A chimpanzee stripping a twig forced scientists to redefine what makes us human

In 1960 Jane Goodall watched a wild chimpanzee strip leaves from a twig to fish termites from a mound -- the first confirmed tool use by a non-human animal. Her mentor Louis Leakey said humanity would now have to 'redefine tool, redefine man, or accept chimpanzees as humans.'

— Jane Goodall, In the Shadow of Man — Houghton Mifflin, 1971
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