Bonobos recognize the ignorance of others, a trait once thought to be unique to humans

Shy and rarely seen outside the dense African forests south of the Congo River, bonobos have a strong social memory. They can be aggressive at times but also resolve conflicts through affectionate gestures and sex. Now, researchers at Johns Hopkins University have identified another striking similarity between bonobos and humans: the ability to recognize ignorance in others, communicate to correct it, and cooperate accordingly.

Once again, a cognitive ability once thought to be uniquely human is revealed to exist in other animals. The bonobo (Pan paniscus), along with its close relative, the chimpanzee (Pan troglodytes), is the species most closely related to humans. According to the authors of the study, published on Monday in PNAS, the sophisticated social ability to recognize gaps in others’ knowledge is fundamental to human cooperation, communication, and strategic collaboration. Their findings suggest that “these elaborate mental capacities must have emerged millions of years ago in the common ancestors we share with other apes.” During evolution, hominids diverged from the lineage of chimpanzees and bonobos approximately 8 million years ago.

To reach these conclusions, researchers conducted a simple experiment with three bonobos living at the Ape Initiative, a U.S. research center dedicated to the conservation of these apes. The test involved three cups and a hidden grape as a reward. In the first sessions, the bonobos were placed in a cooperative setting with doctoral student Luke Townrow, who sat across from each ape. To receive the treat, the bonobos needed to help their human partner find it.

In the next phase of the experiment, the study’s lead author, Christopher Krupenye, sometimes hid the grape under one of the cups while Townrow was watching; other times, Townrow was unaware of its location. The bonobos, however, always saw where the grape was placed.

The results showed that when Townrow asked, “Where’s the grape?”, the bonobos eagerly pointed to the correct cup — especially when he hadn’t seen where it was hidden. However, if Townrow had seen where the grape was placed and still asked the question, the bonobos usually remained still, waiting to be given the treat.

“We work with a bonobo population that has been highly socialized with humans, so they have a lot of communication. We thought this would make them particularly useful for testing our hypothesis,” explains Krupenye, a professor of psychological and brain sciences at Johns Hopkins University.

Indeed, one of the bonobos, Kanzi, is something of a superstar. The 40-year-old ape is considered the first great ape to demonstrate an understanding of spoken English, as shown in a separate study.

The scientists suggest that bonobos “may act to communicate and coordinate effectively” when recognizing another’s ignorance. According to primatologist Josep Call, a researcher at the University of St Andrews, who was not involved in the study, “there are other results in the literature that are consistent with what they found.”

The new research also complements a 2017 study led by scientists at Duke University, which observed that wild bonobos living in the Lola ya Bonobo sanctuary in the Democratic Republic of the Congo were capable of helping strangers. Additionally, a 2013 study published in PLOS ONE supports the idea that bonobos share resources with others. However, this is the first time such social and cognitive abilities have been demonstrated in a controlled experiment.

Two contrasting representations

One key ability that helps humans navigate the world is recognizing that others have minds separate from their own. These differing perspectives allow us to understand behavior and coordinate effectively. In this study, explains Christopher Krupenye, bonobos had to recognize when their partner lacked information. The findings suggest that these apes can maintain “two conflicting representations in parallel”: one that reflects reality and another that does not.

This means that when bonobos pointed to the hidden grapes, they appeared to recognize a discrepancy between their own knowledge and their partner’s lack of information. “When they point, they do so in the right place. Therefore we know that they know where the food is. At the same time, they also know that their partner has a different, contrasting understanding. The difference between those worldviews is what leads them to fill the gap in order to communicate,” explains Krupenye.

However, the researchers acknowledge that it remains unclear whether the bonobos pointed to the grapes to prompt a “correct action” from their partner or simply to share information. “This is an important open question for future research,” Krupenye adds.

Shades of understanding in ape cognition

In 1978, U.S. primatologists David Premack and Guy Woodruff posed a fundamental question: Do apes have a “theory of mind” — the ability to infer the mental states of others, as humans do? Research so far suggests that chimpanzees perceive others through a framework of perception-based psychology rather than fully understanding subjective mental states.

“Testing this theory would be a very difficult exercise. What we know is that there are some similarities and some differences,” says Josep Call.

Meanwhile, Luke Townrow raises another key question: are apes truly capable of signaling or communicating with the intent to change another’s mental state? “We think they can recognize that others may have different perspectives, but we still don’t know if they understand that communication can be used to change those perspectives,” Townrow explains.

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