By all accounts the road to the evolution of our species began in Africa. Anthropologists estimate that the human lineage diverged from other primates about 5 million years ago, with chimps being our closest living relative. The most primitive human ancestors yet discovered belong to the genus Australopithecus, which lived about 3 million years ago. Remains of Australopithecines – including "Lucy" – have been discovered primarily in the Rift Valley of Africa. Early members of our own genus, Homo erectus, and its near relative, Homo ergaster, arose in the same region about 2.5 million years ago. These "archaic" hominids migrated out of Africa approximately 1.5 million years ago to found populations in Europe, the Middle East, and Asia.

 Fossils of modern humans, dating to 40,000-100,000 years ago, have been found throughout the "Old World" – Africa, Europe, and Asia – and in Australia. By modern humans, we mean members of our own species, Homo sapiens, who shared with us important anatomical features (skull shape and size) and behavioral attributes (use of blades, bone tools, pigments, burial goods, art, trade, hunting, and varied environmental resources). These humans subsequently spread to Micronesia, Polynesia, and the "New World" (North and South America).

 How and where modern humans emerged is a matter of debate between proponents of two opposing theories. Supporters of the multiregional theory contend that modern human populations developed independently from archaic hominid (Homo erectus or Homo ergaster) populations in Africa, Europe, and Asia. Early modern groups evolved in parallel with each other and exchanged members to give rise to modern population groups. Supporters of the displacement theory, commonly known as "out of Africa," contend that modern human populations are derived from a single modern population group that left Africa about 80,000 years ago. This founding group migrated throughout the Old World, displacing any surviving archaic hominids. So, scientists all agree that our early hominid relatives arose in Africa, but disagree on when the direct ancestors of living humans left Africa to populate the globe.

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