How Do Ancestry Thrulines Work (A Tutorial)

This article looks in depth at how Ancestry Thrulines work. A deeper understanding will help you assess their accuracy and avoid some pitfalls.

What Are Thrulines On Ancestry?

Thrulines is an Ancestry display feature that groups your DNA matches under potential common ancestors. Ancestry combines linked searchable trees to suggest how you and your DNA matches may be related.

It’s important to understand that Thrulines are suggestions based on an analysis of other members’ trees. If the trees are incorrect, then the Thrulines they influence will also be incorrect.

Thrulines was introduced in beta in early 2019 and subsequently rolled out to all Ancestry members. The feature was a little glitchy in beta phase as Ancestry tweaked the algorithms. It’s stable now and can be a valuable tool in your family research. But the suggestions can also be drastically wrong and should be thoroughly researched before making additions and changes to your tree.

How To Use Ancestry Thrulines

You are presented with a grid of your direct ancestors from the tree that is linked to your DNA. In the image below, I’ve hovered over one of my 2nd great grandparents in the Thrulines display. Ancestry is suggesting to me that there is one DNA match that is also a descendent of my ancestor.

Clicking on the evaluation link gives the next display, which is the visual representation of your suggested relationship with the DNA match.

Thrulines are built on Private and Public Trees

Here is one of my Thrulines with a match labelled as “MF”. The tree of this match happens to be private. So how come her suggested mother’s name and dates are being shown to me?

Those details are pulled from my tree. Ancestry is telling me that the same person is possibly in her private tree, based in part on a comparison of name, dates, and other facts.

If I click on the DNA match to view her tree, I get the usual advice to ask for permission to access the private tree. I happen to know that in this case, the Thruline is completely correct.

We Don’t All Get Thrulines

Yes, I only have one match grouped under this particular ancestor. For a long time, that’s the only Thruline I had at all. Most of my ancestors had no Thrulines and my solitary cousin turned up under each generation of our common line.

Then in early 2020, almost a year after the introduction of Thrulines, I received five or six more. It’s all about new or extended trees linked to your matches. If they do the work, you reap the benefits!

What Are Potential Ancestors?

In the ThruLine for my single match, our common ancestor is displayed within a solid box. So what do dotted lines mean for an ancestor in your grid?

The dotted lines denote a Potential Ancestor. This means that the person is not already in your tree. Ancestry has found the entry in one or more trees elsewhere and is saying this is potentially an additional ancestor of yours.

Ancestry hasn’t changed your tree, of course. You don’t have the entry yet, hence the dotted line.

These ancestor boxes behave similarly to the solid ones. Hover to see how many DNA matches are grouped under this ancestor, and click into the box to investigate the ancestral paths.

So, this feature may be hugely beneficial…if the information is correct. It gets you back to higher generations and breaks down brick walls. But I’ll sound a note of caution, as in many cases there are layers of uncertainty piled on top of uncertainty.

Combining Multiple Trees

Ancestry does not simply compare the trees of you and your match. Neither of you may have the ancestral line in your tree.

Take a look at the Thruline for my match J.D. Every generation is a dotted box, which means none of those persons are in my tree.

Yet when I look at J.D.’s tree, I see a three-person tree with J.D. and her parents. Both parents are living, so I cannot see their details.

So three of the generations between J.D. and our Potential Ancestor are neither in my tree or hers. Where did they come from?

In this case, Ancestry has combined information from nine trees, none of which are linked to any of my DNA matches. I know this because Ancestry helpfully displays how many DNA matches are involved, zero in this case.

How the heck does that work? To answer that question, and to evaluate if this is more than tossing rune stones, we need to take a look at an Ancestry patent dating back to 2014.

Here comes the science bit

How Does Ancestry Thrulines Work?

When Thrulines was first introduced, there was a lot of speculation as to how Ancestry was serving up people who weren’t in the trees of you and your matches.

Ancestry themselves haven’t been particularly clear about it. They have published white papers on the methodologies and genetic algorithms underpinning their DNA matching and ethnicity features. But not on Thrulines or the Hints engine.

Sure, there are a few support pages – but they don’t lift the hood and let us have a good root around in there.

The Family Networks Patent

Ancestry filed a patent way back in 2014, which describes a system that would combine DNA analysis and family trees to identify what it called “family networks”. Patents aren’t easy to read, so I’ll try to paraphrase in easier terms.

Let’s say you add your great-grandparent, John Smith, to your tree.

An Ancestry engine compares his details (name, dates, locations, etc.) to all other searchable trees in its index. This is the Hints engine, so it’s not restricted to trees linked to DNA matches, yours or otherwise. At this point, you may start seeing those green leaf hints appear on John’s profile in your tree.

