Dispersal Episodes of Anatomically Modern Humans Occurred Under Differing Hydroclimate Regimes of the Last Interglacial – Glacial Cycle in Northeastern Africa

Abstract:

Some of the earliest records of Anatomically Modern Humans (AMH) have been identified from various parts of the Main Ethiopian Rift, implying this region was one of the possible source regions of AMH dispersal. The paucity of continuous and high resolution climate records from this region has influenced the debate on the impact of climate variability on human evolution and dispersal “Out of Africa”. The debate has also been further hampered by the usually piecemeal consideration of individual records from specific sites, either at the origin or along the possible dispersal routes. We will present a synthesis of existing paleoclimate proxy records (speleothem, archaeological, lake sediment, and marine records) of the last interglacial-glacial cycle from the source region (the Ethiopian rift and surrounding highlands), along the dispersal routes (the Nile river, across the Gulf of Aden and the Arabian Peninsula) and the sink (Mediterranean sea and the Levant). The high resolution speleothem hydroclimate proxy records from the southeastern Ethiopian highlands show general but internally complex drying trend from the LIG to the Late Holocene, while the associated major AMH dispersals occurred during both wet (~125 – 120 ka dispersal episode) and dry (~75 – 50 ka dispersal episode) conditions at the source region. Comparison of the speleothem records with those from lake sediment, archaeological and marine records from the source region (Ethiopian rift and highlands) and the surrounding regions depict more complex trends and variabilities. The significant regional and local variabilities and trends in hydroclimate during this period imply that the climate context of AMH dispersal out of eastern Africa has been complex, and locality level environmental conditions (availability of water and food resources) might have played more significant role in the AMH decision making process.