Scientists have experimentally shown for the first time that bonobos (Pan paniscus), our closest living relatives along with chimpanzees (Pan troglodytes), are capable of pretend play previously thought to be unique to humans.
Kanji, a unique bonobo that can understand English, was able to track imaginary juices and grapes during pretend tea parties, much like a 2-year-old, according to a study published in the journal Science on Thursday, February 5th.
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“We were absolutely awed by this finding,” study co-author Christopher Krupenier, assistant professor of psychology and brain sciences at Johns Hopkins University, told Live Science. “What we’re seeing in this case is that something that seems fundamentally human and that is emerging early in human development is also shared by our closest relatives,” he said.
This suggests that humans’ ability to imagine objects that aren’t actually there may have evolved before humans and bonobos diverged from their last common ancestor more than 6 million years ago, Krupenier said.
imaginary reality
Anecdotal evidence so far suggests that great apes in captivity and wild great apes engage in pretend play. For example, a 3-year-old chimpanzee in the wild in Guinea was observed playing with a discarded artificial leaf cushion on its head. Captive bonobos also “picked” and “ate” blueberries from pictures of real blueberries.
But this anecdotal example could be explained by other explanations, such as the ape believing that the pretended object was actually real, so Krupenier and his colleague Amalia Bastos, a comparative psychologist at the University of St. Andrews in the UK, wanted to pose the question: “Can animals really pretend?” to a controlled experimental environment.
Kanzi was an obvious first animal to study because it could understand and respond to English, Krupenier said.
First, Kanzi was trained to point to a container of juice. He was shown two clear bottles, one containing juice and one empty, and asked to point out where the juice was. If you answered correctly, you received juice as a reward. Kanzi achieved a perfect score on 18 repetitions of this training phase.
In the test, the experimenter placed two clear empty cups side by side on the table in front of Kanzi. They then pretended to pour juice from an empty jug into each cup, then poured the pretended juice from one of the cups back into the jug. Kanji was then asked to point to the cup of juice, but was not told whether it was correct or not, and was not rewarded.
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Kanzi correctly located the fake juice 68% of the time. This suggests that he can track imaginary liquids.
However, it remained possible that he simply thought the empty cup actually contained real juice. To see if this was the case, the researchers ran a second experiment in which they placed a cup of juice and an empty cup on a table. They pretended to pour juice into an empty cup and held the empty jug over the full cup without making any pouring motions.
Krupenier said that if Kandi really thought both cups contained juice, he would have chosen them equally often. However, when asked which cup he would like, Kanzi chose the cup containing real juice 77.8% of the time, suggesting that he could clearly distinguish between real and imaginary juice.
“That gave us confidence that we were really investigating some ability to track imaginary or pretend objects,” Krupenier said.
Bastos said he was still a little skeptical at this point. It is possible that it was a fluke that Kanji was able to point out the location of the fake juice. So the team repeated the same steps, but pretended to be grapes. Kanzi correctly located the fictitious grapes in 68.9% of the trials.
“By the end of Experiment 3, I was confident that what I saw was exactly what I saw,” Bastos said.
Although the study is limited because only one bonobo was tested, it is still the first clear evidence that great apes can pretend, Laura Simone Lewis, an evolutionary anthropologist and psychologist at the University of California, Santa Barbara, who was not involved in the study, told Live Science in an email.
“This is a major advance for our field because it provides direct evidence that supports anecdotal reports from the wild that our great ape cousins are able to use their imaginations in all kinds of activities, including pretend play,” she said.
This study shows that Kanzi was able to understand shared pretense created by humans, but was unable to create pretense scenarios on its own.
“So I think it’s a big leap forward to say that in some ways we’re seeing something similar to what we see in 2-year-olds, where pretend behaviors like drinking from an empty glass are routinely seen,” Paul Harris, a Harvard psychologist who was not involved in the study, told Live Science.
Krupenier and Bastos hope that pretend play can be studied in other great apes as well. “If the anecdote is correct, other great apes should also share this ability,” Krupenier said.
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