If you go back 7 generations you end up with 64 different last names, baring incestuous relations... That’s a lot of different last names.
Unless you are Icelandic. I knew a married couple with children years ago. I don’t recall exactly, but the husband was Lars and the wife was Frea. Their last name was Thorson.
Their young boy was named Thor (after Grandpa) but his last name was Larson (son of Lars). The daughter’s last name was Freadotter (daughter of Frea).
My last name is a place name from Norway. It is an odd one, and anyone with it is from the four brothers that lived on that farm.
As opposed to the Norwegian last name of “Nes”, which means point of land on a Fjord. Lots of those around.
It is not incestuous when two people who might share a 5th or 6th or 7th set of great-grandparents have a child...and the further you go back in your family the more likely it is you will find someone who occupies two places on that tree in different branches.
As a result you may come up with less than 64 different last names if you go back 7 generations. Not as a result of incestuous relations either.