Board Thread:Manga/@comment-33873869-20200317050453/@comment-25933225-20200317212301

Here's the first possibility, and the one evocated on the wikia :

Ackermans have always been SoY. Since their creation. But, for uncertain reasons, they're immune to the Founding Titan's power. And, as they're labelled as "byproducts of Titan science", it's not something that was asked by a Founding Titan to Ymir in the Path Realm, otherwise it wouldn't be labelled as such. What kind of "experiment" could have been done to create them ? It's entirely up to theories. Furthermore, the fact that they've always been SoY is supported by their ability, which enterily rely on their link with the Paths (receiving through paths experience of previous Ackermans).

Second possibility :

Ackermans haven't always been SoY, which explain why they were immune to the Founding Titan's power when the Walls were created (it's not the case anymore, as we've seen with Mikasa in 123). But now, they're all SoY, because if they weren't, that would mean they practiced incest for a century. I suppose that in this possibility, the first Ackermans born as a SoY is Grandpa Ackerman, as he was born after the creation of the wall, so there's a strong possibility that his Ackerman parent had a child with a SoY (remember that the Ackermans were ostracized after the creation of the walls, meaning they couldn't have any children with the non-SoY, because they all belong to noble bloodlines alined with Karl Fritz). And, automatically, Kuchel, Kenny, Levi are SoY by birth. Same applies with Mikasa and her father, even if we don't know any of their ancestors.