THIS IS YOUR BRAIN ON MUSIC, by Daniel J. Levitin
It's hard to answer to answer with hard evidence, but I read I think music invokes the pleasure centers of the brain and causes the release of endorphins. This can be accomplished by many other exteranl stimuli but the bigger question is why repetative listening to the same music elicits the same response over and over again. Any ideas?
As far as I know, nearly all societies have developed music, as part of their cultural development. 10000 years ago, there were instruments to make what we would recognise, as music. I am not sure how good their HiFi systems were, but they had music. From memory, researchers have looked at changes in EEG's when people are listening to music.
Another very interesting recent discovery, is that speech and musical ability are quite separate. A stroke sufferer, I believe, lost speech, but could communicate by signing sentences. Weird, but true.