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News

New DNA study in Science traces the genetic roots of modern Europeans

American Association For The Advancement Of Science (AAAS) : 20 July, 2006  (Company News)
Photograph of 'Neolithic burial HAL2' from Halberstadt, Germany. This burial exemplifies the Linear Pottery culture of the first Central European farmers, who lived about 7,500 years ago. The banded pottery and the flexed position of the legs are hallmarks of this farming culture.
The skeleton, excavated in 2000, was found in an excellent state of preservation and yielded mitochondrial DNA type 'N1a.' The fact that 6 of the 24 skeletons are from this rare human lineage allowed the researchers to investigate the mark the first European farmers left on the genetic makeup of modern Europeans.

The farmers who brought agriculture to central Europe about 7,500 years ago did not contribute heavily to the genetic makeup of modern Europeans, according to the first detailed analysis of ancient DNA extracted from skeletons of early European farmers.

The passionate debate over the origins of modern Europeans has a long history. This work strengthens the argument that people of central European ancestry are largely the descendants of 'Old Stone Age,' Paleolithic hunter-gatherers who arrived in Europe around 40,000 years ago rather than the first farmers who arrived tens of thousands of years later during the Neolithic Age.

This paper appears in Science published by AAAS, the nonprofit science society.

The researchers from Germany, the United Kingdom and Estonia extracted and analyzed DNA from the mitochondria of 24 skeletons of early farmers from 16 locations in Germany, Austria and Hungary. Six of these 24 skeletons contain genetic signatures that are extremely rare in modern European populations.

Based on this discovery, the researchers conclude that early farmers did not leave much of a genetic mark on modern European populations.

'This was a surprise. I expected the distribution of mitochondrial DNA in these early farmers to be more similar to the distribution we have today in Europe,' said Science author Joachim Burger from Johannes Gutenberg Universität Mainz in Mainz, Germany.

'Our paper suggests that there is a good possibility that the contribution of early farmers could be close to zero,' said Science author Peter Forster from the University of Cambridge in Cambridge, UK.

To get at questions surrounding the ancestry of modern Europeans, the researchers studied mitochondrial DNA from early farmers in Central Europe. Mothers pass mitochondrial DNA to their offspring primarily 'as is,' without mixing or recombination with mitochondrial DNA from fathers. Mitochondrial DNA, therefore, provides a way for researchers to piece together how closely members of a species are related, using maternal lineages as a guide, explained Burger.

In the new study, the researchers attempted to extract mitochondrial DNA from the skeletons of 56 humans who lived in various parts of Central Europe about 7500 years ago. These ancient humans all belonged to well known cultures that can be identified by the decorations on their pottery, the Linearbandkeramik and the Alföldi Vonaldiszes Kerámia. The presence of these cultures in Central Europe marks the onset of farming in the region. These farming practices originated in the 'Fertile Crescent' of the Near East about 12,000 years ago.

From bones and teeth of these 56 skeletons, the researchers extracted mitochondrial DNA sufficient for analysis from 24 of the skeletons. Six of the 24 early farmers belonged to the 'N1a' human lineage, according to genetic signatures or 'haplotypes' in their mitochondrial DNA that the researchers studied. These six skeletons are from archeological sites all across central Europe. Few modern Europeans belong to this N1a lineage, and those that do are spread across much of Europe.

The other 18 early farmers belonged to lineages not useful for investigating the genetic origins of modern Europeans because their genetic signatures from the scrutinized region of mitochondrial DNA are widespread in living humans, according to the authors.

Using the tools of population genetics and a worldwide database of 35,000 modern DNA samples, the researchers investigated the genetic legacy of early European farmers based on the fact that six of the 24 early European farmers are from a lineage that is now extremely rare in Europe and around the world. At least 8 percent of the early farmers belonged to the N1a lineage, according to the researchers who estimate the range was between 8 and 42 percent.

Even this conservative estimate of 8 percent stands in stark contrast to the current percentage of central Europeans who belong to the N1a lineage, 0.2 percent. This discrepancy suggests that these early farmers did not leave much of a genetic mark on modern Central Europeans, the authors say.

'It's interesting that a potentially minor migration of people into Central Europe had such a huge cultural impact,' said Forster.

Small pioneer groups may have carried farming into new areas of Europe, the authors suggest. Once farming had taken hold, the surrounding hunter-gatherers could have adapted the new culture and then outnumbered the original farmers, diluting their N1a frequency to the low modern level. A range of archeological research supports different aspects of this hypothesis, the authors say.

Alternatively, a different population may have replaced the early farmers in Central Europe, eliminating most of the N1a types, but archaeological evidence for this scenario is scant, according to the authors.

The authors: Wolfgang Haak, Barbara Bramanti, Guido Brandt, Marc Tänzer, Kurt Werner Alt and Joachim Burger at Johannes Gutenberg Universität Mainz in Mainz, Germany; Peter Forster, Shuichi Matsumura and Colin Renfrew at University of Cambridge in Cambridge, UK; Richard Villems at Tartu University in Tartu, Estonia; Detlef Gronenborn at Römisch-Germanisches Zentralmuseum in Mainz, Germany.
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