The combined evidence from molecular systematics, comparative morphology, and primatology has established that the African great apes—gorillas and chimpanzees—are more closely related to humans than they are to the Asian orangutan and other extant primates. Since our closest primate relatives are restricted today to Equatorial Africa, it can be deduced (as Charles Darwin and Thomas Huxley did more than a century ago) that humans are descended from a last common ancestor that also lived in Africa. Using a “molecular clock” model, in which the time scale of genetic change is calibrated against the fossil record, and based on the degree of genetic similarity between humans and chimpanzees (we share about 98% of our genomes), scientists can infer that humans diverged from the African apes about 6–7 million years ago (Ma).