3 Degrees of Separation: Genetic Connectivity

When we learn about our ancestors, who they were and where they came from, the discoveries become part of how we define ourselves and how we understand ourselves to be unique. The PBS series Finding Your Roots has taken this a step further, showing us how much we share with others and how interconnected our stories are.

This has been a theme of the 10-part series, something that the show’s host, Professor Henry Louis Gates, Jr., has returned to again and again — that despite our differences, whether racial or cultural, Americans are more interconnected than we know.

It isn’t just that our stories share parallels, but that the connections run deep and can be seen in our DNA. It’s an irony that as the world’s population has grown exponentially in the last 500 years — from about half a billion to now seven billion — we are actually closer and more connected.

During the filming of the show, Professor Gates visited 23andMe and talked to scientists Mike Macpherson and Joanna Mountain, both of whom served as consultants to the show. At one point Macpherson taped up photographs of the roughly two-dozen guests who appeared in Finding Your Roots onto a whiteboard. Then he sketched out the genetic connections that linked this seemingly random collection of people.

Scientist Mike Macpherson and Henry Louis Gates, Jr.

Scientist Mike Macpherson and Henry Louis Gates, Jr.

This was the first time that someone had demonstrated the genetic connectivity of any two people on earth. Macpherson was able to make some surprising links that connected, for example, Martha Stewart to Samuel L. Jackson, and Barbara Walters to the Imam Yasir Qadhi.

Unlike previous examples that relied on social connections — friends of friends of friends — this connection is through cousins matched within a genetic database of over 150,000 people.

This wasn’t just a parlor game. Indeed that notion that any two people — a cop in New York and a street vendor in Mumbai, say — could be connected through five other people was first written about by Stanley Milgrim from experiments he did in the late 1960s. It’s a little more complicated than what Milgrim theorized but he got the gist right.

These previous theories of connectivity focused on social connections; the idea that we are all — all seven billion of us — linked to each other by six degrees of separation. This theory of connectivity even spawned a game named after one of Gates’ guests, “Six Degrees of Kevin Bacon.” The game links any actor to Kevin Bacon by five other performers. Bacon — whose wife Kyra Sedgewick was also on the show — said for a long time he hated that his name was the punchline for a joke. But he has since embraced it and is using the idea of social connections to link people to worthy causes.

More recently Facebook and LinkedIn have shown that just four “connections” could link any two people together.

Macpherson connected the Finding Your Roots guests via a much shorter genetic chain. Any two people are connected through just one or two other individuals.

Why is this a revelation?

It’s new because this isn’t the notion that you are connected to someone else because of who you know. It’s the notion that you are connected to someone because of who you are related to.

People are no longer isolated by geography and so the differences between people are smaller than in the past.

Perhaps in no other place has the convergence of people of different cultures and histories been as dramatic as the Americas. And while the clash of cultures and histories has been both painful and brutal at times, it is what forged our history more than anything else, Gates argues.

“I’ve always thought that it was that story of America,” said political commentator Linda Chavez in the last episode of the Finding Your Roots series.

People came here from all over the world, some voluntary and some involuntary, and mixed, she said, “and that’s made us stronger.”
About the Authors:
Joanna Mountain is a geneticist who is a consultant to the PBS series “Finding Your Roots,” and consulted previously on the PBS series “Faces of America.” Dr. Mountain completed her PhD in Genetics at Stanford University and has spent over 20 years studying human genetic diversity. Currently, she is Senior Director of Research at 23andMe, Inc.

Scott Hadly is a writer with extensive experience as an investigative reporter. Currently Mr. Hadly is Content Editor at 23andMe, Inc.