So, what has this got to do with the future feature of ThruLines? First, let’s take a brief moment to remember a predecessor of ThruLines: the Shared Ancestor Hint.

Shared Ancestor Hints (Retired)

The patent describes several alternative systems. One is much simpler than the others. The simpler system takes a pair of DNA matches and searches their trees to locate one or more common ancestors.

In other words, the ancestor must be in both trees. Ancestry would attach a special leaf to show you that an ancestor was in both trees. This feature was called a Shared Ancestor Hint. It co-existed for a while with the introduction of Thrulines, and then was quietly shelved.

When I say simpler, I’m talking in terms of the complexity of processing. In 2014, Ancestry’s data systems were beginning to strain at the seams. They embarked on a transformation of their data onto a new platform for indexing and searching.

Then Ancestry introduced a system that was more complex than Shared Ancestry Hints. But it wasn’t Thrulines. The new process was called DNA Circles. It too co-existed alongside the introduction of Thrulines for a while, and then it was retired.

DNA Circles (Retired)

A more complex process identifies all descendants of John Smith across all Ancestry trees. Let’s say John had eight children. But you only have one son, your grandfather, in your tree. Ancestry goes looking for the seven siblings and pulls them into what it calls a descendant group.  Rinse and repeat, all the way down to the person in the tree who is linked to a DNA test. These tree profiles, usually the Home Person, are also group members.

At this point, the process looks to see if any group member has a DNA relation amongst the other members. If there are, they are pulled into a subset called a Family Network.

So, this Family Network is based on both trees and DNA. And that was the advantage of DNA Circles – it was definitely based on DNA as well as trees. Here’s a direct quote from the patent:

In this embodiment, a family network includes only a common ancestor and individuals who are shown to be related via both genealogical and genetic data and is more likely to exclude tree members who were added incorrectly, for example through errors in the curation of the genealogical data.

Personally, I never received a DNA circle. And one of the more frequent questions on forums was: why don’t I have any DNA circles? Some people were genuinely upset and frustrated by seeing lots of discussion about them on forums, but not getting the benefit of the feature themselves. Some said they would cancel their subscription as they weren’t getting the same benefits as others.

I think people understood that it wasn’t Ancestry’s “fault” if some people have a thousand fourth cousins and some people (like me) have a hundred. But Ancestry did puff up DNA circles as a big offering and competitive advantage. So, it was a let-down to be outside the circle (every circle!), so to speak.

Thrulines Do Not Involve DNA

There is another process described in the patent, which is a variation of the above Family Network. It basically doesn’t bother with the consideration of a genetic relationship. Each descendent group, i.e. all descendants of a single ancestor, is defined as a family network – without the extra evaluation of DNA.

This process is actually described first. Then the patent moves on to the alternative process that includes genetic consideration. And points out, in a paragraph that I’ve already quoted, that the subsequent process is more likely to exclude tree members who were added incorrectly. Ya think?

I’ll say it again because it’s important. Thrulines is based on the process whereby every descendent of a common ancestor – identified purely through member trees – are added to a family network without consideration of DNA.

You may be thinking – all my Thrulines end in a DNA match, so surely DNA is involved. No, not in the creation of hypothetical pedigree lines descending from a common ancestor. That all comes from trees without the additional check that they are associated with your DNA matches.

It’s just that when it comes to the display, Ancestry restricts the Thrulines to be those who end with a DNA match to you.

Thrulines And Trees – Gigantor Or Minions?

There is one other crucial difference to Shared Ancestor Hints and DNA circles. Those earlier features required each DNA match within the family network to have a tree with a common ancestor.

Thrulines combines multiple trees to produce a hypothetical pedigree line. My match, JD, who only has her parents in her tree? I get to see her at the bottom of a five-generation pedigree, in which neither of us has the common ancestor at the top.

There was a lot of speculation when Thrulines rolled out as to how they were being generated. One forum commenter suggested that Ancestry was using a hidden merged tree.

A genealogist suggested it might be a reincarnation of the World Tree, which Ancestry had discontinued. This was the same kind of giant tree of mankind that the FamilySearch organization uses. All trees are mashed together, with a view to getting us back to Adam and Eve.

I don’t believe there’s one gigantic super-tree (to rule them all). The patent provides the mathematics underlying what happens behind the scenes when any of us create a new linked tree with one or more direct ancestors.

For each ancestor, Ancestry evaluates whether this person is completely new and unknown in its database of ancestors and their descendants.

If the person isn’t recognized, Ancestry creates a new descendent group of children, grandchildren, and so on down the line. Now, all future tree entries will also be compared to these new descendant groups.

So, it’s not one Gigantor behind Thrulines. It’s a multitude of smaller descendant groups.

How Far Back Do Thrulines Go?

