I am thinking about having multiple races in my story but I also want them to have relationship (Love/Mating). For the moment lets go with generic types, Humans, Elfs, Dwarfs and Orcs. How could these species remain as they are without them mixing to the point where they are just one species?

FYI - Each species can mate with each other and have their own offspring with little to no trouble

Just to let people know who read this, all of the answers in this post could have been accepted however the one that was accepted was just a better fit to the question. I recommend you read them all as each person gives a great answer

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    $\begingroup$ Just like in real life. Members of different human ethnic groups can mate with each other, but different ethnic groups still exist. Even with all social taboos removed they might continue to exist for a long time to come, as most people are more attracted to people who are similar to them. $\endgroup$ – vsz Jun 13 '16 at 21:26
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    $\begingroup$ Just to be pedantic: the definition of "species" is generally given as something like "a population capable of interbreeding and producing fertile offspring". So if they can all interbreed, by definition they're all one species. They might be different races. $\endgroup$ – Jay Jun 13 '16 at 21:38
  • $\begingroup$ You could just make their genitalia physically incompatible or make them smell so bad to each other that it's a total turn off. $\endgroup$ – Hack-R Jun 13 '16 at 22:29
  • $\begingroup$ Just to let people know who read this, all of the answers in this post could have been accepted however the one that was accepted was just a better fit to the question. I recommend you read them all as each person gives a great answer $\endgroup$ – Mr.Burns Jun 14 '16 at 10:04
  • $\begingroup$ glad you ask, that's for you Half-elves, and how they could be entertainingly different short offspring's are not fertile, like mixing horse and donkey = mule, mule + mule = nothing $\endgroup$ – MolbOrg Jun 14 '16 at 19:30

10 Answers 10


Some quick thoughts for you:

  • Social Taboo: yes, they could mate with each other, but that's not socially acceptable. If this taboo is strong enough, it'll result in species differentiation. (Um, I mean "maintain a pure breed..."). I think (American) society is much more accepting than it used to be for this sort of thing. Courting between races may be illegal in some societies. Maybe some of these societies even hunt or kill mix-race individuals!
  • The Mating Ritual: There are some birds whose courtship displays are the reasons they do not interbreed, though they theoretically could. Orcs males could, for instance, try to impress females by smelling like a rotten elk corpse while wrestling a bear. Even though it sounds like fun, it may only do the trick for the orc ladies, but not the other ladies. (To change the race we're picking on: an elf courtships display may involve some very long-winded poem, which the humans find initially very interesting, but then boring due to it's length.)
  • Ideals of Beauty: it could be that these races simply don't think the other ones are pretty. Their genetics/society paint the picture of an attractive female as one of their own race, so interbreeding doesn't happen simply because the other races are not attractive. Maybe elves just find all other races too... meaty. Dwarves may generally think the other races are too tall and anorexic. Or green. Obviously, these ideals can quickly change, so it's not a sure-fire way to prevent interbreeding.
  • Lifestyle Issues: Would you marry and have children with someone who is guaranteed to live only half your life? Such is the issue with long-lived elves. You could marry a dwarf/human/orc, but have fun raising your kids and taking care of an elderly spouse while in your prime. Oh, Sir Dwarf wants to marry a human? They need more oxygen than you, and have no appreciation for gems or masonry. They can't even see in the dark! If these races have unique, and very appreciable adaptations to certain tasks, marrying outside the race can severely impact the "quality-of-life" for the spouses. (Consider milk drinking in real-life humans for a much milder analog.)

  • From Martin Carney: Isolation/Geography: This one is straight from the causes of speciation checklist, but these groups can maintain their breed simply be having geographic barriers which prevent the flow of individuals. Something like the European Alps, the Atlantic ocean, or the Sahara Desert would do quite nicely for tool-using, adventurous, and occasionally promiscuous hominids. It's silly for someone to travel to a distant land for a mate when there is a great selection right here. Once the geographic barrier is overcome, this does not guarantee the purity of breeds. (Well, unless it's sympatric speciation...)

