So this is part of a passion project of mine for an ASB alternate history scenario. Where demons from another universe invade and conquer North America. The demons have been recorded in artwork in the past but most predominately in medieval European artwork. This is due to early expeditions to Earth's past and their sightings being recorded through art. Also, the demons are technologically advanced and it's mistaken for magic. The demon civilization has colonized many planets that are similar to their homeworld in their old universe.

Though demons are one species, they have drastically differing physical features. Here are examples of what I'm talking about.

enter image description here

My Demons don't have extra faces btw. enter image description here Here is the list of different physical features

  1. Scales/skin or fur
  2. Humanoid or animal heads
  3. Beaks or snouts
  4. Wings or wingless
  5. Number of horns
  6. skin/fur colors

Now there are similarities and these include:

  1. Being a chimera of avian, mammalian, and reptilian
  2. All are humanoid
  3. mostly the same size
  4. They can still reproduce offspring, despite the differing app

Though why are demons so drastically different appearance-wise? Could there be some logical explanation behind this? The demons don't seem to mind yet it boggles the mind of humans.

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    $\begingroup$ Why do mammals, birds and reptiles from this part of the universe look different from each other? $\endgroup$
    – sphennings
    Oct 15, 2021 at 10:45
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    $\begingroup$ This seems like a question that will generate a lot of creative but equally valid answers as people brainstorm up compelling explanations for you. Please remember that if a question has many different valid answers then it's probably too broad for this site. $\endgroup$
    – sphennings
    Oct 15, 2021 at 10:49
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    $\begingroup$ It's always been great to know that, for reasons unknown to all, neither demons nor aliens have any interest in invading or taking over anywhere but North America. Thanks guys - much appreciated here in the EU. :-) Or more seriously, why would your demons invade North America when they presumably targetted Europe in the past ? Wouldn't they start where they left off ? $\endgroup$ Oct 15, 2021 at 11:08
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    $\begingroup$ @StephenG When planning an invasion, you pick priorities based on threat level, not population. If you want a ground war to succeed you need to establish air superiority first. Since the United States owns more than half of the world's military aircraft and aircraft carriers, it is logical that you can't control the world's skies without first taking control of the United States. While a modern aircraft may seem like nothing more than a horse archer to aliens, 13,000 horse archers can not just be ignored. $\endgroup$
    – Nosajimiki
    Oct 15, 2021 at 17:10
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    $\begingroup$ @StephenG, "neither demons nor aliens have any interest in invading or taking over anywhere but North America"... really? I was under the impression that only the UK ever gets invaded. Cardiff, in particular. $\endgroup$
    – Matthew
    Oct 20, 2021 at 16:32

10 Answers 10


They Exhibit an Extreme form of Polymorphism

Polymorphism is the tendency in a single species to come in multiple, distinct forms where a single lineage may possibly produce any one of those forms. We humans are considered dimorphic because our male and female forms are distinctly different, but some species have more, and more different forms such as ants.

enter image description here

Answering the Question with Evolution

Ants evolved many different forms so that they could fulfill different roles to the benefit of the colony. However, daemons have much more complex "hives" than ants do, so their roles and subsequent forms may be far more diverse.

While an ant hive uses different forms to fulfill different roles in a single spot, demon hives may be bigger... much much bigger... to demons an entire planet may represent a single hive spanning multiple biomes to which they need to specialize. So the queen produces hairy guys with big lungs to go exploit the resources in the snowy mountains, and makes scaly guys to send off to the desert, and winged guys to wrangle the local birds for live stock, so on and so forth.

The reason demon forms look more or less like mammals/reptiles/birds may be because of convergence. These are forms that are very successful in an Earth like biome; so, these are the forms the demons would produce when colonizing an Earth like world. Since the demons are an inter-planetary species, they may even have forms you do not see in your setting that a queen would produce if she instead landed on Mars, Titan, or Venus.

Answering the Question with Clarke-Tech

An alternative approach, since demons are technologically advanced, is that this Polymorphism may be artificial. It is very possible that demons modify their own genetics to colonize worlds that would otherwise be too inhospitable to them. When they arrive at an alien world, they may not be able to breath the air, or endure the temperatures, of withstand the gravity, etc. So each alien has to find a local animal (or animals) that they like and reshape themselves using that organism's biology. Because the aliens are humanoid in nature, they all maintain a humanoid appearance, but their secondary features all come from whatever Earth forms they supplement themselves with.

So, while each alien is born looking the same, their different appearances are the result of advanced gene therapy necessary for living in our world.


Because we lack a subtle understanding of their features.

If I look around myself in the office today I see many different homo sapiens: they are all homo sapiens, but just to cite two cases, Jim is tall, blonde, has green eyes and his body is covered in blue woolen fabric, while Janet is shorter, has dark curly hair, brown eyes and her body is covered in cotton fabric and synthetic fabric, plus some leather around her waist.

