When ancient DNA studies began to gain attention, a little more than a decade ago, the view took hold among geneticists that everything we thought we knew about the Europeans of modern humans was wrong. The story was simpler than anyone expected: Europe was settled in just three massive migrations from the East.
First came hunter-gatherersmore than 40,000 years ago. Then, after 9000 years ago, there was an expansion of farming people from Anatolia below Neolithic age.
However, this has always been a simplification. Our new paperproduced with colleagues from the United States and across Europe, has highlighted some of the more complex interactions between ancient populations that took place in northwestern Europe.
Our research resolves the origins of prehistoric populations across Belgium and the Netherlands, as well as identifying the source population for a late Neolithic migration to Britain that appears to have led to a 90% replacement of Britain’s Neolithic farmers.
Ancient DNA research already suggested a much more nuanced picture. For example, when early Neolithic farmers first moved into Europe, they interacted little with the local hunter-gatherer peoples. As a result, although they now lived far from their homeland, their genomes still resembled their Anatolian ancestors.
But 1000–2000 years later they had absorbed significant local ancestry. Their hunter-gatherer ancestry swelled from just 10% to 30-40% in some regions. The hunter-gatherers had clearly not disappeared as farmers expanded.
Northern wetlands
The new research takes us even further from the simple picture. Almost a decade ago, our research group at the University of Huddersfield started a collaboration with palaeoecologist Professor John Stewart from Bournemouth University and archaeologists at the Université de Liège, Belgium. We analyzed the genomes of Neolithic human remains excavated along the Meuse River in Belgium, dating to around 5000 years ago.
This work became part of a larger project, led by Professor David Reich and Dr Iñigo Olalde at Harvard University, involving geneticists and archaeologists from all over Western Europe. This expanded the focus to further sites around the Lower Rhine-Meuse area – wetlands and coastal areas as well as rivers – spanning the late hunter-gatherer cultures of the Bronze Age.
The fertile soils south of the Rhine-Meuse wetlands had attracted pioneer Neolithic farming colonists as early as 5500 BC. However, the rich resources of the northern wetlands were more suited to the lifestyle practiced by hunter-gatherers. Nevertheless, the results, generated by our research student, Alessandro Fichera, in collaboration with Harvard, came as a big surprise.
The genomes of later Neolithic humans in Belgium had at least 50% local hunter-gatherer ancestry, along with the expected Anatolian farmer ancestry. Discussing these results with our collaborators led to a “eureka” moment: the same pattern emerged at other sites located in similar water-rich environments across the region.
In particular, many of the earlier Neolithic Dutch samples from further north – such as the Swifterbant culture, known to maintain a hunter-gatherer economy along with some adoption of agriculture – had almost 100% hunter-gatherer ancestry.
Women’s role in the spread of agriculture
We then compared the Y chromosome and mitochondrial DNA, which trace male and female lineages, respectively. The Y chromosomes in the Belgian remains were all characteristic of hunter-gatherers, but three-quarters of mitochondrial DNA lineages had come from Neolithic farmers living further south. The implication was clear: agricultural knowledge had been imported into the “water world” hunter-gatherer societies by women.
Our findings support a version of the “boundary mobility” or “accessibility” model of the Neolithic dispersal, proposed by archaeologists Marek Zvelebil and Peter Rowley-Conwy in the 1980s. They envisioned a contact zone between pioneer farming groups that arrived by “leap colonization” and hunter-gatherer areas.
In the model, the ‘availability’ phase involved contact and small-scale movements across the border, with, for example, trade relationships and marriage alliances gradually forming. This will be followed by a “substitution phase” where farming develops alongside foraging in the hunter-gatherer area, and finally a “consolidation” phasewhen farming dominates.
Our results suggest that the frontier was much more permeable to women than it was to men, and that it may have been the marriage of Neolithic women into the foraging communities that eventually helped hunter-gatherers to adopt full-time agriculture. After all, due to the predominance of agriculture across Europe, the likely long-term option was extinction.
Perhaps this type of model can also apply to other parts of Europe where we lack evidence for how the increased hunter-gatherer ancestors in the later Neolithic arose. In any case, the fact that the “more advanced” peasant women here married into hunter-gatherer groups, contrary to many archaeologists’ expectations that hunter-gatherers women would “marry”suggesting that perceptions need to change.
Beaker, Bronze Age and Britain
But around 4,600 years ago, people were on the move again. A new wave of settlers—pastoralist farmers eventually coming from the Russian steppe—began to infiltrate the Rhine area in the form of the Corded Ware culture. As increasing numbers moved in from the east, they were transformed – we still don’t understand exactly how – into what is known as the Bell Beaker culture.
Within a few centuries, the genetic landscape of the Rhine-Meuse region, including the wetlands, was completely reshaped. Our colleagues found that 4,400 years ago, less than 20% of the ancestry of the people living there was traced back to the earlier farmers and hunter-gatherers. At least 80% of their ancestry was now from the steppe.
The Bell Beaker people expanded rapidly and rippled on in all directions, creating the Bronze Age in Central Europe. And not just Central Europe – they also spread across the English Channel and across Britain, stretching as as far north as the Orkney Islands.
It looks as if the British farmers who had built Stonehenge through the preceding centuries all but disappeared — again, for reasons that remain unclear.
But did they really disappear? Perhaps this rather blunt picture can also become more nuanced as we learn more fine-grained details of what happened from archeology and ancient DNA.
This edited article has been republished from The conversation under a Creative Commons license. Read original article.
