User blog comment:Raul123alin/My theory about the origin of the titans/@comment-93.209.36.203-20140205135314

I regard the "To you, 2000 years from now" as one of the greatest mysteries of the series, however I don't think that the Titans are science fiction after all what the ape did. My best guess is that Titans are made of pure human will power. That explains the shifters, too. When normal Titans are created, humans are reduced to their most brutal basic instinct - killing other people. Eren on the other hand needs a specific goal and tremendous will power to shift. (He wasn't able to fight Annie for a while because he lacked the mental power.) The Titan body is like that of a ghost - it has almost no mass. When a human shifts into a Titan, we see a bright light for a short time. That's when the "soul" becomes physical, creating the Titan body in almost no time. And when a Titan body loses its human core, it evaporates quickly because its lost the will power fueling it. Eren, who can hardly control his feelings, is in constant danger to get absorbed by his Titan body because that simply means he gets consumed by his own dark emotions until he totally loses his human side.

I believe the author suggests that humans are their own worst enemy (frequently explored in the series), and that's why Reiner tells Ymir that the world has no future: All humans are just "TItans in a human body". That also explains Isayama saying he did aim for a dark ending. You can't get rid of the Titans as long as mankind exists.

The wall cult could be about giving humans the will power to protect the walls, so maybe they will be able to turn into wall Titans. The ape could have been able to cause the humans in Connie's village becoming consumed by their "killer instinct", turning them into Titans. The conversion of Connie's mother failed because she had her own child in her mind all the time, what explains why her Titan was able to talk to him.

I admit that the theory has several flaws, like why most Titans can't move at night and why the shifters have to hurt themselves. My aim was not to provide a complete explanation, but rather an idea which can be refined by other people. Why should not forget that Shingeki is mostly about human will poer, however.