Chimpanzees may share more with human thinkers than researchers once realized. A new study published in Science presents compelling evidence that chimpanzees can revise their beliefs in a rational way when they encounter new information.
The study, titled “Chimpanzees rationally revise their beliefs,” was carried out by an international team that included UC Berkeley Psychology Postdoctoral Researcher Emily Sanford, UC Berkeley Psychology Professor Jan Engelmann and Utrecht University Psychology Professor Hanna Schleihauf. Their results indicate that chimpanzees, similar to humans, adjust their decisions based on how strong the available evidence is, which is a central component of rational thinking.
At the Ngamba Island Chimpanzee Sanctuary in Uganda, the researchers designed an experiment involving two boxes, one of which contained food. The chimps were first given a hint about which box held the reward. Later, they received a clearer and more convincing clue that pointed to the other box. Many of the animals changed their choice after receiving the stronger information.
“Chimpanzees were able to revise their beliefs when better evidence became available,” said Sanford, a researcher in the UC Berkeley Social Origins Lab. “This kind of flexible reasoning is something we often associate with 4-year-old children. It was exciting to show that chimps can do this too.”
Testing Whether Chimps Are Reasoning or Acting on Instinct
To confirm that the animals were truly engaging in reasoning rather than reacting on impulse, the researchers used tightly controlled experiments combined with computational modeling. These methods helped rule out simpler explanations, such as the chimps favoring the most recent clue (recency bias) or simply responding to the easiest cue to notice. The modeling showed that their decisions followed patterns consistent with rational belief revision.
“We recorded their first choice, then their second, and compared whether they revised their beliefs,” Sanford said. “We also used computational models to test how their choices matched up with various reasoning strategies.”
This work challenges long-held assumptions that rationality, defined as forming and updating beliefs based on evidence, belongs only to humans.
“The difference between humans and chimpanzees isn’t a categorical leap. It’s more like a continuum,” Sanford said.
Broader Implications for Learning, Childhood Development and AI
Sanford believes these findings may influence how scientists think about a wide range of fields. Learning how primates update their beliefs could reshape ideas about how children learn and even how artificial intelligence systems are designed.
“This research can help us think differently about how we approach early education or how we model reasoning in AI systems,” she said. “We shouldn’t assume children are blank slates when they walk into a classroom.”
The next phase of the project will apply the same belief revision tasks to young children. Sanford’s team is now gathering data from two- to four-year-olds to see how toddlers handle changing information compared to chimps.
“It’s fascinating to design a task for chimps, and then try to adapt it for a toddler,” she said.
Expanding the Study to Other Primates
Sanford hopes to broaden the work to additional primate species, creating a comparative view of reasoning abilities across evolutionary branches. Her previous research spans topics from empathy in dogs to numerical understanding in children, and she notes that one theme continues to stand out: animals often demonstrate far more cognitive sophistication than people assume.
“They may not know what science is, but they’re navigating complex environments with intelligent and adaptive strategies,” she said. “And that’s something worth paying attention to.”
Other members of the research team include: Bill Thompson (UC Berkeley Psychology); Snow Zhang (UC Berkeley Philosophy); Joshua Rukundo (Ngamba Island Chimpanzee Sanctuary/Chimpanzee Trust, Uganda); Josep Call (School of Psychology and Neuroscience, University of St Andrews); and Esther Herrmann (School of Psychology, University of Portsmouth).
