An early replacement of Neanderthals in Iberia by Anatomically Modern Humans

In this post we present selected parts of the paper titled “An early Aurignacian arrival in southwestern Europe“, by Miguel Cortés-Sánchez et al.

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The replacement of Middle Palaeolithic Neanderthal populations by anatomically modern humans (AMHs), which in Europe are associated with Early Upper Palaeolithic (EUP) industries, constitutes a crucial and hotly debated issue in Palaeolithic studies. This biocultural turnover has been addressed from various standpoints, including interspecies competition either in isolation or combined with climate change, environmental crises and episodic events such as volcanic eruptions. In addition, given that biological evidence, whether bones or biomolecules, is transmitted through genetic processes whereas cultural materials are transmitted via learning processes, another issue is to what extent the biological and cultural transitions are coupled with, or decoupled from, each other.

Great effort has been devoted to framing the spatiotemporal features of Neanderthal replacement, as this may help to resolve the processes that triggered population and technological turnovers. This includes determining any directionality of technological and population changes that, according to genetic and archaeological data, become recurrent events in western Europe from the Late Pleistocene onwards, generally exhibiting an east to west trend. Mousterian technocomplex replacement by Aurignacian populations is postulated to be one such east-to-west population turnover. This same directionality is documented for the Gravettian technocomplex that replaced the Aurignacian, the genetically and culturally documented Magdalenian–Azilian transition in western Europe at the beginning of the Bölling–Alleröd interstadial, and replacements within the Epigravettian cultures of southern Europe. Among European east–west population turnovers, the Mousterian–Aurignacian transition has perhaps received the most attention. This is because it is associated with the putative extinction of Neanderthals, given that Aurignacian technocomplex elements have now been securely associated with AMHs.

In comparing the early stages of the Aurignacian dispersal with subsequent transitions, two spatiotemporal anomalies emerge. The first is recorded on the Italian Peninsula, where populations manufacturing the Uluzzian industry (for some authors, a development rooted in the Mousterian lithic tradition) seemingly prevented the expansion of the early Aurignacian. The second anomaly is documented in mid-southern Iberia, where the Aurignacian expansion is postulated to have been delayed to the point of failure. The proposal that the Middle Palaeolithic technocomplex extended to the end of Marine Isotope Stage 3 (Gorham’s Cave, Gibraltar: ~32.5 calibrated thousand years before the present) has lent weight to the hypothesis that the EUP reached southern Iberia at a comparatively late date. This reinforced the validity of a particular version of the east-to-west wave-of-advance mode that set apart the ‘Iberian South’ from the rest of the Peninsula.

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Results and discussion

To reliably pin down the Neanderthal–AMH transition in southern Iberia, 17 new dates restricted to levels covering the transition of the Mousterian to the Aurignacian at the site of Bajondillo in the Bay of Málaga (southern Spain) have been integrated with previous radiometric dates, using a Bayesian approach. The Middle Palaeolithic at Bajondillo lasts for ~120 kyr, as represented by 6 archaeological levels (that is, Bj/19–Bj/14), the last of which features a Denticulate Mousterian (~50–46 cal ka bp).

The typological features of the 13,399 lithics from this Middle Palaeolithic package evidence the stasis of a Mousterian technological tradition dominated by scrapers, notches and denticulates lacking the operative schemes and maintenance items of the nuclei that typify Upper Palaeolithic technocomplexes. Our new dates reveal that the major change in technology occurs at level Bj/13 (~43.0−40.8 cal ka bp). Such a shift is no accident. At Bj/13, coincident with a striking increase in the number of blades and bladelets, blade and bladelet cores and their specific rejuvenation flakes are documented for the first time. These novelties signal the end of a Middle Palaeolithic technological tradition that lasted from ~160–46 cal ka bp.

Given the absence of transitional Middle Palaeolithic–Upper Palaeolithic technocomplexes in southern Iberia, the technological attribution of Bj/13 to the Aurignacian seems secure, but we were not able to distinguish whether Bj/13 corresponds to Proto-Aurignacian or Early Aurignacian technocomplexes. The earliest Aurignacian technocomplexes in western Europe, starting ≤ 43 cal ka bp, have been traditionally classified as Proto-Aurignacian (Mediterranean) or Early Aurignacian, which originally appears in Central Europe but later reaches its westernmost regions. To define Bj/13 as Proto- or Early Aurignacian is far from straightforward.

One reason for this is that the number of tools from Bj/13 falls below the ≥ 100 tools threshold required for a statistically reliable assignment. A second problem at Bj/13 is a lack of the bone tools normally associated with the Aurignacian—a problem shared with other Mediterranean sites. One last crucial issue in the context of this paper is that, according to the most recent studies, the Early Aurignacian is a stage of prehistory that is not clearly defined from technological and typological standpoints.

The evidence that allows us to identify Bj/13 as Proto-Aurignacian or Early Aurignacian results from a combination of chronological and stratigraphic data, complemented by historiographic and technological data. Stratigraphically, Bj/13 is firmly set above a well-defined Middle Palaeolithic package and overlaid by another Aurignacian level (Bj/11) lying below a Gravettian deposit (Bj/10). The stratigraphic package is well structured in sedimentological and micromorphological terms, and shows no inconsistency in the seriation of absolute dates independent of the long- or short-lived nature of the samples.

