Neanderthals and humans interbred in Europe for 5,400 years

The period between ∼45,000 and 35,000 cal B.P. in Europe witnessed the so-called biocultural transition from the Middle to early Upper Paleolithic, when incoming anatomically modern humans displaced Neanderthal groups across the continent (1, 2). Significant questions still remain regarding the precise nature of this transition, the humans responsible for the various transitional early Upper Paleolithic industries, the degree of overlap between Neanderthals and modern humans, and the timing of the disappearance of the former. The European record for the transition retains its interest because it is the best-documented sequence for the disappearance of a hominin group available (3). The latest data, both radiometric and genetic, suggest Neanderthals and modern humans coexisted or overlapped for up to several thousand years in Europe until Neanderthal disappearance at around 40,000 cal B.P. (4, 5). Ascertaining the spatial attributes of Neanderthal and modern human populations in Europe is an area of active research, and a reliable chronology remains essential.



Our understanding of the biocultural processes involved in the transition have been greatly influenced by improved accelerator mass spectrometry (AMS) dating methods and their application to directly dating the remains of late Neanderthals and early modern humans, as well as artifacts recovered from the sites they occupied. It has become clear that there have been major problems with dating reliability and accuracy across the Paleolithic in general, with studies highlighting issues with underestimation of the ages of different dated samples from previously analyzed sites (6). We have been working on redating some of the purported late-surviving Neanderthal sites from around Europe, which have included human and archaeological remains from sites such as Mezmaiskaya (Russia), where a previous directly dated Neanderthal infant yielded a radiocarbon age of ∼29,000 B.P. (7), and Zafarraya (Spain), which was thought to contain Neanderthal remains clustering in age around a small group of U-series–dated animal bones between 33,400 and 28,900 B.P. (8). At Mezmaiskaya, the AMS dates obtained for the Neanderthal excavated above the previously dated individual were substantially older (9). This, along with other AMS dates from cut-marked fauna from the same archaeological horizons, suggested the original date of 29,000 B.P. could not be correct. At Zafarraya, Wood et al. (10) showed that, when redated using ultrafiltration methods, the bones that produced ages of ∼33,000 B.P. were in fact beyond the radiocarbon limit, suggesting the Neanderthal remains were unlikely to be as young as previously thought. In both cases, revised radiocarbon dates produced with more robust chemical pretreatment methods have illustrated significant underestimates in the previous dates that cannot be reconciled with a hypothesis of late-surviving refugial Neanderthals.

The Neanderthal fossil remains from level G1 of Vindija Cave in northern Croatia have remained in the literature as potentially late individuals. Given the evidence from the Peștera cu Oase specimen, which demonstrates a recent Neanderthal ancestry in a 40,000 cal B.P. modern human from the Danube corridor (5), the renewed dating of the Vindija remains is overdue.



Two specimens, Vi-207 and Vi-208, were originally directly AMS dated in the late 1990s at the Oxford Radiocarbon Accelerator Unit (ORAU). Vi-207 is a right posterior mandible and Vi-208 is a parietal fragment, both showing Neanderthal-specific morphology (11, 12). The initial radiocarbon results were 29,080 ± 400 B.P. (OxA-8296) and 28,020 ± 360 B.P. (OxA-8295) (13). Higham et al. (14) attempted to redate these specimens by taking the very small amounts of collagen remaining from the original sample pretreatment and ultrafiltering the product before AMS dating. The revised measurements were 32,400 ± 1,800 B.P. (Vi-207: OxA-X-2089-07) and 32,400 ± 800 B.P. (Vi-208: OxA-X-2089-06), which indicated the previous dates were indeed too young. For sample Vi-208, after ultrafiltration, the C/N atomic ratio was 3.4, which indicates collagen of acceptable quality. However, for Vi-207, the >30-kDa fraction obtained produced a C/N ratio of 4.3, which indicates the presence of a high molecular weight contaminant. The radiocarbon date for this sample could therefore include a higher molecular weight noncollagenous contaminant, possibly cross-linked to the collagen. On the basis of the potential problems associated with the small size of the redated samples and the potential for remaining contaminants, OxA-X-2089-06 was considered to be a minimum age (14). If the dates are even approximately correct, however, it makes them the most recent known Neanderthals. This would imply a more extensive temporal overlap between Neanderthals and early modern humans in central Europe than has recently been documented (4).

In addition to the Neanderthal remains, level G1 has yielded a small archaeological assemblage that contains techno-typologically Middle and Upper Paleolithic lithic artifacts plus several distinctively early Upper Paleolithic osseous points (12). It has been argued that the mix of Neanderthals, Middle Paleolithic tools, and Upper Paleolithic technology was the result of cryoturbation and Ursus spelaeus activity in level G1, with elements mixing into level G1 from both the Upper Paleolithic unit F above and the Middle Paleolithic level G3 below (15, 16). Zilhão (17) has suggested that the G1 lithic assemblage has parallels with the Szeletian technocomplex, and further, that there is a mixture of elements of Szeletian and Aurignacian I and II within the level [see also Svoboda (18)]. Karavanić and Smith (19) have suggested that the mixture of elements may represent the interaction and possible acculturation between modern humans and late Neanderthals. These alternatives are testable by selecting human and organic osseous points, as well as animal bones, for renewed AMS dating. This is what we have undertaken and describe here.