This question is probably better suited for r/AskAnthropology. Still, here’s some more focused answers while you’re waiting.
A deleted user discusses incest in Egyptian mythology here, note that this is in r/AskAnthropology.
u/svaregoteuse briefly covers Greek mythology here, and u/ThuperCool briefly addresses Persian mythology here, though I’ll note that I’ve read answers from our sub’s resident Zoroastrian expert, u/lcnielsen that contradict the latter.