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Supercomputer compares modern and ancient DNA

What if you researched your family's genealogy, and a mysterious stranger turned out to be an ancestor? A team of scientists who peered back into Europe's murky prehistoric past thousands of years ago had the same surprise. With sophisticated genetic tools, supercomputing simulations and modeling, they traced the origins of modern Europeans to three distinct populations.The international research team’s results are published in the journal Nature.

The Stuttgart skull, from a 7,000-year-old skeleton found in Germany among artifacts from the first widespread farming culture of central Europe. Right: Blue eyes and dark skin – how the European hunter-gatherer appeared 7,000 years ago. Artist depiction based on La Braña 1, whose remains were recovered at La Braña-Arintero site in León, Spain. Images courtesy Consejo Superior de Investigaciones Cientificas.

"Europeans seem to be a mixture of three different ancestral populations," says study co-author Joshua Schraiber, a National Science Foundation postdoctoral fellow at the University of Washington, in Seattle, US. Schraiber says the results surprised him because the prevailing view among scientists held that only two distinct groups mixed between 7,000 and 8,000 years ago in Europe, as humans first started to adopt agriculture.

Scientists have only a handful of ancient remains well preserved enough for genome sequencing. An 8,000-year-old skull discovered in Loschbour, Luxembourg provided DNA evidence for the study. The remains were found at the caves of Loschbour, La Braña, Stuttgart, a ritual site at Motala, and at Mal'ta.

The third mystery group that emerged from the data is ancient northern Eurasians. "People from the Siberia area is how I conceptualize it,” says Schraiber. “We don't know too much anthropologically about who these people are. But the genetic evidence is relatively strong because we do have ancient DNA from an individual that's very closely related to that population, too."

The individual is a three-year-old boy whose remains were found near Lake Baikal in Siberia at the Mal'ta site. Scientists determined his arm bone to be 24,000 years old. They then sequence his genome, making it the second oldest modern human sequenced. Interestingly enough, in late 2013 scientists used the Mal'ta genome to find that about one-third of Native American ancestry originated through gene flow from these ancient North Eurasians.

The researchers took the genomes from these ancient humans and compared them to those from 2,345 modern-day Europeans. "I used the POPRES data set, which had been used before to ask similar questions just looking at modern Europeans," Schraiber says. "Then I used software called Beagle, which was written by Brian Browning and Sharon Browning at the University of Washington, which computationally detects these regions of identity by descent."

The National Science Foundation’s XSEDE (Extreme Science and Engineering Discovery Environment) and Stampede supercomputer at the Texas Advanced Computing Center provided computational resources used in the study. The research was funded in part by the National Cancer Institute of the National Institutes of Health.


To read Jorge Salazar’s extended article,visit the TACC website.

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