, the monkey would consistently choose the ‘pro-social’ token.
De Waal also found that monkeys were selfish if their partner received better rewards, such as a grape instead of a piece of apple. The monkeys were unwilling to share rewards when they knew they weren’t profiting equally with their partner. This finding supports previous research showing a sense of fairness in monkeys.
Why use capuchins, rather than another species? As de Waal explains, “Capuchins happen to be, not only smart, but they are also cooperative. They share food with each other, they cooperate sometimes with each other, they hunt together for example in the wild. And so we figured if you want to look at pro-social tendencies, you have to look at cooperative species."
But are monkeys as charitable as people? Not quite. De Waal discovered that if a monkey was unable to see their partner, such as when a large panel was put between them, the monkey would make the selfish choice. Apparently, for monkeys, out of sight really is out of mind, at least when it comes to sharing a reward.
"This is actually quite a difference with humans, because I think humans are more imaginative. So we send money to faraway people in Thailand, who were hit by the tsunami, because we can imagine what good it will do for them," says de Waal.
So while monkeys may not be donating to charity anytime soon, it seems they do know a thing or two about giving.
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Yerkes National Primate Research Center
Proceedings of the National Academy of Sciences
National Institutes of Health
Elsewhere on the Web