Early farmers and hunter-gatherers co-existed and integrated in Europe for many years, study suggests

Research claims it has given the answers to a long-debated question among anthropologists, archaeologists and geneticists: when farmers first arrived in Europe, how did they interact with existing hunter-gatherer groups?

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Prior studies have suggested that early farmers largely replaced the pre-existing European hunter-gatherers. The current study suggests that these groups likely coexisted side-by-side for some time after the early farmers spread across Europe. The farming populations then slowly integrated local hunter-gatherers, showing more assimilation of the hunter-gatherers into the farming populations as time went on.

Early farmers show various amounts of hunter-gatherer ancestry, which had previously not been analyzed in detail.

The current study, from an international team including scientists from Harvard Medical School, the Hungarian Academy of Sciences and the Max Planck Institute for the Science of Human History, focused on the regional interactions between early farmers and late hunter-gatherer groups across a broad timespan in three locations in Europe: the Iberian Peninsula in the West, the Middle-Elbe-Saale region in north-central Europe, and the fertile lands of the Carpathian Basin (centered in what is now Hungary). The researchers used high-resolution genotyping methods to analyze the genomes of 180 early farmers, 130 of whom are newly reported in this study, from the period of 6000-2200 BC to explore the population dynamics during this period.

“We find that the hunter-gatherer admixture varied locally but more importantly differed widely between the three main regions,” says Mark Lipson, a researcher in the Department of Genetics at Harvard Medical School and co-first author of the paper. “This means that local hunter-gatherers were slowly but steadily integrated into early farming communities.”

While the percentage of hunter-gatherer heritage never reached very high levels, it did increase over time. This finding suggests the hunter-gatherers were not pushed out or exterminated by the farmers when the farmers first arrived. Rather, the two groups seem to have co-existed with increasing interactions over time. Further, the farmers from each location mixed only with hunter-gatherers from their own region, and not with hunter-gatherers, or farmers, from other areas, suggesting that once settled, they stayed put.

“One novelty of our study is that we can differentiate early European farmers by their specific local hunter-gatherer signature,” adds co-first author Anna Szécsényi-Nagy of the Hungarian Academy of Sciences. “Farmers from Spain share hunter-gatherer ancestry with a pre-agricultural individual from La Braña, Spain, whereas farmers from central Europe share more with hunter-gatherers near them, such as an individual from the Loschbour cave in Luxembourg. Similarly, farmers from the Carpathian Basin share more ancestry with local hunter-gatherers from their same region.”

(Source: https://www.sciencedaily.com/releases/2017/11/171109093100.htm)

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Abstract Ancient DNA studies have established that Neolithic European populations were descended from Anatolian migrants who received a limited amount of admixture from resident hunter-gatherers. Many open questions remain, however, about the spatial and temporal dynamics of population interactions and admixture during the Neolithic period. Here we investigate the population dynamics of Neolithization across Europe using a high-resolution genome-wide ancient DNA dataset with a total of 180 samples, of which 130 are newly reported here, from the Neolithic and Chalcolithic periods of Hungary (6000–2900 BC, n = 100), Germany (5500–3000 BC, n = 42) and Spain (5500–2200 BC, n = 38). We find that genetic diversity was shaped predominantly by local processes, with varied sources and proportions of hunter-gatherer ancestry among the three regions and through time. Admixture between groups with different ancestry profiles was pervasive and resulted in observable population transformation across almost all cultural transitions. Our results shed new light on the ways in which gene flow reshaped European populations throughout the Neolithic period and demonstrate the potential of time-series-based sampling and modelling approaches to elucidate multiple dimensions of historical population interactions.

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The population dynamics of the Neolithization process are of great importance for understanding European prehistory. The first quantitative model of the Neolithic transition to integrate archaeological and genetic data was the demic diffusion hypothesis, which posited that growing population densities among Near Eastern farmers led to a range expansion that spread agriculture to Europe. Ancient DNA analysis has validated major migrations from populations related to Neolithic Anatolians as driving the introduction of farming in Europe, but the demic diffusion model does not account for the complexities of the interactions between farmers and hunter-gatherers in Europe throughout the Neolithic period.

A principal component analysis of our samples shows that, as expected, all of the Neolithic individuals fall along a cline of admixture between FEF and WHG. Y-chromosome diversity also indicates contributions from ancestral Anatolian farmer and local hunter-gatherer populations, dominated by haplogroups G and I (the latter being especially common in Iberia). The European populations are consistent with a common origin in Anatolia, reflected by the low differentiation among Early Neolithic groups in the principal component analysis. Over the course of the Neolithic period, we observe a trend of increasing hunter-gatherer ancestry in each region, although at a slower rate in Hungary than in Germany and Spain, and with limited intra-population heterogeneity. We also find that this hunter-gatherer ancestry is more similar to the eastern WHG individuals farther east and more similar to the western WHG individuals farther west. Although this pattern does not demonstrate directly where mixture between hunter-gatherers and farmers took place, it suggests, given that European hunter-gatherers display a strong correlation between genetic and geographic structure, that hunter-gatherer ancestry in farmers was to a substantial extent derived from populations that lived in relatively close proximity.

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Our results provide greatly increased detail to our understanding of population interactions and admixture during the European Neolithic period. In each of our three study regions, the arrival of farmers prompted admixture with local hunter-gatherers, which unfolded over many centuries: almost all sampled populations have more hunter-gatherer ancestry and more recent dates of admixture than their local predecessors, suggesting recurrent changes in genetic composition and substantial hunter-gatherer gene flow beyond initial contact. These transformations left distinct signatures in each region, implying that they resulted from a complex web of local interactions rather than from a uniform demographic phenomenon. Our transect of Hungary, in particular, with representative samples from many archaeo logical cultures across the region and throughout the Neolithic and Chalcolithic periods, illustrates the power of dense ancient DNA time series. Future work with continually improving datasets and statistical models should yield many more insights about historical population transformations in space and time.

(Source: “Parallel palaeogenomic transects reveal complex genetic history of early European farmers”, by Mark Lipson et al.)

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Research-Selection for NovoScriptorium: Maximus E. Niles

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