Good questions, Adam... Maybe someone can flag down the musical theorists that lurk around here...

Does anyone else besides me remember a bit from Mel Brooks' Oldest Man in the World bit, where he explains that music came about from calling for help -- because musical notes carry further than spoken language?

I think that is pretty close to the truth: not only can a sung tune carry further that speech, but you can identify a tone and pitch from a distance with much more accuracy than individual vowel and consonant sounds. So it makes sense that certain important information be encoded in music as well as words, especially when than information had to carry over long distances, such as: this is my hunting territory, you stay away (remember that Cromagnon humans were semi-nomadic hunters, much like wolves--perhaps that is where "nanny, nanny, boooo, boo!" started: you are not a member of this group, go away!), or "Come home for dinner!"

It wouldn't do much good if someone decided to change such a tune, because those in ear range wouldn't know what it meant (and a rival wouldn't stay away, and help wouldn't arrive.) So these tunes and their meaning get imbedded in our brains and passed on from generation to generation.

Just a thought.