Seven thousand years of cultural sharing in Europe between Neanderthals and modern humans

Two years ago material excavated from the Bacho Kiro cave in Bulgaria revealed that anatomically modern humans (AMH) had lived there between 44 and 47 ka ago: the earliest known migrants into Europe. Bacho Kiro contains evidence of occupancy by both Neanderthals and AMH. This discovery expanded the time over which Europe was co-occupied by ourselves and Neanderthals. The latter probably faded from the scene as an anatomically distinct group around 41 to 39 ka, although some evidence suggests that they lingered in Spain until ~37 ka and perhaps as late as 34 to 31 ka in the northern Ural mountains at the modern boundary of Europe and Asia. For most of Europe both groups were therefore capable of meeting over a period of seven to eight thousand years.

Aside from interbreeding, which they certainly did, palaeoanthropologists have long pondered on a range of tools that define an early Upper Palaeolithic culture known as the Châtelperronian, which also spans the same lengthy episode. But there have been sharp disagreements about whether it was a shared culture and, if so, which group inspired it. Evidence from the Grotte du Renne in eastern France suggests that the Neanderthals did abandon their earlier Mousterian culture to use the Châtelperronian approach early in the period of dual occupancy of Europe.

Dated appearances in France and NE Spain of Neanderthal fossils (black skulls), Châtelperronian artefacts (grey circles) and proto-Aurignacian artefacts (white squares) in different time ‘slots’ between 43.4 and 39.4 ka. (Credit: Djakovic et al., Fig. 3)

Igor Djakovic of Leiden University in the Netherlands , Alastair Key of Cambridge University, UK, and Marie Soressi, also of Leiden University have undertaken a statistical analysis of the geochronological and stratigraphic context of artefacts at Neanderthal and AMH sites in France and NW Spain during the co-occupancy period (Djakovic, I., Key, A. & Soressi, M. 2022. Optimal linear estimation models predict 1400–2900 years of overlap between Homo sapiens and Neandertals prior to their disappearance from France and northern Spain. Scientific Reports, v. 12, article  15000; DOI: 10.1038/s41598-022-19162-z). Their study is partly an attempt to shed light on the ‘authorship’ of the novel technology. The results suggest that the Châtelperronian (Ch) started around 45 ka and had disappeared by ~40.5 ka, along with the Neanderthals themselves. Early AMH artefacts are known as proto-Aurignacian (PA) and bear some resemblance to those of Châtelperronian provenance. The issue revolves around 3 conceivable scenarios: 1. the earliest AMH migrants brought the PA culture with them that Neanderthals attempted to copy, leading to their Ch tools; 2. Neanderthals independently invented the Ch methodology, which AMH adopted to produce PA artefacts; 3. both cultures arose independently.

Djakovic and colleagues have found that the data suggest that the proto-Aurignacian first appeared in the area at around 42.5 ka. Maps of dated human remains and artefacts for six 400-year time ranges from 43.4 to 39.4 ka show only Neanderthal remains and Châtelperronian artefacts from the earliest range (a in the figure). Two sites with proto-Aurignacian artefacts appears in NW Spain during the next ‘slot’ (b) then grow in numbers (c to e) relative to those of Châtelperronian provenance, which are not present after 40 ka (f) and neither are Neanderthal remains. These data suggest that local Neanderthals may have made the technological breakthrough before the appearance of the AMH proto-Aurignacian culture, which supports scenario 2 but not 1. They also suggest that the sudden appearance of Ch in France and Spain and the abandonment of earlier Neanderthal artefacts known as Mousterian could indicate that the Ch culture may have been introduced by Neanderthals migrating into the area, perhaps from further east where they may have been influenced by the earliest known European AMH in Bulgaria: i.e. tentative support for 1 or 2.

However, well documented as Djakovic et al.’s study is, it considers only 17 sites across only a fraction of Europe and a mere 28 individual artefacts each from Neanderthal and AMH associations (56 altogether). More sites and data are bound to emerge. But the study definitely opens exciting new possibilities for cultural ‘cross fertilisation’ as well as the proven physical exchange of genetic material: the two seem very likely to go hand-in-hand. Seven thousand years (~350 generations) of mutual dependence on the resources of southern Europe surely signifies too that the initially distinct groups did not engage in perpetual conflict or ecological competition, as with small numbers of both one or the other would have been extinguished within a few generations.