The range of dates obtained from the Bayesian model appears to be fully consistent with our hypothesis of the Bj/13 Aurignacian (43.4–40.0 cal ka bp) lying chronologically between Heinrich events 5 (50–47 cal ka bp) and 4 (40.2–38.3 cal ka bp). However, technologically, level Bj/11 (~37.6–32.4 cal ka bp) corresponds to an Evolved Aurignacian with blade and bladelet technologies and the characteristic tools of this technocomplex.

At Bajondillo, all six of the new accelerator mass spectrometry (AMS) dates for the Mousterian from Bj/14 derive from short-lived (< 5 years) shells of marine and terrestrial molluscs, and range between > 50 and 46 cal ka bp, the youngest ages being based on a Bayesian model. These dates calibrate this level to during or immediately after Heinrich event 5. The date obtained on a mussel from the latest Middle Palaeolithic level at the nearby Abrigo 3 site, 20 km away from Bajondillo Cave on the Bay of Málaga, falls squarely within this range of dates (that is, 50–43.1 cal ka bp).

The new Bajondillo dates are crucial for several reasons. First, they confirm the presence of a chronologically early Aurignacian in southern Iberia at ~43 cal ka bp that now shows the first appearance of the EUP to be an essentially synchronous event throughout Europe. This suggests that the dispersal of AMHs was much faster than hitherto postulated, and the expansion of the earliest Aurignacians in Europe is now increased westwards by > 1,000 km. These dates thus call into question both the gradual ‘wave-of-advance’ and the ‘Ebro frontier’ models. They also provide reference points for the attribution of early art work in Iberian caves—something that remains highly controversial. The dates suggest either extremely high mobility of early Aurignacians or well-developed networks of interchange. For early AMHs, rapid dispersal was seemingly only possible over essentially ‘empty’ territories (that is, either completely depopulated areas, as some studies suggest for southern Iberia at the time7, or areas featuring severely depleted human populations).

The Aurignacian early expansion took place between Heinrich events 5 and 4, when cold and steppic conditions prevailed throughout most of western Europe, including the Iberian hinterland. In light of this, it might be no coincidence that a prevalence of European EUP sites has been reported along shores or neighbouring lowlands where milder conditions prevailed and more productive environments, in terms of living resources, existed. The Aurignacian from Bajondillo Cave conforms with this pattern and is not an isolated case in Iberia, where newly recorded Aurignacian sites south of the Ebro river, such as Foradada, Cendres and Pego do Diabo, are all located on the present-day coast or its adjoining lowlands, nor in Italy (Riparo Mochi and Serino).

In eastern and southern Iberia, travelling through coasts and coastal lowlands would have been considerably easier than travelling through one of the most rugged and mountainous hinterlands in Europe. The enhanced mobility of Aurignacian populations can be inferred from their swift spread over western Europe from Glacial Interstadial 12 onwards, thus hinting at dispersals taking place across territories that were easy to traverse.

The onset of the Aurignacian cannot be detached from the demise of the Neanderthals. Inferences about the mobility and settlement patterns of southern Iberian Neanderthals are complicated due to the restricted number of Mousterian sites, as well as the prevalence of low sea-level stands during this period, which means that an undetermined, yet probably substantial, fraction of the evidence presently lies underwater. From this perspective Bajondillo Cave is of great relevance since, due to its topography, it was at all times located on or very close to the shore (that is, not more than 5 km distant), but never flooded. The data from Bajondillo Cave and other coastal Iberian locations reveal that stasis, as exemplified by around 120 kyr of Neanderthal occupation with no clear traces of technological developments, prevailed during the Iberian Mousterian. Similar trends are also documented—albeit in in a more restricted manner—at the Abrigo 3 and Gorham’s Cave sites. All constitute evidence that Neanderthals were settled along the coast well before the onset of the Aurignacian. Although the Bajondillo Cave dates do not indicate any coexistence of Neanderthals and Aurignacians, the fact that the Middle Palaeolithic ceases at around 45 cal ka bp is also worth noting. Indeed, this date is essentially synchronous with the cessation of Middle Palaeolithic levels from sites in the province of Málaga, both coastal (Abrigo 3) and inland (Zafarraya). The idea of a regional, as opposed to local, phenomenon seems compelling, as is the fact that (except for the two Bay of Málaga sites) Late Mousterian settlements are located at a substantial altitude (that is, > 400 m). A putative preferential location of late Neanderthal sites on harsher and less productive habitats than the coastal zones where older Middle Palaeolithic sites occur and the earliest AMH sites are recorded hints at a scenario of competitive displacement of Neanderthals by AMHs. This complex issue is difficult to address when a substantial proportion of the available evidence is circumstantial.

Recent reviews highlighting the genetic complexities that underlie AMH expansion in Eurasia tend to focus on data from Asia, and fail to consider the possibility that a crucial part of that evidence may lie on the westernmost tip of the Mediterranean. Given the relevance of the palaeoanthropological and archaeological data that are slowly emerging from this region, further efforts to determine whether coastal dispersals played a major role in the arrival of modern humans in the region are crucial. Given the growing evidence that humans were also capable of crossing bodies of water before 50 cal ka bp, investigation into whether the Strait of Gibraltar played any role as a connector of European Neanderthals and North African AMHs is also a promising area of research. It is within this interpretative framework that the presence of an early Aurignacian at Bajondillo Cave may bear wider implications for the origin of Upper Palaeolithic industries and the appearance of AMHs in the European subcontinent than can be foreseen now.

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Research-Selection for NovoScriptorium: Maximus E. Niles

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