Friday, March 18, 2022

What About ThruLines?


Exploring the possible family of my fourth great-grandfather, Charles McClellan, it's easy to see there were several other people living near him in that sparsely-populated section of territorial Florida who also claimed the same surname. Some were even mentioned in court documents along with Charles. But were they all his children? Hard to tell from what we've already discovered.

There is, however, another way to explore this possibility: DNA testing. As I've long since tested at all five of the companies which serve the genealogical community, all I need do is explore my results. Since has the largest database for autosomal DNA testing, it makes sense to look there, first. Even though looking for others descended from my fourth great-grandfather pushes us to the outer edge of testing reliability, it's worth considering the suggestions provided by Ancestry's ThruLines computations.

Keep in mind, though, that ThruLines combines the data of DNA testing with the trees of other Ancestry subscribers. And we all know how possible it can be that any given customer's tree can contain errors. Forget those others—my trees can contain mistakes, as well! But we always want to remember that consideration and explore our matches' trees for solid documentation and reasoning.

Opening up my results at AncestryDNA, I could see that ThruLines considered fifty of my DNA Matches to relate to me specifically through Charles McClellan. Among the descendants of Charles, these of his children were named: George (my direct line ancestor, mentioned in his father's will), Andrew, Henry, Charles D., Samuel (also mentioned in Charles' will as his son), and a woman named Mary Jane.

Here is where we can see that warning illustrated clearly. Clicking on the "evaluate" button provided on the readout for Mary Jane at ThruLines, I could see that this match descended from Mary Jane shared only six centiMorgans with me, the lowest that AncestryDNA will report on, and an amount which could just as likely indicate...nothing. From the documentation on the tree of this "match" I could tell immediately we were not talking about the right family. Among the documents attached to this potential relative's tree were records from England and census enumerations from Kansas—clearly not a life story shared by my McClellan ancestors in Florida.

Still, the more hefty cM connections with the McClellan siblings whose names I've already encountered in court records or as neighbors in census records were now showing in my ThruLines records. An encouraging sign, indeed.

Being even more adventurous, I decided to up the ante. I looked for ThruLines to predict the man who would be one generation beyond our Charles McClellan. According to Ancestry, instead of the fifty matches produced when I inspected the connection to Charles, this leap into the unknown produced sixty five mutual descendants. 

Remembering the fluke from the siblings listed as Charles' children, I looked rather askance at this readout, but did explore it, as that is the question I'm entertaining right now in my research. I did, however, note Ancestry's caveat:

ThruLines suggestions come from Ancestry trees and when members make changes to their trees, ThruLines may also change.

Well, of course. But it serves to remind us, lest we become convinced this DNA wizardry is indeed some form of magic. While I will definitely use ThruLines as one form of way marker, it will be the documentation which I can produce by its guidance which will be the foremost and more seriously weighted proof in the analysis.

It was curious to also note this heading that popped up during my exploration of "Unknown," my fifth great-grandfather, whoever he was.

Because of changes in [my tree], the ThruLines for [Unknown] McClellan may be changing. Please check back in 24 hours when the update is complete.

Oh, believe me: I'll be back!


  1. Very good summary of ThuLines and its pitfalls. I also enjoy using it, but it is often wrong. I look for the documentation, though I also love to see DNA matches that give evidence of the link - even (especially) DNA matches with small trees who have no idea about the line of descent. Most don't really care, I think, given the blizzard of users with tiny trees. But I like to figure them out anyway.

    1. There are a lot of us who have learned to give the benefit of the doubt by building out the other person's tree. Of course, looking at it from the other person's point of view, for those just starting out, there is so much to learn. Despite all the pitfalls, Lisa, I'm finding the more matches I am able to confirm, the more those other little mysteries fall into place--even some of the matches with those tiny trees.


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