If you’ve been doing this whole family tree research thing for a while, you might have seen the letters “MRCA”. It’s especially common to see this in the genetic genealogy sphere – and for good reason.
It’s one of the most common notations used in understanding how DNA matches are related to someone. In this post, you’ll learn what this term means, and how to use it for yourself.
What does MRCA stand for?
MRCA = Most Recent Common Ancestor
sometimes you can also see MRCAs = Most Recent Common Ancestors (plural)
Simple enough, right? It is a pretty straightforward term. Your most recent common ancestor is the most recent person that you and another person are related to.
More on this below. The plural form, MRCAs, is when you share a set of common ancestors in the same generation – which is actually usually the case, as in when you share both great-grandparents, or some other married couple in your family tree.
You will sometimes see LCA instead of MRCA. LCA means “last common ancestor”. In my opinion, MRCA is easier to remember because it’s meaning is more clear. That’s just me!
What does “Most Recent Common Ancestor” mean?
The most recent person that you and your family member are related to. You are related to all of your most recent common ancestor’s ancestors, if that makes any sense.
I have three examples below to help illustrate this concept.
First cousin – who is the MRCA?
I have a first cousin named Jane on my mom’s side of the family. We are both related to both of my mom’s parents, since her dad is my mom’s full brother.
This means that we have MRCAs of Grandma and Grandpa on that side. The MRCAs of Jane and I are grandma and grandpa, but we are both related to all of the ancestors of those grandparents.
All of those ancestors are common ancestors that Jane and I share, but the most recent ones (MRCAs) are grandma and grandpa.
1/2 2nd cousin once-removed – who is the MRCA?
One of my favorite cousins is a 1/2 2nd cousin once-removed. Let’s call him “Jay”. Jay and my mother are second cousins.
Full second cousins share great-grandparents. Since my mother and Jay are half-second cousins, this means that they only share one great-grandparent.
In this case, they share a great-grandfather. Jay’s great-grandmother died, and their great-grandfather remarried to my mother’s great-grandmother.
The MRCA is the great-grandfather of Jay and my mother. Jay and I are second cousins once-removed, since I am one generation further away from the MRCA.
Fourth cousin – who is the MRCA?
Most people have a ton of fourth cousins. You share great-great-great grandparents with any given fourth cousin.
This means that your MRCAs are your great-great-great grandparents. Your child’s relationship to the fourth cousin is a fourth cousin once-removed, but the MRCAs are still the same.
Your children and the children of the fourth cousins will now be fifth cousins (since they share great-great-great-great grandparents), but the MRCAs stay the same.
I made this image just for you – feel free to share it!
How should I use MRCA in my own research?
I love to use MRCA when I’m going through my DNA matches. As soon as I spot how we are related, I usually make a quick notation as a note on the match profile.
I’ll note who the MRCA is, or who I think it is. It’s way quicker than writing down “we are related through my great-great-great grandfather William Smith and his second wife, Bessie”. Instead, I’ll just write “MRCA Smith/Bessie”.
If we are only related through my great-great-great grandfather William Smith (but not through Bessie), I’ll write simply “MRCA William Smith”.
You can also use this acronym in communicating with others, since it takes less time and space (text messages or Twitter, anyone?).
I hope this article helped you figure out what MRCA means and how it can help you be more efficient in writing your notes on your family tree.
Thanks for stopping by!