The question has been raised: how did the Sardinians manage to stay genetically similar to the typical European farmers of six thousand years ago? Why haven’t the currents of history homogenized them? I’ve wondered myself.
Sardinia has been conquered over and over again: Carthaginians, Romans, Vandals, Goths, Byzantines, etc, etc. But ever since the Carthaginian conquest, the island has had a serious problem with falciparum malaria, which hit the marshy lowlands, which also happened to be the areas that the conquerors were interested in, because of their high agricultural potential. It looks as if those areas were population sinks – so the foreigners that moved in were evanescent. The Romans, for example, faced labor supply problems, which forced them to constantly replenish the island’s work force with slaves, prisoners, and political exiles. All this time the old-fashioned Sardinians are persisting in the highlands, raising sheep and goats, while resisting Roman control for more than a century.
People in the lowlands eventually developed various genetic defenses to malaria, but their genetic contribution may have been limited by Moslem raids on the coast, which continued for several hundred years.
If I had to guess, I’d explain Sardinian old-fashioned genetics mostly by malaria in the lowlands and outsiders not really wanting the rocky highlands.