system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How were last names created? When did this start and how did we get our last names

This is something that I have always wondered..
gpt
Back in the day, villages were small enough there was probably only one Eric, so you really only need one name.  If there were two, you'd use some quality about them to tell them apart...old Eric and young Eric, redheaded Eric and blackhaired Eric, Eric from by the river and Eric from the hills, Eric the weaver and Eric who runs the mill, Eric son of Hubert and Eric son of Morris.

Eventually these got simplified into last names, Eric Young, Eric Black, Eric Rivers, Eric Weaver, Eric Morrison.  If one of those Erics were particular important, his family would want to keep his name around to remind everyone, so Eric Black's kids would be Black's no matter what color their hair was.