It's called "corpse". Often riddled with diseases.

Or you need to identify those who aren't behaving properly (sickness or other resource intense disability) and should be outcast from the group (something we don't need to do today, but the right wing narrative insists that need to do)

It would be a evolutionary benefit to fear / avoid any person that is behaving strangely in certain distinct ways. Could be a dangerous transmittable disease, i.e. rabies etc.

The humanoids we evolved from were at one point, not the only humanoids around. We coexisted with other, different species (neanderthals being an example). Homosapien is just the one that survived.

Yes. A dead body.

Or the biological need to be afraid of ourselves because if I saw a human standing in my backyard in the shadows I would be as scared as if it were an alien, humans aren't a joke when they want to kill or maim and humans love to kill or maim if they need something you have

Our instincts draw from pretty far back in our biological origins as well. The notion of mimiclike predators is pretty damned ancient and likely a factor for very earliest common ancestry.

Dead bodies probably, as they spread diseases.

"But in general, take my advice, when you meet anything that's going to be Human and isn't yet, or used to be Human once and isn't now, or ought to be Human and isn't, you keep your eyes on it and feel for your hatchet."

Yep and they were called Neanderthals.

Back 4 million years the whole world really was a planet of the apes. So in some ways recognising something that wasn't your species, but looked like it might have avoided conflict, loss of territory, loss of food..

Bleachy-teeth people, this means you

Don't grin at me you fucked up freak 😂

Illness, death, and antisocial behavior. All of these were threats we evolved to handle, people who are "a little bit off" in one way or another, who might endanger the group or individual. This, and that our pattern seeking brains don't like it when something doesn't easily fit within an existing schema, even more so if it lies just outside of our existing preconceptions.

Obviously, I can't say that these definitely are the reasons why we experience the uncanny valley, but I think it's probably a better explanation than... Skin walkers? Or whatever else the meme would be implying.

Still, it's a cool premise for a horror story at least.

The leading theory is Rabies.

I just wanted one funny meme before bed not nightmare fuel but here we go

I mean, we existed as the same time as other early ape species (which we killed off like the monsters we are), so it makes sense.

Or it's just that something feels off, fellow human.

On the other hand, maybe because we're a highly social species and some people are just crazy, which you see in their face or behavior.

Ancient androids, obviously.