Using DNA matches to confirm distant ancestors
Several years ago I took the Ancestry.com DNA test and attached it to my tree there. I have two separate trees – one for my father’s side and one for my mom’s. My mom also took the test, and I attached it to her tree. Ancestry then matches our DNA to the thousands of other testers and then shows me how it thinks we are related. They recently rolled out a new visualization tool called “Thrulines” which creates a tree based on existing trees showing how it believes a DNA match is related. For example, it shows 61 DNA matches to me who share a common ancestor of my 3x great grandfather Peter Thornton.
I have already proven through documents that Peter is my ancestor. So why is the DNA important? Because it corroborates that he is my ancestor even though we don’t have his DNA. Because all those cousins also trace back to Peter Thornton through different descendants, I can “safely” assume I am descended from him. And vise versa even if they haven’t completely finished researching their tree.
I put “safely” in quotes because this method isn’t foolproof because it relies on all our trees being correct.
Let me show you where this fails. I had already proven through the records that Thomas Thornton is my most distant Thornton ancestor. But no one has found a record proving Thomas’ parents. So why is Ancestry.com showing me Reuben as a possible father to Thomas and connecting another DNA match to someone who looks like they descended from Thomas’ brother?
Because nearly every tree on Ancestry is wrong about Thomas Thornton’s lineage! For years people have assumed he descended from a man people call William the Immigrant. It made sense – the given names, time period and region all seem to tie together. But recent y-DNA testing (paternal line) proved that our Thorntons were NOT descended from William the Immigrant.
But Thrulines doesn’t know that. Even though the DNA matches are correct, how we are related is generated from people’s trees, so I’m being shown a false lineage based on existing trees with incorrect data. So on Ancestry, when you see someone who says they have “proven” an ancestor by DNA matches – that proof is only as good as the documentary evidence behind it.
That doesn’t mean we should ignore these unproven matches. They are incredibly valuable because now I can work towards our common unknown ancestor from another direction. By figuring out who their ancestor is (which might be easier), I can extrapolate mine (assuming we can find the records to prove it).
So lately I’ve been working on adding DNA matches to my tree (even if I can’t yet make the connection to a common ancestor) to help support my lineage even when I don’t have documentary proof. I am glad to say that most of my tree seems to be proving correct back to about 6 generations (which is about as far as the Thrulines currently extrapolates). I also uploaded my DNA results to several other sites for even more matches (MyHeritage, FamilyTreeDNA, gedMatch, took the 23andme test, LivingDNA). And it’s fun connecting in with all these cousins. You never know when some distant cousin has a box of old photos or information.