Using genetic sequencing techniques on ancient fossil DNA, a team of researchers from the U.S., Germany and China has shed light on Europe's population history prior to the Ice Age between 45,000 to 7,000 years ago. Two events stand out in particular: a repopulation of Europe by prehistoric humans from southwest regions of the continent as the ice sheet retreated around 19,000 years ago, and populations from the southeast making their way onto the continent around 14,000 years ago.
Prior to the current study, only four samples of prehistoric European modern humans 45,000 to 7,000 years old were available, making genetic data limited and hindering the efforts of scientists in their attempt to understand the migration and evolution of humans during this time period.
"Trying to represent this vast period of European history with just four samples is like trying to summarize a movie with four still images," said David Reich, a researcher from Harvard Medical School and lead author of the study. "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."
Using the newly available genetic data, Reich and his team revealed that the Europeans that lived through the Ice Age came from a single population with ties to various parts of Europe, one being Belgium.
Although this branch seems to have disappeared in Europe 33,000 years ago, another related population from what is now Spain re-expanded across the continent approximately 19,000 years ago after the peak of the Ice Age.
The team also discovered a major population event around 14,000 years ago, but this time from the east instead of the west.
"We see very different genetics spreading across Europe that displaces the people from the southwest who were there before," Reich said. "These people persisted for many thousands of years until the arrival of farming."
Reich and his team also detected some Neanderthal DNA as modern humans spread across Europe 45,000 years ago, with populations containing approximately 3 to 6 percent of this DNA in comparison to the 2 percent observed in modern humans.
The results were obtained by extracting and analyzing DNA from ancient Ice Age bones using a unique technique called in-solution hybrid capture enrichment in order to avoid the contamination of microbial DNA that typically occurs with ancient bone specimens.
The findings were published in the May 2 issue of Nature.