Ice Age Migration and Displacement Shown in Study

Nature on 2nd May, the study analysed the DNA of prehistoric humans to chart population changes over a period that stretched from the initial inhabitation of Europe by modern humans, to the end of the last Ice Age. The research was led by David Reich, Howard Hughes Medical Institute Investigator at Harvard Medical School. Two massive changes in prehistoric populations are revealed by the genetic data used in the research, which seem to be related to the end of the Ice Age around 19,000 years ago. The first has been documented previously, although in less detail. As the ice sheet retreated, northern Europe was repopulated by prehistoric humans from regions of southwest Europe, such as Spain. A second, more surprising event came some 5,000 years after that initial re-population. Populations from the southeast of Europe, such as what is now Turkey and Greece, migrated into Europe and displaced the first group of humans who had relocated there. The findings have the potential to cause a drastic rethink on how we understand the history of European migration and population. Previously, genetic data were only available for four samples of prehistoric European modern humans between 45,000 and 7,000 years old, but Reich and colleagues’ study has changed that; allowing much better insights to be gleaned on human populations in this distant 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. With 51 samples, everything changes; we can follow the narrative arc; we get a vivid sense of the dynamic changes over time,” said Reich, in a press release from the Howard Hughes Medical Institute. “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.” According to the team’s findings, all Europeans come from a single 37,000 year old population that survived through the last Ice Age. One of the branches of this population, which was represented by a specimen from Belgium, was displaced from most parts of Europe around 33,000 years ago, during the height of the last Ice Age. Some 19,000 years ago, a population related to it expanded across Europe, which the researchers believe could have originated in Spain. The second event took place 14,000 years ago, and would define Europe’s population until the advent of agriculture. “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.” Fascinatingly, the study also showed the percentage of Neanderthal DNA in humans is decreasing, it consisting of between 3% and 6% of the prehistoric humans’ genetic makeup, but only 2% in most humans today. The results suggest that natural selection could be removing the toxic Neanderthal DNA. Reich and colleagues’ study shows that migration has long been an integral, complicated part of human history, shaping the world’s populations for thousands of years. Image courtesy of Martin Frouz and Ji?í Svoboda]]>