LETTER doi:10.1038/nature19365 1 Late Pleistocene climate drivers of early human 2 migration Axel Timmermann1,2 & Tobias Friedrich1 On the basis of fossil and archaeological data it has been (Fig. 1b–d) during the Late Pleistocene (126–11 thousand years ago hypothesized that the exodus of Homo sapiens out of Africa and into (ka)) and the Holocene (11–0 ka). Every ~21 thousand years decreased Eurasia between ~50–120 thousand years ago occurred in several precession (Fig. 1a) and corresponding higher boreal summer insola- orbitally paced migration episodes1–4. Crossing vegetated pluvial tion intensified rainfall in northern Africa, the Arabian Peninsula and corridors from northeastern Africa into the Arabian Peninsula the Levant8, thus generating habitable savannah-type corridors1,2 for and the Levant and expanding further into Eurasia, Australia H. sapiens and a possible exchange pathway between African and and the Americas, early H. sapiens experienced massive time- Eurasian populations, which in turn impacted the subsequent global varying climate and sea level conditions on a variety of timescales. dispersal pattern and gene flow of H. sapiens across Asia, Europe, Hitherto it has remained difficult to quantify the effect of glacial- Australia and into the Americas. and millennial-scale climate variability on early human dispersal Elucidating the response of H. sapiens dispersal to past climate shifts and evolution. Here we present results from a numerical human has been hindered by the sparseness of palaeoenvironmental data in dispersal model, which is forced by spatiotemporal estimates of key regions4 such as northeastern Africa, the Levant and the Arabian climate and sea level changes over the past 125 thousand years. Peninsula, by regional uncertainties of global climate model simu- The model simulates the overall dispersal of H. sapiens in close lations (see Methods, Extended Data Fig. 3), and by the prevailing agreement with archaeological and fossil data and features dating uncertainties of fossil or archaeological records. Here we set prominent glacial migration waves across the Arabian Peninsula out to quantify the effects of climate on human dispersal over the last and the Levant region around 106–94, 89–73, 59–47 and 45–29 glacial period, using a numerical reaction/diffusion human dispersal thousand years ago. The findings document that orbital-scale model (HDM, see Methods, Extended Data Fig. 1), which is forced global climate swings played a key role in shaping Late Pleistocene by time-varying temperature, net primary production, desert fraction global population distributions, whereas millennial-scale abrupt (Extended Data Figs 4–6) and sea level boundary conditions (Fig. 1f) climate changes, associated with Dansgaard–Oeschger events, had obtained from a transient glacial/interglacial global earth system a more limited regional effect. model simulation9 covering the last 125 ka, an estimate of millennial- Numerous studies5–7 have postulated that human dispersal and scale variability and sea level reconstructions10, respectively (see evolution were a direct consequence of orbital-scale climate shifts Methods). The LOVECLIM climate model used here (see Methods) a .) 300 f –0.05 –0.05 0 ) Figure 1 | Climate drivers. a, Precession (cyan) 24 ) i and CO2 concentrations (grey). p.p.m.v., parts 250 ( 25 0 0 –50 per million by volume. b, Reconstructed (blue) (p.p.m.v sin 2 200 e –100 and simulated (red) North Atlantic temperatures CO 0.05 0.05 Sea level (m HMW1 HMW2 HMW3 HMW4 HMW5 HMW1 HMW2 HMW3 HMW4 HMW5 (°C) (see Methods). c, Israel (Soreq cave) g Grotta del Cavallo speleothem26 δ18O (orange) and simulated Israel Kents Cavern . 30 b 5 5 Pestera cu Oase desert fraction (brown). d, Turkey hydroclimate 20 reconstruction27 (red) and simulated Turkey net ope 0 0 (ºC) 10 primary production (NPP) (blue). e, Antarctic Eur 28 Spain temp oxy SST (ºC) (Dome Fuji) reconstructed (orange) and Pr –5 –5 0 simulated (blue) surface temperature anomalies Jebel 10 2 h 30 (TS). f, Precession and sea level . g–j, Simulated c Faya 50 2 ) human density (individuals per 100 km ) for early 20 0 t (red), late (blue) and early-without-Dansgaard– 0 10 Oeschger events (yellow) exit scenarios in Europe O (per mil) –2 Deser 18 –50 fraction (% 0 (9.5° E, 48.5° N), Arabian Peninsula (56.5° E, Qafzeh Arabian Peninsula 21.5° N), Levant (37.5° E, 34.5° N) and Australia Skhul ) 30 (144.5° E, 19.5° S). Blue (mixed blue/yellow) boxes d 5 5 i –1 yr 20 indicate archaeological (archaeological and fossil) P n PC1 –2 18,20,29,30 m evidence for H. sapiens . Va 0 0 NP 10 Levant (kgC Lake –5 –5 0 j Lake 40 e 6 6 Mungo 4 4 2 2 tica rc 20 0 0 TS (ºC) Australia –2 –2 Anta Dome F TS (ºC) –4 –4 0 120 100 80 60 40 20 0 120 100 80 60 40 20 0 Time (ka) Time (ka) 1International Pacific Research Center, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA. 2Department