Scientists attribute humankind’s success as a species to its ability to cooperate with each other on large scales. Because the evolutionary mechanisms responsible for these patterns of cooperation are still unclear, researchers have taken to studying similar cognitive processes in apes, the closest living relatives to humans.

A joint collaboration between the University of Michigan’s Department of Psychology and Harvard’s Center for Brain Science found chimpanzees, dubbed ‘humans’ last common ancestor,’ were faster in making cooperative decisions than selfish ones. These results were published in Psychological Science. The findings challenge the idea that prosocial biases are unique to humans and call for scientists to think of new ways to approach the differences between humans and other animals.  

The researchers involved in the project were Alexandra Rosati, a U-M assistant professor of psychology and anthropology; Joshua Buckholtz, a Harvard assistant professor of psychology; and Lauren DiNicola, a Harvard doctoral student studying cognition, brain and behavior.

All three researchers are interested in understanding human cognition. Rosati aims to increase the understanding of how the human mind evolved, and frequently studies other primates to map how human abilities/traits emerged over time. Buckholtz’s work explores self-control and how it’s related to brain function and cognition, and DiNicola is interested in human social processes.

Buckholtz said Rosati was able to combine all of their career focuses in the planning and execution of this project.

“This collaboration is really a testament to Dr. Rosati’s vision,” Buckholtz wrote in an email to The Daily. “She is interested in mapping human cognitive capacities related to cooperation to those in apes as a way of understanding how we evolved this unique ability to get along with each other. Because many models of cooperation emphasize the role of self-control, she approached me about ‘back-translating’ human self-control paradigms into experimental tasks that could be used in apes.”

In order to better understand human cooperation, Rosati and her team assessed 40 wild-born, semi-free-ranging chimpanzees on six tasks for this specific study. The tests measured cooperativeness among the chimpanzees and recorded their decision-making time. 

“The challenge for us is we were trying to look at what are the common cognitive skills that chimps are using in these kinds of cooperative contexts. And it’s not actually possible to do psychology experiments with these wild chimps,” she said. “But to do real experiments the way psychologists do, you need to have close up interactions.”

To gather data for their research, Rosati’s team worked with chimpanzees from Tchimpounga Chimpanzee Sanctuary in the Republic of Congo where the chimpanzees were familiar with humans but spent most of their day ranging freely in tropical rainforests.

“What we tried to do was study chimps that are living in as close to the wild as possible, but where it’s still ethical for us to do, kind of psychology games with them. That’s why we do this work in African ape sanctuaries. They’re animals that have been confiscated from the bushmeat and pet trade, so they’re familiar with people and they actually voluntarily come into buildings at night to sleep. So in those same buildings, we’ll play little psychology games the way somebody who studies adults might do.”

Experiments have shown that humans, when faced with the decision between acting cooperatively or selfishly, will instinctively choose to cooperate. Only if given enough time to think will they potentially respond in a more selfish manner. After analyzing the data she and her team collected, Rosati said she was surprised to find chimpanzees have a fast prosocial bias similar to the one humans have.

“I’d say we were surprised. Chimps, even if they’re cooperative, are not as cooperative as humans. So you wouldn’t predict that they would necessarily have this bias to cooperate — maybe they’re more strategic about it.”

DiNicola said these findings may help refine the kinds of theories scientists need to propose to better understand the distinction between human cooperation and that of other animals.

“Our findings … call into question hypotheses that prosocial biases may be unique to (or can even help explain) abundantly cooperative behavior in humans,” she wrote in an email to The Daily. “These results are vital to our understanding of, and to constraining hypotheses surrounding, how humans became a highly cooperative species.”

Buckholtz also agrees these findings may lead to new ways of thinking about human cooperation.  

“Many people assume that people are inherently selfish and have to actively, effortfully override these selfish impulses to cooperate with other people. This work supports a new idea: that cooperating is a kind of behavioral default, arising from an intrinsic value that we place on prosocial behavior,” Buckholtz wrote. “The current work suggests that our own capacities evolved, in part, from a behavioral bias towards prosocial behavior that is evident in our closest living relatives – chimpanzees.”

In addition to new ways of thinking about human cognition, Rosati thinks this research also sheds light on the complexity of other animals’ minds.

“A lot of work in comparative cognition increasingly shows that other animals have minds and they use these minds to do really complicated things that we might have never thought,” she said. “Even though they don’t have language and they don’t have human-like culture and they are quite different from us in these other ways, they have really sophisticated minds that are operating out there in the world.”

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