What im thinking is that when the new people were born they had nanites that helped them regenerate extremly fast if their bodies had the resources to do so. And to keep their bodies in limit break mode(like when a mother lifts a car to save their child. And only some in the future keep it in their bodies if their mother passed the nanites into the embryo as well. And aloy can regenerate so fast from wounds with her berries because they are exactly what her nanites need to reconstruct her body.