Why does the Uncanny valley exist?
On the surface, let's start with the part between corpse and healthy person. This region is what we are familiar with - it is the way people judge each other subconsciously. It is indicative of health and whether physical, mental status.
We tend to feel worse about zombies than corpses, because corpses, at the least, tend to look peaceful and not in pain or any negative emotion. Zombies look awful and when we substitute ourselves into it, also feels dreadful. Yes, we invariably use what we know and feel about ourselves to fill in what we do not know about someone, to come up with an idea of what a person is like, solely based on appearance and actions.
The scientific evidence supporting this is the activity spike in parietal cortex of the brain, which has lots of mirror neurons, responsible for imagining the performing of actions. Now, if we don't feel like being in that sort of a body and acting like that, we also imagine the emotions and feelings. And that's when we don't like it.
The solution to the valley is either to avoid ticking off the imaginative mirror neurons by being humanoid, or make it look and act so human that the robot/model can really pass as a human. Of course, once the cover has been blown and the truth is out, the mechanical nature is out and I don't think most people will feel very well when imagining themselves with wires and hydraulics.
In the reverse, humans who act too well can also fall into the uncanny valley, but only if we find them strange. Beauty tends to invoke another set of responses, which negates this one. This may be what happens to any "transhumans", so I don't think they fall into the uncanny valley at all. Unless, of course, circumstances has invoked our judgmental senses.
The same effects happen in when people from different races observe each other. People from one race are usually going to think people from their own race look most human. And people with one skin color find it hard to imagine their self-image into something opposite. If one gives up or rejects the image of someone, it can become difficult to accept the rest. That's probably where racism originates too.
At the left end of the curve (left of corpse/zombie) is the range between neutral, cute and not looking cute or funny at all. This part is really kind of a feeling thing with multiple dimensions, except that the scale might as well be called naturalness!
