Roots of human tree remarkably shallow

Whoever it was probably lived a few thousand years ago, somewhere in East Asia — Taiwan, Malaysia and Siberia all are likely locations. He — or she — did nothing more remarkable than be born, live, have children and die.

Yet researchers say this was the ancestor of every person now living on Earth — the last person in history whose family tree branches out to touch all 6.5 billion people on the planet today.

That means everybody on Earth is descended from somebody who was around as recently as the reign of Tutankhamen, maybe even during the Golden Age of ancient Greece. There's even a chance that our last shared ancestor lived at the time of Christ.

"It's a mathematical certainty that that person existed," said Steve Olson, whose 2002 book "Mapping Human History" traces the history of the species since its origins in Africa more than 100,000 years ago.

It is human nature to wonder about our ancestors — who they were, where they lived, what they were like. People trace their genealogy, collect antiques and visit historical sites hoping to capture just a glimpse of those who came before, to locate themselves in the sweep of history and position themselves in the web of human existence.

But few people realize just how intricately that web connects them not just to people living on the planet today, but to everyone who ever lived.

With the help of a statistician, a computer scientist and a supercomputer, Olson has calculated just how interconnected the human family tree is. You would have to go back in time only 2,000 to 5,000 years — and probably on the low side of that range — to find somebody who could count every person alive today as a descendant.

Furthermore, Olson and his colleagues have found that if you go back a little farther — about 5,000 to 7,000 years ago — everybody living today has exactly the same set of ancestors. In other words, every person who was alive at that time is either an ancestor to all 6 billion people living today, or their line died out and they have no remaining descendants.

That revelation is "especially startling," statistician Jotun Hein of England's Oxford University wrote in a commentary on the research published by the journal Nature.

"Had you entered any village on Earth in around 3,000 B.C., the first person you would have met would probably be your ancestor," Hein marveled.

It also means that all of us have ancestors of every color and creed. Every Palestinian suicide bomber has Jews in his past. Every Sunni Muslim in Iraq is descended from at least one Shiite. And every Klansman's family has African roots.

How can this be?