Hunger Games: Chimps play fair -- when it suits them, study finds

Do chimps play fair? A study that compared the behavior of chimpanzees and children while playing a sharing game found that the primates might have a sense of fairness akin to that of human beings.

Such research could help shed light on the role of altruism and fair play in human evolution -- which may help explain the development of human social networks.

The research, released Monday by the Proceedings of the National Academy of Sciences, used the Ultimatum Game, in which one player (the proposer) has the power to split a reward with another player (the recipient).

If the proposers can decide how to split the reward unilaterally, they often leave as little as possible for the recipient, keeping the lion’s share for themselves (this is often referred to as the “dictator game”). But in a version called the “ultimatum game,” if the recipient has the power to veto the reward -- preventing both players from getting any -- the proposer is more likely to offer a 50-50 split.

The researchers from Georgia State University and the National Primate Research Center in Atlanta note several different anecdotes showing that chimps have an understanding of the concept of fairness -- for example, an adolescent female inserting herself between two young chimps squabbling over a leafy branch, splitting the branch in half for each youth and taking none for herself.

And in humans, they noted that the norms of sharing differ across cultures. The Lamelara in Indonesia have a much more socially interdependent framework -- they have to cooperate to hunt whales, and they tend to offer more than their fair share to others when playing the game. The Hadza in Tanzania, by contrast, tend to offer very little to others -- as hunter-gatherers, cooperation is enforced more by fear of ostracism, and the rules of the Ultimatum Game may reduce that fear and allow them to “follow their self-interest,” the authors point out.

For this experiment, the researchers set up the ultimatum game with 20 children aged 2 to 7 (for a reward of stickers) and compared their plays to those of six chimpanzees (with bananas as the prize). They found that in both groups, the proposers tended to keep as much as they pleased if they were given full control -- but they tended to share equally if the recipient’s approval was needed for the deal to go through.

“[Because] cooperation was needed to gain rewards, it is possible that proposers were more generous because they were working with the respondent,” the authors write, “because involvement in a task may increase their sensitivity to inequitable outcomes.”

Here’s the catch, though: Neither the chimps nor the children in this study ever vetoed the offer, even when it was unequal. Thus, it’s not clear the recipients understood that they had the power to influence how much the proposers shared with them.

So proposing chimps try to play fair with a recipient when they realize they need the recipient to gain a reward -- but recipient chimps don’t realize they can use that power as leverage?

Perhaps it’s just that neither children nor chimps quite grasped the rules, because recipients seemed to express their disapproval in other ways, the authors pointed out. One recipient chimp seemed to express outrage at an unfair share, either spitting water at the proposer or banging against the fence separating them.

Rather than spit, children would say things like, “You got more than me,” or, “I want more stickers.”

Follow me on Twitter @aminawrite.