My Thrulines go back to a maximum of seven generations. That is two more than my tree (at the time of writing, I haven’t been able to verify these potential ancestors).

I can’t find an official pronouncement from Ancestry on the maximum number of generations that can appear in a Thruline. But I haven’t seen anyone else say they get more than seven.

When Do Thrulines Update?

Thrulines are not generated or updated immediately in response to new or updated family trees.

The official line from Ancestry is that you will get Thrulines within 24 hours of linking your DNA to a searchable tree. The tree can be private, but it does have to be searchable. Not sure what that means? Chapter 1 of our guide gives the details.

Some people report that it took three days for Thrulines to appear when they switched their linked tree from unsearchable to searchable.

I’ll go into evaluation and problem-solving in another article. But you may notice that when you change your tree (or someone else corrects theirs at your request) – you still have the pesky incorrect Thruline appearing as an annoyance. You’ve got to wait a few days for the underlying descendant groups to change or drop out completely.

How Do You Get Thrulines?

You’ve come a long way through this article if you haven’t got any. But here’s the two requirements:

The absolute rule is to ensure your tree is linked and searchable.

Ancestry also says that you should “build your linked family tree back at least four generations.” So that’s you, your folks, your grandparents, and your great-grandparents. That’s a little misleading. You certainly don’t need all your great-grandparents in your tree to get Thrulines.

 don’t have my paternal grandparents in my tree, although my maternal side is well-populated. Of course, I don’t get paternal Thrulines. but it doesn’t stop the maternal lines from showing.

More Articles?

Your Thrulines are only as accurate as the trees from which they are generated. The bottom line is that some are going to be garbage. You need to evaluate them carefully before using the information to extend your own family tree.

The evaluation of Thrulines is a topic all too itself. There are also known recurring problems such as second marriages and adoption.

Check out our article “Twelve Tips for Using Ancestry ThruLines“. It gives you a lot of strategies, tips, and tricks for using ThruLines in your family research.


Margaret created a family tree on a genealogy website in 2012. She purchased her first DNA kit in 2017. She created this website to share insights and how-to guides on DNA, genealogy, and family research.

9 thoughts on “How Do Ancestry Thrulines Work (A Tutorial)”

  1. Hello Margaret at DataMining,
    My tree on ancestry is called BUTLER-HARRISON PAVIOUR-SMITH
    My maternal grandmother’s brother, Robert T PATON 1884-1856, has descendants attributed to him who all are those of his younger brother Thomas PATON 1887-1944.
    Robert T PATON had one daughter and she had no descendants. I knew her well, saw her at least every year. Those brothers did not live in the same region, ThruLines for Robert PATON are absolutely incorrect. Yet ThruLines has nothing for his brother Thomas who had 6 children and quite a few grandchildren. I knew 3 of his children and saw some at family reunions and shared lots of genealogy data mutually. The eldest son of Thomas’s eldest child has agreed to have a DNA test as an adoptee believes his brother may be her father. So I wait to see where ThruLines places that descent line. Robert had just one daughter Mavis wgho never married and never had children as she had several health problems that deterred her from marriage and children. She was a fine career woman, Matron of Wellington Public Hospital in New Zealand;s capital.
    I cannot afford to subscribe at the moment nor for some time,. So I am unable to contact those with trees that may have incorrect data. I am the one who has been doing this line of PATON ancestry longest and mine is sourced from the people in the tree themselves, who were very keen for the records to be kept correctly. They trusted me and ThruLines is mucking up that trust that was placed on me.
    Can you put all the descendant lines from Robert T PATON on to his brother Thomas PATON please.
    Thank you

    • Hello Aileen,
      This blog is independent of Ancestry so there is no action we could take.
      You could try contacting Ancestry Support. However, once Thrulines came out of beta, I haven’t seen people mentioning that Ancestry agreed to modify their Thrulines.
      Best regards,

  2. Love AncestryDNA-ThruLines!!!! I have been Linking cousins for the past week all day long! Lots of work but once you get your matches organized by Grouping them, hit the Common Ancestry ones first and go from there. I have seen mistakes but that is because of the information of the other Tree’s no having the correct data. I still am able to link them on my Tree the way they should be. If FTDNA had ThruLines, man it would be much better. Linking my hundreds of cousins that our common ancestor are already found for us, it like icing on the cake! I have also been linking cousin between 6-8cMs with known common ancestors. I have all my 6-8cMs matches grouped and named the group, “StayingAlive”! Thanks for posting your info. How do we get to first part and go up to 14?

    • Great to hear about your strategy, its a good one.
      To get the rest of the chapters – there’s a list of chapters at the top of each chapter, each are links that will take you to the chapter. Just scroll up to the second paragraph in the post.


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