User blog comment:Ktrfgfg/Chapter 53 Predictions + Volume12Special/@comment-86.132.20.55-20140106225630

I am new but I was wondering are the titans some kind of parasite ?

Ok my theory is they are some kind of parasitical plant like race (since they just need sunlight like a regular plant). Mindless titans are like drones and sentient ones like the ape titan are capable of spawning new titans by releasing spores that infest a human host and mutate them into a titan form; devouring the human to facilitate growth. Abnormal titans are the result of the spore not devouring all the human leading to the random bouts of sentience. I am unsure about the shifters but I think Eren's dad found a way to slow the spore's growth so Eren's body could adapt to it and not be devoured giving them more of a symbiotic relationship. So when Eren transformed the first time it was anger combined with self preservation on the spore's part.