The cultural dimension of Neanderthal-Homo sapiens interbreeding at the gateway to Eurasia

In the popular imagination Neanderthals are the archetypal ‘cavemen’, but recent research is both challenging the notion of them as simple brutes and suggesting that we Homo sapiens in part owe our global success to our close evolutionary cousins. We now know that we – Homo sapiens with a primarily African origin – benefited from acquiring Neanderthal genes for various features, reflecting their adaptation to Eurasian conditions. However, we know almost nothing about the cultural dimension of this interaction. My forthcoming British Academy postdoctoral fellowship aims to address this gap.

The consensus view until just five years ago was that Neanderthals were merely an extinct side branch of the human family tree, dwindling away in Europe in the face of the last ice age, while our ancestors were going from strength to strength in Africa. While we immodestly call ourselves Homo sapiens (‘wise man’), or ‘modern humans’, Neanderthals do not even generally receive a formal italicized designation. Initial comparisons of short sequences of DNA found no evidence for interbreeding between Homo sapiens and Neanderthals. Then, Green and colleagues (2010) published a draft sequence of the complete Neanderthal genome in the journal Science and found that living non-African humans actually feature around 1-4% Neanderthal DNA. Different people preserve different parts of the Neanderthal genome, and cumulatively more than 20% of the genome is preserved in contemporary humans. Critically, these studies have shown that many of the genes we acquired from Neanderthals were beneficial (although many were not), including genes for aspects of the immune system, the hair, and the skin (see for example Racimo et al., 2015).

It is believed that the initial phase of admixture occurred around 70 to 50 thousand years ago, perhaps in the Middle East. Within a few thousand years our species had reached Australia and Europe, perhaps aided by their new Neanderthal genes. While the Neanderthals subsequently went extinct shortly before the last ice age, our species continued to expand across the world, and in the last few tens of thousands of years our numbers have exploded.

Precisely where and when the populations interacted remains unclear. Neanderthals are best known from Europe, but recent findings have shown that they extended at least as far east as Siberia, and as far south as Jordan. The Levant is the most heavily researched region in Southwest Asia, and well-dated sites there indicate a spatial and temporal gap between Homo sapiens and Neanderthals, suggesting that admixture may have occurred elsewhere.

Ongoing research by the University of Oxford based Palaeodeserts Project (www.palaeodeserts.com), on which I have been a postdoctoral researcher since 2012, is leading to remarkable findings in Saudi Arabia. This includes stone tools very similar to those made by Neanderthals in the Levant, suggesting that the Neanderthal dispersal may have extended south into Arabia. At other sites we have discovered stone tools similar to those made by Homo sapiens in Africa. Most of these sites are located close to ancient lakes and rivers, which appear to have acted as hydrological corridors through otherwise arid regions. In environmental terms, Arabia is an interaction zone between several climatic systems. This context may have influenced demographic patterns of dispersal and population interaction. Could it be that the admixture between the species occurred in what is today the arid Arabian Peninsula? Was the initial interaction between Homo sapiens and Neanderthals calibrated by the region’s particular environmental structure (i.e. aridity and ecological patchworks)?

I will commence my British Academy Postdoctoral fellowship on January 1st 2016 to address these questions. The fascinating insights from genetic studies have so far not been matched by cultural insights. While bones of early humans are extremely rare, stone tools are abundant and by far the most commonly preserved form of material culture. My project involves conducting the first detailed comparative studies of stone tool assemblages associated with Neanderthals and Homo sapiens in the Middle East and neighbouring regions to build a cultural framework for the period of approximately 100 to 50 thousand years ago. By reconstructing patterns of learned traditions and integrating this information with data on chronology and environmental change, this project will test a series of hypotheses on different scenarios of population interaction. Did early members of our species acquire cultural as well as genetic information from Neanderthals who had survived several ice ages in Eurasia, in contrast to tropically adapted African Homo sapiens? Conversely, a lack of evidence for cultural interaction may tell us something about the mode of genetic interaction.

Recent research has radically changed the way we think about human origins. Rather than the dichotomising notions encapsulated in concepts such as the ‘missing link’ and the ‘human revolution’, this emerging evidence suggests greater complexity to human evolution and prehistory. Human prehistory was not about the appearance of modern human uniqueness and then our conquest of the world by club and spear with no help from other forms of human. The emerging picture is both more complex, and more interesting. Understanding the cultural context of Neanderthal and Homo sapiensadmixture at the Middle Eastern gateway to Eurasia will therefore both provide crucial insights into how we changed from being a rare African primate to a global species with more than seven billion living representatives, but also humanise Neanderthals and early members of our species.

References

Green, R.E., Krause, J., Briggs, A.W., Maricic, T., et al. 2010. A draft sequence of the Neanderthal Genome. Science 328, 710-722.

Racimo, F., Sankaraaman, Nielson, R., Huerta-Sánchez, E. 2015. Evidence for archaic adaptive introgression in humans. Nature Reviews Genetics 16, 359-371.

Dr Huw S. Groucutt is a currently a postdoctoral researcher on the European Research Council funded ‘Palaeodeserts’ Project at the School of Archaeology, University of Oxford. He commences a British Academy Postdoctoral Fellowship in January 2016, also at Oxford. Before his postdoctoral research, Huw read for a doctorate in archaeological science at the University of Oxford (2013), a masters degree (MSc) in palaeoanthropology at the University of Sheffield (2008), and an undergraduate (BA) degree in archaeology at the University of Sheffield (2007). Huw’s fieldwork and research focus on the Palaeolithic archaeological record of Saudi Arabia and surrounding regions, addressing in particular the responses of early humans to environmental change and interactions between different populations.