Oh, I have just been told that homo sapiens uses something called "clothes" to hide their bodies because of a concept called "nudity", and also when naked their physical appearance changes a lot in terms of skin color, fat distribution, primary and secondary sexual characters, height and so on.

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    $\begingroup$ +1 "To sheep other sheep no doubt appear different. Or to shepherds." --Tolkien $\endgroup$
    – user535733
    Oct 15, 2021 at 13:07
  • $\begingroup$ You make a good point. Though I guess my demons have more extreme features. $\endgroup$
    – Borbman
    Oct 16, 2021 at 0:36

Demon Bodies are Like Spacesuits

The demons are, ostensibly, from hell. Though with the "no magic but they have tech" caveat they could just as easily be aliens. But since you're calling them demons we'll assume that at a base level they're from another dimension. In that dimension, all demons look pretty similar. Their "souls" as humans would call them, ARE their bodies in their home dimension, and they're as uniform as human beings are on earth.

When they cross over into our reality they need the "protection" of physical bodies. These bodies need certain baseline constraints (two arms, two legs, must take the shape of the "higher" animals such as birds/reptiles/mammals) in the same way that a human's spacesuit has certain universal constraints. But after that, the demon's body can be configured to whatever best suits the demons personal preference/operational needs. They don't change these bodies in our universe for the same reason an astronaut doesn't try to swap space suits/parts of suits mid-spacewalk. So while one demon has 8 horns and a goat's head and another had wings and 7 fingers on each hand, that's no different than comparing a NASA astronaut's suit with full maneuvering unit to a Russian Sokal suit. If you ever looked at the actual thing wearing it, they're pretty similar.

I won't get into the details of demonic mating rituals on a family stack, but suffice to say that there is.... functionality to link bodies, and through the wonders of inter-dimensional travel a baby demon is insulated by the mother's body until it comes out with its own "suit" to live its own life.

  • $\begingroup$ Not a bad answer per say, but the problem I see with this analogy is that spacesuits are very much design follows function, not the other way around; so, all space suits end up looking more or less the same with only minor variations. I think the aliens would quickly discover what features are wasteful and which ones are advantageous and min-max designs accordioning. $\endgroup$
    – Nosajimiki
    Oct 18, 2021 at 14:57
  • $\begingroup$ Not what I was looking for but thanks for trying! $\endgroup$
    – Borbman
    Feb 7, 2022 at 9:30

Magic doesn't exist? No problem!

This can be explained genetically, funnily enough. First of all, the existence of succubi/incubi in mythos. When sperm and egg meet, the result is the two chromosomes required to get a fully functioning human being, right?

You'd think this can only happen with related species, but if this is any indication, you'd be wrong. Add in biological gene modification (see this question's accepted answer for an explanation) and the existence of gene transfer between species through bacterial and viral vectors, and you have a pretty good explanation of sans-magic demons.

In our universe, cells evolved to cooperate in such a way as to form complete organisms, relying on one special cell type to reproduce. In an alternate universe, however, a cell mass developed the means to 'mate by infiltration,' or to hijack the reproductive cell, adding in the infiltrating organism's DNA to create an alien hybrid as offspring.

For whatever reason, these organisms have somehow traveled to and from our world, back and forth, through some sort of warp in dimensional walls, using native organisms as reproductive vectors, and the result was beings like the Chimera, or dragons, or mermaids-the result of these organisms sharing genes amongst their own kind.

These organisms eventually evolved intelligence, and the ability to capture and add their DNA to ingested cells, and by this method they created incubi and succubi to add humanity to their collective might.

However, much to their chagrin, the ways to Earth have been closed...until now...when a portal opened in Salem, Massachusetts, allowing the demon army to invade the world. Seriously, this stuff almost writes itself! If you don't use this idea, I know I will!


Scenario, technology is the key:

They exist in a society (Demon world) which has for most of their history been prosperous. They started much as humans had, gradually growing, going to war discovering medicine until.... their technology gave them an edge so they could eliminate poverty, starvation, and manual labour (and most other work). Socially, the dominant trends in what preoccupies people's minds and time are fashion-based.

The technology eventually developed to the point of allowing them to chose a form suiting their desires, in some locales, the feathered, winged type - more lightweight but fun to own, in others the lizard type, because it's "street" and intimidating, in others a furry feline look for the sleek graceful movers and the proud hunters, and others opt for a more human-like appearance but with other enhancements - horns or a skull bone-ridge. Of course, these can be changed at will, or kept if it's found to suite the wearer's personality. Occasionally, a "tourist" or adolescent seeking thrills would visit the human world and kick-off a local frenzy among a few villagers - rarely a criminal from their world would take it further.

