Multiple hominin dispersals into Southwest Asia over the past 400,000 years

Pleistocene hominin dispersals out of, and back into, Africa necessarily involved traversing the diverse and often challenging environments of Southwest Asia1–4. Archaeological and palaeontological records from the Levantine woodland zone document major biological and cultural shifts, such as alternating occupations by Homo sapiens and Neanderthals. However, Late Quaternary cultural, biological and environmental records from the vast arid zone that constitutes most of Southwest Asia remain scarce, limiting regional-scale insights into changes in hominin demography and behaviour1,2,5. Here we report a series of dated palaeolake sequences, associated with stone tool assemblages and vertebrate fossils, from the Khall Amayshan 4 and Jubbah basins in the Nefud Desert. These findings, including the oldest dated hominin occupations in Arabia, reveal at least five hominin expansions into the Arabian interior, coinciding with brief ‘green’ windows of reduced aridity approximately 400, 300, 200, 130–75 and 55 thousand years ago. Each occupation phase is characterized by a distinct form of material culture, indicating colonization by diverse hominin groups, and a lack of long-term Southwest Asian population continuity. Within a general pattern of African and Eurasian hominin groups being separated by Pleistocene Saharo-Arabian aridity, our findings reveal the tempo and character of climatically modulated windows for dispersal and admixture. Dated palaeolake sequences show that there were at least five Pleistocene hominin expansions into the Arabian interior, coinciding with windows of reduced aridity between 400 and 55 thousand years ago.

