Regarding the tune, it's in the Dorian mode, and slightly unusual in that it starts with a run from the 5th of the scale to the 7th, and doesn't hit the tonic until the end of the first phrase. Sharp used to think that tunes like this were survivals from mediaeval church music, but not many people do now. It's a common enough mode in the traditional song repertoire, although it has to be said this is a particularly good example of a Dorian tune.