While fairness has always been considered a uniquely human trait, scientists have now found that chimpanzees also possess an innate sense of fairplay.
Until now, it was assumed that animals would choose the most selfish option when presented with a reward.
Working with colleagues from Georgia State University, the researchers Emory University 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.
The findings published in the Proceedings of the National Academy of Sciences (PNAS), 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.
“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, researcher Darby Proctor said.
“Humans typically offer generous portions, such as 50 per cent of the reward, to their partners, and that’s exactly what we recorded in our study with chimpanzees,” Proctor said.
“Until our study, the behavioural 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,” said study co-author Frans de Waal in a statement.
For purposes of direct comparison, the study was also conducted separately with human children.
In the study, researchers tested six adult chimpanzees (Pan troglodytes) and 20 human children aged 2-7 years on a modified Ultimatum Game.
One individual chose between two differently coloured tokens that, with his or her partner’s cooperation, could be exchanged for rewards.
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.