The names are primarily of German origin and were adopted by Jews living in Germany. They were often known as the Yiddish (and also why the Yiddish language can be understood by people who speak the German language). This is why 'Yid' is sometimes used as a pejorative against Jews. When the Third Reich rose many of the Yiddish fled Germany. When they arrived in the U.S. (and elsewhere) their family names were put into official government record. Prior to this vast, intrusive governmental record keeping apparatus it was easy for people to change their identity by simply moving somewhere they were unknown and making what ever claim they wanted. Many people joined the Roman patrician class through this method. There is a story (probably apocryphal) about a general serving under Julius Caesar who was shown to be an escaped slave and Caesar turned him over to his owner.