THeory 1- Titans are the result of mutated genes. As in they are humans who's Dna/genes mutate for some strange reason.
What that would explain- humanistic features.
What it doesn't explain- Lighter than their height would suggest bones. So low density bones , typical for small creatures like small domestic cats, wild animals, which contrast their giant body types. strange, they also appear to not have bone marrow. NO reproductive organs, or organs in general, don't have the need for oxygen, eat breathe, and they are somewhat docile at night.Can regenerate their limbs.
THeory 2- tHey are some kind of physical manifestation of all the evil deeds of mankind, etc.
It would explain Hanji's findings, why they seem sooo focused only on humans, their appearance.
What it doesn't explain- their origins, the Colossal titan, since then that would suggest he would be the only manifestation...
THeory 3- Aliens. Lets face it, they might as well be...
So these re some of my less crazy theories i have about the Titans origins. I wonder what are other people's theories?