 See also: Devlin, H. 2022. Neanderthals and modern humans may have copied each other’s tools. The Guardian, 13 October 2022; Davis, N. 2020. Humans and Neanderthals ‘co-existed in Europe for far longer than thought’. The Guardian, 11 May 2020.

Wider traces of the elusive Denisovans

We know that when anatomically modern humans (AMH) arrived in Asia they shared the landscape with ‘archaic’ humans that had a much longer pedigree. In 2010 an individual’s little-finger bone dated to around 30 to 49 ka old was found in the Denisova Cave in central Siberia (at 50°N). It yielded a full genome that was distinctly different from those of AMH and Neanderthals (see: Other rich hominin pickings; May 2010). Four other fossils found subsequently in the Denisova Cave contained similar DNA. Checking the DNA of living humans and fossil Neanderthal remains revealed that the newly discovered human group had interbred with both. In the case of AMH, segments of Denisovan DNA are found in the genomes of indigenous people living in East and South Asia, Australia, the Pacific Islands and the Americas, at levels of 0.2%, rising to 6% in Melanesian people of Papua-New Guinea. But such introgressions have not been found in Europeans (but see below), suggesting that the Denisovans were restricted to Asia.

There have been suggestions that at least some of the ‘archaic’ human remains found widely and abundantly in China may have been Denisovans; although they might equally be of Homo erectus. But none of the Chinese fossils have been subjected to gene sequencing – those found in caves outside tropical and sub-tropical climates might retain DNA just as well as Neanderthal and even older remains in temperate Europe. Yet a partial lower jaw discovered in a cave on the Tibetan Plateau (at 35°N) did yield proteins that had close affinities to those recovered from Siberian Denisovans. Now similar analyses have been performed on an abnormally large molar found in a cave in Northern Laos, showing that it too is most likely to be from a young (as suggested by its being little worn), possibly female (it lacks male-specific peptides), Denisovan. The locality lies at about 20°N, far to the south of the other two Denisovan sites (Demeter, F. et al. A Middle Pleistocene Denisovan molar from the Annamite Chain of northern Laos. Nature Communications, v. 13, article 2557; DOI: 10.1038/s41467-022-29923-z). Sparse as the evidence is, Denisovans were able to tolerate climate differences across 30 degrees of latitude.

A probable Denisovan molar from 164 to 131 ka old cave sediments in northern Laos. (credit: Demeter, et al.; Fig. 2)

The Wikipedia entry for Denisovans is a mine of additional information. For instance, detailed analysis of the roughly 5% of their genome that indigenous people of New Guinea carry suggests that the two groups may have interbred there as late as 30 ka. Since Both New Guinea and Australia were until 8 thousand years ago part of the Sahul landmass when sea level was low during the last ice age, these inferences add tropical occupancy to the Denisovan range. Does this suggest that Papuans and indigenous Australians migrated with Denisovans, or had the latter crossed the sea from Timor earlier and independently, after moving from Asia by ‘hopping’ from island to island through eastern Indonesia? There is a possibility that Denisovans could even have survived in Sahul until as late as 14.5 ka. Even more odd, modern Icelandic people are unique among Europeans in having detectable traces of Denisovan DNA. However, rather than having been directly shared between Denisovans and ancestral Scandinavians – a possibility – it may have been carried by Neanderthal-Denisovan hybrids migrating westwards from Siberia with whom the Icelanders’ ancestors interbred. There are other interesting points in the Wikipedia entry. One is that the consistently lower Denisovan ancestry in living East Asians compared with people of Oceania, may indicate two separate waves of eastward migration by AMH. The latter may have arrived first, had greater contact with Denisovans and then moved on across seaways to remain isolated from the later migrants.

Finally, something that puzzles me as a non-geneticist. If both Denisovans and Neanderthals died out as genetically distinct groups tens of millennia ago how could the genetic traces of interbreeding with AMH have been retained at such high levels until the present; i.e. through thousands of generations? Each of us carries a 50% deal of genes from our parents. Then with each subsequent generation the proportion is diluted, so that we inherit 25% from grandparents, 12.5 % from great-grandparents and so on. Yet Papuans still have 5 to 6 percent of Denisovan DNA: much the same holds for Europeans’ Neanderthal heritage. Does such a high level of retention of this ancestry suggest that a large proportion of the earliest migrating AMH individuals stemmed from generation to generation interbreeding on a massive scale? Did the ‘newcomers’ and ‘locals’ band eventually together almost completely to merge genetically, or am I missing something … ? Probably