Farming Conquered Europe at Least Twice

by Michael Balter 

Southern stock. Ancient DNA extracted from a collection of bones (upper right) excavated at the Treilles cave in the south of France indicate that some prehistoric farmers entered Europe along the Mediterranean.

Credit: © Jean-François Peiré/DRAC, Midi-Pyrénées

The rise of agriculture in the Middle East, nearly 11,000 years ago, was a momentous event in human prehistory. But just how farming spread from there into Europe has been a matter of intense research. A new study of ancient DNA from 5000-year-old skeletons found in a French cave suggests that early farmers entered the European continent by at least two different routes and reveals new details about the social structures and dairying practices of some of their societies.

Scientists studying the spread of farming into Europe have numerous questions: Was agriculture brought in primarily by Middle Eastern farmers who replaced the resident hunter-gatherers? Or did agriculture advance through the spread of technology and ideas rather than people? And was there just one wave of farming into the continent or multiple waves and routes?

Until recently, researchers had to rely on the genetic profiles of modern-day Europeans and Middle Easterners for clues. Numerous such studies, especially of Y chromosomes, which are transmitted via the paternal line, suggest that actual farmers, not just their ideas, spread westward over the millennia, eventually reaching the British Isles. Yet other studies, based on mitochondrial DNA (mtDNA), which is inherited maternally, have come to the opposite conclusion, suggesting that farmers had local European ancestry.

Now, new studies have begun to resolve these issues by sequencing the DNA of the prehistoric farmers themselves. Some of this research, most notably in Germany, suggests that male farmers entering central Europe mated with local female hunter-gatherers—thus possibly resolving the contradiction between the Y chromosome and mtDNA results.

The new paper, published online this week in the Proceedings of the National Academy of Sciences, backs up that idea. A team led by molecular anthropologist Marie Lacan of the Paul Sabatier University in Toulouse, France, reports work on ancient DNA—both mitochondrial and Y-chromosomal—from more than two dozen skeletons found in the 1930s in a cave called Treilles in southern France. Archaeologists think Treilles is a communal grave site because the bones add up to 149 individuals, 86 adults and 63 children. The team took DNA in such a way as to ensure that each individual was sampled only once (using teeth that were still attached to a lower jaw) and was able to obtain ancient DNA from 29 people.

They found that the female and male lineages seemed to have different origins. The mtDNA showed genetic markers previously identified as having deep roots in ancient European hunter-gatherer populations, but the Y chromosomes showed the closest affinities to Europeans currently living along the Mediterranean regions of southern Europe, such as Turkey, Cyprus, Portugal, and Italy. The team concludes that, in addition to the spread of farming into Central Europe suggested by the German studies, there appears to have been at least one additional route via southern Europe.

The communal grave also yielded additional intriguing details about these ancient Europeans. Most of the skeletons were males, and many appeared to be very closely related: At least two pairs of individuals were almost certainly father and son, and another pair were brothers. That suggests that the incoming male farmers established a so-called patrilocal society, in which the men stay put on their land but mate with women who come in from surrounding regions, the team concludes.

The study also showed that, in contrast to ancient DNA findings from central Europe, the people from Treilles lacked a key genetic variant that allows the body to digest lactose into adulthood. That’s consistent with other archaeological evidence that central European farmers herded dairy cows, whereas Mediterranean farmers herded sheep and goats and drank fermented milk, which has much lower lactose levels.

Lounès Chikhi, a geneticist at Paul Sabatier University who has studied the spread of farming for many years, praises the team for getting both Y chromosome and mtDNA from the same skeletal collection. “We have been calling for exactly this kind of data,” Chikhi says, “so I am very excited.” Colin Renfrew, an archaeologist at the University of Cambridge in the United Kingdom, agrees that the findings support a second, southern European spread of farming. “They do indeed suggest a significant population influx from the Eastern Mediterranean.”

But Wolfgang Haak, a geneticist at the University of Adelaide in Australia, says that Treilles may be too young to provide reliable information about the spread of farming in southern Europe, which began at least 2000 years earlier. While these earlier migrations “should have left a genetic mark in later periods,” Haak says, Treilles might not be the “best candidate” for tracing them. The ancient DNA Lacan is now extracting from skeletons across France and Spain, Haak says, should provide more “piece[s] of the enormous puzzle we are trying to put together.”