Note: The first post was Who qualifies as a European anyway?
A generation ago, the line on prehistoric migrations in archeology and genetics was simple: first, a powerful wave of humans pushed out of Africa, which then begat secondary waves that spread across the world as branches off the main trunk. The default assumption was that the earliest modern humans to settle a region were likely the predominant ancestors of all that locale’s later inhabitants, claimants to a sort of prehistoric first-mover advantage. Obviously, there were exceptions (for example, the New World today), but the idea was that 10-50,000 years ago, the continents outside of Africa were settled by early arrivals, and any subsequent human population movements only changed these original genetic contours a bit on the margins, even if language and culture proved vastly more susceptible to wholesale change.
Today we know this is mostly wrong. We still see cases where the older model holds, at least until colonial migration. Oceania is one; indigenous Australians seem to descend exclusively from the first humans to arrive some 45-50,000 years ago. But across Europe and Asia, the only constant has been change, as turnover after turnover reshaped the genetics and culture of the Eurasian supercontinent. In Europe, this cycle of churn began as early as 40,000 years ago when modern humans arrived, replacing Neanderthals. And it continued down to the Bronze Age, which saw Indo-European speakers associated with the Yamnaya culture migrating out of the Pontic steppe en masse. But unlike the Neolithic farmers that had expanded out of Anatolia 10,000 years ago, these Indo-European steppe nomads didn’t just impact Europe; their kin would transform Eurasia to the east and south of their homeland in prehistoric Ukraine as well. The dialects of these steppe nomads would seed the whole Indo-European family of languages which accounts for tongues spoken today by half the world, from the fjords of Norway to the jungles of Sri Lanka. Additionally, while the earliest farmers seem to have incrementally opened the land for cultivation in small clusters of families that diffused outward as a gradual wavefront, colonizing new territories over thousands of years, the herders from the steppe hit Europe like a thunderclap. It took just a few centuries after 3000 BC for masses of young men on the hunt for new pasturelands, wives and slaves to remake most of the continent in their patriarchal, pastoral image.