Several bonobos in captivity were recently given a straightforward challenge: find a delicious treat hidden beneath one of three cups. Given their high intelligence, identifying the correct cup should have been easy for them.

However, there was a complication: the bonobos had to rely on a human to reveal the hidden snack, rather than a fellow bonobo. To make matters more challenging, the human occasionally did not see where the treat was placed. In such scenarios, the bonobos took the initiative to indicate the right cup to their human collaborator.

“The bonobos were aware when their partner lacked knowledge, and they proactively communicated to ensure the unaware partner still made the right choice,” explains Christopher Krupenye, an evolutionary cognitive scientist at Johns Hopkins University, and one of the experiment’s leaders.

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Krupenye, along with his graduate student Luke Townrow, detailed the behavior of the bonobos in a study published today in the journal Proceedings of the National Academy of Sciences USA. Their research provides strong evidence that bonobos can discern when someone is uninformed and take steps to resolve this uncertainty.

The concept of understanding the mental states of others is known as theory of mind. Humans use this ability to communicate effectively and coordinate actions. Being able to guess when someone is missing information allows us to decide when and how to convey what we know.

It has been suggested that our closest evolutionary relatives, including chimpanzees and bonobos, might also possess this cognitive skill. However, few studies have tested this theory in controlled settings, the researchers noted.

Krupenye and Townrow conducted their experiments with three male bonobos at the Ape Cognition and Conservation Initiative in Des Moines, Iowa. During each test, one bonobo would sit opposite Townrow as a treat, like a grape or peanut, was concealed under one of the cups on a table between them. If Townrow turned over the correct cup, the bonobo would get the treat.

In some instances, Townrow watched as the treat was placed under a cup. In other cases, his view was obstructed by a piece of cardboard. After hiding the treat, Townrow would wait 10 seconds before choosing a cup.

The bonobos seemed to understand whether Townrow had seen where the treat was placed. In situations where he had a clear view, the apes calmly waited for him to select the right cup. But if Townrow’s view was blocked, the bonobos would point to the correct cup to clue him in. “They grasped the task instantly and knew exactly where to point,” Townrow remarked.

Kanzi, the oldest of the bonobos and now 44 years old, was particularly expressive in his gestures to ensure Townrow made the right choice. Always eager for a snack, Kanzi frequently pointed and tapped to draw Townrow’s attention and secure his reward.

Michael Tomasello, a comparative psychologist at Duke University not involved in the study, noted that chimpanzees also show the ability to recognize ignorance and adjust their communication accordingly. A 2012 study found that wild chimpanzees made sounds to alert their peers to unseen dangers, like a nearby snake. Even human infants demonstrate similar capabilities. “They point to things that others are unfamiliar with while still very young,” Tomasello observes.

These findings suggest that the ability to perceive and respond to the unawareness of others could date back to the last common ancestor of humans and bonobos, which lived between eight and six million years ago. It also shows that such sophisticated understanding can occur without spoken language, according to Laura Lewis, a biological anthropologist at the University of California, Berkeley, not involved with the study. “This suggests that our great ape relatives can recognize both knowledge and ignorance in others and use this understanding to guide their communication, even without complex language,” Lewis states.

However, it’s still uncertain whether the bonobos are merely pointing to obtain a treat or if there’s a deeper intent behind their actions. “Do the bonobos realize that their communication changes someone’s mental state, or is that an insight that evolved later in humans?” Krupenye wonders.

The research team plans to explore this question further in future studies with bonobos. Unfortunately, these great apes, native to the forests of the Democratic Republic of Congo, are endangered due to habitat loss and poaching. Krupenye hopes his research will emphasize the similarities between these apes and humans, highlighting the importance of understanding our place in the natural world.