kuuskytkolme wrote:So all pairs only get children in the genders they themselves are?
That's my current design, yes. (As the usual condition; trans, intersex, and other surprises may not respect that rule.) I'm not strongly attached to it but I like more of its consequences I've thought of than I dislike.
Edit: discounting elf/elf, which requires a third elf before you get your elf baby.
My intuition says yes for otherworldly humans and approximately-humans, no for the fully general case of, like, aranea or Thilanushinyel dragons or Devices or what have you.
The baby plant can't handle children of two unrelated species at once, it has to be for one or the other; and the elf hair in the seed isn't chiefly for the making the babies part, it's for the growing a plant part, so it loses out.