Despite these advances, the few reported sites in interior and northern Arabia 20,24-29 (Supplementary Information, section 1) have small sample sizes of artefacts, and are often raw material procurement and workshop sites, with a very different character to the cave and rockshelter 'living sites' that dominate the Levantine woodland record. The absence of permanent fluvial systems and deeply stratified cave sequences in Arabia has hampered the construction of long-timescale archaeological and hydroclimatic sequences. This has limited efforts to recognize important patterns in archaeological and palaeontological records associated with changes in hominin distribution, demography and behaviour.
Here we report multiple palaeolake sedimentary sequences with associated lithic (stone tool) assemblages and fossil fauna in the Nefud Desert of northern Arabia, representing the first detailed long-timescale record of hominin occupations in Arabia (Figs. [1][2][3]. Khall Amayshan 4 (KAM 4) consists of a series of superimposed lake sequences within a single interdunal basin (Extended Data Figs. 1, 2, Supplementary  Information, sections 2, 3). This site, currently unique in Arabia, has preserved a record analogous to the detailed fluvial archives preserved in regions such as northwest Europe. Additionally, we present further evidence for multiple hominin occupations from excavated sites dating to Marine Isotope Stage (MIS) 7 and MIS 5 from the nearby Jubbah palaeolake basin. Together the KAM 4 and Jubbah assemblages show that there were multiple hominin dispersals into Arabia over the last 400,000 years, in association with a unique hydroclimate record.
Each KAM 4 palaeolake deposit is stratigraphically similar, being predominantly composed of massive or finely-laminated carbonate rich marls overlying sands (Extended Data Figure 3, Supplementary  Information, section 3). The similarity of these marls, each formed by a discrete lake phase, implies that the palaeoenvironment of KAM 4 was broadly similar during successive humid phases. The sediments are comparable to other palaeolake deposits from the western Nefud Desert 18,20 , but are notable for their stratigraphically distinct and superimposed character, and abundance of associated lithics and fossils. The sediments at the site are fine-grained (sands, silts and marls), reflecting deposition under low-energy or still-water conditions. Larger clasts (gravels) are absent, emphasizing the lack of higher-energy current flow processes feeding the basin during sediment accumulation. Reworking of lithics and fossils from the surrounding landscape into these lake bodies is therefore highly unlikely. Consequently, we argue that the assemblages of lithics and the fossils found in association with these deposits are in situ, which was confirmed by excavations in the case of the Northwest Lake.
The unique KAM 4 record has survived owing to migrating sand dunes that moved in a conveyor-belt-like fashion across the basin, protecting older parts of the sequence from erosion and preventing the mixing of the distinct archaeological and palaeontological assemblages associated with each lake phase. KAM 4 provides the first long-term composite sequence for the later Middle Pleistocene and Late Pleistocene in Arabia, with each phase of hominin occupation associated with a broadly similar environment and lithic raw material availability.
The oldest deposit at KAM 4, the Central Lake, is dated by luminescence to 412 ± 87 ka (Fig. 2, Extended Data Figs. 2, 3, Supplementary Information, section 5). The Central Lake deposits are also heavily iron-stained compared with other deposits at the site, attesting to their greater antiquity within the basin. The Central Lake is stratigraphically overlain by the southernmost edge of the Northeast Lake, which yielded luminescence ages of 337 ± 39 ka and 306 ± 47 ka. Although the age estimates for both the Central and Northeast Lakes have large uncertainties, we emphasize evidence for regional aridity in the millennia either side of both MIS 11 and 9 (Fig. 2), making attribution of Central Lake to MIS 11 and Northeast Lake to MIS 9 parsimonious. The Northwest Lake, which partly overlies the Northeast Lake, is dated by a suite of luminescence estimates on carbonate-rich sands bracketed between two phases of marl deposits to between 192 ± 20 ka and 210 ± 16 ka. A direct U-series age estimate of a bovid fossil from the same layer produced a consistent date of 205 ± 2 ka (2σ) (Supplementary Information, section 6). The Northwest Lake can therefore be correlated with MIS 7, the final humid phase of the Middle Pleistocene. The Southwest Lake has a luminescence estimate of 143 ± 10 ka, and therefore dates either to late MIS 6 or, less probably, to the transition to MIS   Article the Southeast Lake, which overlies the Central and Northeast Lakes, yielded luminescence estimates of 159 ± 11 ka to 149 ± 9 ka, similar to the South Lake at 168 ka ± 12 ka to 142 ± 13 ka. These maximum age estimates derived from underlying sand indicate that the Southeast and South Lakes date to either the final millennia of the Middle Pleistocene or, more probably, to the subsequent Late Pleistocene. As discussed below, we hypothesize on archaeological grounds that the South Lake dates to MIS 5 and the Southeast Lake to early MIS 3. The Jubbah record, consisting of excavated stratified lithics, enables us to further extend the occupation sequence of the region. Substantially enlarged excavations at Jebel Qattar 1 ( JQ 1) increased the sample size of lithics dating to 211 ± 16 ka reported by ref. 28 by 250%. At Jebel Umm Sanman 1 ( JSM 1), four new trenches were placed immediately west of earlier test excavations 28 . The JSM 1 trenches revealed deep (more than 1.5-2.5 m) stratigraphic sequences, comprising a series of silty sands with variable frequencies of local gravel clasts. Luminescence dating indicates that the lower part of the JSM 1 sequence dates to 130 ± 10 ka, whereas the upper part, in which lithics were found, dates to approximately 75 ka (77 ± 7 ka, 72 ± 6.4 ka) (Supplementary Information, section 5).
Each phase of lake formation (apart from the Southwest Lake) at KAM 4 is associated with a distinct lithic assemblage (Fig. 3, Extended Data Figs. 4-8, Supplementary Information, section 7). Assemblage A (Central Lake, approximately 400 ka) consists of handaxes and associated debitage (Extended Data Fig. 4) and is the oldest dated Acheulean assemblage in Arabia. It shows the production of small and refined handaxes produced by shaping (façonnage) of angular slabs of quartzite. Assemblage B (Northeast Lake, approximately 300 ka) is also characterized by the production of small handaxes (Extended Data Figs. 5, 6). These handaxes are rather homogeneous in their technology and morphology, being small and pointed. Core reduction technology to produce flakes is also present in low frequencies in assemblage B, mostly characterized by preferential Levallois reduction. The subsequent assemblage C (Northwest Lake, approximately 200 ka) shows a Middle Palaeolithic technology. Lithics recovered from the surface and from excavations show a complete absence of handaxe manufacture, and a focus on Levallois technology, often centripetal in character (Extended Data Fig. 7), but somewhat diverse (Supplementary Information, section 7). Assemblage D (Southeast Lake, approximately 125-75 ka) and assemblage E (South Lake, approximately 55 ka) are both of Middle Palaeolithic character-assemblage D has a focus on centripetal Levallois technology and assemblage E has a somewhat diverse technology, but with a strong component of unidirectional-convergent preparation to produce convergent Levallois flakes.
