Chimpanzee Metacognition Allows Humanlike Belief Revision

Chimpanzees can evaluate evidence and update their beliefs like humans do

By Cody Cottier edited by Sarah Lewin Frasier

You usually have reasons, good or bad, to justify your beliefs. You can think about these reasons: “Why do I think there is a serial killer in the attic? It’s because the floor creaked.” And, being the model of rationality that you are, you can also adjust your beliefs when additional evidence demands it: “After searching the attic, baseball bat in hand, I must conclude that it is just an old, creaky house. »

This cognitive skill is known as belief revision. This has long been considered a feature of human rationality that distinguishes us from other animals. It relies on a reflective awareness of our own thought processes – thinking about thought, or metacognition, which other species obviously do not possess. But a new study, published today in the journal Science, shows that our closest evolutionary relatives also reason in surprisingly sophisticated ways.

In a series of experiments, researchers tested chimpanzees at the Ngamba Island Chimpanzee Sanctuary, Uganda, to see how the animals juggled different sources of evidence. Each experiment revolved around food hidden in one of several boxes: the chimpanzees chose the box they thought was most promising based on an initial cue. They then obtained another clue, sometimes in contradiction with the first. If given the opportunity to update their decision, they almost always chose the box predicted by a rational choice model and only changed their minds when the new information was stronger than what they already knew. “The chimpanzees knocked it out of the park,” says Brian Hare, an evolutionary anthropologist at Duke University who was not involved in the study. “It’s obvious it’s so easy for them.”

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Most impressively, the animals even represented clues that undermined previous evidence. If they heard something bouncing inside Box 1, they would assume, at first, that it was an apple, but then the experimenter would remove a rock. Realizing they had been misled, the chimpanzees immediately opted for box 2, even though it seemed uninspiring a moment before. It was “the icing on the cake,” says Jan Engelmann, study co-author and comparative psychologist at the University of California, Berkeley. “None of us thought we could do it because it’s so complex.”

Of course, many animals obey reason without thinking; an amoeba acts rationally, in a sense, when it follows chemical signals in the direction of food. This “thoughtless reactivity to evidence,” as it is called, is only a shadow of human rationality. But Engelmann argues that chimpanzees’ ability to examine evidence and assess the certainty of their own knowledge comes much closer to reality. “It is very difficult to explain the behavior of chimpanzees without appealing to some notion of reflection,” he says.

Christopher Krupenye, who studies animal cognition at Johns Hopkins University and was not involved in the study, agrees. He is agnostic about the content of this reflection: without language, it is difficult to understand how animals could mentally represent the propositions that constitute human beliefs (“I hear clicking noises, so there is probably an apple in the box”). It is possible that chimpanzees think primarily in images. Either way, Krupenye says, “all this suggests that they are not just motivated by simple emotional responses. They have a rather complex consciousness.”

However, it is clear that there is more to human rationality than this alone. According to Hanna Schleihauf, co-author of the study and a comparative psychologist at Utrecht University in the Netherlands, the crucial ingredient may be social interaction: we are able to refine our beliefs through discussion. “That’s really what makes humans so special,” she says. “We give and ask for reasons.” Indeed, some cognitive scientists believe that our reasoning abilities have evolved in a way that allows us to argue with each other.

This study reminds us that these skills have evolved Since somewhere, namely from cognitive abilities already present in the common ancestor that we share with chimpanzees and bonobos. More than 150 years ago, Charles Darwin predicted that our extraordinary mental powers would prove to be extensions of abilities found throughout the animal kingdom. If chimpanzees are truly capable of thinking, the gap between us and our primate cousins ​​narrows a little further. As Hare says, there is no need to search the stars for intelligence similar to ours. “We already know we are not alone,” he said. “There are beings here who view the world in a way that we consider rational.”

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