Surprise Y Matches – What do they Mean?

One of our blog followers, Tom, encountered the following situation, which, really isn’t so uncommon.

“I started up a Y-DNA surname project and recruited my only three living male 1st cousins who carry that name.

The first set of 67 results have recently been posted and within a day an exact match appeared with an individual who had only tested to 37 markers back in 2008.  Apparently the individual has had very few close matches and never a perfect match like my cousin’s.  But the individual has a different surname.

Is it possible to have an identical match as a random event?  How common are such occurrences?  What possible explanations could there be?”

Let’s look at Tom’s situation from different perspectives and see what we can find.

When I do DNA Reports for people, I still find people who don’t have any matches.  It’s not as unusual as people think.  In a way, it’s a blessing as compared to people who have so many matches that they can’t even begin to sort through them.  But to the person who doesn’t have any matches, it surely doesn’t seem like there’s a positive side to the situation.

First of all, remember that mutations can happen at any time in any generation….or not.  In the Estes line, Abraham Estes, one of two Estes immigrants to colonial America was born in 1647.  He had 8 sons.  We had DNA from the descendants of all 8 sons.  We reconstructed Abraham’s DNA using triangulation, so we know what his original genetic “signature” looked like.  One of those sons’ lines has 4 mutations in 8 generations, and one line has none.  The rest fall in the middle someplace.

I only mention this to illustrate that mutations are truly random events.  We use statistics to look at the “most likely” scenario, based on averages, but mutations are personal events and while they, as a whole, fall nicely into statistical models, individually, they happen when they happen.  You can see that the mutation rate can vary quite a bit, even within families.  Keep that in mind during the rest of this discussion.

Family Tree DNA gives us some tools to work with these kinds of situations.  The TIP calculator, available for every match by clicking on the little orange TIP button, tells us, statistically, how likely people are to match at which generational level.  This is called the time to the most recent common ancestor, or MRCA.  I did an earlier blog about this.

Comparing two exact 37 marker matches, below, we see that, statistically speaking, on the average, these two people are most likely to share a common ancestor about the second generation, meaning grandparents.  Again, word of caution, these are averages, which is why you have a range shown here.  DO NOT TAKE THEM LITERALLY.  I can’t tell you how many people obsess over these numbers and think that these numbers are telling them exactly when they share a common ancestor.  They don’t.

So let’s answer the questions that Tom asked.

Is it possible to have an identical match as a random event?

No, it’s not.  These men share a common ancestor at some point.  The question is, when and where.  However, it is possible to match on many markers, and then not on others.  I would suggest that these men upgrade to 111 markers and see how closely they match at that level.  I have seen at least one instance where 2 men matched at 37 and then had 5 or 6 mutations at the 67/111 marker level.  Unusual?  Yes.  Impossible?  No.

How common are such occurrences?

This isn’t as unusual as you would think.  I see this fairly often.  I always tell people to do four things.

First, upgrade the people you have to 111 markers.  If they continue to match at 111 markers, exactly, you probably have a very close match genealogically.

Second, find a second person to test from each line, as far back as possible.  In other words, if you’re testing the Abraham Estes line, you would want to find another son from Abraham to test to see if the DNA of the two sons match.  If they do match, then you know you have the lines proven back to 1647.  If not, then you know you have a non-paternal event (NPE) of some type, otherwise known as an undocumented adoption.  I call them undocumented adoptions because everyone knows what that means, and regardless of how it happened, it’s “undocumented” because we didn’t know about it.  In Tom’s case, he already has his 3 cousins, so his line is proven back to the common ancestor of those men.  Hopefully the person with the other surname can also find someone else from his line to test.

Third, enter the results into Sorenson at and also into for Y-line results to see if you come up with any other people who also match with that surname.  This is especially useful if you are having difficulty finding people to test.

Note: Neither SMGF nor Ancestry’s Y data base are available.

Fourth, look around the neighborhood – genealogically.  Are there reports of the two families in question being allied or intermarried in some location?  Were they neighbors in the same county?  In many cases, once you figure out that an undocumented adoption occurred – you can figure out in which generation through selective DNA testing, and often, which families were involved through DNA combined with historical and genealogical records.

In essence, to solve this type of puzzle, you need to become somewhat of a genealogical detective.

Tom’s last question was what kinds of situations could explain these results.

In some cases, especially where there are some mutations involved (meaning not exact matches), suggesting some time distance between common ancestors, matches between surnames occur because the families involved simply adopted different surnames.  When surnames were adopted varies dramatically by the location of the families and the circumstances involved.  For example, in the US, some Native American families were still using Native names in the 1880s.  Freed slaves adopted surnames upon obtaining their freedom in the late 1860s and early 1870s, and sometimes changed that surname at will.  In the Netherlands, some families didn’t take names until in 1811 when Napoleon mandated that they do so.  In England, some wealthy families had surnames by 1066, but peasants didn’t adopt surnames, for the most part, until in the 1200s and 1300s.  Jewish families in some parts of Europe didn’t adopt surnames until in the early 1800s.

Sometimes surname changes that look to us like undocumented adoptions occurred not at birth, but later in life.  Some people simply changed their names for a variety of reasons.

In one case, a man named John though he killed a man in Tennessee, ran off to the frontier which was at that time in Texas and changed his name, only to discover years later that not only had the man he shot not died, but that man had then married John’s wife he abandoned when he left.  Hmmm….karma at work.

One of the most common reasons for ‘undocumented adoptions’ is that a step-father raised the children and the kids simply used his name….forever.  So maybe John’s kids, above, took the surname of the man John shot.  Now this is getting interesting!!!  No wonder we have trouble figuring these things out retrospectively.

Another reason, of course, is that illegitimate children took the mother’s surname, but carry the father’s DNA signature.  In Native American cultures, matrilineal naming was very common, as is it in the African American culture, especially immediately after the end of slavery.  Children took whatever surname their mother adopted at that time.

Of course, the one thing we haven’t mentioned is the obvious….where someone was unfaithful.  Generally, that’s the first thing people think of…but it’s really not the most common reason.  But sometimes, indeed, it appears that Granny might have been a “loose woman.”  Don’t judge Granny too hardly though, because you really never know what happened in Granny’s life.  She could have had no choice in the matter, or her husband could have been abusive. We often see these conceptions during periods of war, especially the Civil War.  In one case, we know that a woman exchanged sexual favors for food for her children.  It’s really hard to be critical of that woman.

So the real answer for Tom is that there is no cut and dried answer, but lots of possibilities to explore.  You’re going to have to get out your Columbo tools and sleuth away….



I receive a small contribution when you click on some of the links to vendors in my articles. This does NOT increase the price you pay but helps me to keep the lights on and this informational blog free for everyone. Please click on the links in the articles or to the vendors below if you are purchasing products or DNA testing.

Thank you so much.

DNA Purchases and Free Transfers

Genealogy Services

Genealogy Research