Modern Europeans descended from three groups

Modern Europeans are descended from three major groups of ancient humans, not two as was previously thought, according to a gene analysis published on Wednesday. Until now, the mainstream theory was that Europeans descended from early farmers who moved into Europe from the Middle East about 7,500 years ago, and local hunter-gatherers they interbred with. But a DNA analysis in the journal Nature says there was a third group in the mix: people from northern Eurasia.
The finding means that North Eurasians - who inhabited a vast swathe of land stretching across much of Russia and northern Asia - contributed to the gene pool both in Europe and North America. Their influence on the Americas were borne out in previous studies which showed that North Eurasians crossed to modern-day Alaska more than 15,000 years ago via an "ice bridge" that connected islands in the Bering Strait at the time.
"What we find is unambiguous evidence that people in Europe have all three of these ancestries," said David Reich of Harvard Medical School, who led the study with Johannes Krause at Germany's University of Tuebingen. The 100-strong team of scientists drew on a vast collection of resources. They unravelled DNA teased from nine ancient skeletons found in Sweden, Luxembourg and Germany. The remains were those of eight hunter-gatherers who lived about 8,000 years ago, before the advent of agriculture, and one farmer from about 7,000 years ago.
"There was a sharp genetic transition between the (era of) hunter-gatherers and the farmers, reflecting a major movement of new people into Europe from the Near East," said Reich. The genomes were overlaid with the genetic codes of 2,300 present-day people living all over the world.
"The ancient North Eurasian ancestry is proportionally the smallest component everywhere in Europe, never more than 20 percent, but we find it in nearly every European group we've studied and also in the Caucasus and Near East," said Iosif Lazaridis, one of the Harvard team. Northern Europeans have relatively more hunter-gatherer ancestry - up to about 50 percent in Lithuanians - whereas southern Europeans have more farmer ancestry, he added.