Bonobo Can Play Pretend Games, Like a Young Child

Scientists have done an experiment that shows a bonobo can play pretend. Pretend play means treating an object that is not there as if it is real. For a long time, people thought only humans could do this. The scientists studied a famous bonobo named Kanzi.

Before this study, there were only informal stories about apes pretending. For example, a wild chimpanzee played with a leaf as if it were a hat. Another bonobo pretended to "pick" and "eat" blueberries from a picture. But these stories could be explained in other ways. Maybe the apes thought the pretend objects were real.

The researchers wanted a clear answer. They designed a careful experiment to test if an animal could truly pretend. They chose Kanzi because he can understand spoken English and can answer questions. This made him a perfect first subject.

First, Kanzi was trained to find a real liquid. He was shown two clear bottles. One bottle had juice, and one was empty. He was asked to point to the juice. When he got it right, he got a small reward of real juice. Kanzi did this task perfectly over many training sessions.

In the main test, the scientists put two empty, clear cups on a table. They pretended to pour juice from an empty jug into each cup. Next, they pretended to pour the imaginary juice from one cup back into the jug. Finally, they asked Kanzi to point to which cup still had the "juice." In this test, Kanzi was never told if he was correct, and he got no reward.

Kanzi pointed to the correct cup 68% of the time. This result strongly suggested he could follow the invisible liquid in his mind.

An important question remained. Did Kanzi truly understand the juice was imaginary? Or did he think the empty cup actually had real juice? To check this, the team ran a second, clever experiment.

They placed one cup filled with real juice and one empty cup on the table. They pretended to pour juice into the empty cup. Then, they held the empty jug over the full cup but did not pretend to pour. This created a special situation. If Kanzi believed in the pretend action, then both cups should have held juice in his mind.

When asked which cup he wanted, Kanzi chose the cup with the real juice 77.8% of the time. The lead scientist, Christopher Krupenye, explained that if Kanzi thought both cups had juice, he would have chosen them equally often. His clear choice for the real juice showed he could tell the difference between a pretend substance and a real one.

The other lead scientist, Amalia Bastos, said she was still a bit skeptical after the juice experiments. Kanzi's success could have been a statistical accident or just luck. To confirm the finding, the team repeated the procedure using a pretend grape instead of juice. Kanzi correctly found the location of the imaginary grape in 68.9% of the trials.

"By the time we finished experiment three, I was very confident that what we saw was what we saw," Bastos stated.

An expert who was not part of the study, Laura Simone Lewis, called the research a "huge development." She noted that the study is limited because it tested only one bonobo. However, it gives the first clear experimental proof that supports old stories of pretend play in great apes.

Experts warn that this study shows Kanzi can understand and join a pretend scenario made by humans. It does not prove that he, or other apes, make up their own pretend games. Young children do this on their own.

Another expert, psychologist Paul Harris, made this point clear. "I think it would be a big leap to say that, because of this, in some sense we're seeing something comparable to what we see in 2-year-old children," he told Live Science.

The researchers hope their work will lead to more study of pretend play in other great apes. "If the anecdotes are right, it should be the case that other apes also share this capacity," Krupenye said.

This discovery suggests that the human ability for imagination and pretending has very deep roots. It might have evolved before humans and bonobos split from their last common ancestor. That split took place more than six million years ago. Understanding the origins of imagination helps scientists map the evolution of complex human thinking. This research on Kanzi opens a new window into the minds of our closest living relatives.