Great Apes show pretend play abilities: New study challenges human uniqueness

A new study published in the journal Science suggests that great apes possess the capacity for pretend play, a skill previously thought to be uniquely human. Researchers at Johns Hopkins University conducted experiments with a bonobo named Kanzi, using juice and grapes to test his ability to distinguish between real and imaginary objects. The findings provide experimental support for anecdotal observations of simulated play in apes.

Previous observations had raised the possibility of simulated play in animals. A young, captive chimpanzee was seen dragging what appeared to be imaginary blocks. Female chimpanzees in the wild were observed carrying and playing with sticks as if they were dolls. However, the anecdotal nature of this evidence left room for doubt, as animals might have been imitating human behavior or mistaking representations for reality.

To address these concerns, researchers conducted controlled tests with Kanzi in 2024. In one experiment, Kanzi was presented with two squirt bottles, one empty and one containing juice. He correctly identified the bottle with juice in 18 trials.

In a subsequent task, Kanzi was given two empty, transparent cups. An experimenter pretended to pour juice from an empty pitcher into each cup, then poured the imaginary juice out of one cup. When asked, "Where's the juice?" Kanzi correctly chose the cup with the imaginary juice 68% of the time. This result was higher than random chance.

To ensure Kanzi could differentiate between real and imaginary juice, a second task was performed. Kanzi was presented with one cup containing real juice and another empty cup filled with imaginary juice. When asked, "Which one do you want?" Kanzi chose the cup with real juice 14 out of 18 times. This demonstrated his ability to distinguish between real and pretend.

A final experiment used a grape instead of juice. Kanzi successfully identified which jar contained the fictitious grape 68.9% of the time. He even completed this task faster than the juice experiment.

The researchers concluded that their "findings suggest that the capacity for representing pretend objects is not uniquely human."

Primate behavioural ecologist Nicholas E. Newton-Fisher commented on Kanzi's contributions.

"Throughout his life, Kanzi repeatedly demonstrated skills that required us to reevaluate our understanding of ape cognition."

"It seems suitable, therefore, that he has also provided experimental evidence of imagination. This is an exciting finding that lends experimental support to anecdotal reports from both captive and wild-living individuals," added Newton-Fisher, who was not involved in the study.

Kanzi, who died in March, was considered a particularly good subject due to his language training. He understood verbal prompts and responded using a lexigram of over 300 symbols. Kanzi participated in various cognitive research projects, including a study showing bonobos can point out a hidden object if their human partner does not know its location.

Due to Kanzi being the only bonobo tested, it is unclear if the results apply to other apes.

"But, because there’s lots of these anecdotes out there, I wouldn’t be surprised to see that this extends beyond Kanzi," stated Bastos.

Newton-Fisher acknowledged the need for further investigation.

"As the authors of this research note, generalising from Kanzi to other bonobos, and to other ape species, will require further investigation."

He also expressed a broader perspective on ape cognition.

"However, while it is appropriate that we proceed with a degree of scepticism," he added, "I suspect that we systematically under-appreciate the cognitive abilities of these species."

Newton-Fisher cautioned against direct comparisons between ape and human cognitive abilities.

"the apes have their own ape minds and brains. So, how — imagination, for instance — manifests in an ape may not be a ‘cut-down’ version of the equivalent ability in humans."