Why do we like music? Is it related to speech? Is it entirely social? The only animals I know of that enjoy it as much as us are birds. (most mammals, even chimps and dogs, ignore music)
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I think that one of the core enjoyments derived from music is the same that we get from humor. The ability to both be surprised and the pleasure that comes from recognizing a pattern and using it to predict what's "coming next". Both humor and music have a rhythm and require a sense of timing, spotting the pattern, knowing that something is about to happen, and going "aha!" when it occurs makes our brains feel as if they have "done a good job".