Biology of Fantasy: Let’s Get Real, Shall We?

John Dailey
Universe Factory
Published in
12 min readOct 5, 2016


Throughout human history, mythology is alive with “humanoids”, creatures with certain human qualities. There have been particular cases in trying to justify their existence, but those cases focus on an evolutionary angle. If I were to find some evolutionary justification, I’d be writing a whole novel’s worth of information, and that’s not what we are here for. This article is my own list of proposals of humanoid creatures who, in this fantasy world, have been abundantly reported to perform interbreeding with Homo sapiens, us.


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Undoubtedly, one of mythology’s most iconic creatures is the centaur, a human being with his or her waist glued to the torso of a horse. Why? Just…WHY? No other animal on Earth has two separate torsos in one body simply because one is good enough. My proposal is that the transition between human and horse is in the midriff. That way, we can have two separate sternums fused into one. That still raises the question as to which organs will be in which ribcage. Here is my proposal:


  • Brain
  • Eyes
  • Tongue
  • Esophagus
  • Lungs (in all humanoids, the lungs make up 15% of the total body volume, rather than the typical mammalian 7%.)


  • Stomach
  • Kidneys
  • Heart (so proportionately large that if it were human, we’d diagnose him with cardiomegaly)
  • Liver
  • Intestines

The next issue is what would a centaur eat? Would it eat grass, like regular horses? I say no and here are two reasons why not:

  1. Grass isn’t ideally nutritious, which is why some grazers spend the most part of the day mowing the lawns.
  2. Grass grows low, far out of reach for the centaur’s augmented torso.

Instead, let’s put those hands to good use — leaves, fruit, nuts, eggs and even insects.

Traditional pictures put centaurs using modern horses. While I say we keep that traditional image, I propose that this not be the be-all-end-all. Some tribes would keep the ancestral three-toed design.

Miohippus, an ancient, three-toed horse. Image retrieved from

Classical image often portrayed centaurs as being sexually unrelenting. Fortunately, biology can justify that behavior — just look up musth, a bi-annual condition in which a bull elephant’s testosterone skyrockets, making him excessively aggressive.

This next issue is for anyone who wants to write a romance fantasy between a human and a centaur. Traditional centaurs are simply too tall for interbreeding to be merely as burdensome as regular breeding. My proposal is this — make the average centaur four to six feet tall. Which means structuring the centaur less like a thoroughbred and more like a pony or, even better, an Icelandic horse (the only one to have a fifth gait, ambling, which made this horse the ideal traveling companion during the Middle Ages).

A pair of Icelandic horses, the only breed to move around in five gaits, not the traditional four. Image retrieved from

(If you want to use the traditional thoroughbred, though, then go right ahead, but I’ll warn you this — labor pains will reach critical.)

The final issue that needs addressing is color. In traditional art, the human half and the horse half are never in pigmentary sync. In nature, you have to be one color scheme or the other. So here’s my proposal — the centaur’s human half will be of either Caucasian, Asian or Polynesian design, but both halves will be the same color, be it:

  • Bay
  • Chestnut
  • Grey
  • Black
  • Pinto
  • Appaloosa
  • Palomino
  • Roan
  • Smoky black
  • Silver dapple
  • Smoky cream
  • White

Just as both halves will be the same color, both halves will grow the same coat in the winter. It’s less clear-cut and more believable that way.


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The classic image of the angel is a winged humanoid superior to humans in power and intelligence. How do we make this biologically real?

For starters, no wings anchored to the shoulders! Finding an evolutionary justification for this is a massive headache. Besides, it’s also a cliche unto itself.

My first proposal is that there are actually two major groups of angels — the “common angels”, inspired by both bats and pterosaurs; and the “classic angels”, inspired not by modern birds, but by the “four-winged dinosaur”.

But before we differentiate the two groups, let me list my proposals on how alike they are:

  1. Respiration — all humanoids have lungs taking up 15% of their overall body volume, rather than the typical mammalian 7%. In both angels, air sacs are added so that they can both breathe and cool down more efficiently.
  2. Circulation — all humanoids have hearts so proportionately large that if they were human, they would be diagnosed with the condition called “cardiomegaly”.
  3. Chest — both angels have an enlarged sternum, or “keel”, equal in size proportion to a pigeon’s (by itself, proportionately larger than a raptor’s) for maximum takeoff strength.
  4. Legs — in proportion to length, both angels have human legs, but human legbones are thick and wide, so my proposal is to narrow them down so that they are more gibbon-like than human-like. Another proposal involving the legs is to place the heel at the apex of the hock joint, allowing them to stand on their toes.
  5. Abdomen — the previous proposal applies to the ribcage as well, thus allowing the bulk of the musculature to be focused on the chest and arms, crucial for flight.
  6. Bones — obviously, hollow bones help reduce the body’s weight without sacrificing its strength, another cruciality for flight.
  7. Brain — both angels have proportionately larger brains than ours. For example, the common angels have a cranial area averaging 1720 cubic centimeters. In both angels, the flocculus, a region that integrates signals from joints, muscles, skin and balance organs, makes up 2% of the total brain mass. (I was originally going to propose raising the percentage to 7.5%, so it can be more pterosaur-like, but recent science has proposed a potential relationship between flocculus size and behavior complexity.)
  8. Arms — If we are to compare our arms to angel arms, we’d see that the humerus (upper arm) has lengthened to 150% and the radius and ulna (lower arm) each to 175%. The hand is still human-like, though instead of nails, they’d have claws.

