It is not at all uncommon that people with different surnames Y-DNA test exactly the same. In fact, it is to be expected. In our case, anyone with our Y-DNA profile, regardless of the surname, is likely to be closely related to all others with that same Y-DNA profile. All of us descended from a common ancestor somewhere back in time. Surnames are a relatively new idea, only begun about the eleventh or twelfth century AD, well into our modern times. Our ancestors existed way before the use of surnames. When surnames began to be used, many genetically connected people took entirely different names. At the time, that seemed perfectly reasonable, nowadays that sometimes confuses people.
There are many reasons one person can have the exact same YDNA profile as another person, even in modern times, all the way up to and including current times. It is always possible that people with different surnames test alike when a child of one family was born into or adopted by the family of the other and the descendants of that child have assumed the surname of the other from that point on. Another common example could be where the widow of one family remarried to a male of the other and the widow and all the children of the first marriage assumed the surname of the second husband. The descendants of this family would then have the YDNA from the first husband and the surname of the second, on down is successive generations, forever. Or similar confusion in cases of unwed birth, divorce, abandonment or other estrangements where the child takes the surname of the mother, yet has the YDNA of the unknown or unrecorded father.
It is also possible that for reasons unknown, a different surname may have been taken by any male and/or family and the descendants known by that surname for all successive generations. Moldau specifically says this about the Thompson family in his book; "Several other families now using the name of Thompson etc., in Ireland were originally of another surname entirely. Mc Lavish and Mc Lavish are two such instances. People of these names have changed their names into Thompson on occasion, as documented by the Registrar-General in relatively recent times."[1] This could be true of any person with our Y-DNA profile, born into one of our Jameson families, then legally change his name. All of his male descendants would have the new name and the Jameson Y-DNA profile.
As common as this might be, we know of no specific instances where a child born into a Jameson family changed his name and carried the same Y-DNA profile onto a new surname. Nor do we know of any common ancestor to any other male with a different surname and same Y-DNA. As noted, this would have been quite likely before the time of surnames. A time before most records were kept and a time before we are ever likely to connect in any specifically known way. But even if we did know of these connections, they are unlikely to be recorded here as it is our intention her to collect all known people with the surname Jameson and our particular Y-DNA profile. At some point someone may want to take our particular Y-DNA profile and do a study of everyone with that profile, surnames not considered. That is not our intention or our goal, even though that could be considered a truer collection of our larger family.
