Chimps Can Weigh Evidence and Update Their Beliefs Like Humans Do

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Most impressively, the animals even accounted for clues that undermined earlier evidence. If they heard something bouncing around inside box 1, they would assume, at first, that it was an apple—but then the experimenter would pull out a stone. Realizing they had been misled, the chimps would immediately opt for Box 2, even though it appeared uninspiring a moment before. This was “the cherry on top,” says study co-author Jan Engelmann, a comparative psychologist at the University of California, Berkeley. “None of us thought they could do it because it’s just so complex.”

Of course, lots of animals obey reason without reflecting on it; an amoeba is acting rationally, in some sense, when it follows chemical signals toward food. This “unreflective responsiveness to evidence,” as it’s been called, is a mere shadow of human rationality. But Engelmann argues that chimpanzees’ ability to scrutinize evidence and gauge the certainty of their own knowledge comes much closer to the real thing. “It’s very hard to explain the chimps’ behavior without appealing to some notion of reflection,” he says.

Read the whole story (subscription may be required): Scientific American