Now, I'm not an evolutionary biologist, either. But I have a problem with the theory that dunyain have evolved to become a different species. It's not just that dunyain-human union does not produce viable offspring. It produces monstrosities and kills potential mothers in the process, as this quote from TJE shows:
But if his divine seed was a burden she could scarce bear, then it broke all the others. Of the seventeen concubines he impregnated, ten died in childbirth, and the others gave birth to more... nameless ones. Thirteen in sum, all drowned in wine.
So on the one hand we have a genetic difference so big that it produces a baby with eight arms and no eyes, but on the other, it does not preclude "normal" children (normal in that their bodies are fully human). Somehow it does not seem possible to me.
(No eyes, that's something I could accept as a genetic glitch, but eigth arms?)
@mrganondorf - not Akka, at one point he muses about Mimara's father and this is what he thinks:
For the first time, it seemed, he noticed how much lighter her skin was than his or her mother's. For the first time he wondered about her real father, about the twist of caprice that had seen her born, rather than aborted by Esmenet's whore-shell.
So it seems her father must've been a Norsirai.