The differences between common and classic angels, though present, still don’t hold a candle to the similarities. But propose them, I must.

The common angels still have their extra-long arms, but if we compare their fingers to our own, we’d find that the common angel’s ring fingers and pinkies have lengthened to 850%. Connecting them all the way down to their ankles are solid sheets of skin strengthened by actinofibrils, fibers spaced closely together. The wing membranes also contain a thin layer of muscle, fibrous tissue, and a unique, complex circulatory system of looping blood vessels, exactly like pterosaurs. Their whole bodies are covered not in regular mammalian fur, but pycnofibers, again like pterosaurs.

The classic angel, on the other hand, are coated in feathers. They have not the traditional two wings, but four, just like the ancient dinosaur Microraptor. They are also smaller — whereas the average male common angel is 5'2" in height, the average male classic angel is 5'0". (Females from both groups are 3/4 the male’s size.)

Microraptor, the famous Four-Winged Dinosaur. Image retrieved from


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Believe it or not, the diminutive but rough dwarf is the closest of all the humanoids to be biologically realistic. How?

Let’s look up Homo neandertalensis, the stereotypical caveman, in comparison with modern man:

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My proposal is that the dwarf’s skeletal design and proportion be identical to the neandertal’s, only compressed in a smaller body — average male height, 4'0".


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The traditional description of the mermaid is half-girl and half-fish. That, both biologically and dramatically, is just ridiculous. If the mermaid were half-fish, then why does she move her tail up and down and not side-to-side as fish should? No, my first proposal is to make the mer (the whole race, not just the females), half human and half dolphin (or porpoise).

Now the first issue to address is hair. In classic literature, the girl half of the mermaid has long, flowing hair. Not only is this too clear-cut, which is biologically impossible, but it would create way too much drag. So my proposal is this — either make the mer short-haired (think “pixie cuts”) or all-out bald. Either choice would reduce drag substantially.

As for the face itself, my original proposal was to reduce the nose into flat nostril slits, since smell is of no use to an air-breathing mammal that spends its entire life underwater. But my proposal to keep the human face is way more interesting, and here’s how, retrieved from Worldbuilding Stack Exchange:

Let her have a throat system much like ours, but instead being a collection of air pockets, her lungs are hollow cavities. Inside these cavities there is a large set of gills. Let the mermaid also have one or more pair or slits on her sides, right under the lower ribs and connected to those lungs. These slit can vary in size, say from five to twelve inches in length according to your creature designing taste. They can also be located more frontally if you like.

When underwater, she breathes like a fish, just with a longer circuit for the water to flow through. She takes water from the mouth and nose, let it go through the gill/lung system (“gillung”?), then it is pumped out through the rib slits.

In order to breathe air, she first expels water through the rib slits, then she closes those slits. Now she can pump air in and out of her “gillungs” (I really like this neologism) just like a human. She just has to keep a little water in to keep her internal gills moist, so that they don’t collapse over each other (this is actually how land crabs breath). She might evolve some bodily fluid, maybe some mucus, to make sure that her gills won’t dry out fast.

Add a very large concentration of myoglobinin to her muscles, and she would be able to keep that boost for long dives just like whales do. With the advantage that she won’t drown if she spends too much time diving deep — she’ll just revert to her slower metabolism until the next time she surfaces.

Oh, and about salt…

Just use the same solutions that nature has already found. A large tolerance for urea, like sharks; and super kidneys like those of cetaceans.

How would a mer vocalize to attract a mate — be it mer or human? Would it echolocate using the melon, as cetaceans do? Or maybe something less front-heavy — an enlarged vocal sac, just like frogs or gibbons?

The final issue to address is coloring. Unlike the centaur, the mer’s transition between two species is smooth and natural, but they are still colored separately. My proposal is to give both halves one color scheme. I was originally going to use whales for color schemes, but what I’ve got on Worldbuilding Stack Exchange is a more interesting idea:

Having a coloration and body shape that can blend in with or mimic other creatures would be a potential advantage in cohabiting and/or cooperating with native ocean creatures, as well as times when hiding amongst the crowd has benefit. On the other hand, it could also get them mistaken for valid prey by certain creatures.

