The Davis surname is a patronymic meaning "son of David", which originated in Wales in the last few centuries. Permanent surnames were late to take hold in that nation, where men and women traditionally had only a given name followed by the name of their father. A woman whose father was named David would be called "Emma ap Dafydd".
After the Laws in Wales Acts of 1535 and 1542, English officials worked to harmonize Wales with England, making English the official language and gradually impressing surnames on the people. Usually the Welsh would simply adopt a variation of their patronymic as their surname, adding an "s", with "son of John" becoming Jones and "son of David" changing to Davies or Davis. Interestingly, the name "Davies" is more common in Wales but as you move into England, Wales, or North America then "Davis becomes more common.
Also, sometimes English officials would record the surname as the closest sounding English name so some names typically regarded as Welsh can have Saxon or Norman roots.
The challenge for genealogy is that the children of hundreds of unrelated Davids each created a new Davis family. Meanwhile, our distant David ancestor had a brother named John, whose children created a family surname of Jones, to whom we are related. This means that when looking for a distant cousin, his name is as likely to be Jones as it is to be Davis.
My Davis family traces back to County Wexford, Ireland. Not surprisingly, our family historians believe the Davis family originated first in Wales before migrating to Ireland. Well, my cousin, Barry Davis, took a Y-DNA test that might prove that.
In genealogy, DNA testing is only valuable in the relationships it uncovers. Y-DNA tests look deeply but not broadly. When you consider your 5x great-grandparents, only 1 of the 128 is on your direct paternal line. And the cousins with whom you share Y-DNA are those men who also have a direct paternal line to him. This amounts to an miniscule percentage of your cousins. However, unlike autosomal DNA, which can only identify perhaps 4th or 5th cousins, Y-DNA can reveal 10th, 20th, and 100th cousins.
So most of the cousins that Y-DNA testing reveals are only very distantly related, unless we recruit known or possible cousins to test to prove a relationship. Happily, in this case, Barry's closest Y-DNA matches are surprisingly closely related, and may share a common ancestor only 8 to 10 generations back, if not closer.
The haplogroups of those men are L21, the native British "Celtic" haplogroup. L21 is found throughout the British Isles so that alone doesn't tell us much except that the distant paternal line was very likely not Saxon, Norman, or Viking but lived there before the Romans.
Examining Barry's matches, we see exactly what we would expect to see of a paternal line that traces back to Wales. Here are the surnames of his matches:
Humphrey (Welsh): there are 4 men on Barry's match list with this surname, the closest an exact match, meaning he is very likely to be related within 8 generations, probably closer. While Humphrey is a Norman name, these Humphrey men do not have a genetically Norman paternal lineage. It is likely that English scribes translated a Welsh name into most similar sounding English name. These Humphreys appear to be relatively closely related to each other and trace their paternal lineage back to Massachusetts in the 17th century.
Jones (Welsh): there are 15 men with this surname on the list, with the closest Jones match probably related within 6 to 12 generations but most of them are probably not even closely related to each other. Several of these Joneses trace their paternal lineage to Ireland while a few others go back to different parts of the United States. Meaning son of John, this is the most common surname in Wales.
Davis (Irish/Welsh): there are 6 men with this surname on the list. Those with ancestor information also trace their paternal lineage to Massachusetts, back in the 18th century. It's difficult to determine exactly how closely these Davis men are related. It's possible that some descend from different David ancestors and are related more distantly.
There are a number of other surnames, such as Cox (English), Watkins (Welsh), Moynes (Scottish), Powell (Welsh), Hughes (Welsh), Price (Welsh), Bridges (English), Stickles, Morton (Scottish), etc.
If we weren't before, I believe we can be certain that the Davis line goes back to Wales. However, other than the few closest matches, it's really hard to tell how closely Barry is related to some of these men. The next step is to see if the genealogy of any of these men might cross paths with our Davis family history.