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    $\begingroup$ I'd like to add another; physical separation. As long as the main group of each species has their own lands, especially with no easily-crossed borders to the other species' lands, you will have low interbreeding. But that goes away if you get a melting pot country like the USA, or if one species invades and controls another's land. $\endgroup$ – Martin Carney Jun 13 '16 at 18:28
  • $\begingroup$ @MartinCarney "if one species invades another's land" But only to the extent that large numbers of the invaders actually move in, or large numbers of the losers are exiled to the invaders' country. If the invaders put a tiny ruling elite in place, there's still not much opportunity for interbreeding. Especially if the other factors -- cultural differences, whatever -- come into play. $\endgroup$ – Jay Jun 13 '16 at 21:33
  • $\begingroup$ @MartinCarney Good point! I considered adding that point as I was writing this, but figured it was not a strong method. Obviously, you and (as of now) 3 other people disagree, so I'm glad you wrote that comment. $\endgroup$ – PipperChip Jun 13 '16 at 22:01
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    $\begingroup$ Your #3 isn't going to work too well: humans have demonstrated a willingness to mate with anything that moves and many things that don't. The Darwin Awards, for example, have documented attempts to produce human/vacuum cleaner and human/park bench hybrids. $\endgroup$ – Mark Jun 13 '16 at 22:24
  • $\begingroup$ @Mark I think the last sentence in that point addresses your point rather well. Besides, this isn't about the mating habits of some deviant individuals, but the mating habits of the race as a whole. If 98% of a breed says "no thank you" to mating outside the breed, it's going to maintain that breed just fine. $\endgroup$ – PipperChip Jun 13 '16 at 23:35

I would think along the lines of Ligers, Mules and other mixed species mating. They produce offspring but their offspring are infertile.

The number of "ligers" in general population would be unlikely to reach large numbers due to inter-species cultural differences and possibly more importantly, inter-species attraction. I can't see myself going for a lady Orc for example..

In these conditions the "ligers" would be quite rare, and as a result almost undoubtedly suffer from social stigmatisation and possible persecution (directly and for the parents).

  • $\begingroup$ I like your train of thought but what prevents them from all becoming "Ligers"? If you could expand towards that in your answer it would become alot better $\endgroup$ – Mr.Burns Jun 13 '16 at 15:38
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    $\begingroup$ Seems I didnt read what you had actually put as your answer, the infertile offspring is a very good idea, I will see what other people say but this is a good one $\endgroup$ – Mr.Burns Jun 13 '16 at 15:44
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    $\begingroup$ I like it, but for fairness sake I will keep the question open a bit longer and see what else pops up $\endgroup$ – Mr.Burns Jun 13 '16 at 15:56
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    $\begingroup$ Mules, a real life breed between horses and donkeys, are infertile. No male mule has been recorded to be fertile, but female mules have been known in very rare cases to be able to carry offspring of pure-bred horses. As a sort of addition to the answer you're posting, I'd suggest a look at why mules cannot reproduce if the science is important to you. In this way, races can remain "pure", except for half breeds. Half breeds exist, but cannot reproduce and so their lineage is a single dot. Over time, half breeds could look different from half breeds eons before, but they are not related at all. $\endgroup$ – Premier Bromanov Jun 13 '16 at 18:58
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    $\begingroup$ @Mr.Burns: This isn't actually a "idea" this is the way it goes in real life. The offsprings of tigers and lions actually EXIST and they ARE ininfertile. $\endgroup$ – Zaibis Jun 14 '16 at 8:18

Evolution should already ensure that species will not want to mate with other species often. This is due to a principle of Koinophilia. On the most basic level The odds of a hybrid species being healthier then non-hybrid is unlikely and thus we all have an instinctual aversion to mating with someone from another species because it's likely our children would be less fit then if we had a child with someone of the same species.

Actually avoiding mating with another species is a specific example of a more general principle. We will instinctual avoid mating with anyone that looks abnormal compared to the average for our species, it just happens another species usually looks pretty abnormal compared to our own. People that look substantially different usually had mutations and, despite mutations being mandatory for evolution, most mutations were detrimental. Thus we institutionally learned to avoid anyone that looks significantly different from the norm because the odds are they have a mutation that would harm any child we had with them. This effect is a major part of how distinct species came about a all!

The lack of more numerous hybrid sub-species in present day, or in the fossil records, is often refereed to as Darwin's Dilemma, he couldn't figure out why individual species existed at all, he would have expected a whole gambit of intermediate stages between species to exist due to multiple levels of hybridization. He listed this confusion, that distinct species came about when it was possible for species to interbreed, as a potential argument against his evolutionary theory in fact, it wasn't until a little later the Koinophillia was recognized as the cause for distinct species. Once two groups of animals looked distinct enough they would avoid mating with each other, allowing them to evolve and diverge further over time into clearly distinct and separate species.

