[situationista]

Ironic that for all the elite lineage captured here, the one that he ended up stuck with is a very plebeian surname of non-hispanic (Ligurian) origin.

[PaulDavisThe1st]

I would like to know more about the conditions under which Spanish family names became "X y Y" rather than "X" or "Y".

[HelloNurse]

Inheriting both surnames is traditional, picking one is nontraditional or foreign. The interesting option is between using a conjunction or not (Paul Davis Thefirst or Paul Davis y Thefirst), which seems mostly a matter of sounding better or, as Wikipedia suggests, disambiguating between first names and surnames (if it precedes the conjunction it is a surname).