With the enlarged excavations at JQ 1, the assemblage dating to approximately 210 ka has a clearly Middle Palaeolithic character; Levallois flakes are present, and bifacial technology is absent (Supplementary Information, section 8). The JSM 1 assemblage from approximately NW Lake IL U-series US S1 S11 S10  28 . c, Al Wusta 20 . d, JSM 1 (present study). e, Central (C), Northeast (NE), Northwest (NW), Southwest (SW), Southeast (SE) and South (S) lakes at KAM 4. US, an age for sands underlying the lake (that is, a maximum age for overlying phase of lake formation); IL, in lake (direct date on sediments within lake-related deposits). Black arrows pointing to the left (Southeast and South Lakes) reflect that the luminescence ages provide maximum ages, and the overlying lakes are younger. Filled symbols show quartz ages and open symbols show feldspar ages. f, East Mediterranean sapropel record 35 , insolation 36 (grey), monsoon index 37 (black) and oxygen isotope record 38 (blue). Southern Arabian humid periods are defined by speleothems in green 21 . Luminescence ages are presented with 1σ uncertainties and the single U-series age is presented with a 2σ uncertainty. northern Arabia, and shows a clear focus on centripetal Levallois reduction, with 83% of Levallois flakes having centripetal scar patterns (Extended Data Fig. 9).
This unique record of hydroclimate and associated hominin occupations demonstrates that Acheulean Lower Palaeolithic technology was present during late Middle Pleistocene wet phases, with Levallois technology being present in the final stage of the Acheulean. Assemblages showing similarities to the Acheulo-Yabrudian of the Levantine woodlands have not been identified in Arabia, highlighting distinct trajectories within Southwest Asia. From MIS 7, Arabian Middle Palaeolithic assemblages appear with each phase of increased precipitation, showing varying technological foci in terms of the reduction methods used, from varied Levallois in MIS 7, to centripetal Levallois in MIS 5 3,20 , and unidirectional-convergent in MIS 3 23 Animal fossils (primarily vertebrates) from KAM 4 allow us to reconstruct the palaeoenvironmental and biogeographical context of hominin occupations. Hippopotamus fossils had previously been reported in Arabia from MIS 5 contexts (fer example, in refs. 20,33 ). KAM 4 shows that hippopotamuses were also present during MIS 7 and, provisionally, MIS 9 ( Supplementary Information, section 10). We also identified hippopotamus in the surface scatter of fossils at the nearby site of Ti's al Ghadah. The repeated presence of hippopotamuses, which are obligate semi-aquatic mammals that require permanent water bodies several metres deep, provides powerful evidence for the extent of environmental amelioration during repeated 'green Arabia' pluvial phases. In addition, the KAM 4 palaeontological assemblages contribute to a growing corpus of evidence indicating that Arabian mammal fauna had stronger affinity with Africa in the Middle and Late Pleistocene than with the Levantine woodland zone 4,33 . The presence of African bovid taxa such as Syncerus and Hippotragus in northern Arabia indicates the repeated establishment of contiguous regions of grasslands across North Africa and Arabia with abundant freshwater, providing dispersal routes for a variety of species, including hominins. Arabia, however, also features Eurasian and endemic taxa ( Supplementary  Information 10), indicating that it was a key biogeographical nexus between Africa and the rest of Eurasia that may have also comprised an important interaction zone for hominins.
The northern Arabian late Middle Pleistocene lithic assemblages likewise show greater similarities to African assemblages than to those of Levantine woodland zone sites. The continued production of large handaxes and cleavers in central Arabia at the time the Middle Palaeolithic had appeared in northern Arabia 24 indicates high levels of population structure at this time, perhaps to the extent of different hominin species occupying the region. In MIS 5, it seems that much of Northeast Africa and Southwest Asia shared similar material culture, consistent with widespread dispersals of H. sapiens 20 . Subsequently the cooling and aridification of the last glacial cycle led to the fracturing and decline of populations. Renewed dispersals, perhaps including Neanderthals from the north, occurred during the partial amelioration of early MIS 3 (around 59-50 ka). Comparatively stable environmental and ecological conditions in areas such as the Levantine woodland fostered the development of distinctive localized material culture phases 11 . By contrast, the record of interior northern Arabia indicates pulses of occupation during episodic phases of increased environmental humidity, seemingly followed by repeated regional depopulation under increasing aridity.
We have identified at least five pulses of human dispersal into northern Arabia, each associated with a phase of decreased aridity. The differences in material culture between these phases-with two phases of Acheulean technology and then three distinct forms of Middle Palaeolithicsuggests that diverse hominin populations, and probably even species, were expanding into the region at different times (we discuss the implications of our findings further in Supplementary Information, ~400 ka~300 ka~200 ka~125-75 ka~55 ka (?) Article section 11). The emerging palaeoanthropological record of Arabia highlights the dynamism and regional distinctiveness of Middle and Late Pleistocene hominin demography and behaviour in different parts of Southwest Asia. These processes were intimately connected to regional climatic changes. The available record emphasizes pulsed, long-ranging terrestrial dispersals followed by local variation, and finally population contraction. Given the temporal overlap of radically different technologies within Arabia, and the biogeographical evidence for faunal mixture, it is possible that some of the hominin admixture processes identified by genetic analyses occurred in this region. Arabia, and Southwest Asia more generally, is therefore a key region for unravelling not only the increasingly complex history of how our species spread beyond Africa, but more broadly, how our species' recent success relates to a longer history of hominin dispersals, regional developments and admixture, which occurred in a context of marked environmental oscillation.

