Y-DNA Ancestry Testing - Why Do I Match Different Surnames?

Don't Assume a Non-Paternity Event!

There are several reasons that you may have Y-DNA matches to individuals with a different surname.
Getty / KTSDESIGN/SCIENCE PHOTO LIBRARY

Even though Y-DNA follows the direct male line, matches with surnames other than your own can occur. This can be disconcerting for many until you realize that there are several possible explanations. If your Y-DNA marker results closely match an individual with a different surname, and your genealogy research does not seem to indicate a past adoption or extra marital event in the family line (often referred to as a non-paternity event), then the match may be the result of any of the following:

1) Your Common Ancestor Lived Prior the Establishment of Surnames

The common ancestor you share with individuals of different surnames on the Y-DNA line may be many, many generations back in your family tree, prior to the establishment of hereditary surnames. This is the most likely reason for populations where a surname that passes down unchanged from generation to generation was often not adopted until a century or two ago, such as Scandinavian and Jewish populations

2) Convergence

Sometimes mutations can occur through many generations in completely unrelated families which result in matching haplotypes in the present time frame. Basically, with enough time and enough possible combinations of mutations, it is possible to end up with matching or closely matching Y-DNA marker results in individuals who do NOT share a common ancestor on the male line. Convergence is more plausible in individuals belonging to common haplogroups.

3) A Branch of the Family Adopted a Different Surname

Another common explanation for unexpected matches with different surnames is that either your or your DNA match's branch of the family adopted a different surname at some point. A change in surname often takes place around the time of an immigration event, but may have occurred at any point in your family tree for any one of a number of different reasons (e.g. children adopted the name of their step-father).

The likelihood of each of these possible explanations depends, in part, on how common or rare your paternal haplogroup is (your Y-DNA matches all have the same haplogroup as you). Individuals in the very common R1b1b2 haplogroup, for example, will likely find they match many people with different surnames. These matches are likely the result of convergence, or of a common ancestor who lived prior to the adoption of surnames. If you have a more rare haplogroup such as G2, a match with a different surname (especially if there are several matches with that same surname) is much more likely to indicate a possible unknown adoption, a first husband you may not have discovered, or an extramarital event.

Where Do I Go Next?

When you match a man with a different surname and you are both interested in learning more about how far back your common ancestor likely lived, or whether there may be a possibility of adoption or other non-paternal event, there are several steps you can take next:

  • Upgrade the Y-DNA test to 111 markers (or at least 67) for both you and your match. If you both match with only 1 or 2 mutations at that level then you are likely to connect within a fairly recent genealogical time frame (7th cousins or closer)
  • Find a second person to DNA test from both your line and your match's line. This will need to be another male relative on your direct paternal line, preferably as far back as possible on the line based on generation, not age. If both of the new men tested also match each other as well as the two original test takers, this further confirms the genealogical connection.
  • Go through the genealogical research done on the direct male ancestors of the two matching men with a fine-tooth comb, looking for locations that each family may have had in common. Were any of their ancestors neighbors in the same county? Or perhaps attended the same church? This may help you to determine in which generation the common ancestor likely lived.