Hydroclimate changes in eastern Africa over the past 200,000 years may have influenced early human dispersal

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.

A Spatiotemporally Explicit Paleoenvironmental Framework for the Middle Stone Age of Eastern Africa

“…This is supported by the pollen records at nearby Lake Magadi where the general trend of increased aridi cation for this period is also reported [22]. Late Pleistocene records from the Chew Bahir basin similarly demonstrate a series of wet-dry transitions of varying amplitude and duration through K counts [23], with the early modern human fossil site Omo Kibish lying close to (but not within) the basin. This record therefore could potentially offer a climatic context for MSA occupations of the site, considering that highly favourable humid conditions are reported at 200 − 125,000 years ago (ka) [23] which broadly corresponds to the new date of the Omo fossils of 212 ± 16 ka [24].…”

“…Late Pleistocene records from the Chew Bahir basin similarly demonstrate a series of wet-dry transitions of varying amplitude and duration through K counts [23], with the early modern human fossil site Omo Kibish lying close to (but not within) the basin. This record therefore could potentially offer a climatic context for MSA occupations of the site, considering that highly favourable humid conditions are reported at 200 − 125,000 years ago (ka) [23] which broadly corresponds to the new date of the Omo fossils of 212 ± 16 ka [24]. Despite this improvement in resolution, paleoclimatic patterns and the records used to generate them are diverse (demonstrated in Fig.…”

A Phytolith Supported Biosphere-Hydrosphere Predictive Model for Southern Ethiopia: Insights into Paleoenvironmental Changes and Human Landscape Preferences since the Last Glacial Maximum

“…Highly variable water availability in the EARS during the Pleistocene and Holocene must have caused a significant reorganization-pressure on plant habitats and subsequent adaptation of habitat preferences of early humans [4,5]. During the past 25,000 calibrated years before present (herein ka), the region has been characterized by high amplitude Figure 1.…”

“…Highly variable water availability in the EARS during the Pleistocene and Holocene must have caused a significant reorganization-pressure on plant habitats and subsequent adaptation of habitat preferences of early humans [4,5]. During the past 25,000 calibrated years before present (herein ka), the region has been characterized by high amplitude climatic change, including the drier and colder episode during the Last Glacial Maximum (LGM, 25-18 ka) [6,7], the African Humid Period (AHP, 15-5 ka) [8,9] and present-day dry conditions.…”

“…On top of the Dendi caldera, Ethiopia (3000 m a.s.l) humans created handaxes [30]. Thus, based on the Upper Pleistocene and Holocene archaeological record, humans seem not to have shown a preference for a specific single landscape type, but rather occupied complex landscapes and developed flexible strategies to respond to a transforming environment [4,5,31,32]. For southern Ethiopia, a comparison of occupation frequencies between the lowlands and hypothesised refuge areas in, e.g., the SW Ethiopian Highlands suggested that during short-term dry spells puncturing the AHP the humid highlands could have been the sink area for vertical migration of highly mobile hunter-gatherer groups [33].…”