A study of ancient DNA obtained from prehistoric human remains has revealed details about modern humans before farming began, going back to their arrival in Europe around 45,000 years ago.
In one of the largest studies of its kind, researchers on four continents analysed DNA from 51 Eurasians dating back to the beginning of modern human occupation and identified significant population changes linked to the end of the last Ice Age.
In particular, the DNA analysis revealed that modern humans who lived in Eurasia between around 37,000 and 14,000 years ago descended from a single founder population that persisted through the Ice Age.
Following this period, and probably driven by fluctuations in the climate, European populations became more closely related to those migrating from the Near East. The researchers speculate that the warm weather that followed the Ice Age around 14,000 years ago could have driven early Near East residents to Europe and could have led to gene fusion.
'We see that the founding European populations persisted over the last glacial maximum some 25,000 to 14,000 years ago, but afterward there were dramatic re-jiggerings as people moved back from warm-weather refuges in the southwest and the southeast, transforming the human landscape of Europe,' said co-senior author Professor Svante Pääbo, director at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
The study, which was published in Nature, provides a picture of how migration events have been recurring throughout European history. Branches of the founder population were found in different parts of Europe, with one specimen from Belgium showing how a population was displaced and then re-expanded thousands of years later.
Professor David Reich, co-author of the study from Harvard Medical School in Boston, Massachusetts, told BBC News: 'During this first four-fifths of modern human history in Europe, history is just as complicated as it is during the last fifth that we know so much more about. We see multiple, huge movements of people displacing previous ones.'
The test results also showed that, over the same period of time, the proportion of Neanderthal DNA in the genome of modern humans decreased from around 3–6 percent to around two percent. The decrease was more pronounced in areas of the genome that encode for proteins, suggesting that Neanderthal DNA probably had a negative effect on modern humans and therefore was progressively lost due to natural selection.
Future work to generate similar ancient genomic data from South East Europe and the Near East could help draw a more complete picture of Eurasian population history.