How possible is the following scenario for a hard sci-fi werewolf?


  • Evolved, not infected. Natural-born this way.

If an animal can serve up the required capabilities, please mention it in the answer.

Can do the following within an hour :

  • Massive facial re-modeling to change from a human appearance to a wolf-like appearance;
  • Surfacing of 10 more teeth (42 for wolf vs. 32 for human). Teeth would show up in an X-Ray.
  • Pointing of ears (less human-like) and conscious or unconscious pivotability of ears in the direction of a noise
  • Movement of the tarsis (ankle) about 1/3rd further up the femur; or a hidden joint that is straight during "human" appearance, giving the appearance of a straight femur.
  • The ability for fingers and toes to extend by about 1 cm.
  • Skin flexible enough to tolerate the size change without tearing.
  • The ability to produce about 1 to 2 cm of body hair.
  • A tail. Furry, but maybe not bony.

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This is very similar to this question, but takes it up a step.

  • 3
    $\begingroup$ "Can do the following within an hour"... pretty much that entire list is right out if you really want to stick to hard science. $\endgroup$
    – Matthew
    Aug 30 '21 at 14:54
  • 1
    $\begingroup$ Mitosis has some maximum rate, and things like teeth are even slower to generate (though perhaps those can merely be hidden/unhidden... the human jaw is pretty small though, even 3rd molars are problematic). I don't know that this is feasible from a hard science standpoint. $\endgroup$
    – John O
    Aug 30 '21 at 15:02
  • $\begingroup$ @JohnO "Mitosis has some maximum rate" Yep, it pretty much means the only option here is some sort of meat transformer with all these structures tucked away somewhere ready to slide into place. $\endgroup$
    – Pelinore
    Aug 30 '21 at 15:15
  • $\begingroup$ Naturally evolved nanotechnology, mmm soo sweet, spiced with hard science tag, mm soo good, can't wait for answers to come, so much rep to spend, lol. What kind of hard science do you expect there? $\endgroup$
    – MolbOrg
    Aug 30 '21 at 15:58
  • $\begingroup$ During the reverse transformation (wolf to human), does body hair need to be retracted into the skin? $\endgroup$
    – Alexander
    Aug 30 '21 at 16:29

We're not shapeshifting, which is cool

But you're also asking for a hard-science evolution-oriented justification for a fantasy animal — which isn't as cool. Evolution usually chooses the simplest change that favors continued survival. The really complex aspects of humanity (eyesight, our brain...) are the result of a long series of simple changes, each overcoming a disadvantage and promoting continued survival.

Werewolves will never meet that basic criteria. They're too complex for too little benefit (if any). To really meet your hard-science expectation, we would also need to address disease and healing — both of which will be massive disadvantages for a creature as complex as a werewolf. How, for example, would the human-form aspect deal with a disease that's afflicting the wolf-form and vice-versa? The illness wouldn't simply go away with the change. What happens if the human-form werewolf is playing soccer and tears one of the tendons I advocate for the second ankle? The more complex something is without a justifying benefit, the less likely it can be rationalized evolutionarily because it breaks (and therefore is eaten) too easily.

Consequently, my answer will focus only on real-world physiology that can be used to explain how a hard-science werewolf would behave.

1. Facial Appearance

Honestly, you made this a LOT simpler by only focusing on appearance. Shifting bone plates around would be no small thing and incredibly hard to justify from an evolutionary standpoint. They'd always represent an exploitable weakness without a compensating strength. But appearance can be explained using the same basic mechanisms as a male erection.

An erection results from a complex interaction of neurologic, vascular, hormonal, and psychologic stimuli. Pleasurable stimuli cause the brain to send nerve signals through the spinal cord to the penis. The arteries supplying blood to the erectile tissue (the corpora cavernosa and corpus spongiosum—see figure Male Reproductive Organs) respond by widening (dilating). The widened arteries dramatically increase blood flow to these erectile areas. At the same time, muscles around the veins that normally drain blood from the penis tighten, slowing the outflow of blood and elevating blood pressure in the penis. This combination of increased inflow and decreased outflow is what causes the penis to become engorged with blood and increase in length, diameter, and stiffness. (Source)

I believe it's a small ignorance to allow the human face to remain soft, but reasonably rigid, perhaps like an overweight person's face. The change to a werewolf would simply require the (obviously not necessarily "pleasurable") stimulus to increase blood pressure to the previously collapsed snout. The action would also flatten the human nose in the process, resulting in a canine look. Obviously, it would be much simpler if your werewolf were based on a Pug or a Bulldog than a Doberman or a Shepherd.

