Merfolk and Beastmen origins
I want to credit "d4lucia" for giving me this idea, as they had a post asking about the difference between merfolk and beastmen and how they developed, and I stumbled upon it. I'm going to be going over different possibilities, along with what ones I think are most likely and why! This will be long...
Beastmen take on the appearance of kemonomimi when we first see them in the story (A mostly human character with small animal traits like cat ears or a tail) however, they seem like they may be slightly more animal-like at birth.
The babies have a more animal build, mostly indicated by their feet, and seemingly lacking a human nose. Since this is a black-filled outline, it's hard to see how different they truly look.
I can't find it confirmed in-game, but most of the fandom has come to the conclusion that beastmen evolved from animals thanks to magic and intelligence. I support this idea the most.
Some others theorize that potions or curses could have been used, like with the Octavinelle trio. I doubt this mainly because they came from extremely different places with different beliefs. Sunset Savanna makes a point of not changing the natural land much, so I would doubt changing their entire body would be very agreeable, plus transformation potions are illegal and have time limits, so if they had used those, there would have been a point where everyone started reversing. Or cases of the curse being lifted, as it's pretty unbelievable if it was a curse that it hadn't been lifted long enough to create a long-standing kingdom with a long-standing history.
A different theory is that humans got "involved" with animals. I refuse this both morally and logically. Sheep and goats are quite similar, and they can have babies, those babies tend to die young due to the genetics being against each other. So even if somehow a baby was born from something like that, it would be highly likely to die, and if they did live, they would still need to be multiple cases, and those multiple cases, as they wouldn't be an actual species in itself, would all likely have different issues that would then also kill their babies.
A fusion spell is what I haven't seen discussed and have considered. It is possible some mages used magic to take features or genetics from certain animals and put it into themself, or combine themself with an animal companion to create 1 being. Not impossible, but not likely either.
I personally believe them to be naturally developing from animals without human interference.
Merfolk are not Kemonomimi like the beastmen. Merfolk have over half non-human bodies, with their tails, skin colour, gills, and webbing of some species making this obvious. We have not seen newborn merfolk like we have beastmen (Sadly) and likely won't.
It is possible merfolk developed from marine life, however, due to the context of the Little Mermaid movie, it's also possible they naturally occur without having to evolve. Naturally, they could have just evolved before the beastmen, but Greek mythology is somewhat canon. Disney DOES have an official Poseidon design, as underutilized as it is.
He makes an appearance in the background of the Hercules movie, and actually has a few lines in the TV series. It's possible Triton became a passed-down name along with the actual Triton, and merfolk are distantly descended from Poseidon and other sea gods(Like Idia being possibly descended from Hades), or were created by him at least, which would mean no need for evolution. Now greek mythology doesn't really have actual merfolk as far as I know, but they do have monsters with sea features like Scylla, having eels attached to her in several depictions. Or they're one of the many results of a god entwining with a human or who knows what else. (There are MANY variations of children from gods, it's like a randomizer) And Nymphs, specifically Naiads, who are freshwater-based. Them being naturally occurring without much evolution would also explain the lack of indications of any domestic-style fish merfolk.
Beastfolk have ever so slightly alluded to domestic animals having turned into beastfolk with Chenya and Lucious. Chenya does not look at all like any wild cat, and Lucius has high intelligence, plus there are classes where students learn to speak with animals. Mainly Lucius, as we see a panel with Azul speaking to him.
It isn't explained why they really do this or if other students hate this class, but I think beastmen coming from animals would make this something mages would realize is useful and create classes on. Yes, the princesses talk to animals, and maybe it came from that, but with NRC being a villain school, I would assume them more likely to just learn to enchant their animals to be understandable or something. Sadly, it isn't expanded on if this has ties to beastfolk or not, but it isn't impossible. With Merfolk, though, this doesn't seem to be the case, as while we don't see them try talking to fish, we do know Jade and Floyd have eaten octopus, and Jade specifically has tasted eel (Ignoring the cannibalism theory). This would be extremely morally questionable if merfolk could naturally speak with or evolve from animals/marine life. While I can certainly imagine them doing it anyway, it would garner a more negative reaction from others that we just don't see.
Now Racism... I wasn't planning to touch on this, but I think it may be important. Many players have noticed the racism towards beastmen, but nothing is mentioned about merfolk. I would assume if they were evolved the same way, there would be little to no difference. This could be an attempt to show racism towards POC since merfolk tend to be pasty, butttt Ruggie looks like a white child anyway, and it's still directed at him sometimes, plus Jamil and Kalim are spared and also have tann/darker skin. Which furthers my idea that beastmen are evolved from actual animals, and merfolk aren't. After all, people would respect merfolk more on a religious idea of them being special and created by gods, somewhat like humans and tales of demihumans, whereas beastmen wouldn't be seen the same, as they don't have the Greek gods as a possibility and have different beliefs. I play eng so I know a lot is watered down over here. I could be wrong on this point, but this could cause a subconscious idea that the Beastmen are unnatural for how they developed so human-like without humans or gods to explain it.
Another factor could be that merfolk can appear fully human, unlike the beastmen, but I feel they would still get some of that treatment once more people found out they were merfolk then. They could also be used for a talking point on animal abuse and humans seeing anything not exactly like them as lesser. Merfolk can appear exactly like them, but beastmen can't, since they wouldn't be allowed the transformation potions. Kinda like the humans not liking the fae in the past because they are visually different and live differently.
I really wish Twst would give some clearer lore on the species, relationships, development, and history between and within species. I know it's fun to have some uncertainty and get creative when it comes to OC's and fanfic, which I truly enjoy, but I also really want to see more of the actual world and why it works the way it has been. That's all I can think of about merfolk and beastmen for today, though, lmk if you have any ideas not here as for how they developed and why they could be different.
