One of the key new features of the 2019 update to the Ancestry group of websites is the Common Ancestor feature. This is a little different, both in content and display, from Ancestry’s previous Shared Ancestor Hints feature. Common Ancestors does not rely on you both having a, ahem, common ancestor in both your trees. Instead it does what many genealogists already do and build a link between the two trees using both your trees and other people’s trees. This will typically mean you have more Common Ancestors than Shared Ancestor Hints. In my case I have 25 Shared Ancestor Hints but 51 Common Ancestor hints. I’m guessing that the algorithm Ancestry is using is actually quite computationally heavy. This would mean that building and refreshing this list takes time. This would fit in with the fact that yesterday I only had 40 Common Ancestors.
It’s probably now time to cover how the Common Ancestor feature works.
To begin with, Common Ancestors can be found in your DNA match list and you can use the filter function there to show only Common Ancestor matches. Clicking on a match you are presented with the compare screen for the match. This shows how your Ethnicity results compare, your shared Migrations as well as any shared Matches. On top of this you will get an information box showing which common ancestors the Ancestry algorithm has identified (see below). In this case my gg-grandparents John Stewart and Jane Bell have been identified. I’ve already written about them here. You have to select which one you think is the common ancestor, although in reality, I have no way (yet) of knowing which one it is.
Once you have completed this selection you are then shown Ancestry’s best guess on the connection (see below). For privacy reasons, I’ve removed some of the identifying information on the match, so I’ll just refer to them as RB.
Note that the suggestion box shows a grey drop-down box, which also indicates the number of intermediate generations skipped. These drop-down boxes can be expanded, as per the image below.
The important detail here is that Ancestry is using the details from RB’s tree to identify their mother, however their grandfather’s information is from my tree. As an aside, RB only has the surname of their grandfather in his tree. There are other public trees on Ancestry that make this link between CS and O clearer. My tree did not have his mother, O, in it. From this example it is unclear if Ancestry’s algorithm used the intermediate trees.
There are other examples where it is much clearer that Ancestry is using intermediate trees. Below is one such example. It features my 4th Great Aunt, Margaret Angus, who was incidentally a Mormon Handcart Pioneer. I have a DNA match to TM, who is identified via the Common Ancestor feature as a descendant of Margaret. Our two online trees do not connect, in fact TM has only 9 people in their tree. My family tree, as is typical for the way I work, only has siblings of my ancestors and one further generation in it. Normally you wouldn’t be able to identify the link between our two trees.
There is however at least one other online tree which links myself to TM (it has person A, the grandson of Margaret Angus, as well as L, her great-grandchild in it).
There is one problem with this methodology, it may not be correct. I’ve done a little research on the ancestors of TM and I’m not sure Ancestry has got the correct link.
Caveat Emptor – beware false trails
Obviously, as with any automated research, there is the risk of “false postive” hints. Those hints that suggest a relationship, but aren’t correct. Needless to say, you should review all hints you receive. As part of this you should look at the number of different trees used to create a common ancestor hint. In the example below 8 different trees are being used. More importantly I do not believe that the hint linking my ancestor, Ann Atkinson, with her father is correct. (She is recorded as Illegitimate in both baptism and marriage records).
Firstly I should say that this tool is in Beta. This means it may change before general release or it may even never reach that stage and remain in Beta (like the New Ancestor Discoveries feature). It could even be withdrawn.
This tool automates a methodology that many genealogists, myself included, already perform in reviewing DNA matches. Having the tool both saves time and guides people in their research.
There will be people who get upset about the “false positives” that it generates. This is understandable. The reality is that this is mostly due to errors in existing family trees. Every family tree, including my own, has errors in it. We just don’t know where they are. Some of these errors are more obvious than others. Hopefully this new algorithm finds the correct relationships and doesn’t end up propagating the errors.
Does it change the way we develop our family trees ? Perhaps. As I mentioned, I try to include my ancestors siblings and their children in my family tree. Having this information, available and correctly researched, should help the algorithm build out the Common Ancestors.
The question is should I build out further ? Normally I’m not a fan of such extended trees. Ancestry (and all other public family tree sites) has a number of “Monster” family trees (typically over 10,000 individuals). These trees tend to be error-prone, both due to their size and the fact that they are normally deeply researched. Will this new feature propagate the errors in Monster trees ?
Overall this is a great step forward for Ancestry. As an organisation Ancestry has always tried to push “guided research” i.e. suggesting the most-likely information that will help people build-out their family trees. There are many people who take a DNA test “just for the fun of it”. They typically have only small online family trees, although in many cases the information on there ancestors is available. I hope that this guided approach will encourage them to look deeper into their family history.
P.S. One thing I’ve noticed from going through these screens is how often my mugshot appears on them. Perhaps I should try and get a better one !