"The new genetic data, published May 2, 2016 in Nature, reveal two big changes in prehistoric human populations that are closely linked to the end of the last Ice Age around 19,000 years ago. As the ice sheet retreated, Europe was repopulated by prehistoric humans from southwest Europe (e.g., Spain). Then, in a second event about 14,000 years ago, populations from the southeast (e.g., Turkey, Greece) spread into Europe, displacing the first group of humans. "
"The genetic data show that, beginning 37,000 years ago, all Europeans come from a single founding population that persisted through the Ice Age, said Reich. The founding population has some deep branches in different parts of Europe, one of which is represented by a specimen from Belgium. This branch seems to have been displaced in most parts of Europe 33,000 years ago, but around 19,000 years ago, a population related to it re-expanded across Europe, Reich explained. Based on the earliest sample in which this ancestry is observed, it is plausible that this population expanded from the southwest, present-day Spain, after the Ice Age peaked. "
"The second event that the researchers detected happened 14,000 years ago. “We see a new population turnover in Europe, and this time it seems to be from the east, not the west,” said Reich. “We see very different genetics spreading across Europe that displaces the people from the southwest who were there before. These people persisted for many thousands of years until the arrival of farming.”
[SPECIAL NOTE: Why Neanderthal DNA has diminished in the Sapiens Population]
"The researchers also detected some mixture with Neanderthals, around 45,000 years ago, as modern humans spread across Europe. The prehistoric human populations contained three to six percent of Neanderthal DNA, but today most humans only have about two percent. “Neanderthal DNA is slightly toxic to modern humans,” explained Reich, and this study provides evidence that natural selection is removing Neanderthal ancestry. "