The point being that preventing hybrids from diluting your prue-bred genepool isn't much of a problem, evolution would have already instilled instincts that prevent this, if it hadn't you wouldn't have distinct species. After all when's the last time you heard anyone say they thought that chimp was HOT? If tomorrow all great apes were able to produce hybrids with humans, and the hybrids were healthy & sapient, would you be attracted to a gorilla? I think the thought of producing a child with an ape would feel wrong, even revolting, to many people, that is koinophillia, and it's how your species would feel about inter species relationships as well.

The harder part to justify is actual the presence of a non-trivial number of hybrids in your world despite the evolutionary instincts to avoid this. Still, this may not be a big problem, humans focus on thinking/learning has resulted in less focus on instincts and thus it's a bit more excusable that humanoids violate the usual koinophillia instinct then many other species are prone to. Plus, it may be that hybrids set off the "koinophillia' radar even more then each distinct species, making the hybrid struggle to find mates even if produced. Basically a degree of hybridization which is low enough will still be sustainable, particularly if hybrid species rarely find people interested in having children with them.

I should stress, this koinophillia does not require overt racism or hatred between the species. koinophilia is purely instinctual affect on mate choice, not view on species as a whole, and even the most open minded of humans still show signs of instinctual Koinophillia! It doesn't require one to believe one species is somehow less important then them, or to believe that a species or hybrid species is wrong. However, one may simply happen to find one women attractive, on an instinctual level, and another not attractive; just as someone may be attracted to blond hair over red in women (in fact, koinophilia almost certainly plays a role in hair color preference....)

From a story perspective imagine someone saying "she is nice and all, but I just can't deal with scales" or "The gnomes are so small, Id feel like I'm dating a child" or "I just prefer red heads, not tentical hair". basically the overt physical differences will feel 'off' to a different species and unattractive to most people, without their recognizing the cause is koinophilia. They may still respect and get along well with another species, just as someone may love their dog or a zoo warden may grow to respect apes in their care, they just won't find them attractive on a sexual or romantic level as often.

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    $\begingroup$ its a shame how you have so few up votes, your anwer is very high quality $\endgroup$ – Mr.Burns Jun 13 '16 at 21:16
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    $\begingroup$ @Mr.Burns thank you, though the low votes is likely because I posted it just a few moments before you read it, no time for up votes. Though, I posted it late enough that I likely won't get many because people never read past the first 3-4 answers to see other ones worth voting on lol. Still, thank you for your comment. It's amazing how often known evolutionary principles answer these sort of questions without any creativity required :) $\endgroup$ – dsollen Jun 13 '16 at 21:19
  • $\begingroup$ I agree with this theory, I am a Caucasian, never attracted to anything but, and found through dna and ancestry that I am 100 % European !. Apparently my ancestors felt the same. I am amazed that this happens. Another factor is the O negative blood factor-of which I am a member. Berfore 1935, there was no blood typing. I believe such families tended to interbreed somewhat more than the usual populations. If you didn't marry family, you married into families who were time tested. Its my opinion that King Henry the 8th of England made just such a mistake, his queens were probably O Neg- not him $\endgroup$ – Fey Ray Jun 14 '16 at 5:34
  • $\begingroup$ @FeyRay actually in humans the different races demonstrate the opposite phenomenon, inbreeding depression. This means that a multi-racial child is likely to be healthier then a child who's parents have the same race. This is because each race is prone to carrying recesive genes for genetic defects, but they don't tend to carry the same defective genes. Thus a multi racial child may potentially get a deleterious (bad) gene from each parent, but he probably won't get the same deleterious gene from both parents so he's less likely to be born with special needs then a single racial child. $\endgroup$ – dsollen Jan 10 '18 at 18:20

how about dominant genes?

with dominant genes one race would be so dominant that the influence of the other race is practically negligible.

for your example i would suggest the following pairing results:

  • an human-elf couple has human children
  • a human-orc couple has orc children
  • a human-dwarf couple has human children
  • a dwarf-elf couple has dwarf children
  • a dwarf-orc couple has orc children
  • an elf-orc couple has orc children

orcs are very ugly, so whoever they mate with, the outcome is always an orc. elves can't have elf children from a mixed couple. that is not a problem because elves live very long, so they don't need to have many children in order to preserve their race.

compared to other races humans have a short lifespan so they need more chances at getting human children to preserve their race.

this can be changed around to suit the setting. aren't orcs and elves closely related? an orc-elf pairing could also produce elves.

