Chimpanzees may think much more like humans than previously believed, according to new research published in Science. The study provides evidence that chimpanzees can rationally revise their beliefs when presented with new information - a behaviour long thought to be uniquely human. The research, titled "Chimpanzees rationally revise their beliefs," was carried out by a team including UC Berkeley psychology postdoctoral researcher Emily Sanford, UC Berkeley psychology professor Jan Engelmann, and Hanna Schleihauf, a psychology professor at Utrecht University. Working at the Ngamba Island Chimpanzee Sanctuary in Uganda, the team presented the animals with two boxes, one containing food. Initially, the chimpanzees were given a clue suggesting which box held the reward. Later, they received stronger evidence pointing to the other box - and many switched their choice accordingly. "Chimpanzees were able to revise their beliefs when better evidence became available," said Sanford, who works in UC Berkeley's Social Origins Lab. "This kind of flexible reasoning is something we often associate with four-year-old children. It was exciting to show that chimps can do this too." To ensure the findings reflected genuine reasoning rather than instinct, the researchers used tightly controlled experiments and computational modelling. These ruled out simpler explanations, such as a preference for the latest clue (recency bias) or reacting to the most obvious signal. The models confirmed that the chimps' decision-making closely matched rational strategies of 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." The study challenges the long-held view that rationality - the ability to form and revise beliefs based on evidence - is a uniquely human trait. "The difference between humans and chimpanzees isn't a categorical leap. It's more like a continuum," Sanford said. Sanford believes the findings could have wider implications for understanding learning, child development and artificial intelligence. "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 involves bringing the same tasks to children. Sanford's team is currently collecting data from two- to four-year-olds to compare how toddlers and chimps revise their beliefs. "It's fascinating to design a task for chimps, and then try to adapt it for a toddler," she said. Eventually, she hopes to extend the research to other primate species, mapping reasoning abilities across the evolutionary tree. While Sanford's previous work has ranged from studying dog empathy to numerical cognition in children, one lesson stands out: animals are capable of much more than humans often 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."