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Methods
Site identification and survey KAM 4 was initially identified through remote sensing analysis 26 (Supplementary Information, section 2). Two main seasons of research were conducted at the site (2014 and 2017) as part of the Palaeodeserts/Green Arabia Project. The site was systematically surveyed with pedestrian transects. Using a total station and Trimble XRS Pro Differential Global Positioning System, the topography of the site was recorded in detail, and all points of interest (stone tools, fossils and sedimentary features) were recorded and entered into a geographic information system. JSM 1 and JQ 1 were first identified in 2011 28 . We carried out renewed excavation of the sites in 2013. With JQ 1, the stratigraphic sequence was already understood, so the aim was simply to increase the sample size of lithics. At JSM 1, the original excavations had rapidly hit bedrock, so renewed excavations were conducted slightly further west in the hope of identifying deeper stratigraphic sequences.

Stratigraphy and sedimentology
Sections for sedimentary analysis and luminescence sampling were excavated for each of the palaeolake phases at KAM 4 ( Supplementary  Information, section 3). The Northwest Lake was identified as having the best potential to recover buried material, as fossils and lithics appeared to be emerging from sediments, so four trenches (1-4) were dug here. These trenches and the excavations at JSM 1 and JQ 1 ( Supplementary  Information, section 4) were conducted using single-context excavation methods. All sediments were dry sieved through 5-mm mesh. The focus of this paper is on the archaeological assemblages, and not detailed palaeoenvironmental analysis so our sedimentary description consists of field observations from logging sections. Fossils from KAM 4 have previously been reported 33 .

Chronometric dating methods
We used luminescence (OSL on quartz and pIRIR on feldspar) methods to date the sedimentary deposits at KAM 4 and at JSM 1 ( Supplementary  Information, section 5). These measure the time since sediments were last exposed to sunlight. Opaque metal tubes were hammered into cleaned sections, transported to the UK and analysed as described in Supplementary Information, section 5. Environmental dose rates were calculated using location and overburden density (cosmic rays), field gamma spectrometry (gamma), and thick-source beta counting (beta). A bovid tooth (KAM16/85) was recovered from unit 3 of the Northwest Lake at KAM 4. A direct age was obtained using the U-series dating method, which dates the moment uranium is incorporated into the fossil. Powdered samples of both enamel and dentine tissues were drilled from the tooth at Griffith University, and U-series analyses were subsequently carried out at the University of Queensland. While it was initially planned to combine with electron spin resonance analyses, the U-series results obtained showed that the tooth was not suitable for that purpose ( Supplementary Information, section 6).

Lithic analysis
Lithics (stone tools) from the excavations at all sites and from the systematic transect survey at KAM 4 were studied using the methodology described previously in refs. 9,20 and in Supplementary  Information, sections 7, 8. Our initial focus was on describing the basic typo-technological features of the assemblages. We selected illustrative examples for photography, 3D scanning, and illustration. For the Middle Palaeolithic samples, we carried out a full metric and attribute analysis following the above references and references therein. As well as allowing the description of the assemblages in quantitative terms, we focussed on the characteristics of Levallois flakes from these assemblages as a way to compare assemblages. We did this both in terms of univariate features (such as dorsal scar patterns), and using PCA to compare the morphology of Levallois flakes between the assemblages ( Supplementary Information, section 8).

