taimatsu no monogatari

I gather it was all started by the practice in the US of passing both parents' surnames on to the children - the mother's maiden name would be incorporated as an additional middle name*. So e.g. John Blake and Mary Penn get married and call their children David Alexander Penn Blake and Susan Elizabeth Penn Blake, known as David Blake and Susan Blake. When Susan grows up she marries Michael Chace and her kids get Blake as a middle name. Gradually the surnames stop sounding odd as given names, and people start giving their kids old family surnames as first names. Goodness knows how they decide whether $surname sounds better as a girl's name or a boy's, though.

* similar to custom in present day Spain I believe - there, people are known as Name Middlename(s) PaternalSurname MaternalSurname and both surnames are used on an everyday basis.