Wednesday, April 19, 2017

Erroneous AncestryDNA Genetic Community

North American Genetic Communities map from AncestryDNAReader Clytee Gold wrote me about an apparently erroneous AncestryDNA Genetic Community assignment. One of her two communities is “Mormon Pioneers in the West.” (First, I am jealous that she has two community assignments.) She is rather positive that none of her ancestors were ever Mormons. She has done extensive research and has never found any connection to the Church. As there are still pockets of prejudice against members of The Church of Jesus Christ of Latter-day Saints, this assignment could be highly offensive to some people. Coincidentally—or not—it is not offensive to Clytee. Forty years ago she joined the Church and moved to Utah. She is, literally, the “Mormon Pioneer in the West” of her family.

I’m not qualified to explain how this misassignment occurred, but fools rush in where angels fear to tread. Perhaps experts among my readers can correct me. Clytee gave one possible explanation:

The only thing I can figure out is that is based on OTHERS testing (guess that makes a community - who else took the test to compare to), and that somewhere, 5-6 generations back a sibling of a great-great something of mine joined the church in Denmark in the late 1800's and came to Utah as a "Mormon Pioneer in the west" and populated the west and there are lots of descendants who took the DNA test.

Ancestry has explained that they use an algorithm called community detection to detect groups of individuals with a large number of interconnections. I think of it like large DNA Circles that don’t require common ancestors. The Mormon Pioneers community contains 89,000 testers. Just like a DNA Circle, Ancestry states a confidence level for your membership in the genetic community. My connection to the Mormon Pioneers community is “Very Likely.”

Ancestry says they then examine the Ancestry Member Trees of the genetic community “to learn about the historical forces that may have brought their ancestors together.” Of course, some testers don’t have trees, some don’t include all their ancestors, some have ancestors without complete location information, and some have complete garbage in their trees. I assume Ancestry looks for common locations in 25-year increments. If they find a large number of ancestors who lived in the same place at the same time, they look into the history of that time period and why there was a large number of individuals there. Then they give that community a name.

For example, the sweet spot for one genetic community is centered on Massachusetts in 1725-1750 (shown on the map, below left). Ancestry chose to name that community, “Settlers of Colonial New England.” Another centered on Utah at a much later time period, 1875-1900 (below, right). Ancestry called this one “Mormon Pioneers in the Mountain West.”

AncestryDNA genetic community map for Settlers of Colonial New England, 1725-1750. AncestryDNA genetic community map for Mormon Pioneers in the Mountain West, 1875-1900

I assume Ancestry can follow the group forward and backward in time, up and down the member trees. This provides additional touchpoints to compare against historical sources and decide if they have correctly identified and named the genetic communities. Moving forward in time gives an interesting view on migration that may not be available from other demographic sources. This may truly be groundbreaking demographic tools. For example, look at the 1900-1925 map (below) of the descendants of early residents of Chihuahua and Durango. If I am interpreting the map right, by that time they were as likely to be living in El Paso as Chihuahua. (The large circle over central Texas represents ancestors whose member trees didn’t specify where in Texas they lived.)

AncestryDNA genetic community map for early residents of Chihuahua and Durango, 1900-1925

Moving backwards in time gives an interesting view on where the Mormons who settled in Utah came from. In the period 1825-1850, most were living in England, with a fair number in Denmark. (See map, below.) The surnames associated with the Mormon pioneer genetic community further point to Denmark:

Jensen, Christensen, Larsen, Hansen, Allred, Nielsen, Olsen, Sorensen, Nielson, Rasmussen, Christiansen, Madsen, Peterson, Anderson, Barney, Leavitt, Child, Andersen, Petersen, and Jorgensen

AncestryDNA genetic community map for Mormon Pioneers in the Mountain West, 1825-1850

Once they are sure they have identified the genetic community, Ancestry can take information from history books about that group and display it next to the migration map. However, the information may not apply to your ancestors who didn’t participate in the chain migration. That is how Clytee may have been put in a migratory group that her ancestors didn’t participate in. She told me her ancestry:

My father was half Swiss (4 generations from the immigrant to Missouri) and half German (5 generations from the immigrant to Missouri).  Mother half Norwegian (2nd generation from the immigrant to Iowa) and half Danish (2nd generation from the immigrant to Iowa).

