Chimpanzees rationally revise their beliefs

The selective revision of beliefs in light of new evidence has been
considered one of the hallmarks of human-level rationality. However, tests
of this ability in other species are lacking. We examined whether and how
chimpanzees (Pan troglodytes) update their initial belief about the
location of a reward in response to conflicting evidence. Chimpanzees
responded to counter-evidence in ways predicted by a formal model of
rational belief revision: they remained committed to their initial belief
when the evidence supporting the alternative belief was weaker, but they
revised their initial belief when the supporting evidence was stronger.
Results suggest that this pattern of belief revision was guided by the
explicit representation and weighing of evidence. Taken together, these
findings indicate that chimpanzees metacognitively evaluate conflicting
pieces of evidence within a reflective process.