First, here's an excerpt from the article:
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.
Citation: Ralph P, Coop G (2013) The Geography of Recent Genetic Ancestry across Europe. PLoS Biol 11(5): e1001555. doi:10.1371/journal.pbio.1001555
So it says that even an individual in England and another in Turkey "share all each other's ancestors" if we go back 1000 years.
Now here's why I find this so remarkable personally. I have worked really hard to find my ancestors. I have found lines in England that go back to the mid 1500s. I also know about ancestors who came to Massachusetts Bay Colony soon after the first pilgrims in 1620, and these folks were adults when they came. In other words they were born in the late 1500s.
And that means these ancestors whose names I know and who are connected systematically down to my parents, me, and my kids, were born as much as 600 years ago. And all of them were born in England.
So that leaves 400 years back to our common ancestor, yours and mine (if you're 100% European).
Four hundred years is about 12 generations, maybe 16.
Going back 1000 years, we all have 2 to the 30the power ancestors. Or more likely the 40th power. That's about 1000000000000 ancestors. But in reality there were only about 30 million Europeans, so clearly we were descended from the same couples over and over again - or at least from the same individuals.
There's no way we are going to know for our own family lines how many duplicates there were. Of the 3 or 4 couples I know about from about 1600, I have about 66000 ancestors in 1000AD - but many of those are going to be duplicates.
Somewhere back there our attempt to know all our ancestors loses all meaning! In 1000AD, there were 30 million Europeans. Even though any family could have known the names of some of their lines, the task even over a few hundred years becomes impossible to track. Here is the number of ancestors that you have back just till the American Revolution, a mere 240 years ago, assuming 4 generations per hundred years. (With reproductive age beginning at 16, it could easily have been more generations per hundred years.)
1 - 2 (meaning, 1 generation ago you had 2 ancestors, namely your parents)
2 - 4
3 - 8
4 - 16 (this is how many you had about 100 years ago, or in about 1900. Do you know their names?)
5 - 32
6 - 64
7 - 128
8 - 256 (this is how many ancestors you had about 200 years ago, or in about 1800)
9 - 512 (this is how many ancestors you had who were alive at the time of the American Revolution)
Of course it depends on when you were born and the details of what age they were when they had kids and so on.
But of those 512 ancestors, how many are there whose names you know? How many duplicates were there? Most of us don't know these things going back just 200 years, maybe not even in 100 years.
Now take it back to 1700. That's 2^12 ancestors, or about 4100 ancestors - 3500 more than a century later!
And of these certainly some were duplicates.
How far did your ancestors travel to find mates? How often did they marry cousins?
Actually we have some clues about these things. People - unless they were male Vikings - didn't travel far. And they married cousins a lot, most of the time without knowing it.
For our families, though, it's impossible to know these things from the historical record, from any existing written record.
And that's where the DNA record comes in. According to the article mentioned earlier, the same long unvarying strands of DNA - which implies close relationship - occurred in every European (2000 in all) whose DNA was tested!
Bottom line, from the UK to Turkey, we all drew from the same pool of ancestors in 1000AD. The DNA says so.
We're not going to know their names. They're cousins, of that we are now certain. Or I should say we're cousins. WE are.
(I'm really sorry we can't know the details, I have to say. I really would like to know where I've been all these generations!)