Finding Bio-Ancestors

After exhausting all genealogy research, try letting your DNA Matches identify your bio-Ancestor(s).

Think about any bio-Ancestor (bA) for a moment…

1. It doesn’t really matter how or why this bio-Ancestor is known or unknown to you – adoptee, foster child, brick-wall, no records, family story, found under a rock, etc., etc. The issue is you are stuck.

2. However, the bio-Ancestor absolutely had a bio-father and a bio-mother! This is key!

3. These two bio-parents had their own bio-parents – four more Ancestors of the bA; there were eight Great grandparents of the bA; 16 2xG grandparents; etc. The bA had a full Tree of Ancestors, just like you and me.

Yes, there are some negative factors that may come into play (each situation is different):

1. The bA, and/or his/her Tree of Ancestors, may be from outside the US.

2. The bA, and/or his/her Tree of Ancestors, may be from communities in the US with few records and Trees going back – think African Americans, Native Americans, Jews, etc.

3. With every generation going back, the search/research gets harder! The records are harder to find. DNA Matches with deep Trees are harder to find.

But… the bA did have a full Tree of Ancestors. Although not guaranteed, most of those Ancestors were known and left records. Most of those Ancestors had multiple children and multiple descendants – and, almost certainly, multiple descendants who took a DNA test and are Matches to you. Although you don’t know how you are related to them, yet, these Matches exist – they are in your Match list and in your Cluster Groups or Triangulated Groups.

Most of us will have tens of thousands of DNA Matches at AncestryDNA. Some of them will have good Trees going back enough generations to Ancestors of the bA. In my experience, atDNA “works” back to 7xG grandparents (8th cousin level) – I have over 1,000 Matches with Common Ancestors with me at the 8C level. Ancestry’s ThruLines, finds Common Ancestors at the 6C level – their (now defunct) Circles routinely found cousins out to the 8C level. You should have many Matches who are related to you out to the 8C level. The issue is not with the DNA testing, it’s finding Matches with good Trees that go back that far.

So how do we find a bA that we know little or nothing about. We let our Matches identify them! Let our Matches identify the bA or the bA’s parents and/or grandparents! If our target bA is a Great grandparent, we need to find Matches who are about 2nd cousins (2C). These 2C would usually be from a Great grandparent couple. To more precisely target the bA, we’d need 3Cs who descended from a 2xGreat grandparent couple who were the parents of the bA. Or if we don’t have enough 3C, we’d need 4C Matches from the grandparents of the bA.

Each situation is different, but the concept is the same: look at the Trees of Matches for Common Ancestors among the Matches. It helps, a lot, if we can identify, and cull out, Matches who are clearly from a different line than the bA. Or, to put it in a positive sense, we’d like to work with Matches we believe are related to us through the bA line. This is where groups and grouping play an important role. If we can identify Clusters or Triangulated Groups (TGs) from other lines (or ethnicities), we can cull them out. Perhaps we have already determined the grandparent for each of our groups – using the Leeds Method or TGs with known cousins in them.  

The concept here is that each group is focused on an Ancestor (or ancestral line) – whether we know that line or not! We need to look at the available Trees and determine the CAs among the Matches in each group. We are actually looking for information that we didn’t know before, often, but not necessarily, new Ancestors.

The point is that we need to clear our minds, and let the Matches tell us their Common Ancestors.

Here are three graphics that may help you:

1. This is a Crib Sheet to help get oriented:

Column 2 is you and your Ancestors:

Column 1 shows the relationship of Matches who would nominally be related to you. Example:  2C Matches would be related from your Common Great grandparents.

Column 3 shows how many of each type of Ancestor. Example: we all have 32 3xGreat grandparents.

Column 4 is the average birth year for each level of Ancestors (in my case for this chart). You should amend this column based on the average birth years of your Ancestors. This works out to about 30 years per generation in my case.

Column 5 is the number of Triangulated Groups that would be expected to “pass through” each Ancestor. Example: all of my 372 TGs are in me. About 47 of those TGs probably passed through each of my 8 Great grandparents. This provides a rough order of magnitude of the number of groups which might be available for each level of Ancestor. The total number of Clusters would depend on the lower cM threshold.

2. This is the Crib Sheet combined with Ancestral levels – in this case showing a Target bio-Ancestor (TBA in the chart) who is a Great grandparent of the DNA Test Taker (DTT):

The key points here include the F (father) and M (mother) of the TBA; and the TBA’s four grandparents; and the oval that highlights a lot of additional Ancestors of the TBA. All of these Ancestors, as yet unknown to the DTT, are Ancestors of the TBA – AND all are Ancestors of the DTT! These Ancestors are NOT known to the DTT, but they ARE known to many of DTT’s Matches.

