- Why are the ears of fairies/elves pointed? What acoustic benefits do the points have? Or were the points originally for attracting mates? In which case, do male elves have pointier ears than females? Ethereal beauty I get, but not the ear issue.
- I can understand goblins and orcs being kind of squat and dark in color, since they live underground, but why did they evolve to be ugly? How are hooked noses, facial warts, and beady eyes an advantage? I think it's generally assumed that goblins have evolved better night vision to deal with their cave environment, but why haven’t they gone the route of a number of cave-dwelling species and evolved blindness? Do they echolocate?
- If goblins are short, why are trolls traditionally tall? They both live in caves. I prefer the Scandinavian version of trolls, because they’re human-sized or smaller. Then again, the Scandinavian trolls have tails. Why?
- Why do trolls turn to stone in sunlight? The only author I’ve encountered who explains this is Terry Pratchett, whose trolls are made of stone and become much slower when hot.
- What advantages do pixies and gnomes have in being small? Are they better able to hunt small prey that way?
- How did pixies’ wings evolve, and why do they sometimes look like insect wings? Leaves I understand; they’re camouflage. Are the insect wings the same principle? Convince predators (or prey) that you’re a harmless bug and they’ll ignore you?
- Speaking of size, how did giants and trolls evolve to be incredibly tall? People have done math to show that in Earth-gravity, that kind of size would be instantly fatal. Bones would break under the pressure of the muscles moving them.* Therefore, we have to assume that fantasy worlds have a different sort of gravity, that the bone-muscle ratio is different, or that the bones are stronger than human bones. Are they made of something other than calcium, then? Volcanic rock, perhaps?
- What evolutionary pressures created giant, sentient winged lizards that breathe flame and speak? Why are there only ever Great Dragons and never an evolutionary tree of dragons, some without flame, some without sentience, some with six legs and no wings? For that matter, why are dragons the only seven-limbed** creatures on a fantasy world? (Except for Pern, where many of the life forms have that trait.) And how did the voice boxes enter the picture?
- Assuming that dragons exist, why would they evolve the ability to form a psychic or telepathic link with a human? We could breed them for that, I suppose, and create dragonis domesticus, such as those in the Temeraire series, but aren’t most wild dragons born with the trait?
- Would the pressures that created dragons also be responsible for winged horses, and why aren’t there multiple species of semi-winged or six-legged horses?
- What the hell is responsible for centaurs, fauns, weres, and merfolk? Especially the centaurs. Fauns I can see adapting for rocky terrain, weres for self-defense or better hunting or … something, and merfolk for aquatic environments. But what kind of pressures would result in a half-human, half-horse?
- What do centaurs eat, anyway? Hay and grass, human food, a mix?
- Are griffins, hippogyphs, cockatrices, minotaurs, and sphinxes truly hybrids? If so, how do such incompatible species produce viable offspring? If not, how did such strange creatures evolve?***
- I can understand the reasoning behind a three-headed dog, and the multi-headed hydra, but why does nothing else have multiple heads?****
- Why are there sentient trees? Why are there mobile trees? Are ents animal or vegetable, or a descendant of the common ancestor of the two?
- Why are there sentient bodies of water?
This isn’t to say that I don’t understand everything about fantasy evolution. Dragons obviously breathe fire for self-defense. The unicorn’s horn is surely for the same reason, though that doesn't explain the healing properties. Dwarves would have started as humans (or hominids) who adapted to fit into narrow cave tunnels and lift lots of heavy ores. Harpies would be humans who went through the same adaptations, more or less, as dinosaurs did to become birds, or mice-like things to become bats. Anything using magic would have evolved that trait to a) defend themselves or b) make their lives easier.
The rest of it? I still want to know the whys and hows, and hand-waving by saying, "it's magic!" gets a bit old.
* I think the first essay on the topic might be this one.
** Counting the tail
*** And what’s the biology behind the cockatrice turning people to stone, anyway? Is it a magical defense mechanism? How much energy does the average human consume or release during petrification? Could that energy be harnessed for nefarious purposes?
**** How much energy is needed to regenerate a hydra’s head on short notice? The hydra must either have energy stores like a camel, or become weaker with every regeneration.