In the October 5th, 2007 issue of the journal Science, Keith Jensen, Josep Call, and Michael Tomasello published an article entitled “Chimpanzees are Rational Maximizers in an Ultimatum Game.” This article can be found here: http://www.sciencemag.org/cgi/content/full/318/5847/107

The authors study the ultimatum game and contrast human behavior with chimpanzee behavior. The ultimatum game is played between two individuals. One is the “proposer,” who is offered a sum of money and can decide how to divide it between himself and the “responder.” The responder can decide whether to accept or to decline the proposer’s offer. If the responder accepts the offer, the players receive the proposer’s division. Else if the responder rejects it, both do not get anything. Using the theories we learned in class, we would assume that the proposer would propose an unequal split. For example, if $100 were at stake, the proposer would keep $99 and offer $1 to the receiver. The dominant strategy of the receiver would be to accept whatever offer the proposer gives him—because the alternative would be to receive nothing at all. As we learned in class, the proposer holds the most “power” in this relationship and should get a majority of the value.

However, the article mentions various studies that have shown that proposers tend to make offers of 40 to 50% of the value, and responders will reject offers if they are less than 20%. This implies that responders realize when an offer is unfair and will punish the proposer for the unfair offers. Proposers who understand this will equalize their proposals.

Currently, chimpanzees are the closest relatives to humans and display some types of coordinated or altruistic behaviors (coordinated food gathering, for example). The authors decided to test the ultimatum game on chimpanzees because they wanted to assess whether chimpanzees were similar to humans in their understanding of fairness. In a modified version of the ultimatum game, the scientists confirmed that humans tended to reject unfair offers. Chimpanzee responders, on the other hand, would rarely reject any offer. Unlike humans, the chimpanzees did not even appear to be angry (i.e., throwing tantrums) when they were faced with unfair offers.

From this, the authors conclude that chimpanzees are not sensitive to the concept of fairness. In this ultimatum game, it seems that chimpanzees—not humans—are the ones who may behave “rationally” according to the economic theories of maximizing payoffs that we are currently studying.