The change to a tough, blackened canine proboscis is something I think you'll need to walk away from.

2. Teeth

This most sophisticated fang type evolved once, in the ancestor to all modern vipers, which lived in Asia about 40 million years ago. ... Solenoglyphous fangs are long and tubular and are attached to the snake's maxillary bone. (Source)

Your werewolf can utilize solenoglyphous teeth, meaning through bone and muscle structure, they lay down, perhaps in a fold of skin, and only rise when in "werewolf mode."

And this is why I appreciate that you're only looking for the face to change appearance. Changing the bone structure of the skull to reflect a wolf's mandible is, from a hard-science perspective, impossible.

3. Ears

Pointing the ears operates on the same premise as the snout, nose, and face. As for rotating the ears, humans already have the genetic flotsam to rationalize this.

Ear wiggling happens through muscles above and behind your ears called auriculars. In some animals, these muscles are useful because ear movement is helpful. A cat, for example, can move its ears to help it listen for tasty birds. But why would humans have these muscles? Way back when, humans and cats had the same ancestors. Ear wiggling was useful to this shared ancestor. (Source)

Your real problem, and you're stuck with it, is that you can't move the ears to the top of the skull. That would either require moving the holes/passages through the skull (and the channels inside the skull) or having stretchable channels between the ear and the skull such that muscles could pull them up. I simply don't like this idea. I think it's on the impossible side of believable, especially in a hard-science context. So, you have pointed ears and they can rotate, but they're on the side of the head.

4. The ankle

You've already solved this problem. There isn't a hard-science solution to making bone stretch and contract. Sorry. It's very purpose is to not stretch and contract. The only solution is a hidden, second ankle that is locked in place in human-form and released in werewolf-form.

This isn't that unbelievable. Birds do exactly what you require.

Two thin tendons, called flexor tendons, extend from the leg muscles down the back of the tarsus bone and attach to the toes. When a bird lands on a perch, these tendons tighten and so the toes lock around the perch. This involuntary reflex keeps a sleeping bird from falling off a perch. The tendons stay tight until the legs straighten. As the bird stands up, it jumps up, its legs straighten, the tendons relax and the toes unlock to release the feet. Falling asleep doesn’t change the grip, as the weight of the bird keeps the leg in the locked position. (Source)

Where birds don't have a lot (if any) of muscle in their legs and claws, I think it's reasonable that your werewolves do. The tendons run from the knee to the lower ankle. The hard part is rationalizing how they tighten. For a bird, it's mechanical. Their weight when they land automatically tightens the tendons. For your werewolves, a unique muscle connecting from bone to tendon would be required to cause the tendons to tighten.

5. Fingers and toes

This one's almost as tough as the ears and ankle. Bones can't stretch and contract or they don't do what you need them to do: act as the foundation of everything else on the body. It would be like building a house on Styrofoam rather than concrete.

But we have those fangs we mentioned in snakes, and we have the fictional character of the Wolverine. Frankly, this is the least believable solution I'm going to offer, because I can't find an example in nature of a bone that is extended (pushed) between two other bones to create an extended something. And yet that's what you need.

Think of holding a toothpick in a pair of tweezers, then imagine a muscle or combination of muscle and bone that would push that toothpick out and pull it back.

This is a MASSIVE WEAKNESS. Yes, I can imagine the physiology of the solution, even if you had to use a leveraging bone (like used for the fangs or similar to the ear drum assembly) to push the extending bone out. The problem is that this is incredibly weak and easy to break. We're talking about fingers.... From a hard-science perspective, I hate this particular recommendation and hope someone else can come up with a better solution — because I'd leave the fingers and toes unchanging over doing this. It's weakening the body for the purpose of aesthetics, and that's not evolutionary at all.

6. Flexible skin

So far I've not advocated anything that would require this, so I'm going to ignore it. If I was forced to not ignore it, I'd point out that skin is already malleable — it just normally takes months or years to stretch and contract as you desire.

7. Body hair

I was surprised to find some interesting facts about rapid hair growth.

“Eating a well-balanced diet with adequate protein intake is important for optimal hair growth,” she added. “Generally, we recommend 50 grams of protein or more per day.”

According to the study, caffeine may help promote new hair growth at the molecular, cellular, and organ levels in both men and women.

Specific vitamins, minerals, and fatty acids are especially important for your overall health and also play a key role in providing your body with the energy needed for hair growth.

And then there's my favorite...

