Details on the origins of all the peoples that make up the population of highland Ethiopia were still matters for research and debate in the early 1990s. Anthropologists believe that East Africa's Great Rift Valley is the site of humankind's origins. (The valley traverses Ethiopia from southwest to northeast.) In 1974 archaeologists excavating sites in the Awash River valley discovered 3.5-million-year- old fossil skeletons, which they named Australopithecus afarensis. These earliest known hominids stood upright, lived in groups, and had adapted to living in open areas rather than in forests.