Ancient DNA analysis on hair samples confirms that Europeans who live in Ireland today are all descended from just a small group of hunter-gatherers who came here from what is now southeast Turkey more than 6,500 years ago. That's the picture emerging from the findings of research published this week in the journal Nature Communications. Since at least the 1980s scientists have known that the population of hunter-gatherers who once lived across Europe and Asia began moving into Europe about 6,500 years ago, as part of what's called the so-called "Corded Ware" culture. But the size of this small group, its cultural connections, and when it arrived remained a mystery, with some estimates placing its numbers at only a few thousand or tens of thousands. The new study confirms that the first hunter-gatherers to arrive here were only a few hundred people, and it marks a dramatic reduction in diversity that's likely to occur any time people are isolated from the rest of their population for long periods. "It's as though all the rest of European hunter-gatherer ancestry were wiped out at that time," said John Weir, a biochemist at the University of Manchester, England, who coauthored the study. "All the hunter-gatherers that moved into Europe after that initial wave, most of them died out." The main evidence in favor of such a sharp population decline comes from analyses of the maternal DNA contained in 50,000-year-old remains from a hunter-gatherer site in the Altai Mountains of Siberia. That analysis shows just 4 to 5 percent of the DNA present at that site was likely carried by the first European-settlers to arrive in that region, Weir said. The DNA also shows that all the current European women descend from just a few women who arrived first. "We can make these deductions because we can see that the Y chromosomes are not being carried in a balanced fashion," he said. "Y chromosomes, as far as we know, are passed along perfectly." That means, Weir said, that although there is a lot of variety in Europe today, that variance comes from more recent settlers. "The first wave was relatively small," he said. The first European-settlers probably reached Europe about 6,500 years ago during the ice age, with the oldest known hunter-gatherer site in Europe dating to about 6,000 years ago. But the DNA analysis suggests there may be several waves of settlers after that time, Weir said. "In the past, we thought the spread of European farmers was a single event that happened at the end of the ice age and swept across Europe, wiping out the hunter-gatherer population," he said. "But the new evidence suggests the first wave was fairly small and was replaced by many more people who were of hunter-gatherer ancestry." That first wave seems to have ended more abruptly than the genetic data would suggest, however, since many of the hunter-gatherers remained long after that time, including a group called the Yamnaya that spread into Europe and Asia from 7,000 to 5,500 years ago and settled the region. To examine that question, a team of researchers, led by Weir, a biochemist at the University of Manchester, sequenced and analyzed DNA from 24 ancient European hunter-gatherers—14 of them dating to before 7,000 years ago and the other 10 dating from between 7,000 and 5,500 years ago. In addition, the team analyzed the DNA from five early farmers—three dating to about 5,500 years ago and two dating to about 5,000 years ago. That included two from the earliest-known farming site in Europe, a 7,000-year-old settlement in the Netherlands. The DNA from the hunter-gatherers revealed them to be of a unique genetic type that Weir said would likely not occur outside of Europe. For example, these hunter-gatherers had a high percentage of DNA from mitochondrial and Y chromosomes derived from Neanderthals, and some had a gene variant that, if you compare it to Neanderthals, could be related to resistance to malaria. In the case of the first European farmers, the analysis suggests they were also descended from a group of hunter-gatherers, although this group seems to have been less closely related to the modern human population. The results of the study are consistent with the notion that the European hunter-gatherers—in this case the Neolithic population called the Yamnaya—appeared in Europe earlier than was thought, Weir said. "The Yamnaya are a group of people who moved into Europe from the east about 7,000 years ago," he said. "And that's not very long after the previous group of hunter-gatherers, which we call the Epipalaeolithic people, seem to have left." The fact that hunter-gatherers and farmers are found in the same settlements at the same time is also consistent with the possibility that they may have been in the same places at the same time, he added. "The traditional view has been that farming spread from the south—and they call the people who did that the Yamnaya—but these results are consistent with a picture in which the Yamnaya got to Europe first and were displaced by farmers," Weir said. "And we now know that farming is not a single event, because our data suggests that there are traces of both farming and hunter-gatherer DNA in the same sites." The DNA analysis, however, provides little support for the idea that either the hunter-gatherers or the farmers in these early populations came from outside of Europe, the researchers said. "The fact that the DNA sequences are very similar is indicative that everyone living in Europe today—whether they are hunter-gatherers or farmers—came from the same region, and it's as simple as that," Weir said. "We also can rule out that they were from southeastern Asia, which is what everyone thought was the origin for hunter-gatherers." The genetic data also provides no evidence for the idea that the first European settlers were directly ancestral to today's Europeans. "They had a certain amount of genetic input from this ancient population and we don't know how much that is, but it doesn't appear to be much," he said. Weir said the results of the study—the first of its kind—help to resolve a number of mysteries. For one thing, they resolve a historical mystery. "There were large gaps in the genetic record over the past 20,000 years and some of these gaps make no sense to us—like there's a 40,000 year gap and there are people living there, but there are no settlements," he said. The data also clarify our view of how human populations across the world have moved and interacted over the past 15,000 years. "The results shed light on this question, and help explain some of the gaps in genetic evidence," he said. Another longstanding question is why the first European farmers, who settled about 10,000 years ago, were able to expand their population so rapidly, Weir said. "At that time there were a lot of mammoths and other game animals on the steppe," he said. "I think they were using agriculture as a defense mechanism. It gave them a good diet so they didn't have to leave and venture out, and it allowed them to defend their territory against other people. Once you put in a fence, you don't have to keep patrolling the boundary." The results also shed light on the nature of human evolution, Weir said. "In a big-picture sense, our work highlights the fact that genetic changes were occurring through the European population, but in a regional scale," he said. "I think this shows that we were really a mosaic of different populations." ### The paper, "Genetic evidence for a surprisingly large founder population size in Neolithic Europe," is available online from Nature Communications at http://www.nature.com/ncomms/2014/141113/ncomms4343/full/ncomms4343.html. The study was funded by the Natural Environment Research Council (NERC) and the British Society for Population Genetics. The School of Medicine and Center for Complex Systems at Arizona State University are both on the Tempe campus. The Center for Complex Systems, established in 2008, has emerged as a leader in the study of complex systems, their mathematical and computational properties, and their possible application to a wide range of problems in the biological and physical sciences. Note to Editors: Follow the School of Medicine and Center for Complex Systems on Twitter @mbschool of Medicine and http://twitter.com/ASUmedcomplex. A full list of Arizona State University research and faculty available online at http://www.asunews.asu.edu/. About Arizona State University: Arizona State University, an intellectual and technological powerhouse ranked as one of "America's Best Colleges" by U.S. News & World Report, is a leading public university of more than 40,000 students with more than 220,000 alumni around the globe.