Study Explores Fairness in Chimps
Think the common chimpanzee, or Pan troglodytes, doesn’t know how to play fair? Think again.
At Emory’s Yerkes National Primate Center, post-doctoral researcher Darby Proctor and Emory professor and primatologist Frans de Waal recently discovered a preference for fairness in chimpanzees once believed to be a solely human characteristic.
Proctor, a Fellowships in Research and Science Teaching (FIRST) fellow and the study’s author, tested 20 human children between the ages of two and seven along with six adult chimpanzees by engaging both species in the Ultimatum Game, a game which the behavioral economics community once believed animals were incapable of playing.
In the game, researchers pair two individuals of the same species and named one a “chooser” and the other an either passive or cooperative partner.
The chooser is given the choice between two tokens that can be exchanged for prizes — the children received stickers, while the chimpanzees received small foods.
The chooser can pick either one token or the other: one would give him or her the entire reward, while the other would split the reward evenly between the two partners.
When paired with cooperative partners, who were required to deliver the token of choice to those doling out rewards, both human and chimpanzee choosers select the token giving each partner 50 percent of the prize.
Choosers of both species paired with passive partners, who were not required to transfer the token, preferred the selfish option.
One experiment, Emory assistant Biology professor Todd Schlenke said, placed two chimpanzees in adjacent cages.
When one was given peanuts, the primate appeared relatively satisfied.
When the other was given a banana, the commonly preferred treat, the first furiously discarded the peanuts, revealing an innate sense of jealousy.
“These findings have a major impact for economics and human evolution studies,” de Waal, who has worked at Yerkes for more than 20 years, said. “Anthropologists play the Ultimatum Game all over the world.”
“Over the last century, scientists have repeatedly found behaviors in chimpanzees that were thought to be uniquely human,” Proctor said. “I think my work continues this path by showing one more way that chimpanzees and humans share many similarities.”
Proctor said she hopes the study’s results will encourage more people to engage in conservation activities for chimpanzees and other endangered species.
Common chimpanzees are now extinct in four African countries — including Gambia, Benin, Burkina Faso and Togo — due to excessive deforestation and commercial hunting, the World Wildlife Fund (WWF) warns.
However, these not-so-distant relatives — they share 98 percent of our DNA, according to the WWF — continue to reveal their “human” tendencies.
“A bunch of stuff has come out of Dr. Frans de Waal’s lab that explains social behaviors, humanizing chimpanzees, our closest relatives,” Schlenke said. “These behaviors didn’t originate in us.”
Proctor said believes her and de Waal’s findings revolutionize explorations in the idea of fairness for non-human animals.
“We think a sense of fairness is likely tied to the evolution of cooperation,” she said. “When individuals cooperate, there must be some mechanism in place for them to recognize unfair partners.”
As for future research, Proctor said, “We may see something like a sense of fairness in other cooperative species.”
— Contact Lydia O’Neal at