The human striving for beauty is really quite amazing. I was looking at a household hints book that my wife got, no doubt in part for my edification. Quite a significant percentage of these (40% or so?) have to do with making things look better. The sheer amount of effort that goes into looks is amazing. In fact, just about every non-consummable ready-made good that I can see around me has been made at least in part with a view to looking good, say by choice of color or choice of shape. There is a pretty ugly hard drive enclosure to the right of my laptop. But it is obviously made with a view to looking good—it has a shape and color choice that someone thought to be futuristic or modern or whatever. No doubt, a few cents could have been lopped off the production costs, and some environmental benefits realized, by just having a plain monochromatic box in whatever shade of gray the plastic would be if no dye were added. Even the really, really cheap goods I order directly from China via ebay or DealExtreme tend to have decorative elements. My digital calipers, for instance, have some lines sticking out in the plastic element that seem to be designed for largely aesthetic purposes. The incremental cost per item is very small, no doubt, but the mould must have been a little slightly more expensive to design than a plainer design would have been, and probably a bit more plastic is used per item than necessary for engineering reasons.
So we value beauty greatly. Now unless we take a sceptical line here (and if we do, I doubt we can arrest the scepticism before it takes away all much of our knowledge), we need to say that beauty is indeed valuable, and we have an ability to recognize this value. This should trouble naturalists. It is difficult to see what evolutionary benefit there is in recognizing and pursuing beauty, since beauty does not appear to correlate with survival/reproduction benefits (apples are beautiful, but so are tigers). Of course, one might say that the recognition of beauty is a spandrel. But it is still a great coincidence that this spandrel should have hit on the genuinely valuable property of beauty. Probably, if one has the spandrel view of our recognition of beauty, one has to say that beauty is not an objective good that we observe (and down we go on the slippery slope of scepticism). Moreover, causal theories of reference—which seem to be the best bet of the naturalist—seem to have a difficulty with beauty. For beauty as such does not appear to be a causally efficacious kind of property.