In a series of experiments, researchers tested chimpanzees at the Ngamba Island Chimpanzee Sanctuary in Uganda to see how the animals juggled different sources of evidence. Each experiment revolved around food hidden in one of several boxes: The chimps would pick the box they thought was most promising based on an initial clue. Then they’d get another clue that sometimes conflicted with the first. Given the chance to update their decision, they almost always chose the box predicted by a rational-choice model and only changed their mind when the new information was stronger than what they already knew. “The chimps 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 this is so easy for them.”