Can animals engage in pretend play? A fascinating tea party experiment with bonobos provides new insights.

In this series of innovative experiments, researchers presented a bonobo named Kanzi with imaginary juice and grapes, framing the test as a playful child’s game.

The findings, published in Thursday’s Science Magazine, reveal that Kanzi is capable of participating in imaginative scenarios. The researchers concluded that primates can visualize and track invisible juice being poured between a pitcher and a bottle.

“He can follow a pretend object and track its location, while simultaneously grasping that it’s not physically present,” stated Chris Krupenier, assistant professor of psychological and brain sciences at Johns Hopkins University.

Previously, scientists believed the ability to conceptualize multiple realities was exclusive to humans. However, evidence such as a young chimpanzee engaging with a “log doll” moving imaginary blocks challenges this notion. Recent studies provide compelling evidence that animals can engage in pretend play under controlled conditions.

“We believe that imagining other worlds and future scenarios is a unique aspect of human cognition,” Krupenier explained. However, great apes “may share some foundational cognitive processes that enable a certain level of imagination.”

In their research, the scientists loosely based their experiments on common childhood developmental tests.

Krupenier elaborated, “In early childhood, we often see kids engage in pretend play, making imaginary friends or hosting tea parties with stuffed toys. Much of child psychology research has focused on these playful scenarios.”

The researchers conducted three main experiments with Kanzi. In the first, they used an empty clear pitcher and two clear bottles. The researcher pretended to pour fictional juice from the pitcher into both glasses, then asked Kanzi to indicate where he believed the juice was located.

Kanzi correctly indicated the cup containing imaginary juice 34 out of 50 times, resulting in a 68% success rate—consistent with typical results in great ape cognitive tests.

In the second experiment, Kanzi was given one cup of real juice and one cup of pretend juice and asked which one he preferred. He selected the real juice 14 out of 18 times, demonstrating his ability to differentiate between reality and pretense.

The final experiment mirrored the original test but used grapes instead of juice, yielding similar results.

These findings collectively suggest that Kanzi could distinguish between imagined scenarios and actual experiences while maintaining both in his cognitive process.

“This represents a significant advance in understanding non-human primate cognition,” remarked Jan Engelmann, associate professor of psychology at UC Berkeley, who was not involved in the study.

Engelmann noted that the experiment supports evidence indicating that great apes demonstrate “second-order representation”—the cognitive ability to model multiple scenarios, encompassing reasoning, planning, and cause-and-effect relationships, which offer evolutionary advantages.

“This ability lets one test scenarios mentally before attempting them in reality,” said Kristin Andrews, a philosophy professor at the State University of New York Graduate Center who studies animal cognition. “It allows individuals to decide whether to act on those tests.”

Andrews, who did not participate in Kanzi’s research, found the results compelling.

“A similar study with human children would lead to analogous conclusions,” she said, referencing classic studies of children using bananas as makeshift phones.

Kanzi, who passed away last year at 44, was a profound bonobo. He was the first bonobo born in captivity to grasp elements of spoken English, learning language by understanding symbolic meanings represented by lexigrams used to communicate with caregivers.

Kanzi began his language training at an early age.

“As a toddler, Kanzi clung to his mother while she received dictionary training, absorbing knowledge all along,” Krupenier recounted. “Eventually, the focus of research shifted to Kanzi and another bonobo, Panbanisha.”

Over the years, Kanzi identified hundreds of symbols representing objects and activities, responding to English prompts by pointing to the appropriate symbols.

Because bonobos are humans’ closest living genetic relatives, Krupenier and the study’s authors propose that the capacity for imagination and pretense likely originated 6 to 9 million years ago, coinciding with the divergence of the two species.

However, it’s unclear if other non-human primates, or even different bonobos, possess the same cognitive abilities as Kanzi. New research suggests that Kanzi’s vocabulary development might have enhanced his symbol recognition, potentially altering his brain functions.

Engelmann posits that “all apes may possess this ability, though humans might only fully access it due to language.” Alternatively, language could provide Kanzi with unique skills.

Overall, the continuous study of animal cognition reveals that many traits once thought to be exclusive to humans are increasingly recognized in other species.

Some scientists are exploring a new hypothesis suggesting that, from an individual perspective, humans might have cognitive abilities that are less powerful than those of chimpanzees. Rather, it may be our exceptional social skills and collaborative abilities that make us unique.

“Humans excel in social rationality, social cognition, and collaborative thought,” Engelmann concluded. “Language is one of the key adaptations enabling this capability.”