Abstract
Reconstructions of climatic and environmental conditions can contribute to current debates about the factors that influenced early human dispersal within and beyond Africa. Here we analyse a 200,000-year multi-proxy paleoclimate record from Chew Bahir, a tectonic lake basin in the southern Ethiopian rift. Our record reveals two modes of climate change, both associated temporally and regionally with a specific type of human behavior. The first is a long-term trend towards greater aridity between 200,000 and 60,000 years ago, modulated by precession-driven wet-dry cycles. Here, more favorable wetter environmental conditions may have facilitated long-range human expansion into new territory, while less favorable dry periods may have led to spatial constriction and isolation of local human populations. The second mode of climate change observed since 60,000 years ago mimics millennial to centennial-scale Dansgaard-Oeschger cycles and Heinrich events. We hypothesize that human populations may have responded to these shorter climate fluctuations with local dispersal between montane and lowland habitats.
Highlights
Reconstructions of climatic and environmental conditions can contribute to current debates about the factors that influenced early human dispersal within and beyond Africa
The climate of eastern Africa is controlled by the annual migration of the tropical rain belt (TRB) following the zenith of the sun with a 3–4 week lag
Our results show that high amounts of coarser-grained sediments mostly coincide with lower K/Zr, higher Al/Si and Ca/Ti ratios, higher total organic carbon (TOC), lower δ18O values and vice versa
Summary
Recent discoveries of human fossils and related stone tools between ~315 and 75 ka in age in several parts of Africa (e.g., northern Africa[2], southern Africa[3,4], and eastern Africa5,6) have initiated a lively discussion of hypothesized multiregional origin and development of Homo sapiens within Africa[7] This hypothesis includes a temporary availability of suitable, interconnected habitats, providing sufficient resources for our species to succeed and establish vital populations. The climate of eastern Africa is controlled by the annual migration of the tropical rain belt (TRB) following the zenith of the sun with a 3–4 week lag This intensive insolation causes the build-up of mesoscale convective systems (MSCs), modulated by the possible influence of the West African (WAM) and South. Anomalies of the Indian Ocean sea-surface temperatures (SSTs) in combination with the Indian Ocean Dipole (IOD), modulate the intensity of the rainy seasons in eastern Africa[8,9]
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