3. This figure shows some DTT 3C, 4C and 5C Matches from several Groups (Clusters or TGs):

In general, the Matches with a Common Ancestor to one of the TBA’s grandparents will be in one group.

As the four grandparents are identified, we usually see grandparent marriages, and then, somewhere, there is usually a marriage between their children. This is a strong indication that the TBA (the bio-Ancestor) is a child of that marriage.

This process is part work, part logic, part luck. As I mentioned before, each situation is different. But this concept should provide a framework for finding Ancestors who had children and left records.

Once we have a probable set of parents and/or grandparents, we can usually build the rest of the Tree back using basic genealogy skills. And the DTT in this case should also find DNA Matches who share Common Ancestors from the 8 Great grandparents of the TBA and the 16 2xGreat grandparents and the 32 3xGreat grandparents (provided, of course, they each had multiple children and descendants).

Recommendation: When looking for a bio-Ancestor this way, wipe your mind clean of any pre-conceived ideas, from any source. Rely solely on the input of your Matches. After you have a “solution”, you need to think of ways to validate (or disprove) it.

This is a concept, and not a guarantee. But hopefully it will get you beyond where you were, it will provide new family lines to research, and new Ancestors who should show up as Common Ancestors with your Matches.

Summary: Focus on the red oval above the bio-Ancestor – there are lots of Ancestors in that oval that many of our Matches probably know about. Determine potential DNA Match groups that include the bio-Ancestor and find the Common Ancestor within each group. Look for intermarriages within each group. Let our Matches tell us our Common Ancestors!

[30B] Segment-ology: Finding BioAncestors by Jim Bartlett 20220602

3 thoughts on “Finding Bio-Ancestors

  1. Hi Jim, First of all, I really want to thank you so much for addressing those of who have very few records like me because most of my family was enslaved. I exhausted my genealogy research after my 2nd great-grandparents. I decided to try to find my bio-ancestor, my 3rd great-grandfather. It took me 3 months of research but I think I found him. I am going to present my case to my African American genealogy research group. We are not as well versed in genealogical ways, probably because we get less practice. I hope you can help me. I have several questions for you. I am sending my research plan which hopefully shows how I proceeded. (It is in draft form). My first question is did I do the same thing you were recommending? My second question is what format is clearest to present my findings which I will turn into a PowerPoint presentation? I ending up with cM results from both my mother and her first cousin. My third question is, should I make a chart for each? Finally, you said focus on the people above the red oval, what is the most effective way to start that process? Again, I so appreciate any assistance you can give me. Donise Smith Lei 2nd great-granddaughter of Ewing W Robinson



  2. Thank you for this hopeful and well-reasoned post! I am doing this currently in hopes of finding a mysterious maternal 2xgrgrandmother. I only have her first name, a possible last name that hasnt yielded any paper records and a birthdate range based on when her daughter, my grgrandmother, was born.(1845-1873)
    I found a DNA match cluster in my mom’s side that doesnt match other ancestors on my matenal side. Almost all that I can check on 23andMe or FTDNA or GedMatch share a chunk of C13, at least 20 cms. I am building out their trees and using a few good big match trees. I’ve found 4 sets of common ancestors shared by two each of my TH/Cluster people, and clues to a couple of surnames showing up a lot. AND some common locations are emerging.
    exciting! but this is like looking fir life on other planets! how many CAs should I aim for before drilling down to look for my Elizabeth? should I look for CAs shared by more than 2 of my matches? how will I know if Im looking at her parents generation or grandparents or earlier?
    I could ask my own siblings to test but we have no 1st or 2nd cousins on that line.


    • Sari, There is not set reply – the data is very different in each situation. The correct Common Ancestor (which you should share), should show up in almost all of your grouped Matches. But, as we all know, most of them don’t have good Trees. I start with the surnames that are shared the most within the group. I then look for a Common Ancestor for that surname – hopefully the Patriarch of that family and then work on the children. There should be several (more than 2) Matches who tie into the same Tree. Eventually, with the right CA, I’ve been able to find dozens of Matches to the CA or the CA’s parents or grandparents. Sometimes I’ve tried a surname, but just couldn’t find a common Tree for it – so I moved on to another shared surname. You are on the right track. Jim


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.