Most “old hands” in the discipline of historical population genetics remember when grand narratives were constructed out of Y chromosomal haplogroup distributions. One of the most distinctive ones is that of haplogroup R1b, which exhibits very high frequencies in the west of Europe, as high as more than 80% among the Basques. Because the Basques are the only non-Indo-European population which exists today in Western Europe, it was presumed that they are more ancient than other groups. And, their high frequency of R1b (along with other peculiarities such as a high frequency of Rh-), was taken to indicate that they reflected the genetics of Europe’s aboriginal hunter-gatherers when farming arrived.
This turned out to be wrong in a lot of details. Genetically the Basques are quite like the European farmers from Anatolia who replaced the original hunter-gatherers. Less so than the Sardinians, as they have more hunter-gatherer ancestry. But instead of being the language of European hunter-gatherers, it seems plausible that the Basque language descends from that of the Cardial culture.
So what about R1b? Well, it turns out that the particular branch of R1b that is very common in Europe is not found in the Neolithic farmer populations. Rather, its arrival in places like Britain and Iberia is associated with cultures with original origins in the Eurasian steppe. In the eastern half of Europe and in Central Asia and South Asia, R1a expanded in the period after 2000 BC.
New Scientist is now quoting David Reich has having asserted that this population turnover in Iberia occurred ~4,500 years ago. Reich, in particular, is emphasizing the disruption in the Y chromosomes. I don’t know if Reich’s group is coming out with new data, but we do have some evidence on this in Iberia from earlier publications.
This figure from Four millennia of Iberian biomolecular prehistory illustrate the impact of prehistoric migrations at the far end of Eurasia basically says it all. Around the transition between the Iberian Neolithic and the Bronze Age a new element came into the Iberian peninsula with affinities with populations to the north and east. The samples are not dense enough in terms of time to give a precise date, but this paper seems to suggest somewhere between 4,000 and 4,500 years as the most likely interval. The Reich group probably has more samples and so can date it more precisely. Interestingly, ~4,500 years ago is exactly when R1b bearing males arrived, and there was massive genetic turnover, in the British Isles. Perhaps the correlation between these two regions being overrun at the same time is not coincidental?
Please remember that the post-steppe Corded Ware people had settled in Central Europe by 2900 BC. Time elapsed between this period, and the later expansion west and south. And, I wouldn’t be surprised if the arrival on the eastern steppe of people with ancestry from Europeans (that is, they had some ancestry from Neolithic Europeans) was also due to changes in Central Europe around 2500 BC.
With the demographic superstructure getting really into place for Europe, it’s really time that archaeologists, cultural evolutionists, and anthropologists, start to think about how these processes occurred.