More and more it looks as if Robert Howard (as well as most of the physical anthropologists in the first half of the 20th century) had it right: every now and then, invaders move in and largely replace the the locals. So those potsherd-smoking archaeologists of the past few decades , who attributed all material cultural changes to learning and imitation, rather than spear-din, were wrong.
Usually, though, the replacement is not complete. Even Neanderthals, a population that split off hundreds of thousands of years ago, left a trace in Eurasia. My question is what local circumstances give the best chance for a substantial dollop of the formerly-common genotypes persisting for a long time – ideally, to the present day. Where do we find the blood of the Old Ones?
For example, what about the first agriculturalists of southern Europe, the Cardial culture? Their dominant Y-chromosome haplotype was G2a, but today that is not too common in Europe. It reaches 10% frequency or higher in southern Italy (especially the Apennines), Sardinia, Thessaly, and Crete. It’s close to 10% in Asturias, Auvergne, Switzerland, the Aegean islands, and Cyprus. Looks to me as if they did best in out-of-the-way places, mountainous regions and islands. Places that the newcomers didn’t want that much.
You might compare this to the way in which some Romanized populations survived the onslaught of barbarians. Vlachs, speaking a Romance language, persisted as shepherds in the uplands of Eastern Europe as the Slavs flooded in – while the Greeks did best on islands. People are still speaking Romansh in central Switzerland. Britons survived in Wales, etc.