I have recently registered at "Anthrogenica.com" forum.
After journal "Nature" published a genetic study on prehistoric Kennewick Man, showing that he was "racially" a Native American, and even showing with which modern tribes he was most closely related (for example with the Colville tribes, as it turns out), I started a thread at Anthrogenica, asking other users whether it is possible to establish similar links between individual prehistoric Europeans, and modern ethnic groups from Europe - can it be established which prehistoric groups are ancestral to which modern groups?
Here is what one of other users answered, comparing Europeans and Native Americans:
the problem is that all Europeans from across the north of the continent share a lot of ancestry with Corded Ware and Yamnaya, because the Early Bronze Age population movements from the steppe into Northern Europe were so massive. This was followed by a lot of local migrations and mixing. It's not like among Native Americans, where there's probably still a lot of [regional] structure dating back 8,000 years.
Corded Ware and Yamnaya are archaeological cultures of early Indo-European speakers, as was the Bell Beaker culture. The study by prof. Dan Bradley which I quoted on 29 Dec 2015 01:28, shows that those Bronze Age migrations swept entire Europe all the way to Ireland. Aboriginal Non-IE populations in some parts of Europe - for example Scandinavia - recorded the arrival of those IE migrants in their art. Rock carvings in Scandinavia were created by indigenous Stone Age hunters, the oldest of them are at least 6500 years old. But then - much later, at the beginning of the Metal Ages (Copper and Early Bronze), these petroglyphs recorded the arrival of new strange immigrants, arriving on ships, in large fleets, carrying weapons such as battle axes, and carrying sun disks. Those were groups of Indo-Europeans.
Another user at Anthrogenica wrote the following answer to my question:
Northern Europe was homogenized a couple times over by massive long range population movements.
And by "Northern Europe" they basically mean everything north of the Iberian Peninsula, the Italian Peninsula, and the Balkan Peninsula - all the way from Ireland and Bretagne to Estonia and Russia. There is a lot of genetic similarity between Slavs and Germanics mostly because of common origins of both groups, but also due to more recent mixing such as mentioned by Linamonsen and Michael Mills above.
So not only do most of Europeans descent from largely the same ancestral prehistoric populations, but also there has been a lot of mixing within Europe later on (as Michael and Linamonsen wrote), including Germanic and Slavic migrations back-and-forth.
The main genetic divide in Europe is between Southern Europe and Northern Europe, while differences between Europe's North-Western and North-Eastern populations are much smaller, thought with a high enough resolution they might still be traced.
By the way, I was actually disappointed by those answers because I hoped that it would be possible to establish which prehistoric skeletons belonged to direct ancestors of ethnic Poles, which of ethnic Germans, etc., but apparently it is not so easy in Europe.
Europeans are too similar to each other. There are only some genetic outliers (like for example Sardinians and Lapps). Even the Basques are not as indigenous to Europe as they think - genetic studies show considerable Steppe admixture in them. They just preserved the language of the Non-Indo-European part of their ancestors, but their genetic heritage is mixed, with Indo-European blood as well.
Sardinians are the only perfect proxy for Neolithic Europeans, before Indo-European migrations described by Marija Gimbutas in her Steppe Hypothesis (which has now been confirmed by genetic studies). Sardinians have nearly no "Steppe admixture".
https://en.wikipedia.org/wiki/Marija_Gimbutas
Scandinavians have a lot of their ancestry derived from the Early Bronze Age Steppe, as do Balto-Slavic peoples.
The Steppe itself was also a place where huge migrations have taken place - original Indo-European inhabitants eventually mixed with Turkic and Mongolic tribes, who came later (during the Iron Age and the Middle Ages) from Eastern Siberia and Mongolia. Proto-Turks and Proto-Mongols originated from two very multi-ethnic tribal confederations mentioned in Ancient Chinese texts - Xianbei and Xiongnu.
The Steppe worked as a "highway" connecting peoples and ideas all the way from East Asia to Europe. The Steppe is what made Eurasia the center of human civilization. Cultures which evolved in the Americas had much harder time to exchange ideas and genes - between the Anasazi culture, Mesoamerican cultures, and Andean cultures, there were nearly impenetrable jungles, deserts and mountains.
At the same time, the steppe was also home to many of the most warlike and dangerous groups in Eurasian history. Steppe nomads (first PIEs, then other groups) either migrated to, settled in, or repeatedly invaded both Europe, the Middle East, India, and China.
There are words which carry the presage of defeat. Defence is such a word. What is the result of an even victorious defence? The next attempt of imposing it to that weaker, defender. The attacker, despite temporary setback, feels the master of situation.