In a series of tea party-like experiments, researchers demonstrated for the first time that apes can use their imagination and play pretend, an ability thought to be uniquely human.

Consistently and robustly across three experiments, one bonobo engaged with cups of imaginary juice and bowls of pretend grapes, challenging long-held assumptions about the abilities of animals.

“It really is game-changing that their mental lives go beyond the here and now.”

The findings suggest that the capacity to understand pretend objects is within the cognitive potential of, at least, an enculturated ape, and likely dates back 6 to 9 million years, to our common evolutionary ancestors.

“It really is game-changing that their mental lives go beyond the here and now,” says co-author Christopher Krupenye, a Johns Hopkins University assistant professor in the psychological and brain sciences department who studies how animals think.

“Imagination has long been seen as a critical element of what it is to be human, but the idea that it may not be exclusive to our species is really transformative.

“Jane Goodall discovered that chimps make tools, and that led to a change in the definition of what it means to be human. And this, too, really invites us to reconsider what makes us special and what mental life is out there among other creatures.”

The findings are published today in Science.

By age 2, human children can engage in pretend scenarios, like tea parties. Even at 15-months-old, infants show measures of surprise when they see a person “drinking” from a cup after pretending to empty it.

There had been no controlled studies of pretense in nonhuman animals, despite several anecdotal reports of animals seemingly engaging in pretending behavior from both the wild and captivity.

For example, in the wild, young female chimpanzees have been observed carrying and playing with sticks, holding them like mothers would hold their infants. And a chimpanzee in captivity seemed to drag imaginary blocks along the floor after playing with real wooden blocks.

Krupenye and coauthor Amalia Bastos, a former Johns Hopkins postdoctoral fellow who is now a lecturer at Scotland’s University of St. Andrews, wondered if they could test this capacity to pretend in a controlled environment.

They created experiments very similar to a child’s tea party to test Kanzi, a 43-year-old bonobo living at Ape Initiative, who had been anecdotally reported to engage in pretense and could respond to verbal prompts by pointing.

In each test, an experimenter and Kanzi faced one another, tea party-style, across a table set with either empty pitchers and cups or bowls and jars.

In the first task there were two transparent cups on the table, both empty, alongside an empty transparent pitcher. The experimenter tipped the pitcher to “pour” a little pretend juice into each cup, then pretended to dump the juice out of one cup, shaking it a bit to really get it out. They then asked Kanzi, “Where’s the juice?”

Kanzi pointed to the correct cup that still contained pretend juice most of the time, even when the experimenter changed the location of the cup filled with pretend juice.

In case Kanzi thought there was real juice in the cup, even if he couldn’t see it, the team ran a second experiment. This time there was a cup of real juice alongside the cup of pretend juice. When Kanzi was asked what he wanted, he pointed toward the real juice almost every time.

A third experiment repeated the same concept, except with grapes. An experimenter pretended to sample a grape from an empty container, then placed it inside one of the two jars. They pretended to empty one of the containers and asked Kanzi, “Where’s the grape?” Kanzi again indicated the location of the pretend object.

Kanzi was never perfect, but he was consistently correct.

“It’s extremely striking and very exciting that the data seem to suggest that apes, in their minds, can conceive of things that are not there,” Bastos says.

“Kanzi is able to generate an idea of this pretend object and at the same time know it’s not real.”

The findings inspire continued study, especially trying to test whether other apes and other animals can engage in pretend play or track pretend objects. The team also hopes to explore other facets of imagination in apes, perhaps their ability to think about the future or to think about what’s going on in the minds of others.

“Imagination is one of those things that in humans gives us a rich mental life. And if some roots of imagination are shared with apes, that should make people question their assumption that other animals are just living robotic lifestyles constrained to the present,” Krupenye says.

“We should be compelled by these findings to care for these creatures with rich and beautiful minds and ensure they continue to exist.”

Support for the work came from the Johns Hopkins Provost’s Postdoctoral Fellowship Program, Templeton World Charity Foundation, CIFAR Azrieli Global Scholars, and an Early Career Collaboration Enhancement Award from the Diverse Intelligences Summer Institute.

Source: Johns Hopkins University

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A series of hide-and-seek experiments with a bonobo named Kanzi shows for the first time that apes can mentally keep track of multiple familiar humans at once, even when they are out of sight.

Kanzi could also recognize caregivers from their voices alone, an ability never before tested on bonobos.

The work, led by Johns Hopkins University’s Social and Cognitive Origins Group, answers key questions about how animals manage to keep track of their groupmates and uncovers yet another aspect of human social cognition shared with our closest relatives.

“People think social intelligence is a thing that makes humans unique—that because we have to manage so many different relationships, we might have a range of cognitive tools for doing so that will only be found in an ultra-social species like humans,” says senior author Chris Krupenye, a Johns Hopkins assistant professor who studies how animals think.

“But most of us who study apes have a strong intuition that because the social world is so important for them too, they must, like humans, be keeping track of these critical social partners. They must share with us at least the foundations of our rich social intelligence.”

The findings appear in Proceedings of the Royal Society B.

Humans intuitively track the whereabouts of others, mentally. If you’re at home and your partner leaves the room, they don’t leave your mind—you mentally maintain information about their whereabouts, as well as the locations of your other friends and family in the world, near and far.

Bonobos and chimpanzees in the wild often live in dense forests where their groupmates regularly go out of view, so they too would benefit from the ability to keep mental tabs on groupmates they cannot see.

Research has shown that bonobos and chimpanzees recognize the faces and vocalizations of familiar groupmates, even after years apart. Chimpanzees have recognized familiar humans, even when they had masks on. While field studies have hinted that apes might be able to mentally track groupmates, this is the first study to test in a controlled environment whether any animal can track multiple individuals at once.

During experiments, as Kanzi watched, two caregivers that he knew well would hide behind different barriers, in an array of three, that blocked them from his view. An experimenter would hold up a photo of one caregiver and ask Kanzi to point to where that person was. The test was repeated and switched up many times.

“Kanzi very quickly understood the task and performed well,” says lead author Luz Carvajal, a PhD student in Krupenye’s lab who studies apes’ knowledge of their social relationships, adding that the team also wanted to see if Kanzi could identify the caregivers not just by photos of their faces, but by the sound of their voices.

For this further test, the caregivers again hid behind barriers, but this time Kanzi was not able to see which barrier they hid behind. Once they were hidden, however, they each called out to Kanzi, saying “Hi Kanzi,” so that he could hear who was behind each barrier. The experimenter would then show Kanzi a photo of one of the caregivers and ask Kanzi to point to where they were.

“Here he also performed above chance and especially well with one of his two caregivers,” Carvajal says. “He does have the capacity to use voice as a marker for identity. This face matches this voice.”

While Kanzi did make mistakes across trials, the results demonstrate a fundamental capacity to mentally track, and keep straight, the locations of multiple familiar people at once.

“Across these studies the results suggest that Kanzi has a memory of these individuals that brings together their vocal and visual of identities—who they are and what they sound like, and where they are in space,” Krupenye says.

“If he hears them he might imagine what they look like. If he sees them he might bring to mind an idea of what they sound like. We think this is one integrated memory. He’s using the same photo prompt to refer to an individual whether he can see them or not.”

Next the team hopes to test the boundaries of how many individuals can apes mentally track at once and how long those memories last, to better understand what is happening in the minds of apes during these separations.

“These animals are rich and complex,” Krupenye says. “Even if we just want to understand ourselves better there’s an urgency to this work and to saving this endangered species.”

Support for the work came from the Templeton World Charity Foundation and the CIFAR Azrieli Global Scholars Program.

Source: Johns Hopkins University

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