Why do we appreciate music or beauty?

I read in seveal places that seeing beauty in the opposite sex is considered to be a health or fitness judgement for being a mate.

I think yourblurry said it best,

art, and appreciation thereof is primarily about validation of some sort.
or it’s about validation of idealized notions. Did i say that right? What i mean is that art is about validating who we are, and what we wish we could be.

Good point. But does “appearance” connote beauty, or something else? In what way is appearance important?

Another example might be the antlers on stags; I’d heard something about the one with the biggest set of antlers being the most desirable, or something along those lines. But is that because big antlers makes the stag seem beautiful, or is it because it makes him seem intimidating or powerful (or something else)? Couldn’t that go for peacocks too? More importantly, is there an example of a feature like that which couldn’t possibly demonstrate anything significant but beauty?

Well, that’s where you run into the problem of defining beauty in scientific terms. AFAIK, the only good answer to those questions are: “we don’t know.”

I’ve seen a few episodes of that show, and IIRC there was also an article in Discover magazine awhile ago about the evolutionary advantages of sexual attractiveness (a large jaw in a man is a sign of a strong immune system, a proportional face is a sign that the person doesn’t have certain congenital defects, etc), so it does appear that some ideals of beauty are evolutionary advantageous. However, most (perhaps all) of these ideals can be overridden by culture – f’rinstance, waifish supermodel Kate Moss is considered beautiful in some circles (hence her career as a model), even though her narrow hips and emaciated body significantly reduce her chance of successfully carrying a child to term.