I think the conjunction on Denmark is more than coincidence. Clytee’s Danish ancestors didn’t have to join the Mormon church for her ancestors to share DNA with those that did. I don’t think it had to have been a sibling in genealogic-time, either. I think Ancestry is looking at shared DNA in a closed community with hundreds of years of intermarriages.

There is a possibility that the genetic community Ancestry has identified is actually more specific than “all Mormon pioneers.” Ancestry may have identified DNA of Mormon pioneers of Danish origin. Look back at the dominant surnames for this genetic community. Does it look more English or Danish?

There are other possibilities. Remember the mention of confidence level? Clytee may not belong to the genetic community at all. Her DNA may just be a statistical anomaly. Remember the mention of garbage trees? Ancestry may be running calculations overwhelmed by erroneous information.

GIGO. Garbage in—garbage out.

Thank you, Clytee, for your message.


  1. It's time for ancestry to split into 2 companies independent of each other. We need a data base company that concentrates on data bases and for those who care, a DNA company that concentrates on DNA and all the bells and whistles that can go with it. And stop using trees to mine "facts".

    1. No thanks, then I'll be paying for two subscriptions annually!

    2. T, I agree completely, when I get hints from Member Trees most of the time the trees that have the same exact facts and no sources outnumber the trees with sources and then some of the sources are wrong. They are also giving me DNA Hints based on Surnames but I find no common ancestors and no
      DNA matches; a wate of time, especially since I have so many pages of matches.

      At least I know my Genetic Community - French Settlers of Montérégie, Québec is correct as that part of my Ancestry has been thoroughly researched and proven by DNA!

  2. That is interesting. One of my granddaughters has the "Mormon Pioneers in the Mountain West" as one of her 3 genetic communities and I have found a nice cluster of them in her tree. Her other 2 communities are consistent with one of mine (Colonial New England) and one of her grandfather's (Settlers of Virginia). All 3 are shown with confidence level "Possible."

  3. First, prepare to be REALLY jealous - I'm a member of THREE genetic communities.

    I think the problem may lie in taking the results too personally. If ones ancestry has a similar migration pattern as others - even if they didn't join the Church - they are likely to be lumped in. The same goes for if you have distant relatives (as opposed to direct ancestors) who joined the Church, you are likely to be included.

    It's a tool that has some benefit if you are discovering you genetic past; it's less useful if you already know it.

  4. I have two DNA communities one says most likely Scotland and the other Irish.
    Guess what? I was born in Scotland, only link I know of to Ireland is my gr-grandparents, one born in Ireland and the other Germany. I need to find more Catholic record to go further on the Irish side.
    I have built my entire tree on Ancestry, and pull documents to add and source from Scotlandspeople to prove the records, and do get some Scottish record from Ancestry (wish for more), Scots it seems keep their record very close to home, as the site Scotlandspeople is a paid site.
    I just wish Ancestry could emphasize to the people who only get a DNA test, that it would open and entire new world to them if they built their tree on Ancestry.

  5. Part of the problem will be limited samples in the groups. My wife had her Ancestry DNA test done over a year ago and it gave her completely wrong information. She had Family Tree test her DNA and it showed correct information. The reason was that Ancestry has mostly US samples in their data and Family Tree has mostly British samples in theirs. My wife was born in England and her research shows about 95% English!

  6. I'd rather see them cut out the bells and whistles and TV commercials until they can actually deliver results within a reasonable time frame. Can't help wondering about what new customers who respond to the commercials think after waiting months--even way past the estimated dates--to receive any results for the money they've sent Ancestry.


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