Board Thread:Manga/@comment-33873869-20200317050453/@comment-25933225-20200402134231

Deppintosh wrote:

I don't think the first SoYs became such by eating Ymir's daughters or the first 9 shifters. Remember when Ymir was hit and killed by that spear? Just before she finally closes her eyes and dies, the king orders her to stand up and work because she was born to be a slave. I think when she awoke in the Path Realm she chose to grant the power to turn into Titans only to Eldians because she was brainwashed to advantage Eldians for all her life. So I think that right after Ymir's Death all the Eldians of that time (which, given the more "tribal" society they lived in, were also ethnically Eldian) got the ability to turn into Titans all at once, thus becoming SoYs.

This is what I've always assumed, but now, re-reading chapter 122, especially the king's speech on his death bed, I see that it's kinda ambiguous and it could also be interpreted your way. Yup. There's no absolute answer (yet?) and your theory could make sense, but we can't say if one of us is right or if we're both wrong x)