Share and Share Alike

A growing number of studies are looking at whether non-human animals have a moral sense. One of my favorites from a few years back focused on fairness. Scientists at the Yerkes National Primate Research Center placed two cups of food on a tray that was counterweighted so that, in order for the capuchin monkeys in a nearby cage to reel it in and have a snack, both had to pull a bar. By cooperating, the monkeys could move the tray against the cage so that Sammy could reach one cup and Bias the other. The monkeys figured it out and cooperated.

Here’s where it got interesting: when the scientists filled only one food cup, the monkey whose efforts brought him the full cup shared the spoils with the monkey who worked just as hard but got only an empty cup. By sharing, of course, a monkey may figure that when he is the one to work hard but get an empty food cup, his companion will share. When the companion is a relative, monkeys are even more willing to work even if their food cup (which they can see) holds nothing, perhaps expecting this generosity. “Winners were, in effect, compensating their partners for received assistance,” Yerkes’

Then the scientists changed things so that it took only one monkey to reel in the tray. In this case, when the monkey who did the work all by himself reached the food cup, he almost never shared the treat with the monkey who hadn't worked. Again, fairness dictates that you don’t get a reward if you don’t work.

It turns out that monkeys know their own kind pretty well when it comes to sharing. In their latest work, reported online this evening in

“The fact that the capuchins predominantly selected the pro-social option must mean that seeing another monkey receive food is satisfying or rewarding for them,” said de Waal. “We believe pro-social behavior is empathy based. Empathy increases in both humans and animals with social closeness, and in our study, closer partners made more pro-social choices. They seem to care for the welfare of those they know.”

You have to wonder, though, if it was more Machiavellian than that. With a stranger, the monkeys might figure, "why bother doing a kindness if I’ll never see her again?" With a friend or relative, the calculus might be, "I’d better select the token that gives her an apple slice, too, so she’ll do me a favor when we get out of this dumb experiment and back to the troop."

It’s always risky to anthropomorphize animal behavior by, in this case, imputing a sense of generosity or empathy. De Waal and his team admit that their next task is to determine whether capuchins act to get their friend or relative food because they like to eat together, because they like to see another monkey enjoying food, or because they expect a quid pro quo down the line.