Below I will outline a process to find a Target Ancestor (TA) – often a Bio-Ancestor, or a brick-wall Ancestor, or maybe to confirm an “iffy” Ancestor. This is a follow on to Manual Clustering From the Bottom Up. But first, here is a little background.
DNA – We all get exactly 1/2 of our autosomal DNA (atDNA) from each parent. Pretty close to 1/4 from each grandparent ; 1/8 from each Great grandparent; etc. Yes, beyond parents, these fractions are not exact, but for genealogy they are pretty close. The point is that for several generations going back, we get a lot of DNA from each Ancestor – and roughly the same amount from each one in any generation.
Matches – All things being equal, we would get roughly 1/2 of our Matches through each parent; 1/4 through each grandparent; etc. But all things are often not equal:
1. We tend to get fewer Matches from Ancestors who are recent immigrants (say in the last 4-5 generations). It’s because most test takers are Americans.
2. We will get fewer Matches from “skinny” families – an Ancestor who had 2 children will have far few descendants (and Matches) than an Ancestor who had 15 children.
3. Endogamy results in many more Matches than usual (think Jewish, Mennonite, Polynesian, etc.)
Each of these factors will unbalance, or skew, the number of Matches we get for each Ancestor.
For the purposes of this process, I’m going to assume that our Matches are generally spread fairly evenly over our bio-Tree. To the extent this isn’t true in your case, this process may be more complex, or it may not even work.
When we are looking for a TA, the concept is that a good chunk of our DNA came from that Ancestor (depending on the number of generations back), and a good chunk of our Matches will be cousins – either to or through that Ancestor. Although the Ancestor is not known to us, the TA did have 2 parents, 4 grandparents, etc., and those more distant Ancestors may be well known to our Matches. NB: an immigrant Ancestor may throw us a curve ball here.
The process overview is:
1. Group Matches;
2. Find the Common Ancestor (CA) in each group;
3. Build down from the CA to find links between groups (usually, but not always, a marriage);
4. Build down from those couples;
5. Repeat as necessary (usually down to parents or grandparents of the TA);
6. The end-game may involve date and location issues and further DNA target testing to isolate and identify the TA.
More step-by-step details:
Step 1: Group Matches – this is basically Manual Clustering at AncestryDNA. Start with the Match list from 400cM down. How far down depends on the generation of the bio/brick -wall Target Ancestor (TA). You want to go back 2 more generations. So, if the TA is a one of 4 grandparents (1C level), you’ll want Matches who are 3C level, say a 50cM lower threshold. You want 16 groups. NB: if you can filter out some Matches – say you know one “side” and can identify those Matches, you can cut the groups to 8. And you may be able to quickly identify 4 of those groups to a known grandparent. This would leave you with the 4 groups that represent the 4 grandparents of the TA.
1A. List these Matches in a spreadsheet or write on a piece of paper
1B. Select a Match about 3/4 of the way down the list [avoid starting at the top!]
1C. Open that Match’s Shared Match (SM) list
1D. Put an A next to that Match and each Match on your List who is on the SM list. This forms a Manual Cluster A, which tends to have a Common Ancestor (CA).
1E. Start over at Step 1B, selecting a Match who is not A, and use B.
1F. Repeat as often as necessary, using new letters, until all Matches on your list have at least one letter. NB: The Matches at the top of your list may wind up with multiple letters.
1G. If lower cM Matches have multiple letters, review their SM list – usually one of the letters is a one-of-a-kind and that letter can be deleted. If there is a lot of overlap, between two letters, they can be combined, using one letter. Use judgment.
Usually this Step can be done in a few hours.
Step 2: Find CA for each Group – this takes some poking around…
2A. Select a Group, and open any available Trees (including Unlinked Trees)
2B. Type/write next to the Match the closest 10-15 surnames
2C. Repeat for as many Matches in the Group as possible
2D. Look/search among the surnames for common surnames
2E. Open the Match Trees and select Ancestor information with the common surnames
2F. Analyze and record the probable Common Ancestor for the Group [if necessary, look at more SMs for the Group Matches for confirmation of the CA]
2G. Repeat for each Group
2H. Note the place/date-range for each CA [these may be a clue to links between Groups]
This Step will take a little longer, depending on whether you want a quick result, or if you want to document the CA with records for the longer term.
If you recognize some Groups as being from known Ancestors in your Tree, they can be set aside. Ideally you want to end up with 4 Groups who would represent the 4 grandparents of the TA.
Step 3. Build down from the CA to find links between Groups – a genealogy exercise…
3A. Use genealogy tools to list the children, spouses, and grandchildren of the CA
3B. Pay particular attention to dates and places
3C. Sometimes a marriage between Groups will pop right up; but sometimes it takes a process of elimination (dates/places help here). It’s possible the bio-parents were not married; or other scenarios. You’ve narrowed the possibilities down a lot, but sometimes, there just isn’t a record of what really happened.
3D. Repeat for other groups
3E. Once you have linked some Groups (by marriage or by place/date or by ethnicity, etc), this helps link the remaining Groups.
If records exist, this Step may follow relatively easily; if not, follow-on DNA testing may be necessary
Bottom line: This Step will provide some family lines that are ancestral to the TA. The top DNA Matches have led you to specific CAs. These may, or may not, mesh with information you already had.
Steps 4 & 5 – see Step 3
Step 6. The end-game – This may involve date and location issues and further DNA target testing to isolate and identify the TA. The best solution is that the TA is obvious. However, sometimes the TA is still buried, but you are somewhat closer.
Sidebar: I do this manually in Excel and Word. It is possible to use one of the auto-Cluster programs to group the Matches. However, I prefer “getting to know” the Matches and their Trees, and this process is fairly straightforward. It also lets me see any overlap between groups. I prefer to manually Cluster for a targeted case. I use the auto-Cluster programs when I’m grouping my entire Match list.
In one recent case I did, the marriage between two Groups popped right up – no secrets. The children included 5 potential sons as the bio-father. All five from PA, went into WWII, 4 came back to PA; and one settled in another state a few blocks from the bio-mother!! We’d never have sorted this out without the process above. And luck is sometimes the key factor.
In another case I’ve worked on for years, I used SMs and records to group many Matches on 8 Great grandparents, and 4 grandparents of the TA. Places and dates all work out, and all the top Matches are in agreement. WATO points to the same place. It now appears the father and mother were not married, and both of them apparently died without out any other issue, or any records. It’s frustrating to have basically 100% of the Matches all pointing at the same TA, but without revealing the parent’s names. No luck on this one – just a lot of work. Maybe someday a Newspaper article from the 1880s will shed some light. The DNA can only do so much…
SUMMARY – The process above is my current best practice to squeeze out what I can from Matches and Shared Matches at AncestryDNA. This whole process can be done on notebook paper, in a relatively short time, but I still prefer Excel. Note that the process does not depend on knowing any genealogy of the TA, it relies totally on information from Matches and Shared Matches. Hopefully the TA, the last puzzle piece, “fits”.
[19M] Segment-ology: Manual Clustering to Find Ancestors by Jim Bartlett 20220226