• 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.

    Dian Fossey (2000). “Gorillas in the Mist”, p.16, Houghton Mifflin Harcourt