This is not that much of a surprise

Civil rights activist Angela David appeared on the program hosted by Henry Louis Gates and was surprised to learn something about her ancestry.

On Tuesday’s episode of “Finding Your Roots,” civil rights activist Angela Davis learned a series of surprising facts about her ancestral history, but one revelation left her outright shocked.

Born in Birmingham, Alabama, Davis grew up not knowing her maternal grandparents since her mother had grown up in a foster home, so she was eager to see if host Henry Louis Gates Jr. could solve that life-long mystery for her. But after digging into her family tree, and then digging even further, he presented Davis with answers to questions that she would have never even thought to ask.

“You are descended from one of the 101 people who sailed on the Mayflower,” Gates said, presenting Davis with a manifest including the name of her 10th great-grandfather.

“No, I can’t believe this,” Davis said. “My ancestors did not come here on the Mayflower . . . That’s a little too much to deal with right now.”

She should really not be that surprised. If one goes back far enough, one will almost certainly come across outliers to the picture one has of one’s ancestry. This is simply due to statistics. As we go back up our family tree, the number of ancestors doubles with each generation: two parents, four grandparents, eight grandparents, and so on. If you go back 400 years to when the Mayflower arrived in 1620, and assume that each generation takes an average of 25 years, then that will give you 216=65,536 ancestors. Given such a large number and that the population was also much smaller then, having one person from any of the people who were there then as one’s ancestor would not be a shocker, whatever ethnic group one is identified with now, since we know that there has been considerable mixing between the races, including between slave owners and slaves.

What is unusual is the ability these days to identify specific named ancestors from that far back, as the DNA and genealogical analyses purport to be able to do.


  1. Matt G says

    The numbers get big even more quickly when it comes to descendants. You can have just two parents, but many children.

  2. Rob Grigjanis says

    If you go back 400 years to when the Mayflower arrived in 1620, and assume that each generation takes an average of 25 years, then that will give you 2^16=65,556 ancestors.

    That doesn’t take pedigree collapse into account. According to this article, the likely number of descendants of the 22 Mayflower families is in the neighbourhood of 3 million. The number living in the US would be even less than that.

    So, maybe a bit surprising.

  3. Matt G says

    Rob@2- An extreme example would be Iceland, where the vast majority of the island’s 200,000 residents are descended from a founding population of about 1000 around 1000 years ago. There is a cell phone app which allows you and your date to tap your phones together to query a database and determine when you share ancestors.

  4. ardipithecus says

    They can’t pinpoint that accurately from DNA alone. All that DNA can show is that they have certain genetic markers in common. It could mean that they had a more remote common ancestor. Angela Davis’s ancestor could have been anyone in Mayflower Davis’s generation who also had those markers, such as a third cousin.

    It would take pretty much complete genealogical records to fine tune it that precisely. Given the human propensity for adultery and other out-of-wedlock sexual liaisons, skepticism is advised.

  5. says

    2 to the 16th is 65,536, not 65,556. As someone with a long history of programming, this one caught my eye like a man with an upside down nose. [Corrected! -- Mano]

    All experienced micro programmers use the 8 bit rollover at 255 and the 16 bit rollover at 65535, so these numbers are permanently tattooed in the brain, just like 3.14159…

  6. Ichthyic says

    “What is unusual is the ability these days to identify specific named ancestors”

    no, what is unusual is that you can’t spot a scam like this apparently. because that’s what this crap is… a scam. that’s why you never see an episode where the featured person’s ancestor is just a normal random person. because it’s literally impossible to do what they are claiming to do. duh.

  7. Mano Singham says

    Ichthyic @#7,

    I do not know what goes into the process so I hesitate to label it a scam.

    What I think is likely is that given the large number of ancestors, there is some chance that, after sifting through many of them, one of them will be a recognizable figure. It is just these ancestral discoveries that are publicized. You are right that almost all our ancestors were ordinary people but that would not make for good TV.

  8. Holms says

    Icthyic, It’s not a scam. This program, and similar ones, use proven genetics relatedness calculations in combination with mundane genealogical methods. The genetics calculations gives them information such as the probability of being X ethnicity based on the degree of similarity to known markers, the lineage checking provides the specifics. The probabilities are always less than certainty, which is why the records checking is always necessary. If one of these companies promises certainties, then it is over-promising and may be a scam, but I don’t think this program does that. I seem to recall even Larry David and Bernie Sanders were given less than 100% chance of being Jewish.

  9. Tethys says

    The program ‘ Finding Your Roots’ has ordinary people with normal random ancestors in every episode. (As does the similar ‘Who Do You Think You Are’ franchise)

    Researching genealogy is not some scam, and DNA doesn’t lie, unlike humans. The DNA is especially useful for people who do not know their ancestors due to being orphans, or simply due to a lack of records.

    It’s atypical for anybody to be 100% of any ethnicity, unless they have some 1st cousins marrying and having children in their recent lineage. It’s considered inbreeding now, but marrying your cousin was once common practice.

  10. says

    I do not believe that this is a scam, either. It’s not as if every guest on the show has some famous relative. Very often it’s just interesting quirks, and I’d bet that sort of thing is common given the huge number of ancestors our “line” can be traced back to. It is amazing the sorts of information that are out there and available, if you’re willing to sift through it all.

    A relative of mine has been researching our family history for years. Typical immigrant stories for the most part, but it turns out that one of my great grandfathers was robbed and murdered while working on the railroads. His son then chased the culprit across Canada to Alaska, but eventually lost the trail. This info came from a newspaper story printed at the time along with subsequent follow-up. No one in the family knew any of this (that son/grandfather had died many years before my parents even met), but the info is out there in the public record. Now imagine that you have a team of people trained to do this sort of research, and I think it would odd if they didn’t come up with surprising tidbits.

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