Before genetics came into the picture, researchers interested in the introduction of agriculture to Europe had only the archaeological record to go on – a limited collection of primarily stone and bone artifacts that left much room for interpretation. But as researchers began applying population genetics to the question of how farming spread across Europe, beginning with the work of Luca Luigi Cavalli-Sforza nearly 40 years ago, there began to be hope for a better understanding of how agriculture spread through the continent beginning about 10,000 years ago.
Decades of genetic research have produced some clarity. But geneticists have also created their own new sources of new debate surrounding the spread of agriculture.
Over the years, two schools of thought have jockeyed for dominance: one argues that farmers from the Near East came into Europe around 10,000 years ago, spreading both their knowledge of farming AND their descendants throughout the continent. Known as the ‘Demic Diffusion Model’, this hypothesis predicts that the majority of today’s Europeans trace their ancestry to early farmers from the Near East. The alternative hypothesis, dubbed the ‘Cultural Diffusion Model’, argues that while the practice of farming likely spread from the Near East into Europe, the farmers themselves did not. Instead, the technology was passed along from settlement to settlement, until it reached northern Europe 5,000 years later. It predicts most modern Europeans should trace their ancestry to the original Stone Age inhabitants of Europe.
As the debate has continued, newer studies have begun breaking the puzzle down into more manageable pieces, looking at particular regions within Europe to see how farming changed the demographics on a more regional level. This is exactly what new research published in the European Journal of Human Genetics seeks to do, by examining the genetic history of the Balkans in Eastern Europe in an effort to work out what was happening there nearly 10,000 years ago.
The authors of the study, including Stanford professors and 23andMe scientific advisers Drs. Peter Underhill and Roy King, focused on the Balkans chiefly because the archaeological record in this area hints at interactions between farmers from the east and the hunter-gatherers who were already living there. The researchers chose to examine the Y-chromosome, which is passed down from father to son, to see if any traces of such interactions remained in people living in the Balkans today. They sampled more than 1,200 men from Greece, Albania, Slovenia, and many other countries on the Balkan Peninsula and throughout Eastern Europe.
What they found were three major Y-chromosome haplogroups (clusters of men who share deep ancestry along the paternal line). One group pre-dated the arrival of agriculture into the region, a second arrived along with agriculture, and a third fell somewhere in between.
Specifically, more than 60% of those sampled belonged to branches of either haplogroup I or haplogroup R, both of which are believed to have arrived in Europe tens of thousands of years ago. In addition, a unique branch of haplogroup E is found at levels of 15-25% among the men tested, but only in those people hailing from the southern Balkans (such as Greece or Macedonia). Finally, up to one-fifth of the men tested fell into haplogroup J, which is common in the Near East and thought to be closely associated with both Mediterranean seafarers and the origin and spread of agriculture.
What do these figures mean? First of all, it is clear that over half of the men in the Balkans and Eastern Europe belong to haplogroups that pre-date the arrival of agriculture in the area. These mens’ paternal ancestors likely trace back to the Mesolithic hunter-gatherers. On the other hand, the 20% of men belonging to Haplogroup J likely trace their ancestry to the same Near Eastern populations where agriculture originated.
So it stands to reason that – because the authors’ samples contain both hunter-gatherer and farmer haplogroups – there was likely some kind of interaction between the two populations when they came into contact with each other nearly 10,000 years ago. More importantly, it reveals that the spread of farming into Europe cannot be pigeonholed into either the Demic Diffusion or Cultural Diffusion Model. Its spread is far more complex – and intriguing – than many initially thought.
But what about the men who traced their ancestry to that sub-branch of haplogroup E, which is typical of North or East Africans; what is it doing in the Balkans? Haplogroup E has a unique history, stretching back some 40,000 years to East Africa. From where men carrying it expanded into the Nile Valley. The authors believe this branch of Haplogroup E exited Africa almost 16,000 years ago, well before the arrival of farming, making it to the southern Balkans a few thousand years later. Men bearing the haplogroup may have been among the first converts to agriculture when Neolithic farmers arrived in the area a few thousand years after that.
So it would seem that by using genetics to piece together ancient interactions between Mesolithic hunters and Neolithic farmers, we are actually left with new questions surrounding the arrival of Haplogroup E. Who were these men who carried it? What made them expand from the Nile Valley into the Balkans, just prior to the arrival of farming? And did their presence in the Balkans influence interactions between the hunter-gatherers and the farmers from the Near East? Once again, research into the genetic signatures of the first farmers has given us both new answers, and new questions.