Human Evolution in Late Quaternary Eastern Africa

Eastern Africa (broadly Ethiopia, Somalia, South Sudan, Kenya, Uganda, and Tanzania) has yielded the earliest fossils of modern humans, the earliest evidence for Mode 3 technologies (Middle Stone Age), and is one of the areas in which modern humans may well have been endemic. This paper reviews the genetic, archaeological, and fossil evidence for the evolution of modern humans across MIS 6-2 in eastern Africa, and places this into the context of Middle Pleistocene human evolution, the development of the Middle Stone Age across the continent, and climatic change over the last two glacial cycles. We argue that while there is a paucity of well-dated sites that reduces the resolution of any interpretation, the available evidence indicates a major role for eastern Africa as an area of endemism, most probably related to the interaction of mosaic environments and refugia. We show that the evolution of modern humans has roots that extend well before MIS 6, and propose four overlapping stages, making this a much more prolonged process than has traditionally been described. There is a broad relationship between evolutionary history and major climatic oscillations; nevertheless , a closer examination reveals a more complex pattern. There are periods of synchrony and asynchrony in both contextual and evolutionary/behavioral changes, and these show variable links to both northern and southern Africa. Although eastern, northern and southern Africa (with central and western being largely unknown) show similarities and ultimately the same evolutionary and behavioral outcome, they also exhibit independent trajectories that require further research to throw light on the processes involved.