Apes can tell when humans don’t know something
02-04-2025

Apes can tell when humans don’t know something

For a long time, researchers believed that only humans could recognize when someone else lacked information. This ability, known as “theory of mind,” allows people to communicate, teach, and cooperate in complex ways. Many thought that animals, including apes, did not share this skill.

However, new research from Johns Hopkins University challenges that idea. The experts found that apes actively pointed out hidden treats to humans who did not know where they were.

This seemingly simple action suggests that apes understand when others lack information and take steps to help them.

The findings, published in Proceedings of the National Academy of Sciences, provide the clearest evidence yet that apes can track ignorance in others. This discovery offers insight into the shared cognitive abilities of humans and great apes.

Apes share cognitive abilities with humans

Study co-author Chris Krupenye is an assistant professor of psychological and brain sciences at Johns Hopkins.

“The ability to sense gaps in one another’s knowledge is at the heart of our most sophisticated social behaviors, central to the ways we cooperate, communicate, and work together strategically,” said Professor Krupenye.

He explained that this cognitive ability forms the basis for skills like language and teaching, both of which are considered uniquely human. The study suggests that these abilities may have evolved millions of years ago, long before modern humans emerged.

Testing ape intelligence

In collaboration with Luke Townrow, a Johns Hopkins PhD student, Professor Krupenye worked with three male bonobos to explore apes’ understanding of others’ knowledge.

The apes – Nyota, 25; Kanzi, 43; and Teco, 13 – live at Ape Initiative, a research and education nonprofit.

The experiment was designed to test whether the apes could recognize when a human lacked information. One bonobo sat across a table from Townrow. Another person placed a treat (a grape or a Cheerio) under one of three cups.

Sometimes, Townrow could see where the treat was placed. Other times, he could not. The bonobo could only get the treat if Townrow found it.

Apes anticipate what humans know

Townrow always asked the same question: “Where’s the grape?” and then waited for ten seconds. If he had seen where the treat was hidden, the bonobo usually remained still, waiting for him to retrieve it.

But when Townrow did not see the treat being hidden, the bonobo reacted differently. Instead of waiting, it quickly pointed to the correct cup. Some bonobos even pointed multiple times, making sure their message was clear.

Clear and repeated gestures

“Their fingers would point right through the mesh – it was clear what they were trying to communicate,” said Professor Krupenye.

One of the apes, Kanzi, reacted especially strongly. He was highly food-motivated and would tap repeatedly to ensure Townrow noticed his pointing. His eagerness highlighted the urgency with which the apes tried to share information.

This reaction supports previous observations from the wild. Researchers have seen chimpanzees vocalize to warn others of danger when a group member appears unaware of a threat, such as a nearby snake.

Recognizing gaps in knowledge

“We predicted that if apes are really tracking ignorance, when their partners lacked knowledge, they would be pointing more often and more quickly, and that’s exactly what they did,” Krupenye said.

The ability to recognize when someone lacks knowledge suggests that apes can hold two different perspectives at the same time. They know where the treat is, but apes also recognize that their human partner does not.

This cognitive skill is fundamental in human social interactions. People adjust their communication based on what they believe others know or do not know. The findings suggest that great apes share this ability at a basic level.

Apes have advanced mental abilities

“There are debates in the field about the capabilities of primates, and for us, it was exciting to confirm that they really do have these rich capacities that some people have denied them,” Krupenye said.

By demonstrating that apes can track others’ ignorance, the study provides new evidence that great apes possess more advanced mental abilities than previously believed. This research could reshape how scientists view the evolution of human intelligence.

Can apes change human beliefs?

The next step is to investigate why apes behave this way. Are they simply trying to influence their partner’s behavior, or do they understand that they are changing someone else’s thoughts?

“What we’ve shown here is that apes will communicate with a partner to change their behavior, but a key open question for further research is whether apes are also pointing to change their partner’s mental state or their beliefs,” said Townrow.

Future studies will explore whether apes communicate to correct others’ misunderstandings or simply to achieve a goal. Either way, the findings suggest that the roots of human social intelligence stretch back millions of years.

The study is published in the journal Proceedings of the National Academy of Sciences.

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