Over the past several years ancient DNA has opened a startling window onto the settlement of the European continent during the Holocene. The story is one of migration, replacement, and repeated pulsing of populations from the fringe toward the North Sea. In short, the model that farming spread to Europe predominantly through cultural diffusion is dead. Though the genetic legacy of the indigenous hunter-gatherers persists in modern Europeans, it is through their amalgamation into the populations of farmers with roots in the Near East, as well as later peoples who arrived from the Eurasian steppe. Not because they adopted the culture of the newcomers.
But while the cultural diffusionist model has been falsified, the customary alternative, demic diffusion, has not been entirely validated either. This model posits the expansion of farming as a mechanistic, mindless, process analogous to thermodynamics and the expansion and diffusion of heat. It is in many ways a “culture-free” model, as farmsteads expand in an ad hoc and uncoordinated fashion across an empty landscape. And, as L. L. Cavalli-Sforza pointed out it was actually compatible with a predominant Pleistocene period ancestry for modern Europeans, because as the wave of demographic advance proceeded it would mix with the indigenous peoples on the frontier, diluting the distinctive original genetic signal.
I won’t repeat what’s been stated a thousand times in this space. Basically, rather than a gradual movement, the DNA is suggesting that there were starts and fits, and later equilibrations. For a thousand years or so it looks as if in the region of modern Germany during the early Neolithic the farmers and hunter-gatherers remained apart, with genetic distances comparable to that between modern Northern Europeans and Han Chinese. To account for this I have presented a rough model which I termed “leapfrogging,” as farmers migrated to ecologically favored terrain, leaving much of the hinterland in the hands of Mesolithic hunter-gatherers.
It turns out that none of my ideas were original, down to the terminology! A book chapter in The Colonization of Unfamiliar Landscapes: The Archaeology of Adaptation, prefigures almost all of my thoughts. Additionally, though published in 2003 I would argue it was relatively prescient. Here is one section:
The Neolithic colonization of Europe was a complicated process that took more than 2,500 years to unfold. Analysis of calibrated radiocarbon dates reveals a series of punctuated, rapid expansions, interrupted by periods – 500 to 1,000 years long – of stasis and in-filling. The earliest colonists in Southeastern Europe sought out floodplains and lake basins that were close analogues to familiar ancestral habitats in Anatolia and optimal for their farming practices. The two-stage structure of the Early Neolithic expansion and the selectivity of initial settlement locations imply carefully planned colonizing ventures, based on detailed prior knowledge of the landscape. The second-stage farmers may have derived this vital geographic information from fishing groups that initially created settlement facilities on the Greek coast to support long distance fishing trips. These frontiersmen probably shifted opportunistically from hunting and fishing, to herding, to trading.
You can read the whole chapter, Deerslayers, pathfinders, and Icemen: origins of the European Neolithic as seen from the frontier, at Academia.edu.