The Times had a piece on changes in the most common last names, the hook being the fact that Latino last names are moving up.
What caught my eye, though, were two of the other most common names: "Smith" and "Miller". (Jones and Williams and Johnson were also big). Why? They're occupational names. Back in the day when surnames first were assigned, the predominant occupation was farming, but we don't see "Farmer" as a big surname. Miller and smith would be higher income occupations back in the 16th century. It appears that higher income people had more surviving offspring then, and in the future.
On a related issue Megan McArdle has a piece on the inheritance of status, giving a brief summary of some work tending to show that socioeconomic status is very inheritable.