In the Scandinavian (Nordic) countries i.e. Denmark, Finland, Iceland, Norway, Sweden, (also Northern Germany and the Netherlands before 1811) the patronymic naming system was used. That means, a Scandinavian's surname was formed by taking the first name of their natural father, and adding “-sen -sson or -datter -dotter” to it. It was a very good and necessary system for the time period it was in use. It also means, however, that you could find several people living in the same record keeping jurisdiction at the same time, with the same surnames, who are totally unrelated to each other. Proving which “Lars Larsen” is YOUR ancestor is the task.