From Ireland to the Balkans, Europeans are all closely related according to a new study of the DNA of people from across the continent. The study, conducted by Graham Coop at the University of California, Davis, and Peter Ralph of the University of Southern California, examined relatedness among Europeans up to about 3,000 years ago, comparing genetic sequences from over 2,000 individuals. Their results are published in the open access journal PLOS Biology.

The researchers found that the extent to which two people are related tends to be smaller the farther apart they live, as one might expect. However, even two individuals as far apart as the UK and Turkey are still likely to share all of each other's ancestors from only a thousand years ago.

"What's remarkable about this is how closely everyone is related to each other," said Graham Coop, Professor of Evolution and Ecology at UC Davis. "On a genealogical level, everyone in Europe traces back to nearly the same set of ancestors within a thousand years.

"This was predicted by theory over a decade ago, and we now have concrete evidence from DNA data." Although the data was from Europeans, the same pattern is likely to apply to the rest of the world as well, he added.

"Imposed on top of this high level of relatedness are subtle local trends that probably mark demographic shifts and historic migrations," Ralph noted. "Barriers like mountain ranges or linguistic differences have also had the effect of slightly reducing relatedness between regions."

"There are lots of tantalizing hints at history," he explained. For example, although the differences are relatively small, Italians tend to have a lower level of relatedness to each other, and to other Europeans, perhaps resulting from the long history of many distinct cultures within the peninsula.

Also, many eastern Europeans showed subtly higher levels of relatedness, possibly influenced by the expansion of Slavic peoples into Europe over a thousand years ago.

To learn about these patterns, Ralph and Coop used ideas about the expected amount of shared genome between relatives of varying degrees of relatedness. For example, first cousins have grandparents in common and share long stretches of DNA. Ralph and Coop looked for shorter blocks of DNA that were shared between cousins separated by many more generations.

Because the number of ancestors doubles with every generation, the chance of having identical DNA in common with more distant relatives quickly drops, but in large samples, rare cases of distant sharing could be detected.

With their analysis, Coop and Ralph were able to detect these blocks of DNA in common between different individuals spread across Europe, and calculate how long ago they shared an ancestor.

The authors hope to continue the work with larger and more detailed databases, including much finer resolution data on individuals from regions within countries.

However, Coop noted that while studies of genetic ancestry can be informative about history, they do not tell the whole story. Archaeology and linguistics can tell us much more about how cultures and societies moved and changed-but in turn cannot always inform us about the movement of people, since people can learn a new language or a new cultural practice whatever their ancestry.

"These studies need to proceed hand in hand, to form a much fuller picture of history over the past thousands of years," Coop said.

Ralph P, Coop G (2013) The Geography of Recent Genetic Ancestry across Europe. PLoS Biol 11(5): e1001555. doi:10.1371/journal.pbio.1001555 FAQ PAGE