In 2012 I wrote Post-Neolithic revenge of the foragers. There were two proximate rationales for my thoughts at the time. First, I thought Peter Bellwood’s thesis of agricultural based demographic expansions in First Farmers was being vindicated in the broadest sketch, but there were many countervailing details. Second, there were already suggestions that genetic data was not indicative of a final victory of farmers by pastoralists.
There were several immediate issues that came to mind in the non-genetic domain. Bellwood argued that agriculture shape the distribution of modern language families, but the spread of Turkic and Finnic peoples seem likely to have been post-agricultural, and not based on farming. Both these groups were arguably nomadic, one pastoralist, and the other engaging in mixed use lifestyles which were reminiscent of classic hunting and gathering. And, there has been anthropological evidence that though pure hunter-gatherers, such as indigenous Australians, do not take to cultivation easily, they quickly transition to pastoralism. In other words, the skills and mores which are common among hunter-gatherers can translate rapidly once domesticate based nomadism spreads.
The Turks, or the Saami with their reindeer, are evidence of this transition, and its success. It seems plausible that the same was the case with Indo-Europeans, and that is what I thought at the time.
Now we have more data from ancient DNA. It does seem there was a “resurgence” of Mesolithic hunter-gatherer ancestry as time passed, with Neolithic farmers exhibiting a more indigenous genetic profile in Europe. Additionally, the arrival of Indo-European steppe ancestry brought another dollop of “hunter-gatherer” ancestry from beyond the fringes of Europe proper.
So what story can we tell of the transition between the Late Neolithic (LN) and the Early Bronze Age (ENA) in Europe? First, the proto-Indo-Europeans were people from the fringes and boundaries. Their genetics indicate some sort of influence from the Near East, likely via the Maykop people. But their roots were also deep in eastern Europe, from the local hunter-gatherers who had affinities with Siberians to their east and European hunter-gatherers to their west. From from this synthesis emerged something special, a warlike group of mobile pastoralists who quickly swept the field.
This reminds me of something from Peter Turchin’s book, War and Peace and War: The Rise and Fall of Empires. Populations on the borders or frontiers of ethno-cultural (and possibly political) zones may exhibit more group cohesion than those from “core” areas. The Indo-Europeans were a border folk. They may also take to cultural innovations more quickly, in The Making of a Christian Aristocracy it is clear that switching to the new religion occurred faster among elites in outlying regions than in the core.
A second issue, which is not proven, but may be possible, is that once the Indo-Europeans moved into the North European plain, they allied with residual hunter-gatherer populations. A classic enemy-is-my-enemy proposition. This would likely result in a higher proportions of Pleistocene ancestry in later generations due to assimilation.
The moral of the story is that often there is no final victory in the war. Human history is full of reversals.
“Success Is Never Final” by Geoffrey Parker (2002)
https://www.amazon.com/Success-Never-Final-Geoffrey-Parker/dp/0465054773
“… Geoffrey Parker chronicles notable moments in fifteenth-, sixteenth- and seventeenth-century Europe when defeat was snatched from the jaws of victory. … Parker groups his material into three sections. In the first, he examines the rise and fall of the first global empire, the Spanish Empire. In the second, he shows how the spread of the Western military innovation triggered resistance stronger than it could overcome. Finally, he tells of the failure of the Reformation to grow beyond its original, urban milieu. …”