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AnimalsScience

Apes Have A Sense Of 'Fairness' That Is Very Similar To Humans, Research Finds

Chimpanzees apparently possess a sense of what is ‘fair’ that is extremely similar to that of humans, new research has found. Not that it is very surprising, given how extremely similar humans and other ape species are. Previously though, the ‘expert’ consensus had been that ‘fairness’ was a uniquely human trait, though like most assumed ‘human-only’ traits ‘fairness’ has now been found to be present in species other than humans.

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It would very much surprise me if most of the traits assumed to be innately human and separate from other animals was the result of anything other than the cultures of modern humans.

In the new research, the scientists “played the Ultimatum Game with the chimpanzees to determine how sensitive the animals are to the reward distribution between two individuals if both need to agree on the outcome.”


This research establishes that the common ancestor of humans and chimpanzees very likely possessed this trait also. This means that likely all human ancestors back that far did also, in contrast to the stereotypical presentation of pre-modern humans as being dumb, selfish, brutes. In reality, humans as far back as at least one million years ago had brains as large as those of modern humans, and were quite a bit more strongly and athletically built than modern humans. It’s very likely that on an individual/non-cultural level they were as smart or smarter than modern humans.

As the first author 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.”

Co-author 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.”

In order to provide a direct comparison, the researchers also conducted the study separately with human children.

“In the study, researchers tested six adult chimpanzees (Pan troglodytes) and 20 human children (ages 2 — 7 years) on a modified Ultimatum Game. One individual chose between two differently colored tokens that, with his or her partner’s cooperation, could be exchanged for rewards (small food rewards for chimpanzees and stickers for children). One token offered equal rewards to both players, whereas the other token favored the individual making the choice at the expense of his or her partner. The chooser then needed to hand the token to the partner, who needed to exchange it with the experimenter for food. This way, both individuals needed to be in agreement.”

“Both the chimpanzees and the children responded like adult humans typically do. If the partner’s cooperation was required, the chimpanzees and children split the rewards equally. However, with a passive partner, who had no chance to reject the offer, chimpanzees and children chose the selfish option.”

“Chimpanzees, who are highly cooperative in the wild, likely need to be sensitive to reward distributions in order to reap the benefits of cooperation. Thus, this study opens the door for further explorations into the mechanisms behind this human-like behavior.”

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There are many species and populations of chimpanzees that are currently listed as endangered, as many primates are. The threats facing these animals: deforestation, hunting, environmental pollution, introduced diseases, etc, are likely to continue and to accelerate in the future, likely leading to high levels of extinction.

The new findings, are now available in the early online edition of the Proceedings of the National Academy of Sciences (PNAS).

Source: Emory University

Image Credits: Mark Bodemer; Chimpanzee via Wikimedia Commons




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