A chromatophoric integument would have certain advantages as well. Not only could mer pull off the above mentioned tactics, they could also hide against objects and the sea bottom. In areas with light, it could also serve as a non-auditory form of communication. Combine with the optional ability to fluoresce, and you have signalling capabilities even in the depths. (And a possible method to lure prey (or mates) to themselves!)


Now the first question is — which elf?

Santa’s elves?
Shoemaking elves?
Keebler’s cookie-making elves?
Tolkien’s elves?
The Dökkálfar (dark elves) and Ljósálfar (light elves) of the original Norse mythology?

My first proposal is this — let’s mix the latter two together, the “dark” and “light” aspects reflecting an African-European division. The reason I’m mixing Tolkien’s elves with the original elves is that both categories are quite prominent in the high fantasy subgenre.

Now the most obvious difference between us and elves is the pointy ear. In the mammal world, this isn’t so far-fetched. Foxes have pointy ears. But why stop there? Why not adding tufts, just like the ears of a lynx?

Another obvious difference between us and them is that elves are immortal. Now, biologically, we can’t make any lifeform truly immortal, but we CAN lengthen the telomeres, repetitive nucleotide sequences at the base of each chromosome, to make them live longer. A “biologically immortal” organism, as scientists would call it, would still die, but senescence (think “senile”) would not be an existant cause. My proposal is that we lengthen the telomeres to the extent that the average elvish lifespan is triple-and-a-half greater than the average human lifespan.

This would suggest giving the Elvish body HMW-HA, a kind of chemical that prohibits the development of incurable diseases like cancer, as well as censoring pain.

As always, enlarged circulation and respiration will include the elves on the list of humanoids.

Tolkien described his elves as “slender” and “graceful, yet strong”. My proposal to make that description more concrete is to, essentially fit a musculature as dense as a Bowflex body onto a skeleton as slender as a gibbon’s (while at the same time retaining the human proportion.)

My final proposal differentiating elves from humans may be the most radical — hermaphroditism. To be specific, simultaneous hermaphroditism, which means that each and every adult has both male and female sex organs simultaneously active. Unlike humans, there is no clear-cut distinction between a male elf and a female elf. This would make them popular candidates of LGBT campaigns.


Image retrieved from,_Moutain

Giants do exist. It’s just that they can’t be anywhere close to being as big as those in Norse mythology or the story of Jack and the Beanstalk. The best we’d ever have for a giant was Robert Wadlow, who grew to a height of eight feet and 11.1 inches. My first proposal would be to make Mr. Wadlow’s height the average for the giant.

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Unfortunately, human beings of Wadlow’s stature suffer the following biological and medical issues:

  • Pituitary tumor, which can get large enough to shove nerves into the brain, causing headaches and vision problems
  • Excessive sweating
  • Such sleep disorders as insomnia
  • Delayed puberty
  • Irregular menstrual periods
  • Deafness

Here is the best solution I got from Worldbuilding Stack Exchange:

A Larger Heart

Having a large heart , especially in proportion to the giant, would counteract any negative affect associated with blood flow, hormone circulation, and lack of oxygen to the brain

Larger hormone production centers

Such as the thyroid, testes, thymus, pituitary, and adrenal glands , to increase the amount of the hormone in proportion to the body, and it may fix your puberty & menstrual issues

Thicker Bones

This will not only increase bodily support , but also ramp up the production of red blood cells. This may also solve your deafness and insomnia problem by making the bones in the inner ear more sturdy , and increasing the amount of oxygen that gets to the brain

Stronger Tendons / More Skeletal Muscle

To allow the giants to move their added skeletal weight & the added weight in general due to the square-cube law

Larger Cerebellum

Increases coordination proportionately to the larger body

More Mitochondria

Since the muscles will have to do a disproportionately large amount of work , the added mitochondria will be able to compensate

More Capillaries

Especially near the surface of the skin , to increase effective temperature regulation, ( which many other large mammals have issues with ) which fixes the sweating problem

Everything else can be scaled up normally , except for the cerebral cortex, as that might have the side affect of increased intelligence, that is , above that of the average human , but hey , if that’s your intended effect , knock yourself out

Of course, as with all other humanoids, they have lungs making up 15% of their overall body volume and four color receptors instead of our own three.

There is one final issue to address about the giant — how to prevent gravity from crushing them at the base. My proposal is simple — have the giants walk on their toes and make the “heel” actually a soft cushion of flesh, just like an elephant’s foot.

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