Researchers from the Yerkes National Primate Research Center at Emory University have successfully demonstrated that chimpanzees have a sense of fair play. Prior to this study, researchers believed that this was a uniquely human trait. Researchers from Emory University and their colleagues from Georgia State University played the Ultimatum Game with the chimpanzees to see how cognizant the animals are to the reward distribution between two individuals if both chimpanzees have to come to terms with the outcome.
“We used the Ultimatum Game because it is the gold standard to determine the human sense of fairness,” says first author Darby Proctor. “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.”
“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,” says co-author Frans de Waal. “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.” For purposes of direct comparison, the study was also conducted separately with human children.”
Researchers tested six adult chimpanzees and 20 human children on the Ultimatum Game. One individual picked between two differently colored tokens that, with his or her partner’s cooperation, could be exchanged for rewards, such as food for the chimpanzees or stickers for the children. Picking one token resulted in equal rewards to both players, whereas picking the other token resulted in an unequal reward. The decider then had to give the token to the partner, who had to exchange it with the researcher for food or stickers. This way, both individuals were in agreement with the outcome.
According to the researchers, both the chimpanzees and the children acted like adult humans usually do. If the partner’s cooperation was required, the chimpanzees and the children split the rewards equally. However, with a passive partner, chimpanzees and children picked the selfish option.
Researchers think that chimpanzees need to be sensitive to reward distributions in order to receive the benefits of cooperation in the wild. Researchers hope to conduct additional studies on what was previously thought to be a uniquely human trait.
“Both apes and children responded like humans typically do. If their partner’s cooperation was required, they split the rewards equally. However, with passive partners—a situation akin to the so-called dictator game—they preferred the selfish option. Thus, humans and chimpanzees show similar preferences regarding reward division, suggesting a long evolutionary history to the human sense of fairness,” write the authors in their study’s abstract.
For approximately 80 years, the Yerkes National Primate Research Center at Emory University has worked hard to advance scientific understanding and to better the health and well-being of humans and nonhuman primates. The center’s research programs are looking for ways to advance knowledge about the evolutionary links between biology and behavior.
The study’s findings were recently published in the journal Proceedings of the National Academy of Sciences. The findings suggest a long evolutionary history of the human opposition to inequity as well as a shared preference for fair outcomes by the common ancestor of humans and apes.