Upvote:0
I'd say your question itself gives the likely answer. Absent some written source explaining what happened, it is more or less a question of which is more likely:
That in a sparsely populated world, that the proto-Indos did which one of:
1) did not move into a region at all, but exported its culture and language through co-opting the original ruling class
2) moved into a region cooperatively, and culturally absorbed the original settlers
3) moved into a region by conquest, keeping the original settlers as an underclass that absorbed the culture of the conquerers
4) moved into a region and pushed every last settler out to some other region
5) moved into a region and killed every last settler out of hand
If you look at post-historical migrations, there are instances of Case 1 - Rome in Britain, Asia Minor. For Case 2 - Caesar mentions some Germans invited into part of Gaul peacefully. For case 3 - German migrations into West Roman Empire, Turks in Asia Minor post Manzikert. This leaves case 4 and 5 which I can't recall a single provable instance in written history. This would also take a pretty organized state to pursue such a rigorous course, which is unlikely to be possible so long ago.
Up until recently, Linguists seemed to assume that language was almost an innate part of a people and thus a language change meant a change in the people themselves. More recently, though, it is found that if there is an advantage, customs and languages will change without much or any demographic change.
Upvote:1
The Indo-European migration happened relatively - emphasis on relatively - soon after the end of the Ice Age. Much of Europe had been uninhabitable or barely habitable until a few thousand years before the Indo-European migrations are thought to have happened. The Sami were relative newcomers compared to the Basques, since they came from the east after the ice age just like the Indo-Europeans
My point being, when it comes to northern and central Europe, there had simply not been a lot of time for anyone else to develop large population levels. The Indo-Europeans may well have (mistakenly) thought the entire continent uninhabited, since the resistance to the invasion would have been negligible. I would compare the dynamic to the expansion of Americans into the area west of the Thirteen Colonies, which was very sparsely populated due to plague and non-industrialized agriculture. The indigenous population is displaced or absorbed whether or not any violence happens. This is the unfortunate fate of a lot of small, local cultures all over the world today. Kids stop learning their parents' old language, etc.
Upvote:3
Update - February 21, 2017:
A new study ... Genetic data suggest that modern European ancestry represents a mosaic of ancestral contributions from multiple waves of prehistoric migration events. Recent studies of genomic variation in prehistoric human remains have demonstrated that two mass migration events are particularly important to understanding European prehistory: the Neolithic spread of agriculture from Anatolia starting around 9,000 years ago, and migration from the Pontic-Caspian Steppe around 5,000 years ago. These migrations are coincident with large social, cultural, and linguistic changes, and each has been inferred to have replaced more than half of the contemporaneous gene pool of resident Central Europeans.