Chimps Play Raisin Ultimatum Game

October 10, 2007

Primate researchers at the Max Planck Institute report fascinating results for a chimpanzee friendly version of the ultimatum game.

In each version of this mini-ultimatum game, the proposer could pull one tray with 8 raisins for himself and 2 for the other (an unfair split that people routinely reject). However, the proposer would have a choice. In one game, he could choose between this unfair offer and a fair one (5 raisins each). In another, he could choose a hyper-fair option (2 for himself and 8 for the responder). In a third, he had no choice (the second tray also had 8 for himself and 2 for the other). In the fourth game, the proposer’s other choice was hyper-unfair (10 for himself, 0 for the responder).

Unlike humans faced with these games, chimpanzee responders accepted any nonzero offer, whether it was unfair or not. The only offer that was reliably rejected was the 10/0 option (responder gets nothing). The researchers conclude that chimpanzees do not show a willingness to make fair offers and reject unfair ones. In this way, they behave like selfish economists rather than as social reciprocators.

Assuming that the experiment accurately mimics the human ultimatum game, this is a major finding (in my mind anyway). Humans tend to punish the proposer for deviating from an equal split while chimps will take any non-zero amount. How cool is that?

I hope someone tries this experiment with bonobos too. And children (against other children with raisins, not child vs. bonobo).

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3 Responses to “Chimps Play Raisin Ultimatum Game”

  1. tom s. Says:

    It’s a great result that chimps are closer to an economist’s idea of rational behaviour than people are.

  2. RAD Says:

    Yes!!!! The section about the Ultimatum Game was my favorite part of your book, Tom. My love of evolutionary psychology trumps my admiration of the invisible hand.

    For me, the unexpected results of the Ultimatum Game indicate that a very interesting mental adaptation took place in our evolution. A difference between hominids and other great apes is fascinating but if this type of adaptation is unique to homo sapiens (and not other hominids… a little hard to test I admit) then it is truly ground breaking.

    “The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ (I found it!) but ‘That’s funny …'”
    Isaac Asimov


  3. […] is why I found the research on chimps playing the ultimatum game with raisins so fascinating. Chimps play the way rational economists play (they accept any amount) […]


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