Scandinavia's first farmers slaughtered the hunter-gatherer population, study finds

Following the arrival of the first farmers in Scandinavia 5,900 years ago, the hunter-gatherer population was wiped out within a few generations, according to a new study from Lund University in Sweden, among others. The results, which are contrary to prevailing opinion, are based on DNA analysis of skeletons and teeth found in what is now Denmark.

The extensive study has been published as four separate articles in the journal Nature. An international research team, of which Lund University in Sweden is a member, has been able to draw new conclusions about the effects of migration on ancient populations by extracting DNA from skeletal parts and teeth of prehistoric people.

The study shows, among other things, that there have been two almost total population turnovers in Denmark over the past 7,300 years.

The first population change happened 5,900 years ago when a farmer population, with a different origin and appearance, drove out the gatherers, hunters and fishers who had previously populated Scandinavia.

Within a few generations, almost the entire hunter-gatherer population was wiped out.

"This transition has previously been presented as peaceful. However, our study indicates the opposite. In addition to violent death, it is likely that new pathogens from livestock finished off many gatherers," says Anne Birgitte Nielsen, geology researcher and head of the Radiocarbon Dating Laboratory at Lund University.

A thousand years later, about 4,850 years ago, another population change took place when people with genetic roots in Yamnaya -- a livestock herding people with origins in southern Russia -- came to Scandinavia and wiped out the previous farmer population.

Once again, this could have involved both violence and new pathogens.

These big-boned people pursued a semi-nomadic life on the steppes, tamed animals, kept domestic cattle and moved over large areas using horses and carts.

The people who settled in our climes were a mix between Yamnaya and Eastern European Neolithic people.

This genetic profile is dominant in today's Denmark, whereas the DNA profile of the first farmer population has been essentially erased.

"This time there was also a rapid population turnover, with virtually no descendants from the predecessors. We don't have as much DNA material from Sweden, but what there is points to a similar course of events. In other words, many Swedes are to a great extent also descendants of these semi-nomads," says Anne Birgitte Nielsen, who contributed quantitative pollen data which shows how the vegetation changed in connection with the population changes.

The results do not just overturn previous theories about amorous and peaceful meetings between groups of people.

The study also provides a deepened understanding of historical migration flows, and the interpretation of archaeological finds and changes in vegetation and land use found in palaeoecological data.

"Our results help to enhance our knowledge of our heredity and our understanding of the development of certain diseases. Something that in the long term could be beneficial, for example in medical research," concludes Anne Birgitte Nielsen.

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Ancient genomes reveal immunity adaptation in early farmers

Research from the Francis Crick Institute published today in Current Biology has revealed that diversity in genes coding for immunity may have facilitated adaptation to farming lifestyles in prehistoric periods.

Researchers at the Ancient Genomics Laboratory at the Crick studied available genome-wide DNA from 677 individuals dating to Stone Age Europe, spanning the movement of Neolithic farmers from the Near East into Europe about 8000 years ago, where they mixed with Mesolithic hunter-gatherers already in Europe.

They were interested in whether any particular genes might have coded for adaptations important to early farming groups, and looked for evidence of rapid evolution in these populations.

Since about 20% of the ancestry of descendant late Stone Age people could be traced to the local European hunter-gatherers, the researchers also asked whether any particular genes showed evidence of more hunter-gatherer ancestry.

They found that a large genetic region responsible for immune responses to diseases -- the major histocompatibility complex (MHC) -- showed both the strongest evidence of rapid evolution, and more Mesolithic hunter-gatherer ancestry than expected, suggesting that genetic variants in the MHC region already present in Europe were passed down preferentially.

It has previously been thought that the transition to farming was associated with increased natural selection on immunity variants, as people started living closer to animals and eating more animal products. This research supports this view, but also shows that diversity in immune genes may be just as important as adaptation to lifestyle.

The research team speculates that either the hunter-gatherers already had genetic adaptations against bacteria, viruses or other microorganisms in Europe, or that having many different forms of the genes was advantageous.

Tom Davy, PhD student at the Francis Crick Institute and lead author, said: "It was really exciting to see for the first time that immunity is important for the transition to farming in a prehistoric population. The later Neolithic people had far more farmer ancestry in general, so we expected to see the same at the MHC region, especially as many diseases have been linked to Neolithic periods. But we saw about 50:50 ancestry from Neolithic farmers and Mesolithic hunter-gatherers here, showing that natural selection favoured genes from the hunter-gatherers already in Europe.

"At the moment we're not quite sure whythis happened, but a proposal is that the European hunter-gatherers had genetic variations which allowed them to fight Europe-specific diseases. Or picking up a variety of genes from both hunter-gatherers and farmers was beneficial because it resulted in lots of diversity at this major group of genes, allowing people to better fight off disease."

The team also confirmed results from previous studies, showing that genes coding for skin pigmentation showed the greatest representation for Neolithic farmer ancestry, with these variations coming into Europe from the Near East. This may be to maintain vitamin D levels when sources, such as diet and exposure to sunlight, change.

Pontus Skoglund, Group Leader of the Ancient Genomics Laboratory at the Crick, said: "The shift to farming was an important transition all over the world, resulting in changing diets and exposure to infectious disease.

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