With paintings, you often have very nice scenery, something scary or something imaginative. It's pretty obvious why people would like these things. The same is true of writing and other forms of art which tell a story: humans are naturally sociable and talk to each other about things which have happened to them, this is just another form of that.
But, like I say, music is a big mystery. Imagine the first people, living in caves, hunting for survival and all that kind of thing. In their free time (once they had developed language) they may have exchanged tales with one another, or documented them as cave paintings. But how would music have started? I can really think of no reason whatsoever that people would like music. Why, evolutionarily speaking, is there any reason that people would enjoy certain sounds? Sure, something like the sea sounds nice, but I think the main reason that it is enjoyed is due to the lack of any other annoying sounds. Who could have discovered music? Who could have realised that certain sequences of sounds are nice for humans? How was it that the first instruments came into existence?
I guess these are all things that will remain unknown. But I still think it's pretty interesting to think about, which is why I thought it'd make a good blog entry.