Reporting summary
Further information on research design is available in the Nature Research Reporting Summary linked to this paper.

Data and code availability
Data for the PCA analysis are archived at https://doi.org/10.5281/ zenodo.5082293. All other relevant data are included in the paper and Supplementary Information.

Corresponding author(s): Huw Groucutt, Michael Petraglia
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Statistics
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Data
Policy information about availability of data All manuscripts must include a data availability statement. This statement should provide the following information, where applicable: -Accession codes, unique identifiers, or web links for publicly available datasets -A description of any restrictions on data availability -For clinical datasets or third party data, please ensure that the statement adheres to our policy All relevant data is included in the paper and SI, or for the PCA analysis the data and code is archived at DOI: 10 All studies must disclose on these points even when the disclosure is negative.

Study description
Stone tools and samples for chronometric dating were collected from archaeological sites in the western Nefud Desert of Saudi Arabia. Stone tools were described both qualitatively and with descriptive statistics. For the comparison of Levallois flakes, the structure of the dataset was explored using PCA analysis of standard metric measurements, with comparative material selected from neighbouring regions. No experimental factors or control groups were used in such analyses, where PCA was conducted on the dataset and then data were plotted by assemblage name. Luminescence dating was conducted to determine the ages of the assemblages.

Research sample
The locations of study sites were determined by a combination of remote sensing and field prospecting. Systematic pedestrian transects were conducted across the sites and all objects of interest (lithics, fossils, etc.) were recorded using a differential GPS system or total station. Excavations following standard archaeological practices were conducted in areas of particular interest (i.e. with high artefact densities). Sections of trenches were samples for luminescence dating and palaeoenvironmental analysis. For the PCA analysis comparing Levallois flake morphologies, a series of assemblages from surrounding regions were sampled.

Sampling strategy
For the comparative lithic aspect, for large assemblages, Levallois flakes were sampled to give sample sizes of several dozen. Sufficient sample sizes were judged as being larger than the number of pieces included in complete assemblages.

Data collection
The main forms of data collected for this interdisciplinary study consist of 1) lithic artefacts, which were studied by Huw Groucutt, Eleanor Scerri, and James Blinkhorn. Standard metrics and technological classifications were recorded using goniometers and entered into excel files, 2) Luminescence dating was carried out by Eric Andrieux, Simon Armitage and Richard Clark-Wilson, with input from Laine Clark-Balzan; Gamma dose rates for samples prefixed "PD" were measured using an EG&G Ortec digiDart-LF instrument while for those prefixed "JSM" or "KAM4-OSL", an Inspector 1000 was used. Luminescence measurements were performed using Risø TL/OSL-DA-15 or Risø TL/OSL-DA-20 instruments. Beta dose rates for "JSM" and "PD" samples were measured using a Risø GM-25-5 low-level beta counting system, 3) U-Series dating was conducted by Gilbert Price and Mathieu Duval. Drilling was conducted at Griffith University, and U-Series dating at the University of Queensland Timing and spatial scale Fieldwork and initial data collected during field seasons in Saudi Arabia in 2013 to 2015. All analyses were conducted in an intermittent manner from 2013 onwards and were completed in 2020.

Data exclusions
All data collected were analysed and contributed to the final conclusions

Reproducibility
The archaeological analyses are descriptive, and reproducibility is possible by re-analysis of the data. The luminescence component of this study involved measurements of multiple individual quartz and K-feldspar grains, or multi-grain aliquots of the same, yielding distributions of equivalent-dose estimates from which the weighted mean was calculated using well-established statistical models (see SI).

Randomization
The only aspect this applies to is a few cases where Levallois flakes were sampled from large assemblages. A random sample of flakes laid out on a table was taken. These data were used for descriptive statistics, categorised by the relevant assemblage.

Blinding
No blinding was conducted as we are reporting descriptive statistics, not experimental results.
Did the study involve field work?

Yes No
Field work, collection and transport Field conditions Fieldwork was conducted in warm (typically in the 20s C) and dry conditions in Saudi Arabia in two main fields seasons.

Location
The sites are located in the western Nefud Desert, in northern Saudi Arabia. Supplementary table S1 gives more information.
Access & import/export Permission to conduct the research and relevant export permits were provided by the Saudi Ministry of Culture. Multiple permits were provided to M.D. Petraglia from 2010 onwards.

Disturbance
Excavations were backfilled