Analyses of ancient DNA from the ancestry of modern Europeans has now painted a picture of dramatic population change in Europe from 45,000 to 7,000 years ago. The study is now helping to unlock the secrets of Europe’s Ice Age inhabitants.
The genetic data was analyzed from 51 individuals. The results indicated that there were two big changes in prehistoric human populations that are closely linked to the end of the last Ice Age about 19,000 years ago.
It showed that Europe was repopulated from southwest Europe, as the ice sheet was retreating. However, there was a second event somewhere around 14,000 years ago, where populations from the southeast had spread into Europe, which caused the displacement of the first group of humans.
Although it was already known that modern humans had flowed into Europe around 45,000 years ago, causing the demise of the Neanderthals, there had only been four samples of prehistoric European modern humans 45,000 to 7,000 years old where genomic data was available.
This made it almost impossible to understand how human populations had migrated or even evolved during this period. David Reich from Harvard Medical School and who led the study, explained in a statement:
“Trying to represent this vast period of European history with just four samples is like trying to summarize a movie with four still images. With 51 samples, everything changes; we can follow the narrative arc; we get a vivid sense of the dynamic changes over time.
“And what we see is a population history that is no less complicated than that in the last 7,000 years, with multiple episodes of population replacement and immigration on a vast and dramatic scale, at a time when the climate was changing dramatically.”
The study shows that all Europeans had come from a single founding population, which had persisted through the Ice Age around 37,000 years ago. However, the founding population did have some deep branches in different parts of Europe.
One of these branches is represented by a specimen from Belgium, which was displaced in most parts of Europe 33,000 years ago. Nevertheless around 19,000 years ago, a population which was related to it had re-expanded across Europe.
“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,” Reich explained.
In the second event which happened 14,000 years ago that was detected, Reich explained:
“We see a new population turnover in Europe, and this time it seems to be from the east, not the west.
“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.”
Reich also explained that some mixture with Neanderthals was also detected, as modern humans spread across Europe around 45,000 years ago. Prehistoric human populations had contained about three to six percent of Neanderthal DNA; however, today most humans only have around two percent.
Because “Neanderthal DNA is slightly toxic to modern humans” Reich believes that this study also provides evidence that natural selection is removing Neanderthal ancestry. The study was published in Nature for those of you who would like to read it.