Board Thread:Manga/@comment-37661994-20181129140627/@comment-7630054-20181129152049

Do you find this odd that there is no supernatural elements in the story other that the Titans? Because I do. I'm also sure we're given enough info to at least suspect Titans being a purely scientific concept. And the 'deal with the devil' is just a legend.

So, if that's the case, could it just be that whatever biological virus/organism/infection or whatever the ability to turn into a Titan is, it can only affect a specific race/subrace? And in that case, Ymir just spread it.

Again, my own speculation, but it does have some basis in-story.