Chimps can take in new evidence, evaluate its strength, and change their minds.

When Aristotle claimed that humans differ from other animals because they have the ability to be rational, he understood rational to mean that we could form our views and beliefs based on evidence, and that we could reconsider that evidence. “You know—ask ourselves if we should really believe that based on the evidence we’ve got,” says Jan M. Engelmann, an evolutionary anthropologist at the University of California, Berkeley.

Engelmann says that from the beginning of the Western intellectual tradition, people thought that only humans are rational. So, he designed a study to see if rationality shows up in chimpanzees. It turned out that they’re almost as rational as we are.

...