To recap, reverse genealogy is researching from the past to the present, the opposite direction, or backwards, from what we normally do.
Last week I mentioned some uses for genetic genealogy and traditional genealogy as well as cases where non-genealogists might want to try reverse genealogy. How to go from the past to the present is easiest to understand with traditional genealogy so I'll start there and then move to harder situations.
Traditional GenealogyGenealogy always begins with the known and moves to the unknown. With traditional genealogy, it's pretty easy to see how you'd start from the known past and work to the unknown living. You'd start with the ancestor you're trying to confirm (or the oldest ancestor you have confirmed) and research their descendants instead of their ancestors. There is no difference in how you do the research.
If you recall, a great use of reverse genealogy for non-DNA examples is to increase your research cluster for cluster genealogy or using the "FAN principal." Your interest is a traditional genealogy goal, identifying an ancestor, when you get stuck identifying them, you can try identifying their descendants to broaden your available records.
How to do reverse genealogy in this simple example is pretty simple in itself. Instead of researching ancestors, you expand collaterally (siblings and if known, cousins, aunts, uncles, etc.) and then move towards more recent generations by researching the descendants of those people.
You can take this as far as you find helpful (or interesting, hey, it's your hobby, interesting is a good motivation).
That's pretty straight forward.
Verifying and Pre-finding LineagesNext, what if you're doing genetic genealogy? Reverse genealogy is a must when using DNA. Hopefully, you understand you'll need to supplement DNA results with traditional genealogy.
You need to correctly identify the ancestry of the test taker. For a match to be helpful, you need to also correctly identify the match's ancestry.
Reverse genealogy can speed this up. If you're working on a DNA project, focusing on using DNA for a specific genealogical goal, you can go ahead and do reverse genealogy on your ancestor of interest. Instead of going back in time, look for his/her descendants. This is what I'm calling "pre-finding lineages." You find the lineage (i.e. research it) before you have a match.
Not everyone has the same research skills. If you make sure you identify the correct descendants, as far as you can, you will find you have part of the tree done for some matches. Of course, you don't know where to focus if you just do reverse genealogy without having a particular match or matches to direct you, but that's OK.
Researching descendants for a DNA project, without focusing on specific matches, is just like doing reverse genealogy for cluster research. For me, this is a great reason to do reverse genealogy, it can serve two purposes, traditional and genetic, without even focusing on specific DNA matches.
Reverse genealogy can have several uses in genetic genealogy so let's look at another use.
Finding Test TakersYou might do reverse genealogy on the family of a DNA match, looking for others to test, to see if they also match you (or whoever the focus test, is). You may be looking for options to use a different type of test (this is often done to find a male to use Y-DNA). Reverse genealogy is the way to find new testees outside your known relatives. This applies to the more common scenario where you focus on your identified ancestors, finding "cousins" to test, or focusing on your match's ancestors, testing people to find "DNA cousins."
Identifying Possible ParentsI've done reverse genealogy on DNA matches, looking for a possible mystery parent. This is a harder "how would I use reverse genealogy?" scenario to explain.
If there are few enough generations between an identified shared ancestor and the testee, it's possible to identify all the known descendants. This is nearly impossible if there are too many generations because the parental options become too numerous to be useful. It is a somewhat personal choice about what is "too many," though.
Most likely you can already imagine how to use reverse genealogy if you've done DNA analysis that gives you a narrow focus. I've used this technique when I haven't been able to do DNA analysis (usually because matches are only at AncestryDNA and the only information I have is a tree, no segment information such as you could get from FTDNA or GedMatch).
If traditional research is your only choice, reverse genealogy is what you will need to do. In one specific case, I identified closer matches who shared an ancestor with each other but not with the target test. That could mean the match was through the mystery parent.
Without segment information, I couldn't be sure of anything, but the matches weren't responding so I wasn't getting more DNA information anytime soon, if ever. Based on the information I did have, it was possible the shared ancestor could be the grandparent or great-grandparent of the mystery parent I was seeking.
I would not have tried this technique if it seemed like the shared ancestor should be much farther back. That would not have been a good use of my time. Based on the shared amount of DNA, the number of generations is still an estimate so the true shared ancestor (the Most Recent Common Ancestor, MRCA) could easily be two generations farther back.
There were multiple factors that made it reasonable to try researching two generations of descendants to see if there was someone who fit the criteria for the mystery parent I was seeking. You have to judge those factors in your project. This was not in my family. I don't often use this technique in my family unless I have an EXCELLENT lead on a possible MRCA. My entire family is from Georgia so geography is pretty much useless as a criteria and geography is one of the easier ways to choose who to research or not.
[Reverse genealogy has not solved this problem but so far it does appear I'm on the right track. Without more information, including new matches or segment data, I can't determine more.]
Reverse Genealogy for Non-genealogistsFinally, what if you're not a genealogist and you have an unknown parent (whether your own or a few generations back)? How can reverse genealogy help? There are essentially two ways.
The first is if you know of any other relatives. This is the same as doing cluster research. You're looking for information not just in the direct line but by branching out into every other relative you can identify.
If you don't have any other relatives, you may do reverse genealogy on anyone you can associate with the mystery parent. This can be difficult but it's better than having no one to research at all.
The other way is to do reverse genealogy on possible relatives. This is similar to the example for researching the common ancestor of DNA matches.
You could test if someone you think might be the mystery parent could possibly be the same person. You might also then see if you could have a living descendant tested so you could use DNA.
For example, you may know the mystery parent died. This would have to be a case where there was no doubt (as in people saw the body). If there's any chance the person just disappeared, this example doesn't work.
If you have a potential candidate, you can research them to find out when they died. If you find them living after the death of the mystery parent, you can exclude them. If someone is living or dead is a pretty conclusive test but you might also do reverse genealogy just to gather information.
If you're dealing with an adoption you might have non-identifying information. You might do reverse genealogy on a candidate to gather information of the same type to compare. It might be necessary to research a generation or two towards the present to find that information even if it is about the candidate.
In other cases, you may have a family story describing the mystery parent. You might do reverse genealogy to try and gather the same type of information for comparison.
Reverse Genealogy: Does It Answer Your Question?"How" you use reverse genealogy might not be to provide a concrete answer. It's still a helpful technique for many different types of problems.
You may have been doing it already, not even thinking about researching descendants as anything different from ancestors. That's great. Now you know it has a name in case you need to learn more.
If you've never considered researching descendants, now you can.
Reverse genealogy is really a must for genetic genealogy, regardless of your goal. If nothing else, you can identify people to test. You may also be able to exclude candidates, prioritize research, or simply increase the records you can use. Much of this applies to genetic genealogy and traditional genealogy.
How do you do reverse genealogy? Just like "genealogy." You start with what you know and move to the unknown.