Rethinking the dispersal of Homo sapiens out of Africa

Abstract

Current fossil, genetic, and archeological data indicate that Homo sapiens originated in Africa in the late Middle Pleistocene. By the end of the Late Pleistocene, our species was distributed across every continent except Antarctica, setting the foundations for the subsequent demographic and cultural changes of the Holocene. The intervening processes remain intensely debated and a key theme in hominin evolutionary studies. We review archeological, fossil, environmental, and genetic data to evaluate the current state of knowledge on the dispersal of Homo sapiens out of Africa. The emerging picture of the dispersal process suggests dynamic behavioral variability, complex interactions between populations, and an intricate genetic and cultural legacy. This evolutionary and historical complexity challenges simple narratives and suggests that hybrid models and the testing of explicit hypotheses are required to understand the expansion of Homo sapiens into Eurasia.

Keywords: Homo sapiens; Paleolithic; demography; dispersal; genetic ancestry.

Box Figure 1

Alternative models of the retationship between the mtDNA genealogy and demographic history. Models B and C illustrate the possbility of an early divergence of African and non-African ancestors to, with subsequent gene flow, potentially congruent with fossil and archeological evidence of a dispersal of Homo sapiens out of Africa ca. 100 ka. (Color figure can be viewed in the online issue, which is avaitabie at wileyonlinelibrary.com.)

Box figure 2

Distribution of the age of the L3 node in 20,000 simulations for each of the models listed In Table 2. The vertical dashed line at 80 Ka indicates the maximum estimated age of L3 in the human mtDNA tree. (Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.)

Box Figure 1

The distribution of Middle Paleolithic sites across East Africa, the Saharo-Arabian belt, and India plotted on a modeled precipitation map for the last interglacial (MIS 5) with positions of major paleolakes (dark blue areas) and paleorivers, which form extensive riparian corridors (blue lines). The Neanderthal range line shows the estimated extent of Neanderthal dispersal from the north. The map shows that Middle Paleolithic sites are commonly located in interior regions and that their presence in typically arid areas can be explained by the humid climate conditions of periods such as MIS 5, which activated paleohydrological networks and potentially transformed major deserts into savannah grasslands and shrublands (green areas) containing numerous freshwater lakes and rivers. The paucity of sites in Pakistan and eastern Iran almost certainy reflects research history rather than a real pattern. (Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.)

Figure 1

Selected lithics (stone tools) from East and North Africa for MIS 5 (1-11) and MIS 3 (12-25). 1-4: iconic MIS 5 Middle Paleolithic (Middle Stone Age) lithic types and techniques of North Africa, 1-2: tanged/pedunculated Aterian points, widely believed to have been hafted tools, 3, 4: ‘beaked’ (‘Nubian’) Levallois cores), 5-11: other common components of North (5-7, from Bir Tarfawi, Egypt) and East (8-11, from BNS, Omo Kibish, Ethiopia) African MIS 5 MP assemblages, 5, 8, 9: recurrent centripetal Levallois cores, 6, 10: centripetally prepared Levallois flakes, 7, 11: retouched points. Late MP cores (12, 13) and retouched points (14-15) and backed microlithic (16) from Mochena Borago, Ethiopia, ~50 ka. 17-25: Early Late Paleolithic (Later Stone Age) lithics from Enkapune Ya Muto, Kenya ~ 50-40 ka, 17: end and side retouched flake, 18-24: backed flakes/microliths, 25: burin.

Figure 2

Selected lithics from Southwest and South Asia from MIS 5 (1-12) and MIS 3 (13-27). 1-4: Arabian Peninsula. 1: centripetally prepared preferential Levallois core, Jebel Faya, UAE, ~125 ka, 2: bifacially flaked tool, Jebel Faya, 3,4: beaked (or Nubian) Levallois cores from TH-59, Oman, probably MIS 5, 5-8: Qafzeh Cave, Israel, ~100-90 ka, 5: recurrent centripetal Levallois core, 6: centripetally prepared preferential Levallois core, 7: Levallois flake, 8: side retouched Levallois flake. 9-12: MIS 5 lithics from Jwalapurum 22, India, ~75 ka, 9: recurrent centripetal Levallois core, 10: centripetally prepared preferential Levallois core, 11: tanged/pedunculated flake, 12: retouched point, 13-16, typical artefacts of the Levantine Late Middle Paleolithic, Dederiyeh Cave, Syria, ~60 ka, 13,14: unidirectional convergent Levallois cores, 15,16: Levallois points with unidirectional convergent preparation. 17-20, Late Middle Paleolithic lithics from Jwalapurum 3 and 20, India, ~55-30 ka, 17: centripetally prepared preferential Levallois core, 18: recurrent centripetal Levallois core, 19, 20: Levallois flakes. 21-27: Early Upper Paleolithic lithics from the Levant, ~ 40 ka, 21: blade core, 22-26: points, 27: blade.

Figure 3

Map showing topography and bathymetry (SRTM30PLUS). Areas in yellow correspond to currently submerged land that would have been exposed when sea level was ~100m lower than present. Colored dots correspond to key archaeological sites (Howiesons Poort, MSA/LSA transitional and South Asian Late Paleolithic) emphasized by the Mellars et al. model. The inserts show that the landscape can be very different from place to place and that there is no ‘typical’ coastal environment.