my assorted vaguely specbio themed headcanons for ffxiv, specifically to do with having kids:
my headcanon, to try to reconcile canon's lack of mixed race npcs (i know it's probably for cost reasons, since it's cheaper to just re-use existing player models for npcs): most mixed race kids are fairly rare (as per what we're shown in-game) because of biological incompatibility. different races have different gestational periods and, in the case of au ra, a wholly different reproduction than anyone else. setting aside size difference issues, roegadyn, elezen, and hyur are much more easily compatible with each other. miqo'te and hrothgar are somewhat compatible with one another. lalafells are fairly compatible with hyur, elezen, and roegadyn, with some allowances for the size disparity. au ra and viera have trouble reproducing with any other races, and hrothgar have trouble with anyone other than miqo'te, but they can manage it.
re: above, i headcanon that au ra reproduce in a vaguely seahorse manner. male au ra fertilize female au ra, female au ra then have a small window of time to pass the fetus/egg/whatever to a male au ra or their body reabsorbs it. as a result there's really no such thing as an accidental au ra pregnancy. theoretically, if a non-au ra was able to fertilize a female au ra's egg, the female au ra could then pass the pregnancy to a male au ra willing to surrogate for them and have a half au ra baby that way. The other way around, a male au ra could potentially find a female au ra willing to be a surrogate/donor for them, who would then pass the fetus to the male au ra once it took in order to have a (potentially) half-au ra baby. It could potentially happen, it's just rare, especially due to how the au ra population is relatively small and isolated compared to a lot of others. It's probably much more common in Thavnair, where there are a lot more au ra in the general population.
somewhat similarly, female miqo'te really only ovulate when stimulated by the pseudo barbs on a male miqo'te's penis, which means it's nearly impossible for a female miqo'te to get pregnant by anyone else. thats why so many of the sex workers you see are miqo'te
hyur and elezen pregnancies last 9 months, which is why they're fairly compatible. miqo'te pregnancies last 6-7, so they often can't carry a non-miqo'te baby to term. viera pregnancies last nearly 12 months, and their bodies usually fully reject a non-viera fetus. They also have an extremely low rate of conception to begin with.
I'm also toying with the idea that mixed race children tend to heavily take after the one who carried the pregnancy due to aetheric shenanigans or something akin to that - in order to ensure the baby isn't too big or too incompatible with the one actually carrying the pregnancy.
gender relatedly, au ra would likely not have the same concept of binary genders.
viera also have a very different idea of gender - they go based on what you do. if you want to have, do have, or want to raise babies, you're a Village Viera. pronouns & such are entirely unrelated. if you cannot or don't want to have or raise babies, you can be a Wood Warder. pronouns and presentation are your own business. Plenty of viera have "mismatched" secondary sex characteristics (warders with breasts, village viera with facial hair, etc) in part because of how sexually non-dimorphic they are. canonically you literally can't tell them apart until they've reached puberty.
Additional headcanon about miqo'te; they have heat cycles!
female miqo'te usually begin experiencing heats around 15-16 years old, but they're mild and irregular at that point. heats usually don't settle until they're around 20 years old, and that's when they can actually start having kids
heat pheromones DO have an effect on male miqo'te, but it's not like. overwhelming. it's normal for young tias to start peacocking and posturing at each other during female miqo'te's heats once their puberty kicks in, usually about the same age (14-16), but it's considered childish and uncouth for a grown miqo'te to act that way. stop posturing at the other men. you're in your 30s. grow up.
heats are usually every four months or so, and last 5-7 days.
gay tias are still affected by the pheromones, but they tend to posture AT the girls, because the pheromones affect their behavior but doesn't make them attracted to the girls; instead they start peacocking for the other tias.
similarly, lesbians in heat completely ignore any peacocking from male miqo'te, and will either present at or peacock for other girls.