of Oceanography, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA. 00 MONTH 2016 | VOL 000 | NATURE | 1 RESEARCH LETTER 125 ka 120 ka 110 ka 100 ka 90 ka 80 ka 70 ka 60 ka 50 ka 40 ka 30 ka 20 ka 10 ka 1 ka Individuals per 100 km2 0 4 8 12 16 20 24 28 Figure 2 | Late Pleistocene human dispersal. Snapshots of the simulated evolution of human density (individuals per 100 km2) over the past 125 thousand years using the parameters of scenario A (early exit) experiment (see Methods) with full climate (orbital- and millennial-scale) and sea level forcing and with human adaptation (see Methods). simulates glacial temperature and hydroclimate variability in good prominent wave around 60 ka (Fig. 1g) coincides with the youngest agreement with some palaeoclimate proxy data9 (Fig. 1b–e, Extended estimates of the L3-haplogroup-based age range for the time to most Data Fig. 2). recent common ancestor (TMRCA) of 79–60 ka11,12 and the subse- The first climate-forced HDM experiment (scenario A, Extended quent emergence of mitochondrial DNA (mtDNA) haplogroups M, Data Tables 1, 2) covers the time evolution of the past 125 ka (Fig. 2, N and R. Eventually, this wave merges with the Eurasian population Supplementary Video 1) and accounts for a numerical representa- and leads to a boost of population density across Europe (Fig. 1g, h) tion of gradual human adaptation to environmental conditions (see and southern Asia. Meanwhile, H. sapiens cross the sea-level-altered Methods). Diffusing into vegetated regions, the first low-density Indonesian archipelago and arrive in Papua New Guinea and Australia migration wave of H. sapiens reaches the coastline of northeast Africa around 60 ka (Figs. 1j, 2). For the subsequent period from 60–30 ka and the Bab-el-Mandeb around 115–106 ka (Figs. 1h, 2, Supplementary (MIS3) the model simulates a continuous Africa/Eurasia exchange Video 1). Two rapid dispersals through the migration-favourable of H. sapiens through the Levant (Fig. 1i) and an additional wave anomalously wet Arabian Peninsula- and Sinai-corridors (Fig. 1c, (45–30 ka) across the Bab-el-Mandeb and through the Arabian d, h, i, Extended Data Fig. 4) occur between 107–95 and 90–75 ka. Peninsula (Fig. 1h). The dispersal across the Levant region is fur- Very low densities are simulated for Southern Europe from 95–72 ka ther modulated by the millennial-scale drought/pluvial variability (Fig. 2). The subsequent dry conditions during the period 71–60 ka associated with Dansgaard–Oeschger stadial/interstadial transitions (Marine Isotope Stage 4, MIS4) (Fig. 1c, d, Extended Data Figs 5, 6) cut (Fig. 1d, i). Completing the simulated grand journey from Africa off the exchange between the populations in northeastern Africa, and to the Americas, H. sapiens cross the Bering land bridge into North the rapidly eastward-spreading group in southern Asia (Fig. 2). This America during the short period from 14–10 ka. With rising sea levels is in stark contrast to previous suggestions11 of a very active migra- the Bering land bridge gets inundated during the glacial termination tion corridor through the southern Arabian Peninsula during this (Supplementary Video 1), thus terminating the genographic connec- time. During the subsequent precession minimum (increased boreal tivity between Asia and North America. summer insolation) around 60–47 ka (Fig. 1a), simulated rainfall According to this early exit scenario the first H. sapiens arrived in enhances net primary production in northern Africa, the Levant and Europe, India and Southeast Asia and southern China in low den- the Arabian Peninsula (Extended Data Fig. 5) and a second prominent sities (<5 individuals per 100 km2) already between 100–70 ka (see migration wave leaves northern Africa (Fig. 1h, i, 2). The onset of this Supplementary Video 1, Fig. 3a). Whereas the simulated early arrival 2 | NATURE | VOL 000 | 00 MONTH 2016 LETTER RESEARCH ab Supplementary Video 2), it does not explain the early MIS5 presence of H. sapiens in the Levant20, the Arabian Peninsula (Fig. 1g,h) and in southern China15. Both scenario A and B clearly reveal the impact of Dansgaard– Oeschger variability on the desert fraction and habitability of the Levant region (Extended Data Figs 5, 6, Fig. 1i). Whereas Dansgaard–Oeschger temperature and net primary production effects (Extended Data cd Figs 4, 5) on European, Mediterranean and north African population density are visible (Fig. 1g), their overall effect on global human dis- persal and arrival times is negligible, as demonstrated by repeating scenario A without Dansgaard–Oeschger variability (see Methods) (Fig. 1g–i, yellow line, Fig. 3c). To better understand the effect of glacial climate variability on the Late Pleistocene global human dispersal compared to non- ef climatic effects, we conducted three additional highly idealized sensi- tivity experiments (see Methods).