THE NEOLITHIC REVOLUTION WAS A KEY MOMENT IN THE PREHISTORY OF HUMANS. It sparked civilisation as we know it- settlements were established, crops were grown and animals were domesticated transforming the economy of subsistence globally. Beginning in the Levant (Near East) around 12,000 years ago, the Neolithic Revolution spread into Europe 8000 years ago and lasted up until 4000 years ago when the Bronze Age began.
The major question is how did this revolution spread? Did the indigenous hunter gatherers adopt farming solely though cultural transmission? Or did the farmers pass on their practices alongside their genes? These two models (see diagram) – culturally diffused model (CDM) and demic diffused model (DDM) – originally seen as two polar opposites as mechanisms of the spread, have been debated throughout the 20th century. By identifying the proportion of Mesolithic/ hunter-gatherer and Neolithic/ farmer genes within the current gene pool (see diagram), the correct model could be identified.
Classical genetic markers in present day populations (such as blood groups) appear to lend support to the DDM revealing a genetic cline from the Near East towards the West. But modern genetic markers can reflect population processes that have taken place both before and after the Neolithic spread. Instead ancient DNA (aDNA) provides a unique window of opportunity to look back into the past. Ancient DNA studies do come fraught with difficulties. Over time DNA degrades and fragments into short molecules. Usually this means any contaminating modern DNA is favourably extracted and analysed instead. Nevertheless strict and rigorous protocols exist to minimise contamination and new technology has been optimised for aDNA extraction.
The archaeological record has shown that as farmers migrated across Europe, two different routes were taken as indicated by distinct ceramic styles. One route was through Central Europe, from Hungary to Slovakia, Ukraine and through to Paris, as shown by the Linearbandkeramik (LBK) and Alföldi Vonaldiszes Kerámia (AVK) pottery styles. The other route represented with Impressed Ware/Cardial culture was along the Mediterranean coast. aDNA studies have been conducted on samples from these different sites and cultures, and the picture that emerges is one more complex than just picking one model over the other. It certainly appears that the two routes have their own model: while the Central Europe/ LBK route shows little to no genetic continuity between the Mesolithic hunter-gatherers and the Neolithic farmers, the Mediterranean route tends towards genetic continuity and therefore a level of gene flow between the two populations, a pattern which even seems to lead up into Sweden.
But this most certainly is not the end of the story. For one thing, the genetic studies carried out were analysing the mitochondrial DNA (mtDNA), which is inherited solely down the female line (men inherit their mothers’ mitochondrial DNA but will not pass it on). In one study, it was found that of Spainish Neolithic samples while the mtDNA belonged to hunter gatherer groups from the Palaeolithic, the Y chromosome was shown to be from the Neolithic Near East. This does seem to suggest that the role of men and women during the advance of the Neolithic differed to some extent. Additionally, it also appears that the change to farming practices did not happen as rapidly as expected, and was not as clear cut. In two recent papers (with a particular focus on Germany), it was found that hunter gatherers and farmers lived alongside each other for about 2000 years and, interestingly while the Mesolithic hunter gatherers and the Neolithic farmers had their own distinctive gene pools, at some point in the Neolithic there were intermediary groups with shared ancestry and lifestyle undoubtedly reflecting the transition that was taking place.
There is a level of difficulty when studying the past; we cannot always state processes or cause and effects with a perfect degree of certainty, but we can say what the evidence appears to suggest, and in this case it appears to suggest a high a degree of complexity as the Neolithic Revolution took hold. There is never just any one specific model that can answer our questions, and there will always be other lines of evidence to explore. To answer the original question how the Neolithic Revolution spread cannot be placated with just one simple answer. It is never that easy. But as aDNA analyses show, we can still get one step closer to that very complicated answer.