Just a conceptual framework here.
Just so you know going in, whenever reading up on the topic. There are ritual incantations by all the sources that depend entirely on PC money – National Geographic, Smithsonian – that must be made whenever discussing European genetics. They must recite that there are no pure European races dating back endlessly with continuous presence until the present day. Nay, nay. Nazis, thought that, and you don’t want to be like them. Lots of other people thought so, too, and they were also racist. All of your recent European ancestors were likely racist, and good people don’t even come close to thinking like that anymore. Once you understand that this is part of their common religion and they have to say this at the opening of every academic exercise (sort of like everyone saying the Pledge of Allegiance at town meeting, or singing “The Star-Spangled Banner” at sporting events) it becomes more endurable. It is comforting to them, making the appropriate obeisance before proceeding. Because it’s a new religion, they are still working things out. They see heretics everywhere.
Then they go on to explain to you that until very recently, the major sources for European genetics do come from three waves which stabilised thousands of years ago. But don’t get any idea that this means anything. Those were really, really different groups, you know, and there were groups within groups, like Celtic and Slavic tribes both being Indo-European, and groups within those groups. So no one is pure. Got that, you potentially fascist reader?
The first group in were hunter-gatherers 45,000 years ago. Unsurprising, as there was nothing but h-g’s at that point, no farmers anywhere. They outcompeted but did interbreed some with Neandertals, possibly because they were meaner, or maybe smarter. Glaciers came and went and areas were depopulated and repopulated. Who they were has been murky, but we are starting to get some initial narrative. It’s complicated, but a group we call European Hunter-Gatherers, especially West Hunter Gatherers (WHG) became the temporary Indigenous Peoples of their day. Europeans still have lots of that ancestry, as you can note from the Distribution maps of European Admixture I linked to a couple of days ago.