“[Platelet-rich plasma] is a breakthrough treatment that uses injections of a concentration of a patient’s own platelets to restore and accelerate hair growth,” she said. “Platelets are protein derived from one’s own bloodstream and DNA that can act like a stem cell when placed back into the body,” (Source for all of the above)

Will any or all of that cause hair to grow 2cm in an hour? Nope. But I love the setup because werewolves would have a nutrient-rich and protein-rich diet and would need a souped-up version of adrenaline (oh, let's call it a naturally occurring caffeine). Add to this the idea of a much more dense capillary system at the hair follicles (leading the untanned werewolf to look like they were body-blushing all the time) to deliver all that protein, all those nutrients, and a steady supply of stem cells — and you have a fine, fluffy hair in no time.

As for getting rid of the hair when changing from wolf-to-human, you need only look into how animals shed. The feline brain triggers the shedding process based on the amount of natural sunlight. What's being triggered is the follicle pinching off the hair. Your werewolf does the same thing... it's just triggered (a bit of humor here) off the amount of moonlight.

8. The Tail

Ugh. The tail. I may hate this section as much as I hated fingers and toes. A tail is actually an extension of the spine. It's not like you can pull it in (e.g., #1) or fold it someplace (e.g., #2). Worse still, the hair isn't just 2 cm long. It's a lot longer. I may suddenly understand why so many modern movie and game werewolves are sans tail.

I can't think of any real-life animal that does anything other than let the tail be. If you search for "hiding the tail" you'll get a million search results relating to crochet, yarn, sewing, and thread.

I'd vote for going tailless. But if you insist, the only solution I can think of is to wrap the tail between the werewolve's legs and up the stomach when in human-form. You could consider that some lizards practice autotomy, the choice to break or amputate a tail as a defensive reaction, which then grows back. But justifying the growth of spinal column material in an hour is a hard row to hoe. But that's the best I can do.


If you were actually looking for a hard-science explanation of shape shifting into werewolf form — I don't believe that can be achieved. I can't even imagine a valid hard-science solution for modifying, growing, shrinking, or shifting around bones from the skull to the tail and legs. Frankly, the skeleton is your biggest problem. IMO, in a hard-science context, you can't modify the skeleton between states. Otherwise you're not hard-science anymore. But that's just my opinion. Hopefully someone will come up with something that will prove me wrong.

  • $\begingroup$ For fur, I was thinking of a thicker dermis where possible ranging from the usual 1.7mm to maybe 5mm. The coat of fur might be pushed up by some kind of muscle action. Just don’t know if half a cm of fur is good enough. $\endgroup$ Aug 30 '21 at 21:50
  • $\begingroup$ @JamesMcLellan I can't see fur being pushed by muscle through the dermis. It would need to be so rigid you could almost sand wood with it or so short that it's nowhere near the length you want. But, more to the point, you've asked for a hard-science solution, and no real-life example of that (or even feathers) exists that I could quickly find. The density of muscle structure needed is mind boggling. Humans are born with about 5 million hair follicles. $\endgroup$ Aug 31 '21 at 4:33
  • $\begingroup$ A small note the snakes that rotate their fangs are not rotating the teeth but the premaxilla they are embedded it, it won't work for that many teeth. it also means they will have large areas of the jaw with no teeth and pretty pathetic bite strength. also the finger and toe thing won't work because to make it you need to use the fingerbones that exist meaning they end up with only a single joint in the fingers when "retracted". Also the muscle needed to lock your ankle will have to be massive bigger than the thigh muscles, and you don't have enough bones to make an extra joint. $\endgroup$
    – John
    Aug 31 '21 at 22:00
  • $\begingroup$ @John You might be missing the point of this site. The goal is not to help the OP create a fictional world ruled over by the Scientific Truth of the real world, but to help the OP create their fictional world's rules. I believe James was looking for scientifically-based information that would help him rationalize a completely fictional and frankly "unbelievable" (from the perspective of Scientific Truth) creature. That being said, the fangs give him insight into how he can explain his fictional creation - nothing more. $\endgroup$ Sep 2 '21 at 3:10
  • $\begingroup$ @JoinJBHonCodidact and if an explanation does not actually work it is not necessarily better than a handwave. $\endgroup$
    – John
    Sep 2 '21 at 21:50

Warning: bones may bend when and where you don't want them to, they will be very hard to break though.

What you need is a creature that isn't technically human to start with, it would have to have been engineered not evolved because the changes are too drastic and the pay-off is non-existent in a natural selection/survival of the fittest environment. The alterations are quite marked and pretty extensive but if you can engineer an alt-human at all then it's rather simple because the treatment is not varied by bodily location and you're not asking to alter any of the hard stuff, visual or auditory range or acuity etc...

