"None of the three great apes is considered ancestral to modern man, Homo sapiens, but they remain the only other type of extant primate with which human beings share such close physical characteristics. From them we may learn much concerning the behavior of our earliest primate prototypes, because behavior, unlike bones, teeth, or tools, does not fossilize."

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He who lets the world, or his own portion of it, choose his plan of life for him, has no need of any other faculty than the ape-like one of imitation. He who chooses his plan for himself, employs all his faculties. He must use observation to see, reasoning and judgment to foresee, activity to gather materials for decision, discrimination to decide, and when he has decided, firmness and self-control to hold to his deliberate decision.

— John Stuart Mill