If I still had any doubts about how much we can rely on the persistence of family names, Matt Yglesias just fixed them. The article reports the results of a study of wealthy people in Florence, Italy in 1427 and 2011. The richest people today have the same family names as the richest people in the fifteenth century.
The original paper is by Barone & Mocetti of the Bank of Italy. More information is in a column from the Center for Economics and Policy Research.