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 separated from each other guest by at most three degrees — genetically.

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 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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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.

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 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.


  • Tom

    Are these people blocked from showing in my relative finder as cousins? Or do they show up as cousins in other people’s that are cousins? I have no plans to contact them or invite them to a Sunday cookout. It would be fun to be as befuddled as they were about who they are related to in society. Heck, I might even decide to rent some of their movies or go to a concert or watch them on TV. Look a there it is ole cousin Steve on the TV, honey. I will have to put him in our black book of genealogy, if Mr. Gates will send me one of those Fancy Dan books. Heck, I think I will look for one on Ebay for sale, pictures, included.

    After readiing this, they are probably thinking, Dear God, please don’t let him show up in my relative finder.

  • http://www.magazineart.org Michael Ward

    Bequtiful chart. Is there a way to get one like that for my RF matches? I know that all those New Englanders are all interconnected, the the ones from Virginia and Kentucky have me all confused.

    • http://23andme.com Shwu

      There is no timeline for a feature like this at the moment, but we are certainly looking at whether we can incorporate aspects of this concept into the 23andMe service in the future.

  • Ashley

    Aren’t Kyra Sedgwick and Kevin Bacon cousins? Shouldn’t they be linked on your DNA map too?

    • http://23andme.com Shwu

      Hi Ashley,

      Yes, Kyra Sedgwick and Kevin Bacon are also cousins (as was revealed in a Finding Your Roots episode), but the graph has many of the connections cut out so that everyone in the network can be seen and to highlight some of the more interesting and maybe unknown connections, such as the high degree of connectivity with Barbara Walters as a hub. In reality, every single guest is linked to every other guest, at the most through one or two intermediating cousins, but in some cases — as with Sedgwick and Bacon — directly!

  • Dante_G

    Shirley,

    This should more aptly be titled, “Three Degrees of Network Separation” .. Suppose I had a maternal 1st cousin – J, .. and a paternal cousin K, … now J has a paternal 1st cousin Alice .. and K has a maternal 1st cousin Bob ..

    I have *no* genetic connection to Alice .. but this Network Graph, would say I had 2 Degrees of “Genetic” Separation from her … same thing with Bob ..

    Alice and Bob are separated by 4 Degrees, and have no genetic relation at all .. K is 3 Degrees from Alice, and J is 3 Degrees from Bob .. The only genetic connection that is guaranteed, is the 1 Degree of Separation between two cousins at their respective nodes …

    • http://23andme.com Shwu

      Hi Dante,

      That’s a fair point, but I would argue that the way we’re using degrees of “genetic” separation is still in the same spirit as the original “six degrees” concept which used social connections. If I’m friends with B and B is friends with C, I’m two degrees (connections) socially from C even though I don’t have a direct social connection to C. Similarly, if I’m cousins with B and B is cousins with C, I’m two degrees genetically from C even though I don’t have a direct genetic connection to C. In the end, though, it’s the concept that matters, rather than the labels!

  • AD

    I’m glad to hear that , Shirley. Such a feature would bring a dynamical aspect to the existing features. Currently, a new genetic cousin is just that – a new genetic cousin ( especially for those without extensive genealogical trees ). With such a feature, every new genetic cousin would impact one’s network by reducing the distance to some of the nodes, and significantly if they are a “hub” or might bring a new population within one’s network . Such a feature could capture the public’s imagination judging from the popularity of other incarnations of this theme ( especially since a genetic connection is so much more tangible than “knowing” someone).

  • Bailey

    I was told by several computer scientists and bio-statisticians {I’m an anthropology student} that most people share a common ancestor 500 years ago. Do you think there is a connection between that and this finding?

  • http://23andme roydanna (wymer)reando

    my dna says that i am related to susan sorandon,i know that kevin coster is my 5th or 6th cousin but how can I add them or look at there family tree here so i can find out threw there tree how exactley we are related.

    • http://23andme.com Shwu

      Hi roydanna,

      23andMe does not currently offer the ability to contact or view the data of the famous individuals listed in our comparisons.

  • AD

    Is there any update regarding this/ similar feature being available for 23andme customers?

    • http://23andme.com Shwu

      Hi AD,

      There are currently no plans, but it is possible we may develop a feature like this in the future.

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