From Ireland to the Balkans, Europeans are basically one big
family, closely related to one another for the past thousand years, according
to a new study of the DNA of people from across the continent.
The study, co-authored by Graham Coop, a professor of
evolution and ecology at the University of California, Davis in the journal PLoS Biology.
"What's remarkable about this is how closely everyone
is related to each other. On a genealogical level, everyone in Europe traces
back to nearly the same set of ancestors only a thousand years ago," Coop
"This was predicted in theory over a decade ago, and we
now have concrete evidence from DNA data," Coop said, adding that such
close kinship likely exists in other parts of the world as well.
How the study was
Coop and co-author Peter Ralph, now a professor at the
University of Southern California, set out to study relatedness among Europeans
in recent history, up to about 3 000 years ago. Drawing on the Population
Reference Sample (POPRES) database, a resource for population and genetics
research, they compared genetic sequences from more than 2 000 individuals.
As expected, Coop and Ralph found that the degree of genetic
relatedness between two people tends to be smaller the farther apart they live.
But even a pair of individuals who live as far apart as the United Kingdom and
Turkey — a distance of some 2 000 miles — likely are related to all of one
another's ancestors from a thousand years ago.
Subtle local differences, which likely mark demographic
shifts and historic migrations, exist on top of this underlying kinship, Ralph
said. Barriers like mountain ranges and linguistic differences have also
slightly reduced relatedness among regions.
Coop noted, however, that these are all relatively small
"The overall picture is that everybody is related, and
we are looking at only subtle differences between regions," he said.
To learn about these patterns, Ralph and Coop used ideas
about the expected amount of genome shared between relatives of varying degrees
of relatedness. For example, first cousins have grandparents in common and
share long stretches of DNA.
Shared blocks 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 shared blocks of DNA in individuals spread across Europe, and calculate
how long ago they shared an ancestor.
Coop and Ralph hope to continue the work with larger and
more detailed databases, including much finer-resolution data on where
individuals lived within a country.
However, Coop noted that while studies of genetic ancestry
can shed light on history, they do not tell the whole story. Archaeology and
linguistics also provide important information about how cultures and societies
move and change.
"These studies need to proceed hand in hand, to form a
much fuller picture of history," Coop said.