Early to Middle Pleistocene Homo dispersals from Africa to Eurasia: Geological, climatic and environmental constraints
Quaternary International, (2011)DOI: 10.1016/j.quaint.2011.02.043
Abstract
Although the Pleistocene human dispersal is one of the most intriguing issues of paleoanthropology, large sectors along possible migratory pathways are ill-defined or poorly documented. This paper examines the geological, geomorphological, climatic and environmental conditions that could have determined hominin transit from their motherland in the East Africa Rift Valley toward the circummediterranean regions or Arabian Peninsula. For their choice between these two alternatives, the Danakil Depression (Afar Rift) immediately north of the Ethiopian Rift Valley was a strategic area. They could reach the Mediterranean Sea through a northern route along the Nile River valley, the trans-Sahara megalake or riverine belts, or else navigate an eastern route into the Arabian Peninsula after crossing the Bab el Mandeb Straits. It is assumed all of these pathways were possible during convenient geological, climatic and/or sea-level conditions. Hominins had three additional choices once they arrived at the Mediterranean Sea shores with Eurasia as their final destination. The Levant corridor was the easiest because walkable and almost always under favorable conditions. Two other possibilities were the Sicily Channel and the Strait of Gibraltar. These sea arms are located in two extremely active settings of the Mediterranean Sea and were at their embryonic stage during the Early Pleistocene. Because large-scale deformations of the sea floor were associated to prolonged sea-level lowstands, these two sea arms could have been passable. Similar considerations apply to the Bab el Mandeb Straits region. For the trans-Mediterranean and the trans-Red Sea routes of dispersal, the environmental conditions and the submarine and terrestrial topographical features that could have made sea transit possible even without land bridges are underscored. To track the dispersal relations between Northern Africa and Eurasia, three schematic maps are presented to show the distribution of the archeological and paleoanthropological sites currently regarded as reliably dated. They document three groups of dates: between 2.0 and 1.5 Ma, 1.4 and 0.7 Ma, and 0.6 and 0.1 Ma. Their distribution is matched with coeval paleoclimatic proxies such as marine oxygen isotope stages, aeolian dust in the Atlantic Ocean, and sapropels levels and dust fluxes in the Eastern Mediterranean. Dispersal was temporally arranged into cycles of four major exodus waves (2.0–1.6 Ma, 1.4–1.2 Ma, 1.0–0.8 Ma, and 0.6–0.1 Ma) controlled by climatic and environmental changes.