A bonobo tea party: Study shows humans aren't the only species that can pretend

Can animals play pretend? It took a tea party with a bonobo to find out.

In a set of experiments, a team of researchers offered a bonobo named Kanzi invisible juice and grapes, presenting the tests as something of a game, akin to a child’s make-believe tea party.

The results, published in the journal Science on Thursday, show that Kanzi could play along. The researchers concluded that the primate could imagine and track invisible juice being poured between a pitcher and bottles.

“He’s able to follow along and track the location of a pretend object, but at the same time, he appreciates that it’s not actually there,” said Chris Krupenye, an author of the study and an assistant professor of psychological and brain sciences at Johns Hopkins University.

In the past, scientists had assumed that the ability to pretend and consider multiple realities was unique to humans. But then some other observations of primates behaving like they were pretending — young chimpanzees playing with a “log doll” or moving imaginary blocks — called that idea into question. The new study provides the first evidence of an animal pretending in a situation researchers could control.

“We think of our ability to imagine other worlds or other objects, or imagine futures, as one of these rich features of human mental life that are presumed to be unique to our species,” Krupenye said. But apes “might share some of the foundational cognitive machinery that will enable at least some degree of imagination.”

For the new study, researchers modeled the experiments loosely after common childhood development tests.

“Within the first years of life, you see kids engaging in pretend play,” Krupenye said — behaviors like having imaginary friends or tea parties with stuffed animals. “A lot of the studies in child psychology have focused on those kinds of scenarios.”

The researchers staged three experiments for Kanzi. First, they pulled out an empty, transparent pitcher and two empty, transparent bottles. A researcher would pour imaginary juice from the pitcher into both glasses, then pour one glass of pretend juice back into the pitcher. Then they’d ask Kanzi to indicate where the juice was located.

Kanzi pointed to the cup that would still have contained juice, if it were real, 34 times out of 50, or 68% of the time. That’s a common “success rate” in cognitive testing for apes, according to Krupenye.

In the second experiment, researchers presented Kanzi with a cup of actual juice alongside a cup of pretend juice and asked which he wanted. He pointed to the glass with juice 14 of 18 times, confirming Kanzi could distinguish real juice from fake.

Finally, the researchers did another version of the original test but used imaginary grapes instead of juice, with similar results.

The experiments together suggest that Kanzi was able to distinguish an imagined scenario from the present reality and keep both in mind.

“​​That is really a very big step in our understanding of how nonhuman primates think,” said Jan Engelmann, an associate professor of psychology at the University of California, Berkeley, who was not involved in the study.

Engelmann said the experiments bolster evidence that apes can engage in “secondary representations” — cognitive processes in which the mind models multiple scenarios, including hypothetical ones — and carry out complex thought processes such as planning, reasoning, and inferring cause and effect. Such behaviors bring an evolutionary advantage.

“You can then test things out in imagination before doing it in real life,” said Kristin Andrews, a professor of philosophy at the CUNY Graduate Center, who studies animals’ minds. “You can figure out whether you should do it or not.”

Andrews, who was not involved in the Kanzi study, said the results were convincing.

“If we ran a study like this on human children, we’d be drawing the same sorts of conclusions,” she said. “It just brings to mind classic studies with human children where they use a banana as a telephone.”

Kanzi, who died last year at 44, was a unique bonobo. Born in captivity, he was the first bonobo to understand some elements of spoken English. He learned the language by picking up on symbols representing words, called lexigrams, which he used to communicate with his caretakers.

Kanzi learned elements of language at a very young age.

“Kanzi, as an infant, was just on his mom, clinging to his mom’s body as she was being trained on these lexigrams, and she wasn’t doing terribly well,” Krupenye said. “He’d been soaking up all of this knowledge all along, and so they shifted the focus of the research program to Kanzi and to another bonobo, Panbanisha.”

Later in life, Kanzi could identify several hundred lexigram symbols, for objects like “egg” and activities like “chase.” He could respond to some English prompts by pointing to lexigrams.

Bonobos are humanity’s closest living genetic relative, so Krupenye and his study co-authors suggest that the ability to pretend and imagine was likely present 6 million to 9 million years ago, when the two species diverged in evolutionary history.

However, it’s not yet clear if other species of nonhuman primates, or even other bonobos, would perform as well on the tests as Kanzi. The new study notes that Kanzi’s lexigram training could have primed him to better recognize symbols and that his language training might have changed his brain.

It’s possible that “we can only tap into this ability because Kanzi has language, but all apes have this ability” to pretend, Engelmann said. “Another option is that language gives Kanzi a new ability.”

Overall, the more scientists study animals, the more they learn that many things once thought to make humans exceptional are more broadly shared, Andrews said.

Some scientists are even pursuing a new hypothesis: That individual human cognition might not be substantially more powerful than that of chimpanzees, from an individual perspective. Instead, what might make humans special is their exceptional social skills and ability to collaborate.

“What humans are really good at is social rationality, social cognition and thinking together with others,” Engelmann said. “Language is one adaptation that allows us to do this.”

This article was originally published on NBCNews.com