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    $\begingroup$ Oof... that last suggestion almost punishes the prospective interracial parents for trying to conceive. Nice twist. $\endgroup$ – FuriousFolder Jun 13 '16 at 19:17
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    $\begingroup$ You should post that last paragraph as a separate answer, since it is, and I'd vote for that. $\endgroup$ – Mirror318 Jun 13 '16 at 23:33
  • $\begingroup$ @mirror318: i thought about it, but wasn't sure if it was enough for that. i did it now. $\endgroup$ – eMBee Jun 14 '16 at 4:34
  • $\begingroup$ @FuriousFolder: since i split up the answer you may want to move (or copy) your comment to the other answer where it applies. $\endgroup$ – eMBee Jun 14 '16 at 14:56

You have two simple options:

1) Total genetic incompatibility. They just can't reproduce. They're physically compatible, the bit that sticks out on one, fits in the hole on the other, but that's as far as it goes. You're breeding horses with cows, nothing is going to happen.

2) Partial genetic incompatibility. The mule, hinny, zedonk or any zebroid, tigon, liger etc. They can have one generation of crossbreed, but that's the end of the line, the cross breed children are almost always infertile (there are occasional exceptions).

Then you get into the more complex options:

1) They're genetically compatible but not physically compatible. Think of the great dane and the chihuahua. Technically they're fully genetically compatible, but can you imagine the one mating with the other?

2) Social taboo. The relationship is acceptable but having children in it isn't.

3) It's already happened. Humans are what you get if you cross a dwarf with an elf.

4) Weirder incompatibility. Elves actually reproduce like seahorses. It's the male who carries the baby. The "penis" is actually the female reproductive organ and she plants the egg in the male. So the physical compatibility cross species is actually male-male female-female not male-female.

  • $\begingroup$ Chihuahua x [very large dog] has been done, actually. $\endgroup$ – Mason Wheeler Jun 13 '16 at 19:04
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    $\begingroup$ @MasonWheeler, I'm sure it's been done, but I'll bet it wasn't unaided. $\endgroup$ – Separatrix Jun 13 '16 at 19:06
  • $\begingroup$ As nice as an answer this is I cant up vote it. Offspring arent an issue so this answer wouldnt fit ... but a nice answer still $\endgroup$ – Mr.Burns Jun 13 '16 at 21:15
  • $\begingroup$ The third answer made me laugh, but it kinda misses the point: The question was about pure-breeding, and 3. would imply that any crossbreed is simply its own species $\endgroup$ – MechMK1 Jun 14 '16 at 11:20

the race of the child is always that of the mother. the idea is that the race-specific genes are simply not compatible and are ignored when the genes are combined.

also the womb is only capable of growing a child of its own race so any other outcome would result in a miscarriage.

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    $\begingroup$ This offers an interesting thought of the child being an exact DNA replica of the mother, since the father's cross-species DNA is incompatible. $\endgroup$ – Mirror318 Jun 14 '16 at 5:02
  • $\begingroup$ humans share 98% of their genes with chimpanzees, so surely the shared genes among the selected races will be similar. and even if it's less there are plenty of genes to be shared. what's incompatible is only that few percent that define the persons race. the child might still inherit the fathers hair-color, his height, (tall humans from elves, short humans from dwarves, etc) and a number of other traits, so there is plenty of room for very mixed results. $\endgroup$ – eMBee Jun 14 '16 at 14:52
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    $\begingroup$ that said, not applying the fathers genes at all is an interesting variation of the theme. however it would raise questions why the races have not developed the ability to procreate without any father at all $\endgroup$ – eMBee Jun 14 '16 at 14:53
  • $\begingroup$ Your second part of the idea is what really makes it work. If only children of (primarily) the mother's race can survive in the womb, then mixed race couples will have more miscarriages than viable children, and all the children will be (mostly) the mother's race. It doesn't ensure true genetic purity, but does ensure outward appearances remain "pure". $\endgroup$ – Martin Carney Jun 14 '16 at 17:38
  • $\begingroup$ without the first part there would be a lot of miscarriages, otherwise it would only come to effect should a race-specific gene of the father dominate after all... $\endgroup$ – eMBee Jun 15 '16 at 6:58

Not a reproductive barrier, but ...