{Some great disaster befalls their civilisation, it collapses. Chaos, anarchy, lack of food, bloody hell. Of course, they're too concerned about survival to amend their appearance to anything making them able to blend-in. They look to Earth for a second chance.} Your story begins.


Mutations and selected adaptations.

Maybe once upon a time this race from another universe had a more consistent appearance, but a combination of radiation from interdimensional travel, which led to the technology that allowed them to alter and repair their genetics, which then led to them being able to borrow traits from other creatures around them.

Over the generations as these traits are blended as new individuals are born, things have gotten pretty chaotic. The wealthy elite alter things as they want, removing unwanted traits and adding desired ones, but it is an expensive and lengthy process, and so the less wealthy rely on luck, careful choosing of mates, and very rarely genetic alterations. The poorest only have luck to trust in, and it fails them more often than not.


most of these features exist in their DNA

Just like species here, they have a lot of inactive DNA sequences for a lot of different features that can exist, but are just non-coding. Those sequences can be activated with small mutations.

EDIT: the reason they can have features that none of their ancestors had (features from other animal reigns, let’s say, insectoid features), is because of Horizontal gene transfer

They mutate really fast

Most species here don’t mutate a lot. It wouldn’t be viable (since the probability of producing a non-viable specimen are way to high, it wouldn’t be cost-effective)

The demon world is very different: Energy is no problem, there is hellfire everywhere. Plus high levels of radioactivity favorise fast mutations. Problem is species there are very violent, so it is a very harsh environment. Demons are the species that have evolved to survive by being unpredictable in their features (since predators will prefer to hunt what they know). An average demon will have tens of viable babies in a litter, hundreds of non-viable ones, all differents. The ones that actually look too different from human-like features are rejected socially though, so they cannot survive. In the end only one or two in a litter will reach adult age.


They have polymorphic DNA, and can take the DNA of other mammals to enhance their form.

Scales/skin or fur- pangolians have fur, and fur is common.

Humanoid or animal heads- they can adopt the genetics of animal heads.

Beaks or snouts- Snouts are common, and platypus and echidna have beaks.

Wings or wingless- bats have suitably demonic wings as do several other species.

Number of horns- Many mammals have horns.

Skin/fur - There are many mammals with different types of fur.

They do hybridizations of reptile and avian species with a high risk of drastic mutations.

Mammals are closely related to them, and easy for them to take DNA from. Reptile and avian species are much more distantly related. In the past some bad hybridizations resulted in terrible things like second faces on crotches.

Some stable variations were found though, where the mutational difference was less. As such, there's a small but lesser number of demons with such features.

They tend to take genes from hox genes, and similar highly conserved gene clusters.

These have been used in human experiments to make mutatant flies. Their ability to steal DNA lets them do this naturally, and have some sense of the likely outcome, enough for them to most of the time hybridize themselves to other mammals.

enter image description here


Scales/Skin or Fur

Variations in where hair grows already exists in humans to some degree, with alopecia universalis and hypertrichosis. These traits, or at least something like them, could easily explain all the variance in hair cover that you'd want

Similarly, the great variety of scaleless reptiles shows that variance on this scale is just as plausible

Humanoid or Animal Heads

This level of variation is more-or-less already seen in the heads of dogs. The only thing further is the nose, which would need to vary between human-like, mammalian, and reptilian. Non-humanoid noses could simply be noses with very small cartilages as in animals, and non-mammalian noses could be explained as a mutation that deletes the rhinarium

Beaks or Snouts

This feature seems the hardest to explain: All animals with beaks or snouts are very well adapted for their jaw type, and it doesn't seem plausible that a single species could use both

However, you could 'cheat' this point; all demons could have toothy snouts, with some horny lips that approximate beak tomia. Then, the difference between beaked and snouted demons could simply be a difference in skull shape, with narrow pointed faces appearing as beaks, and wide robust faces appearing as snouts

Wings or Wingless

There are many genetic variations that can cause issues to specific limbs. A common variation might cause issues in the wings that require them to be amputated at birth, or perhaps even to not form at all. This will give you a variable presence of wings

Number of Horns

Many horned species already have a variable number of horns, based on sex. There is no reason not to use this system in demons

Skin/Fur Colors

This variation is already seen in humans. And if that isn't variable enough for your purposes, then dogs show an even greater variety


Not mine idea, but still not quite the same as mentioned above.

Individual evolution

The demons, in a strict sense, do not exist as a species. They are a conglomerate of species. Each individual demon has evolved / mutated to fit and counter its individual environment, in its own way. Similarities are due to convergence, dolphins and sharks are also similar enough, but have very different origins.

Basically, if you dig deep enough, each and every demon is unique.

Smile and say "hi" to Lamarck!


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