here and here.)
In the 3500 to 2000 BCE period, the genetic dominance of Europe by the first farmers, people who migrated from the Middle East, was broken. There was a major disruption in the genetic pattern of the continent at this time, which implies major migrations and an influx of new people. At around the same time the cultures of the earlier Neolithic were replaced by more advanced cultures that used animals for plowing and pulling carts and had other improved technologies: better looms, better beer, copper tools, etc. In northern and western Europe the two most important cultures are the Beaker folk in the west and the Corded Ware culture in the center. In the map above, the beaker culture is light green, the corded ware culture is blue, and the rather large region of overlap is dark green.
I want to emphasize that this is a very simple schema, not a detailed picture. All modern populations are genetic mixtures, and this seems to have been true about all important European groups in the past. I expect to see a lot of simplistic crap over the next decade connecting this gene to that people, moving from here to there, etc. Most of it should not be taken very seriously. But it is amazing to think that we have learned so much so quickly about events that took place 5,000 years ago.