Okay, it's a staple amongst certain fantasy settings where you have different races of creatures and beings co-habiting, which leads to certain off-shoots of different races (the half-elf and half-orc perhaps being the most commonly known).

But how feasible is such a thing? Presumably these different races are all significantly genetically different from each other that a viable mixed race would be biologically impossible? Sure, different races with sexual organs that fit each other would be able to enjoy physical relations (if they were into that kind of thing) but would they be able to biologically produce offspring?

Especially when different races seem to have natural, inherent biological traits: elves are typically very long lived and can see in the dark etc.

And then there is the notion of "half-human/half-demon". Not only are the races separated by their genes but also their planes of existence!

In terms of science, would this be possible? (yes, I know that asking for a scientific explanation for a trope in a fantasy setting may be somewhat backwards but I am curious to know).

Specifically, this is for a fantasy type of world that I am building. There are three main races: human, alfar (something akin to elves) and floring (a kind of Halfling), with the possible inclusion of a race of infernals that are a line descended from a mixing of human and "demon".

I hope that makes sense.

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    $\begingroup$ Possible duplicate: Explaining "Half-Breeds" in a world... $\endgroup$
    – Frostfyre
    Commented Nov 7, 2017 at 17:05
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    $\begingroup$ Different breeds of dogs are all able to reproduce. If the races in your world are still related enough then it's not a problem. Demons mating with humans only make sense if demons and humans share a common ancestor which can make sense if a group of protohumans moved to the other realm in prehistory and became the demons but are still related enough to mate with humans. $\endgroup$ Commented Nov 7, 2017 at 17:20
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    $\begingroup$ Consider that genetics is something used to explain stuff only very recently. Most fantasy stuff is set in some pseudo iron age / early middle age hybrid setting. Arguing with genetics should not be the way to go. To establish a believable world, use logic that suits it. Let them have kids and don't worry about biology. $\endgroup$
    – Raditz_35
    Commented Nov 7, 2017 at 17:38
  • $\begingroup$ @A. C. A. C: Even going beyond dog breeds, dogs can reproduce with both coyotes and wolves, and coyotes and wolves can interbreed: en.wikipedia.org/wiki/Coywolf Then of course there are mules (horse/donkey hybrids), ligers and tigons, and many other interspecies hybrids. $\endgroup$
    – jamesqf
    Commented Nov 7, 2017 at 17:48
  • $\begingroup$ VTC:Opinion-Based. Every answer claiming it's not impossible is lying. The fantasy creatures are 100% defined by you. Do you want them to be compatible? Then it's so. You don't? Then it's not. "Feasibility" is meaningless unless you provide all the genetic/physiological data concerning your creatures - but that would answer the question. In short, asking us about realistic compatibility for your unrealistic fictional creatures doesn't make sense and violates the help center prohibitions. What you need to do is make a choice (as every other author before you has done). $\endgroup$
    – JBH
    Commented Jan 17 at 18:04

2 Answers 2


It's not impossible, but its not outright possible either


  • genetic divergence from a common ancestor - Its possible they can reproduce if the different 'breeds' are close enough in lineage such that they have the same amount of chromosomes and complimentary genomes. This does not guarantee success it just increases the odds similar to a horse and a donkey. Dogs are a great example of an organism with large differing physical appearances yet still capable of interbreeding.

  • Mechanics - obviously the mechanics are a factor like a giant cave troll going down on a dwarf might not be physiologically possible. Though sometimes where there's a will there is a way.

So is it possible in the same way we have mules yes. Could they end up being sterile yes and no this is dependent on genetic divergence.

There is another more far fetched possibility of zoonotic reproduction I theorized awhile back.

Basically, one organism is capable of injecting its DNA through a retro-viral like process. Which could both cause pregnancy, pass on traits, and alter the females physiology enough to support the pregnancy. Is this likely, heck no, is it in the realm of possibility; loosely.

  • $\begingroup$ Excellent. Your last idea could also go someway towards explaining how a race from a different plane/dimension could biologically reproduce with a human, resulting in the half-demon idea... $\endgroup$
    – ZanderXL
    Commented Nov 7, 2017 at 16:57
  • $\begingroup$ Dogs breeds are very different one from the next but remain genetically compatible. The state dog of Alabama is actually the pit bull / Chihuahua mix. Re demons: if you are shape shifters you can adopt a shape which is genetically compatible with the real creatures you are mimicking. The god Loki famously adopted the shape of a mare in heat to distract the workhorse of a giant; this succeeded to the point where Loki got pregnant and had a baby horse. $\endgroup$
    – Willk
    Commented Nov 7, 2017 at 17:02
  • $\begingroup$ @The dogs remark, mechanics still factor into that, ive never heard of great dane and Chihuahua being able to work, well without human intervention and I think some breeds don't work genetically. $\endgroup$
    – anon
    Commented Nov 7, 2017 at 17:08
  • $\begingroup$ @anon but this supposes sapient (and I dare say freaky) partners. Baulking at a turkey baster when there is already a monster involved seems non-obvious. I haven't heard of a strictly non-viable dog pairing, though I understand there are breeds that need assistance at various stages. $\endgroup$
    – user25818
    Commented Nov 7, 2017 at 17:43
  • $\begingroup$ @notstoreboughtdirt I'd say the apparent difference between a great dane and a hairless Chihuahua is comparable to the apparent difference between a cave troll and a dwarf. And sometimes will manages to overcome mechanics: youtube.com/watch?v=ABM8RTVYaVw $\endgroup$
    – anon
    Commented Nov 7, 2017 at 18:06

Take a look at various dog breeds, or the definition of race in taxonomy. Surely a Poodle and a St. Bernhard are at least as different as an Elf and a Dwarf. And in between the Poodle and the St. Bernhard is a great bunch of generic mutts -- or, to extend the analogy, the ordinary humans.

Breed Poodles with Poodles and you get a Poodle, or something much like it. Breed Elves with Elves and you get an Elf. Cross-breed with other races of the same species, and you get something that will have recognizable traits of each parent, plus random chance.


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