The whole creature simply doesn't have a solid skeleton, instead it has a lot of cartilage with bladders that it can inflate or contract when needed built into the structure, that means that it can change it's body plan to suit the situation. If the bladders are small enough and spread densely enough through the skeleton the changes can be made quite rapidly as quantity makes up for the fact that each bladder has a limited rate and volume of expansion/contraction. It will owe more of it's functional anatomy to fish genetics than mammalian, although mammalian skin is thinner and more flexible so that will be easier to adapt to purpose. The heavier hair can also be stored in the skin and pushed up through channels in the dermis as a function of the changes to the underlying structures. Such a creature need not be lupine when transformed that will depend on the neural architecture that it is paired with.


I give the advice that I should give to anyone thinking of writing about science fiction shapeshifters, including sceince fiction werewolves.

There are a number of implausible shapeshifters in STar Trek. In the animated episode "The Survivor" a Vendorian can not only shift into the forms of other people, he can also become a medical bed and a machine. Such devices should have computers much less advanced than a human brain and should be incapble of sensing events or having will. So once the Vendorian shapeshifted into such a shape, it hsould have been stuck in it forever, unable to think or feel and so unable to change out of it.

In Harry Potter a wizard turns into a rat. Rats are a lot more intelligent than many people might think, but they are incapable of knowing magic. Thus the wizard should have been stuck as a rat forever, unable even to wish to become human again.

Maybe the wizard only looked like a rat on the outside, but had a different inside so it could have a human-like brain inside the rat body. But a human brain is about as big as an entire rat body, and the rat would need to have a lot of other organs taking up space within its body in order to stay alive.

Therefore, in the case of someone who tranfors into an inanimate object - that isn't a superadvanced computer capable of thought and emotion - or into an anmimal too small to have a sufficiently large brain stuffed into the body, the person's brain must be outside the body.

And If the brain can sometimes be outside the body, why can't it always be outside the body?

Make the werewolf brains be outside of their bodies, connected by a very broadband communication system of some kind (possibly a very science fictional kind), so their brains see and hear and smell and feel everything their bodies do, and everything their brains wish to do the bodies do.

And give them a set of two or more bodies connected to the brain. So when they want to switch from one body to another, they "simply" teleport body number one away and teleport body number two into its place.

And if you want to show a transition from human body to werewolf body, or back again, they will need a number of intermediate bodies to be teleported in and out to give the illusion that a single body is gradually changing from man to wolf or from wolf to man.

It is possible that the werewolf thinks that the same body is transforming. The werewolf may not be scienficially literate enough to realize how impossible that would be. There could be some highly scientifically advanced person, or organization, or government, or species, or galactic federation, or whatever, that switches the bodies whenever the werewolf wants - or possibly whenever the werewolf most dreads changing - and they can switch which body the werewolf's brain receives sensations from as they switch which body is in a location.

And posibly the werewolf protagonist might be the first werewolf scientifically literate enough to deduce that might be the case.

Or possibly the scientifically literate protagonist deduces that must be the case, and even figures out how the body-brain communication system works, and jams it in the nick of time, causing the werewolf body to collapse just as it is attacking.

So your werevolves might think that they evolved, or were created by gods, or imagine some other origin story, but would actually be created by a highly advanced being or beings for some unknown purpose. Unles the writer reveals the purpose in the story.

And much the same goes for any other type of shape shifter that shifts between two shapes.

And it will be more complicated if a being seems to shift between 10, or 100, or 1,000 different shapes, or can learn to imitate a new species or person. Especially if they do not instantly flash from one shape to another, but seem to slowly transform, which will require many intermediate bodies.

If the werewolves don't have to be actual persons in the story, the human and wolf bodies, plus any intermediate stages, might be controlled by members of the advanced society from a distance.

And the most scienticially plausible werewolf would be one a character encounters in virtual reality while thinking the virtual reality is real life.

And the same goes for all kinds of shapeshifters.

If you must try to write a science fiction story with physical shape shifters, specifically werewolves, I say:

I recently watched the movie The Beast Must Die, (1974) that caused me to reread the story it is based, James Blish's "There Shall Be No Darkness", (1950), a werewolf story with werewolves similar to those in the movie The Wolf Man, (1941), but with science fictional instead of supernatural explanations. You might want to make your werewolves similar to Blish's. The TV Trope "Our Werewolves are Diferent" mentions many ways in which fictional werewolves differ, and you might find inspiration in the more scientifically plausible ones - or at least the less extremely, fantastically, incredibly scientifically ridiculus ones.


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