Half-breeds are swiftly killed by fanatics.

Have a powerful organization which hates half breeds. As in, tracks-them-down-and-murder-them-in-cold-blood "hates". They probably have some sort of ideological/religious idea about "the purity of the races", so they're willing to sink a lot of effort into finding and killing half breeds.

The authorities are either in league with the organization, or tacitly turn a blind eye to their activities. (Perhaps not all authorities, but enough such that they have a safe refuge from which to operate.) This means they can work with near impunity across most of the world.

Mixed-species individuals certainly can survive - possibly for quite a long time - but it requires an extensive level of diligence, willingness to move often (and/or live out in the middle of nowhere), and a fair amount of luck. This is especially true if half-orcs (etc.) have a distinctive appearance; the moment they walk into a town of any size, someone from the local branch of the organization will notice them, trail them, and attempt to cut their throat or poison their drink.

Depending on zealotry, this can go even further. You may be a prosperous and well regarded citizen, but if it eventually comes out that your great-great-grandfather was an elf, chances are that pretty soon your family home is going to burn down while you and your children are locked inside. This, of course, is ripe for abuse due to false rumors, but "better that an innocent person should die pure, than suffer a mutt to live". (... as I said, fanatics.)


To keep it realistic, you don't really need to get all elaborate . . . unless you want too.

Realistically, the reason human races remained separated was primarily geography. There may have been a lot of foreigners in different lands, but the vast bulk of the people of any given race were surrounded exclusively by people of the same given race . . . unless you're talking about individual kingdoms in a given area as a race, in which case, they all usually mixed together, which is why the variations between peoples of any given continent and especially country isn't very much, and usually takes several years, even decades to finally distinguish the subtle differences between them.

But there is a difference between each country's people, often between areas of the same country. So even though there was a lot of inter-breeding between them, it still wasn't significant enough to eliminate or avoid development of subtle differences. And again, that's primarily because of geography.

Now, there are some people who avoid mixing on purpose, but they don't make a significant difference in the overall race they belong too. And usually, it's not racially-specific, but rather class-specific or religion-specific, meaning mixing can occur even with them, but typically only if it is acceptable by society for a person of their place and position to do so. And some societies didn't care as much as others about racial differences as they did about religious or class differences

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    $\begingroup$ Tudor England provides an example. Prejudice against people with dark skin was a later invention. Back then sailors occasionally brought back wives from Africa who were fully accepted in society. But there were few sailors and fewer such wives. A one-eighth African was indistinguishable from the population at large. Modern-day racists are likely to get a shock if they have their DNA fully analysed! $\endgroup$ – nigel222 Jun 15 '16 at 10:50

The planet could get its own revenge for interbreeding. Every time a child is produced that is the product of two breeds, one close relative to each parent will die on or shortly after the child's birth. And abortion always kills the mother, also, as the fetus and the mother are interdependent on each other for life from conception until the child's first breath. The first breath could be called something cool like the o'er-weaning.


I'm thinking something along the lines of the children having health problems or 'defects'. This could discourage a lot of people from having hybrid (for lack of a better term) kids.

If there are size differences between the species', it could end up killing the parent during birth. Say, and I know these aren't the species' you mentioned, but if a dwarf and a giant were to have a child together it would most likely kill the carrier and/or the child. even without any social taboo, this would deter a lot of couples from reproducing.

And as others mentioned, social taboos or even laws preventing it could be a huge factor too. Anything from gossiping to refusing to legally recognize a hybrid as part of the family. Perhaps the parents could be disowned from their family, or they aren't allowed to get a birth certificate or legal id for the child, or the doctors and nurses might kill the child shortly after birth. The last one would probably result in a large number of home births, which brings some different struggles. Finding an accepting midwife or doula, for one thing.

There are probably some sympathizers out there though, and mixed-species couples might be able to get a surrogate or sperm donation from one of these sympathizers. Legally, the child wouldn't belong to the couple (depending on the amount of discrimination in the law) and there could still be some social rejection, but it could avoid some legal problems down the road.

I hope this helped, please tell me if you need me to reword anything.


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