I made a mention in my last review that I have a theory about the crystallized titan vomit that was found in the Trost clean up.

WARNING! WARNING! DO NOT READ ANY FURTHER UNLESS YOU WANT SPOILERS FROM THE MANGA OF ATTACK ON TITAN!

Now with that out of the way here is my theory: I believe that the Titans are the very same people living in the walls brought back in titan form and with no memory of their past lives.

It may seem like Im pulling this one right out of my head here but after seeing Episode 13 and reading the manga I have some evidence to support my claim

Evidence piece 1 – Titans CAN talk: There are select moments in the manga that show the Titans making attempts to communicate with the humans and even being able to say one or two words. One soldier in particular documented her experience with a Titan that was able to talk to her briefly and was even shown crying a bit before finally devouring her. Another titan to show the talking trait is one that is found in Connie’s house that is able to say “Welcome” to him as he leaves. Its also worth noting that the titan that spoke to Connie also had small arms and legs, probably indicating that it was just born or developing. The final titan to demonstrate the ability of speech is the 17-meter titan covered in hair. This titan is able to create thought and even have full conversations. I believe that perhaps most grunt titans aren’t able to control their minds long enough to prevent them from eating.

Evidence Piece 2 – The Furious Five Titans: Dumb pun aside there are 5 titans in particular that share one thing in common: they were engineered. Eren, Ymir, Annie, Reiner and Hoover are all able to transform into titans. Eren in particular is given his Titan abilities by his father or so its been hinted at in flashback both in the show and in the manga. This shot also give Eren amnesia which is something Reiner is hinted at experiencing in the manga. While its not clear how the other 4 received their titan curse it does give me a thought: Maybe there were certain titans that were engineered in order to give birth to other titans. This leads me to my last piece of evidence.

Evidence Piece 3 – The Crystal Vomit Egg: Now is where all the loose ends come together. In episode 13 of Attack on Titan Sasha finds a crystallized hunk of Vomit with a naked person inside of it. Jean then says that since titans cant digest they vomit those large hunks of rock out of their systems. While it hasnt been touched upon more in the manga I think this deserves attention since titans usually bumble around without clothes on them and its not clear as to how their made. This crystal egg as I like to call it could very well be how other titans are made which is why their able to increase their numbers. Also notice how no matter what titan it is, Eren or grunt, it is imperative that you slice them at the base of the back of their neck.

With all this evidence my final theory is this: Someone somewhere created the titans as an experiment but this went all sorts of wrong. The titans then ate every human in site and then vomited them out, creating crystal eggs that give birth to new titans.  When the titans are born their memories of the life they used to live are buried away and the only thing on their mind is consuming as many humans as possible to make more titans. One scientist and his son survived and in a desperate attempt to correct his mistake to humanity he injects his son with the power of the titans that will only unlock at the right time. All the research done was hidden in his basement. In other words: Titans are people and the soldiers fighting them are actually killing each other not realizing it.

Now this is all just speculation at  this point since again nothing is confirmed but I think based on these small bits of evidence we can conclude the titans may be more than we think.