Ultimatum Game Shows Chimps Can Practice Fairness
January 15, 2013

Chimpanzees Show The Human Trait Of Fairness Through The Ultimatum Game

April Flowers for redOrbit.com - Your Universe Online

Chimpanzees possess a sense of fairness that scientists previously attributed as being solely human, a new study from the Yerkes National Primate Research Center at Emory University, and Georgia State University demonstrates. To determine how sensitive chimps are to the reward distribution between two individuals if both need to agree on the outcome, the researchers played the Ultimatum Game with them.

The findings of this study, published online in the Proceedings of the National Academy of Sciences, suggest a long evolutionary history of the human aversion to inequity as well as a shared preference for fair outcomes by the common ancestor of humans and apes.

Darby Proctor, PhD says, "We used the Ultimatum Game because it is the gold standard to determine the human sense of fairness. In the game, one individual needs to propose a reward division to another individual and then have that individual accept the proposition before both can obtain the rewards. Humans typically offer generous portions, such as 50 percent of the reward, to their partners, and that's exactly what we recorded in our study with chimpanzees."

Frans de Waal, PhD, adds, "Until our study, the behavioral economics community assumed the Ultimatum Game could not be played with animals or that animals would choose only the most selfish option while playing. We've concluded that chimpanzees not only get very close to the human sense of fairness, but the animals may actually have exactly the same preferences as our own species."

The study was also conducted separately with human children for purposes of direct comparison.

The scientists tested six adult Pan troglodyte chimpanzees and 20 human children ages 2-7 years on a modified Ultimatum Game, which is a game of cooperation. In this modified version, an individual chooses between two differently colored tokens that could be exchanged for rewards — small food rewards for the chimpanzees and stickers for the children — with his or her partner's cooperation. One color of token offered equal rewards for both participants, while the other color gave higher rewards to the individual choosing and lower rewards to the partner. The individual choosing between the tokens needed to hand the token to his or her partner, who then needed to exchange it with the experimenter for food. The two participants have to be in agreement to gain the rewards.

Both the human children and the chimpanzees responded as adult humans do, the study found. If the partner's cooperation was required, the individual choosing the token chose to split the reward evenly. If the partner was passive, however, and had no chance to reject the offer, both the chimpanzees and children chose the selfish option.

Chimpanzees are highly cooperative in the wild, making it likely that they need to be sensitive to reward distributions in order to reap the benefits of cooperation. This study makes further investigation into the mechanism of this human-like behavior possible.