Perhaps as a guard against the suicidal risk that comes with sentience?
Who says we did evolve to appreciate aesthetic beauty? I think this is a misunderstanding of what it is to adapt to a niche. Culture started after modern humans arrived on the scene. Therefore, it's not an adaptive behavior. Darwin and Wallace had some very deep disagreements about this subject. Wallace argued that an aria proves the divine exists, because all features have to be adaptive. There's no advantage to singing an aria, therefore, the ability must have been instilled by God. Darwin, on the other hand, argued that some abilities are non-adaptive, and can be co-opted in certain circumstances. This is eminently more reasonable, as it doesn't require divine intervention at the exact moment modern humans appeared. I think it's far more likely that we evolved complex intelligence to solve food and shelter problems, and a side effect is that we are able to find beauty in creation.
We know some apes have culture, so, do we have a strong reason to believe pre-humans had no culture? I was also under the impression humans have evolutionary adaptations which came after the first Homo Sapiens (maybe skin pigmentation, or finger wrinkling?).Culture started after modern humans arrived on the scene. Therefore, it's not an adaptive behavior.
This is precisely what doesn't happen in juggling, which is why it doesn't fall into the "sport" and "winning" model. Cool!Here is a parable to illustrate the process. Suppose that a primitive maker of cloth decorates her product with a complex design. As it turns out, everybody else in the community shares in the perceptual pleasure she enables, which gives her an economic incentive to produce more patterned cloth. Maybe others copy her as well, and insinuate themselves into her domain. At this point, repeated perceptual attention to the pattern will induce in consumers a greater sensitivity to the subtleties of patterned cloth. Thus, consumers (including the maker herself) become sensitised to imperfections in the patterns – perhaps the spatial interval is not perfectly even, or perhaps the repeated element is not exactly the same throughout. This gives producers the incentive to improve their skills and, because they invest in beauty, it gives consumers an incentive to improve their skills of discrimination. The result is a virtuous spiral in the co-development of perceptual and productive skills.
Sexual selection can take off in an exponential way, according to Dawkins in The Ancestor's Tale -- he has a section on peacock plumage and why it exists. Will read the article. EDIT: so it's about beauty in non-human things; a bit different.
It could still be costly signaling of sexual fitness