Are 'dangerous' and 'aesthetically ugly' one and the same thing? I read somewhere once, that arachnophobia evolved as a defence mechanism against dangerous spiders. Even though most spider species are harmless, this evolved response is still there, as it is better to avoid all spiders, even the harmless ones to avoid being bitten by the really deadly ones. Seeing as this aesthetic disgust and fear arose for the purpose of keeping one safe, and very few spiders are actually dangerous, would it be incorrect to view the harmless ones as ugly? Similarly, there are some dangerous animals I consider quite beautiful: tigers, for example. Would it be incorrect to view them as beautiful because they are dangerous? Basically, what I'm trying to ask is, because perception of ugliness evolved to keep us from danger, is danger synonymous with ugliness and is any visual beauty we ascribe to a dangerous animal simply an illusion? Conversely, are non-dangerous animals that we find ugly actually visually beautiful even if we do not perceive them as such?

I think the answer is pretty clear and is implicit in things you've said. Yes: something dangerous can be beautiful. Tigers would be a widely-accepted example. "Dangerous Beauty" isn't just the name of a movie that got a 70% fresh rating on Rotten Tomatoes. It's an idea that's something of a cultural touchstone.

Maybe the perception of ugliness evolved to keep us from danger, or maybe the story is more complicated than that. (I'd strongly suspect the latter.) But however things evolved, the concepts have long since come apart. If someone commented on the beauty of a tiger, and someone else tried to correct her on the grounds that tigers are dangerous, a blank stare would be an appropriate response. We find the appearance of tigers beautiful. They'd look the same way if, somehow, they magically became the protectors of humans. We also find their movements graceful; same comment.

The second question you ask is whether non-dangerous animals that we find ugly might actually be beautiful. The first point is that the mere fact that they aren't dangerous wouldn't be enough. However implausible it is that "dangerous" implies "ugly," it's even more implausible that "not dangerous" implies "beautiful." The reason is simple: that's not how we use the words. But perhaps more importantly, beauty seems to be a response-dependent property. The idea that something might genuinely be beautiful and yet no one—not even careful, disinterested observers who've taken the time to look—find it beautiful strikes me as very close to unintelligible.

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