What is disturbing?

[FlawlessHappiness]

I think that what we think as disturbing is maybe that we think as something somewhat uncomfortable. It could be a vestigial remnant from our ancestors.

That sentence had a lot of thinking.
I'm guessing what you meant was:
We think something is disturbing because it makes us uncomfortable?

Yes!

Also, I stumbled on Freud's Uncanny concept.

To quote Wikipedia:
"The uncanny is a Freudian concept of an instance where something can be both familiar yet alien at the same time, resulting in a feeling of it being uncomfortably strange. Because the uncanny is familiar, yet incongruous, it often creates cognitive dissonance within the experiencing subject, due to the paradoxical nature of being simultaneously attracted to yet repulsed by an object. This cognitive dissonance often leads to an outright rejection of the object, as one would rather reject than rationalize, as in the uncanny valley effect."

This could explain why things can be disturbing. If the object is a doll then we applied it with this concept, the doll is familiar, as in human-like, but it's also uncomfortably strange. The doll looks human, but it's an inanimate object. It can't move, talk, eat, or even interact! It's so odd, yet familiar.

This creates a cognitive dissonance, because you're both attracted and rejected to the doll itself.

Yup. This is the best form of horror too, IMO.
When something looks familia but isn't exactly that...