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Ancient DNA Indicates Mixing Between Neolithic Farmers, Mesolithic Hunter-Gatherers

NEW YORK (GenomeWeb) – Admixture occurred between Neolithic farmers and Mesolithic hunter-gatherers, according to a new study of ancient DNA.

In much of Western and Central Europe, the transition from hunting and gathering to farming has largely been attributed to farmers arriving and replacing the hunters and gathers there. However, in Eastern Europe, farming was adopted with few genetic contributions from arriving farmers.

By sequencing ancient DNA isolated from four ancient humans from Romania, researchers led by the University of Potsdam's Michael Hofreiter aimed to examine how this transition from hunting and gathering to farming occurred there. As they reported today in Current Biology, the researchers found that there were complex interactions between hunter-gatherers and farmers in the region.

"We expected some level of mixing between farmers and hunter-gatherers, given the archeological evidence for contact among these communities," Hofreiter said in a statement. "However, we were fascinated by the high levels of integration between the two communities as reconstructed from our ancient DNA data."

He and his colleagues sequenced DNA isolated from four prehistoric individuals: an 8,700-year-old Mesolithic hunter-gatherer, two 8,800-year-old Mesolithic hunter-gatherers, and a 5,300-year-old Eneolithic individual. The Eneolithic falls between the Neolithic and the Bronze Age.

Using the Illumina HiSeq2000 platform, the researchers generated genomes for each individual with between 1.1x and 5.3x coverage. Based on the variants they uncovered within those sequences, they predicted the Romanian Mesolithic individuals had dark hair, eyes, and skin tone, and that the Eneolithic individual had dark hair, light eyes, and lighter skin. All were likely lactose intolerant in adulthood.

Hofreiter and his colleagues reported that one Mesolithic individual belonged to the mitochondrial subhaplogroup U5b, which also includes a number of Western hunter-gathers, while another Mesolithic individual belonged to U5a, which is found among Scandinavian and Latvian hunter-gatherers. The third Mesolithic individual and the Eneolithic individual both belonged to the K1 group, to which many early European farmers also belonged. The three male samples belong to the R1 and R1b haplogroups, which are common among modern Europeans.

In a principal components analysis, the Romanian Mesolithic samples clustered with other Mesolithic samples, including with two newly sequenced Spanish samples, and were close to modern Northern European populations. However the Romanian Eneolithic sample fell in a unique spot between the European Mesolithic hunter-gatherers and the Neolithic farmers.

Likewise using the clustering algorithm ADMIXTURE, the researchers found that the Romanian Eneolithic sample contained both Western hunter-gather and Neolithic farmer genetic components. That sample contained a greater portion of Mesolithic ancestry than other previously reported admixed individuals. In calculating shared genetic drift, the research noted that this sample had the closest affinity with Western hunter-gatherers and was not directly descended from the Romanian hunter-gatherers in the sample.

Stable isotope analysis further indicated that the Eneolithic individual ate a varied diet.

The researchers noted that their analysis suggested that there were complex interactions between hunter-gatherers and farmers. "Our study shows that such contacts between hunter-gatherers and farmers went beyond the exchange of food and artifacts," Hofreiter said.

He added that there appears to have been a gradient across Europe, and that increased admixture occurred between hunter-gatherers and farmers in the north and east. "Whilst we still do not know the drivers of this gradient, we can speculate that, as farmers encountered more challenging climatic conditions, they started interacting more with local hunter-gatherers," Hofreiter noted. "These increased contacts, which are also evident in the archaeological record, led to genetic mixing, implying a high level of integration between very different people."