The first were hunter-gatherers who arrived some 45,000 years ago in Europe. Then came farmers who arrived from the Near East about 8,000 years ago. . . .
Finally, a group of nomadic sheepherders from western Russia called the Yamnaya arrived about 4,500 years ago. The authors of the new studies also suggest that the Yamnaya language may have given rise to many of the languages spoken in Europe today. . . .
The Harvard team collected DNA from 69 human remains dating back 8,000 years and cataloged the genetic variations at almost 400,000 points. The Copenhagen team collected DNA from 101 skeletons dating back about 3,400 years and sequenced the entire genomes.
Both teams also compared the newly sequenced DNA to genes retrieved from other ancient Europeans and Asians, and to living humans.
Until about 9,000 years ago, Europe was home to a genetically distinct population of hunter-gatherers, the researchers found. Then, 9,000 to 7,000 years ago, the genetic profiles of the inhabitants in some parts of Europe abruptly changed, acquiring DNA from Near Eastern populations.
Archaeologists have long known that farming practices spread into Europe at the time from Turkey. But the new evidence shows that it wasn’t just the ideas that spread — the farmers did, too.
The hunter-gatherers didn’t disappear, however. They managed to survive in pockets across Europe between the farming communities. . . .
From 7,000 to 5,000 years ago, however, hunter-gatherer DNA began turning up in the genes of European farmers. “There’s a breakdown of these cultural barriers, and they mix,” Dr. Reich said.
About 4,500 years ago, the final piece of Europe’s genetic puzzle fell into place. A new infusion of DNA arrived — one that is still very common in living Europeans, especially in central and northern Europe.
The closest match to this new DNA, both teams of scientists found, comes from skeletons found in Yamnaya graves in western Russia and Ukraine.
Archaeologists have long been fascinated by the Yamnaya, who left behind artifacts on the steppes of western Russia and Ukraine dating from 5,300 to 4,600 years ago. The Yamnaya used horses to manage huge herds of sheep, and followed their livestock across the steppes with wagons full of food and water.
It was an immensely successful way of life, allowing the Yamnaya to build huge funeral mounds for their dead, which they filled with jewelry, weapons and even entire chariots.