Why ThruLines is an Improvement (Really!)

I've been hearing a lot of negativity about AncestryDNA's new feature ThruLines (aka Common Ancestors when viewing your match list - they are the same thing, just different ways to view them), which seems to be replacing both DNA Circles and Shared Ancestor Hints. It works by looking for a tree connection between you and a DNA match through other family trees, not just yours and your match's trees.

Naturally, this opens the system and connections up to a lot of room for error. We all know how inaccurate some trees out there can be, how those errors can get copied by the dozens, and I'm not going to pretend that this isn't an issue. Anytime you're working with trees, you absolutely must verify the information yourself before you accept it as fact.

But that doesn't mean ThruLines can't be useful. I've been working with them for a few weeks now, and I have found that the majority of them can be verified with a little work. Some of them I haven't been able to verify at all and remain unknowns, and others I have actually proven wrong, but the amount of them which I've been able to confirm far exceeds the old Shared Ancestors Hints which were limited to looking at your tree and your match's tree only. ThruLines is finding legit shared ancestors that neither the system or myself doing the work manually could have ever found before. Take the following example.

As you can see, Sally has a family tree with only 3 people in it and on top of that, it's a private tree. In the past, this would be a complete dead end. Unless I contacted her and she responded to tell me more about her tree or at least give me access (which I likely wouldn't do for every match at this distance), I would have completely written off this match in the past.

But now, ThruLines has found a common ancestor! Just by adding those mere 3 people to her tree and making her tree searchable even if it's private, Sally has allowed ThruLines to find a connection between us. Of course, I first have to make sure ThruLines isn't leading me astray, so let's look at the connection.

Part of what you're seeing here is the benefit of researching as far down the descendant lines of your ancestor's siblings as possible. When I first looked at our ThruLines relationship, I had only researched down to Samuel Gross, and Sally's tree only went back to her grandparent. The two generations in between were being filled in by ThruLines finding them in other trees. Of course, to verify the relationship, I had to do my own research and fill in the missing generations, but this was much easier since I'd already gotten a head start. I researched all the way down to Sally's grandfather, Robert. Since her tree was private, Robert was originally shown as private, but you can actually click on deceased people in private trees and get basic details like their name and birth, just like you would from clicking on results of a private tree in the search engine results (see below). If they are still living, you get nothing, as it should be - living people's privacy is always totally protected (also see below).

In the past, if a tree was private, we got nothing unless the tree owner chose to share info or an invite with us. But with ThruLines, we can now see which common ancestor we share and get basic data on each generation even from private trees, enough that we can then go and research the pathway ourselves and verify it, which is exactly what happened here.

ThruLines isn't perfect, of course. It's only as reliable as the trees it's using, and I have found errors in the trees it uses on occasion. Additionally, the system itself is not infallible and I have come across the occasional case where ThruLines is assuming two different people are the same person. In those cases, the error is with the system, not the trees it's using.

But we are genealogists - fact checking and verifying data is what we do. So let's do it! You might find ThruLines just as beneficial as I have so far. It has found common ancestors with people that the old system wouldn't have, and with people I never found have by searching manually on my own.

Are they really a 4th-6th cousin?

At all DNA companies, matching with other testers includes an estimated relationship (usually a range) based on how much DNA you share. The key word is "estimated". There's plenty of examples of finding relatives whose relationship to you actually winds up being outside the estimated range.

AncestryDNA has the option to click on how much DNA you share (when you're on the match review page - click the little "i" icon if you're on the match list page) where previously, it just gave us generic info about that estimated relationship degree. Now (and this may only be available on the new beta match list), it gives us specific probabilities of each possible relationship based on the exact amount of DNA you share. What I found is that sometimes, even their statistical probabilities don't stick within the estimated relationship range.

Above left is an example. This is with a confirmed 3rd cousin of my mom's, an estimated 4th-6th cousin. Again, it's not unusual that the actual relationship is outside the estimated range, but AncestryDNA's predicted relationship range doesn't even seem to be following their own statistical probabilities. As you can see, 65 cM shared has the highest probability (32%) of being 3rd cousins (or 2C2R, Half 2C1R, or Half 1C3R), which isn't even within their predicted 4th-6th cousin range. No prediction system is going to be perfect (because there's a lot of overlap between different relationships so no estimate will be exact), so I'm not saying anything is wrong with the system, I'm just pointing out that this new statistical probability option will tell you a lot more than the predicted relationship range, so don't overlook it.

Of course, this doesn't mean the actual relationship will always be the one with the highest probability. Lower down on my mom's list is a known 4th cousin sharing 57 cM, and the highest probability is still 3rd cousins at 28%. 4th cousins only have a 16% probability, but this match falls into that 16%.

These probabilities will especially be great for unknown close relations popping up, or telling the difference between full and half siblings. My grandfather's half niece, for example, has an estimated range of 1st-2nd cousin, but in the probabilities, it lists all the possible relationships, including half niece/nephew at 96% probability. In fact, at the amount of DNA they share, it doesn't even list 2nd cousins in the probabilities, ruling that out completely even though it's a part of the original predicted range.

DNA Painter offers the same type of probabilities, but collected from multiple companies, not just AncestryDNA data. It's a great tool for matches from companies who don't provide these probabilities, but now that AncestryDNA does, their internal probabilities are likely a better option for your AncestryDNA matches, since the data is specific to them.