DNA analysis solves the mystery of how Europeans came to be farmers

  • @SteveAConnor

It was the biggest cultural shift in European prehistory but the Stone Age transition from a lifestyle based on hunting animals and gathering wild berries to one built on farming and livestock was largely a mystery – until now.

A detailed analysis of the DNA extracted from the bones of 11 prehistoric Scandinavians who lived thousands of years ago around the Baltic Sea has shown that the transition from hunting to farming was more of a one-way takeover than previously supposed.

The genetic makeup of the people who lived through this cultural revolution has revealed that the incoming migrant farmers from southern Europe subsumed the indigenous hunter gatherers of the north, rather than the other way round, scientists said.

For years, archaeologists and anthropologists have argued over the events that led to the replacement of Europe’s long prehistoric tradition of hunter-gathering, lasting tens of thousands of years, by the relatively new practice of farming, which first appeared in the middle-east about 10,000 years ago and gradually spread west and north across the entire continent.

One suggestion was that the incoming farmers simply pushed the indigenous hunters further to the fringes, while another proposition was that it was the technology and ideas of farming, rather than the people, that gradually replaced the older practice of hunting and gathering.

However, the DNA from the 11 Stone Age skeletons dating from between about 5,000 and 7,000 years ago has revealed that the hunter gatherers actually became part of the incoming community of farmers, who were genetically distinct from the people whose lands they eventually occupied.

The study, published in the journal Science, also shows that there was no apparent influx of genes from the farmers into the gene pool of the hunter-gatherers. In other words, it was the hunter-gatherers who married into the immigrant farming families, and not the other way round, said Professor Mattias Jakobsson of Uppsala University in Sweden, who led the study.

“We know that there was a mixture and we know it was happening about 5,000 years ago in this part of northern Europe. But the mixture was not symmetrical – it was the hunter-gatherers who were assimilated into the agricultural people and not the other way round,” Professor Jakobsson said.

“The asymmetric gene-flow shows that the farming groups assimilated hunter-gatherer groups, at least partly. When we compared Scandinavian to central European farming groups that lived about the same time, we see greater levels of hunter-gatherer gene-flow into the Scandinavian farming groups,” he said.

The DNA analysis of seven hunter-gatherer skeletons and four Stone Age farmers – who lived alongside one other at about the same time but in separate communities – immediately showed a genetic difference between the two cultures, Professor Jakobsson said.

“Stone-Age hunter-gatherers had much lower genetic diversity than farmers. This suggests that Stone-Age foraging groups were in low numbers compared to farmers,” he said.

“The practice of hunting and gathering was probably more vulnerable to food shortages which would have led to population crashes that caused a genetic bottleneck and a loss of DNA diversity in hunter-gatherers,” he added.

Farming allows people to store grain in times of plenty which would have helped to keep the farming population high, and so maintaining genetic diversity. But it is clear from the DNA analysis that agricultural technology came in with an influx of genetically distinct people, rather than it being an idea passed on and taken up by bands of hunter-gatherers.

“The study shows that information spreads well when people are moving and it’s not just about the spread of ideas through communication. The change to agriculture did not happen overnight but over many generations,” Professor Jakobsson explained.

The study was not able to show whether the gene flow into the immigrant communities of farmers was the result of indigenous women or men intermarrying with farmers – or people of both sexes. However, there was a clear, asymmetric flow from hunters to farmers, and not the reverse, said Pontus Skoglund of Harvard University, who was part of the team.

“We see clear evidence that people from hunter-gatherer groups were incorporated into farming groups as they expanded across Europe. This might be clues towards something that happens also when agriculture spread to other parts of the world,” Dr Skoglund said.