You can be a tenor without ever having sung a note. Some have the natural ability to produce high notes with relative ease, with or without a "classical" voice training. This seems to include John McCormack, Paul McCartney, and Billy Joel. Obviously it is a genetic property, but I am not at all convinced that Irish genes favour such voice types - our samples are simply too small and selected with a cultural bias.

Finbar Wright seems to be (- though I am not quite sure -) of the opposite "baritonal" type, who may well be at a loss when asked to imitate Paul McCartney. The sophisticated technique he employs is particularly effective for 19th century operatic singing, so McCormack had to learn it as well. Paul McCartney and Billy Joel both came from "Soft Rock'n'roll" - quite a difference in aesthetics, not only in technique and preferences of voice types. A negative illustration of this is McCartney's "Liverpool Oratorio".