Pleistocene climate variability in eastern Africa influenced hominin evolution

Abstract

Despite more than half a century of hominin fossil discoveries in eastern Africa, the regional environmental context of hominin evolution and dispersal is not well established due to the lack of continuous palaeoenvironmental records from one of the proven habitats of early human populations, particularly for the Pleistocene epoch. Here we present a 620,000-year environmental record from Chew Bahir, southern Ethiopia, which is proximal to key fossil sites. Our record documents the potential influence of different episodes of climatic variability on hominin biological and cultural transformation. The appearance of high anatomical diversity in hominin groups coincides with long-lasting and relatively stable humid conditions from ~620,000 to 275,000 years bp (episodes 1–6), interrupted by several abrupt and extreme hydroclimate perturbations. A pattern of pronounced climatic cyclicity transformed habitats during episodes 7–9 (~275,000–60,000 years bp), a crucial phase encompassing the gradual transition from Acheulean to Middle Stone Age technologies, the emergence of Homo sapiens in eastern Africa and key human social and cultural innovations. Those accumulative innovations plus the alignment of humid pulses between northeastern Africa and the eastern Mediterranean during high-frequency climate oscillations of episodes 10–12 (~60,000–10,000 years bp) could have facilitated the global dispersal of H. sapiens.

Wild chimpanzee behavior suggests that a savanna-mosaic habitat did not support the emergence of hominin terrestrial bipedalism

“…The expansion of more open and arid habitats is thought to have been a catalyst for many changes in hominin behavior, anatomy, and/or physiology over the past 10 Ma (3,(55)(56)(57)(58). This includes the emergence of hominin bipedalism in the late Miocene-Pliocene as fossils of the earliest ( putative) hominins, and multiple australopith taxa are found within savanna-mosaic, rather than closed forest, paleohabitats (9)(10)(11)(12)(13).…”

What made us “hunter-gatherers of words”

“…I have argued elsewhere (Boeckx, 2017b , 2021 ; Martins and Boeckx, 2019 ; de Boer et al, 2020 ) that an entire class of evolutionary narratives exemplified by Berwick and Chomsky ( 2016 ), which posit one or a few key changes at the level of the genome and the brain that are claimed to have sparked a recent cognitive revolution in our lineage, have lost their initial conceptual appeal because the evolutionary trajectory of our lineage is clearly vastly much more complex than we used to think even just two decades ago. The twists and turns, booms and busts, carefully uncovered over the past decade in (geography/climate-aware) archaeology (Scerri et al, 2014 , 2018 , 2019 ; Groucutt et al, 2021 ; Kaboth-Bahr et al, 2021 ; Foerster et al, 2022 ; Gosling et al, 2022 ), alongside the numerous instances of gene flow across species that can be inferred from ancient genomes (Bergström et al, 2021 ), leave little room for doubt. There was no “great leap forward” (contra Diamond, 1991 ).…”

High‐Latitude, Indian Ocean, and Orbital Influences on Eastern African Hydroclimate Across the Plio‐Pleistocene Boundary

“…Although long, high-resolution terrestrial hydroclimate records spanning the Plio-Pleistocene boundary from the IO rim are sparse, those that exist-IODP Site U1478 δ 2 H C28 values (Taylor et al, 2021) and International Ocean Drilling Program (IODP) Site U1463 K % (Auer et al, 2019;Christensen et al, 2017)-are paced most strongly by obliquity and eccentricity. In the mid-to later Pleistocene, however, many younger eastern African records have a strong 19-23-kyr precessional imprint (Caley et al, 2018;Foerster et al, 2022;Lupien et al, 2018Lupien et al, , 2022Partridge et al, 1997;Simon et al, 2015). This suggests a complex set of high-and low-latitude African and IO climate forcings (e.g., deMenocal, 1995deMenocal, , 2004.…”

“…, Farrell and Janecek (1991), Karas et al (2011), and Shackleton and Hall (1990) 0.69 The relative importance of high and low latitude forcings to the orbital-scale pacing of the eastern African monsoon is also uncertain. Mediterranean sapropels (Emeis et al, 2000;Hilgen, 1991;Lourens et al, 1996;Rose et al, 2016;Rossignol-Strick, 1983, 1985 and alkenone fluxes (Herbert et al, 2015), some northern African dust flux records (Skonieczny et al, 2019), and other eastern African indices of hydroclimate (Caley et al, 2018;Foerster et al, 2022;Joordens et al, 2011;Lupien et al, 2018Lupien et al, , 2022Nutz et al, 2017;Partridge et al, 1997) and vegetation (Lupien et al, 2018(Lupien et al, , 2021Yost et al, 2021) suggest that low-latitude seasonal insolation, mainly paced by precession (19-23 kyr), exerts an outsized influence on hydroclimate. However, other dust time series (deMenocal, 1995(deMenocal, , 2004Larrasoaña et al, 2003;Tiedemann et al, 1994;Trauth et al, 2009) and elemental X-ray fluorescence (XRF) ratios (Crocker et al, 2022) contain a strong 41-kyr (obliquity) signal.…”