What does an animal see in a mirror? Until 1970, the accepted answer was "another animal": a stranger to be greeted, threatened, courted—or ignored. In that year, psychologist Gordon Gallup Jr. came up with the idea of giving a chimpanzee a mirror and painting a mark on his face while he slept. With one small gesture-reaching to touch the mark on his own face when he awakened—the chimp touched off a revolution not only in psychology, but philosophy as well. He saw himself.
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