|Posted by big mike M on|
Whether they are a Serb and a Swiss, or a Finn and a Frenchman, any two Europeans are likely to have many common ancestors who lived around 1,000 years ago. A genomic survey of 2,257 people from 40 populations finds that people of European ancestry are more closely related to one another than previously thought, and could help to bring about new insights into European history.
The first efforts to trace human ancestry through DNA relied on ‘uniparental genetic markers’ — DNA sequences from the mitochondrial genome, which is inherited through mothers, or on the Y chromosome, which men inherit from their fathers.
Those studies captured the broad strokes of human history, such as Homo sapiens' migration out of Africa less than 100,000 years ago and their subsequent colonization of Europe and Asia. But uniparental markers do little to inform more recent history, in part because they represent only a single lineage in a family tree — such as a mother’s mother’s mother, and so on.
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In recent years, researchers have looked to the rest of the genome — the DNA that can come from either parent — to understand ancestry. In the latest study, population geneticists Peter Ralph, now at the University of Southern California in Los Angeles, and Graham Coop, at the University of California, Davis, looked to the entire genome to reconstruct European ancestry. Their work is published today in PLoS Biology1.
The researchers' approach relies on the way in which genes are reshuffled each generation, when an individual forms new egg or sperm cells by mixing and matching the chromosomes he or she inherited from each parent. As a result of this process, a person’s genome is made from interspersed chunks of his or her ancestors’ chromosomes. The locations where DNA sequences are swapped are different each time, so that the uninterrupted segments a person passes down become shorter with each generation. For instance, the chunks of DNA shared between first cousins are longer than those shared between second, third and fourth cousins.
Gene-sequencing companies such as 23andMe, based in Mountain View, California, use this property to connect distant cousins enrolled in their databases. Ralph and Coop looked for even more distant relatives by identifying stretches of the genome shared by people living throughout Europe. By looking at the length of these chunks, the researchers were able to determine approximately when distant cousins’ common ancestor lived.
They found common ancestors from as recently as 500 years ago mainly within populations. Older stretches of DNA, however, connected more geographically distant Europeans.
The work also uncovered genetic signatures for key events in European history, such as the migration of the Huns into Eastern Europe in the fourth century, and the later rise of Slavic-speaking people there. Present-day inhabitants of Eastern European countries share many ancestors who lived around 1,500 years ago, Ralph and Coop found. Italians, meanwhile, are connected to other European populations mainly through individuals who lived more than 2,000 years ago, perhaps as a result of the country's geographic isolation.
Studies such as this one have the potential to solve longstanding historical questions, says Coop. It has been unclear, for instance, whether the expansion of Slavic languages was driven by migration of Slavic-speaking people, cultural diffusion or both. Genetic studies “can tell us how people moved, rather than just what’s in the written record”, Coop says. John Novembre, a population geneticist at the University of Chicago in Illinois, says that the study marks “a huge step in that direction”.
Europeans appear to be more closely related than previously thought.
Scientists who compared DNA samples from people in different parts of the continent found that most had common ancestors living just 1,000 years ago.
The results confirm decade-old mathematical models, but will nevertheless come as a surprise to Europeans accustomed to thinking of ancient nations composed of distinct ethnic groups like "Germans," ''Irish" or "Serbs."
"What's remarkable about this is how closely everyone is related to each other," said Graham Coop of the University of California, Davis, who co-wrote the study published Tuesday in the journal PLoS Biology.
Coop and his fellow author Peter Ralph of the University of Southern California used a database containing more than 2,250 genetic samples to look for shared DNA segments that would point to distant shared relatives.
While the number of common genetic ancestors is greater the closer people are to each other, even individuals living 2,000 miles (3,220 kilometers) apart had identical sections of DNA that can be traced back roughly to the Middle Ages.
The findings indicate that there was a steady flow of genetic material between countries as far apart as Turkey and Britain, or Poland and Portugal, even after the great population movements of the first millennium A.D. such as the Saxon and Viking invasions of Britain, and the westward drive of the Huns and Slavic peoples.
The study did find subtle regional variations. For reasons still unclear, Italians and Spaniards appear to be less closely related than most Europeans to people elsewhere on the continent.
"The analysis is pretty convincing. It comes partly from the enormous number of ancestors each one of us have," said Mark A. Jobling, a professor of genetics at the University of Leicester, England, who wasn't involved in the study.
Since the number of ancestors each person has roughly doubles with each generation, "we don't have to go too far back to find someone who features in all of our family trees," he said.
Jobling cited a scientific paper published in 2004 that went so far as to predict that every person on the planet shares ancestors who lived just 4,000 years ago.
Experts say the study's findings need to be compared with what we know about population movements in Europe and elsewhere from other fields, including archeology and linguistics.
"Although, as the authors note, the approach is inherently 'noisy' (i.e. error-prone), it still does give results for European populations that are in reasonable agreement with historical expectations," said Mark Stoneking, a professor evolutionary anthropology at the University of Leipzig, Germany, who also wasn't involved in the study. "It would be interesting to see this applied in situations where we don't have such good historical information."
Coop and Ralph said the findings might change the way Europeans think about their neighbors on a continent that has had its fair share of struggle and strife.
"The basic idea that we're all related much more recently than one might think has been around for a while, but it is not widely appreciated, and still quite surprising to many people, even scientists working in population genetics, including ourselves," they said in an email to The Associated Press. "The fact that we share all our ancestors from a time period where we recognize various ethnic identities also points at how we are like a family — we have our differences, but are all closely related."
Just don't expect news of closer family ties to prompt a surge of brotherly love in Europe or elsewhere.
"There have been many studies that we've been involved in showing that groups which are fighting each other furiously all the time are actually extremely closely genetically related. But that's never had any impact on whether they continue to fight each other," Jobling said.
"So for example Jewish and non-Jewish populations in the Middle East are extremely similar genetically, but to tell them they are genetic close relatives isn't going to change their ways."