Is the human family tree really a tree or more like a tapestry? A number of years ago, Joseph Chang, a statistician at Yale calculated that, for example, every European is related to Charlemagne, provided you look far enough out (think fifteenth-cousin, and so on). Now there’s some genetic research to back up that up.
Here’s Carl Zimmer, writing at The Loom:
Even within the past thousand years, Ralph and Coop found, people on opposite sides of the continent share a lot of segments in common–so many, in fact, that it’s statistically impossible for them to have gotten them all from a single ancestor. Instead, someone in Turkey and someone in England have to share a lot of ancestors. In fact, as Chang suspected, the only way to explain the DNA is to conclude that everyone who lived a thousand years ago who has any descendants today is an ancestor of every European. Charlemagne for everyone!