Jun 8, 2012 - Ancestry

Three Degrees of Genetic Separation

(Click to enlarge)

While the PBS series Finding Your Roots made only passing reference to connections between guests, the truth is that each guest is genetically separated from other guests by at most three degrees.


The graph above shows a simplified view of just some of the connections between guests on Finding Your Roots. We’ve cut out most of the interconnections because otherwise, it would look like an unintelligible ball of yarn.

In actuality, every guest is connected to every other guest, and in fact, any two people who have been genotyped by 23andMe’s Personal Genome Service can be connected to each other — or to a Finding Your Roots guest — through one or two 4th or closer cousins.

The connections in the graph reflect 23andMe Relative Finder matches between individuals, which are based on segments of shared identical DNA. Check out your own Relative Finder to see who you’re related to in 23andMe’s database.

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Harry Connick Jr. to Robert Downey Jr.

By tracing paths through related individuals in 23andMe’s database, we learn that Harry Connick Jr., Robert Downey Jr., and Barbara Walters are all direct cousins, that Martha Stewart and Samuel L. Jackson have a mutual cousin, and that Condoleeza Rice, Cory Booker, and Geoffrey Canada each share a mutual cousin with Kevin Bacon.

This concept of “three degrees of genetic separation” results from increased human migration across the globe. Over the last 500 years, as people from different geographic regions traveled and mixed, the genetic distances between people also shrank. Go back in time, and the corresponding distances between two people may have been more like eight or nine genetic degrees.

From the graph, we can see that Angela Buchdahl represents a genetic “bridge” between her Korean and Ashkenazi Jewish heritages, linking people like Margaret Cho to Barbara Walters. Barbara Walters must have also had many ancestors that spanned different regions and populations, as she represents common links between Angela Buchdahl, Kyra Sedgwick, Robert Downey, Jr., and Harry Connick, Jr.

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