Genetic algorithms could eventually produce music that triggered a emotional response in humans. Your "fitness test" would need to be having real people listen to procedurally generated scores and rating the emotional impact (if any) of each sample. Perhaps a task for mechanical turk?

In the end though, I think we seek out music or art that puts us in the mindset or emotional state of the artist. Forging a connection of shared experience.

If the music tugged at all the right heartstrings, but you knew it wasn't made by a human, could you feel that depth of connection?