3 Degrees of Separation, Part 2

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

Three Degrees of Genetic Separation

What the graph above shows is 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 and filed in a particular database can be connected to each other — or to a Finding Your Roots guest — through one or two 4th or closer cousins.

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” is a result of increased human migration across the globe. As people from different geographic regions traveled and mixed over the last 500 years, the genetic distances between people also shrank. Go back in time, and the corresponding distances between any two people may have been more like eight or nine genetic degrees.

Angela Buchdahl represents a genetic “bridge” between her Korean and Ashkenazi Jewish heritages, linking people like Margaret Cho to Barbara Walters. Barbara Walters herself 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.
About the Authors:
Scott Hadly is a writer with extensive experience as an investigative reporter. Currently Mr. Hadly is Content Editor at 23andMe, Inc.

Shirley Wu completed her Ph.D. in Biomedical Informatics at Stanford University and now oversees 23andMe’s pipeline of detailed health reports and health-related features. She also contributes regularly to 23andMe’s blog. Currently Dr. Wu is Science Content Manager at 23andMe, Inc