When presented with multiple clues about the location of food, chimps revised their choices based only on stronger clues, indicating they were comparing the worth of pieces of information
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Marta Hill - Staff Contributor
November 6, 2025 12:35 p.m.
Two chimpanzees sit in the Ngamba Island Chimpanzee Sanctuary in Uganda, where the study took place. [Merryjack via Flickr under CC BY-SA 4.0](https://www.flickr.com/photos/merryjack/6764016289/in/photolist-5ayrYQ-5ayr1w-5ayrRS-5ayrhb-5ayqDf-5ayrvm-5auang-acwaM-biHmo…
When presented with multiple clues about the location of food, chimps revised their choices based only on stronger clues, indicating they were comparing the worth of pieces of information
Marta Hill - Staff Contributor
November 6, 2025 12:35 p.m.
Two chimpanzees sit in the Ngamba Island Chimpanzee Sanctuary in Uganda, where the study took place. [Merryjack via Flickr under CC BY-SA 4.0](https://www.flickr.com/photos/merryjack/6764016289/in/photolist-5ayrYQ-5ayr1w-5ayrRS-5ayrhb-5ayqDf-5ayrvm-5auang-acwaM-biHmov-24Xg28q-6zc56f” target=)
Whether you realize it or not, you spend a large chunk of your day weighing conflicting evidence. It is a hallmark of human rationality that shows up in many of our decisions. But new research shows we might not be alone in our ability to revise our beliefs in light of new information—chimpanzees can do it, too.
Belief revision is the process by which humans evaluate an overall set of evidence and make the best choice, discarding weaker evidence in favor of stronger evidence, like a jury does during a witness testimony. It’s a form of metacognition, or thinking about thinking, that other species don’t outwardly appear to perform.
But in a chimp sanctuary in Uganda, researchers recently showed that when presented with conflicting evidence, chimpanzees seemingly weighed the information and made decisions by belief revision. The findings, published October 30 in Science, indicate that chimpanzees make informed decisions by thinking about their own thoughts.
“Rationality has been linked to this ability to think about evidence and revise your beliefs in light of evidence,” senior author Jan Engelmann, a psychologist at the University of California, Berkeley, tells Becky Ferreira at 404 Media. “That’s the real big picture perspective of this study.”
The researchers took the chimps through a series of five experiments centered on food hidden in one of several boxes. Given an initial clue about the location of a snack, the chimps would pick a box. Researchers would then give the chimps another clue—either a stronger one, like a direct view of the food, or a weaker one, like the sound of food rolling around in the box.
When allowed to update their box choice, the chimps only changed their mind when the second clue was stronger than the initial information.
“The chimps knocked it out of the park,” Brian Hare, an evolutionary anthropologist at Duke University who was not involved in the study but wrote an accompanying perspective, tells Cody Cottier at Scientific American. “It’s obvious this is so easy for them.”
Through the experiments, researchers concluded that the chimps were grading different kinds of evidence based on how reliable they were; seeing food was the strongest clue, followed by hearing food shaken around in a box and lastly seeing only traces of food. In one experiment, chimps were shown that the initial evidence had been faked—that the appearance of an apple behind a glass panel was just a picture or that the sound of food rolling around was really a rock—and the animals then switched their choice to the other box. That was the “most surprising result … for sure,” Engelmann tells 404 Media. It shows that the chimps were able to consider new information that weakened what they previously knew, and they made their choices accordingly.
This study marks the first time research has demonstrated that “not only will chimps weigh evidence to form their beliefs about the world, but that they will modify those beliefs based on the strength of that evidence,” Suzanne MacDonald, a comparative psychologist at York University in Canada who wasn’t involved with the work, tells Cathleen O’Grady at Science. “That is pretty amazing.”
It is difficult to truly assess the internal cognitive processes any animal employs by simply observing their actions, but this new work “goes a long way towards suggesting that chimps might have a genuine capacity for active reflection,” Christopher Krupenye, an animal cognition researcher at Johns Hopkins University who was not involved with the work, tells Science.
The thought processing the chimps exhibited in these experiments is advanced, but it doesn’t rise to quite the same level as human rationality, study co-author Hanna Schleihauf, a comparative psychologist at Utrecht University in the Netherlands, tells Scientific American. Humans notably are able to hone and defend their beliefs through discussion and social interaction. “This is really what makes humans so special,” she says. “We give and ask for reasons.”
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