My favorite theory is that it's about corpses. You know what looks similar to a person but isn't one? A dead person. People who don't like being around human corpses tend to live longer because you know, something killed that guy and it might kill you too

I think it's a pattern recognition issue. We have brain areas specialized for facial recognition. There is a cognitive dissonance where something is almost but not quite a face. This is distinct from pareidolia where the pattern system recognizes that something resembles, but is definitely not a face.

More likely deep code from prior evolution. Similar, but not right, is the difference between life and death for a lot of species. That'd get built in long before anything resembling 'human' existed.

It also can apply to humans that have something wrong with them, like visible signs of severse contagious illness, or just dead people, where being around can risk disease for oneself

We shared the planet with several different human species in the past. We also fucked most of them into extinction.

It wasn't very long ago we lived with australopithecus and neanderthals and other hominins that looked like us.

I think it's less likely to be an evolutionary advantage and just a side effect of having really good pattern recognition. Because the uncanny valley does not only trigger with humans. Anything that is close to something recognizable but not quite right can trigger it. It's what makes liminal spaces feel creepy.

If your brain sees something that isn't human, that isn't human.. there needs to be a theory about that?

It wasn't that long ago on the cosmic scale that homo sapiens lived alongside humans that were not the same species as us.

Or it can mean that our mind is flawed. Unless cats fearing cucumbers mean that they once had to fight cat-hunting cucumbers.

Rabies.

The ultimate "other".

Not all mutations that survive are beneficial. Beneficial mutations are simply more likely to survive.

No, it doesn't.