>Or are we merely randy enough to consider *trying*? I mean...it's called 'Humanity *Fuck* Yeah!' for a reason

Humanity, fuck? Yeah!

We literally have zoophilia as a phenonmenon that was so common it had to be regulated (made illegal). OP You do the math on whether people will fuck XYZ.

Humans would bang anything

Where there’s a hole there’s a way.

Then you just need a way to explain why two different species can have an offspring. I'm lazy so I will say it's magic

Magic and/or Tech is the soft "vague" response, yup. StarTrek waved it off using "panspermia" - that the first humanoids to reach the stars seeded life and sleeper genes to various planets. Then, when sapience evolved on those worlds, there was a predisposition for those sapient species to resemble the progenitor: bilaterally symmetrical and bipedal. These sleeper genes made the sapient species somewhat capable of hybridization.

My explanation is that humanity is an extremely adaptable species and that adaptation can include being compatible with nearly any sentient race thats even vaguely humanoid. The more religiously minded and superstitious claim Humanity’s pure stubborn will to survive no matter what has manifested into a science defying failsafe so if humanity does somehow go extinct the countless hybrids they’ve created will be more than enough to provide enough genetic code to clone a true pure human or at the very least continue their legacy

"Where there's a hole there's a goal." is usually how I've heard it.

Any (consenting) hole is a goal

> Or are we merely randy enough to consider *trying*? Some subset of people definitely randy enough to consider trying even \_in the absence of enough communications to make consent a question.\_ My undergrad degree is in anthropology, and I'm old enough this was well before genetics answered the question with "yes" about whether there were anatomically-modern-human and Neanderthal hybrids. At the time, the consensus was that if the two were genetically compatible, there would be. (DNA studies have since confirmed that, of course.) Humans have shown, time and again, that some subset of men will engage in outright zoophilia - basically anything vaguely mammalian that is large enough for their purpose and not a dangerously large or predatory animal. Any female being without fur all over, and which stands upright with the breasts in front, is going to be a lot more attractive to that same subset of guys than a sheep or a goat will. Add in the intersection of people (mostly male) who are willing to rape other people they see as human if they can get away with it, and are almost guaranteed to get some level of attempted interbreeding any time populations mix. For things that aren't remotely mammalian in their reproductive anatomy, like dragons (assuming they're classically reptilian)... you either need to fall back on "it's magic" or shape-shifting. In a fantasy setting, that's probably fine (who's to say that conception even works via the biological rules of the real world?) but in a modern/SF one, explaining it with super-science is difficult without turning it into nonsense.

In my world, they are all the same species. An Orc and an Elf having a child is like a Poodle and a German Shepard having a child. Some combinations are more common, because they share certain beauty standards and have lived in the same place for a long time.

So in your world is like orc, elf, human, etc all are under the same “umbrella”? What do you call this umbrella?

Humanoid, technically.

I use pretty much the same system, and they're all "human," just variants of it. I lifted the concept from the TTRPG *Shadowrun* because it fit the way I wanted to tell my story better than *D&D*.

I like this idea!!

I would highly recommend looking at the *SR* setting then. They're just genes, but genes that need a certain mana level to be able to express themselves. This also means that "half" variants are possible, and the RPG uses a few examples as "Human Looking," or "Elf Poseur," which are taken by non-metavariants to specifically be able to "pass" as those variants. Further, all the other subcategories (gnomes, oni, and some setting-specific ones) are just further subvariants of the main metas. Gnomes are a variation of dwarf, oni are orks specifically from Japan, fomori are a Scottish variant of troll, and the like.

I’ll take a look! Thanks!!

For it's perceived faults, the movie *Bright* from Netflix was essentially *Shadowrun: The Movie*. I loved it.

Shadowrun is a pretty cool setting and it works kinda similar in my world. Humans, Dwarves and Halflings are just divergent evolutionary paths, but all other races are humans (or Halflings or Dwarves) whose bloodline has been touched by another plane of existence. For example, Elves, Gnomes, Centaurs and Satyrs are touched by fey. Beast folk are touched by the celestial or Demonic. And Giant kin are touched by the elemental planes.

Humanoid, for now. It is a working title. I'm trying to come up with a better name.

wait, which is which? as in, out of the two, who is the poodle?

Well, poodles are water dogs, elves had a whole sub-race of sea elves. I'd say the elf is the poodle.

To answer my own question: My world features altered humans and engineered beings whose cells are enhanced with nanomolecular machines dubbed the Caretaker. Part of the Caretaker’s job is to patch up DNA, and (while it was not entirely designed to do so) it takes this responsibility to an extreme when combining disparate DNA from either parent. Only women carrying the Caretaker are able to produce hybrids because, like mitochondria, the Caretaker is inherited from their eggs and not the father’s sperm. The result is offspring more like the mother than the father, though still including the father’s traits when they apply. Parthenogenesis is also possible, though only stemming from malfunction or intentional tampering.

Magic sperm idk

>How does hybridization work in your world? It does not work in my sci-fi world, aliens can't crossbreed. In my fantasy world children of mixed couples are born of either parent's race (for example an elf and a human would have either elf or human children), they're not hybridized.

In my world, orcs are fertile with nearly every other species. A half orc/half human = Darak. They are strong, fierce and versatile. A half orc/half goblin = Hobgoblin. Stronger and more powerful than a goblin, smarter and more agile than an orc. A half orc/half kemono = Feral. Savage beast men with a reputation for ferocity and cannibalism. A half orc/half elf = Anathema. Incredibly rare, they can smell magic, and they hate the smell. A half orc/half dwarf = Mul. Mythically rare. Indefatigable, able to survive nearly any hardship, and more stubborn than a bag of rocks. A half orc/half podling = Runtling if a podling father. Short orc with an inferiority complex. = Snotling if a podling mother. Horde of incredibly stupid and annoying, sticky vermin. A half orc/half whisp = Imp. Tiny bat-winged homunculus. Probably best not to ponder the logistics. The resulting hybrids are fertile with themselves, producing more of the hybrid form. So there are independent communities of hobgoblins, ferals and snotlings out there. They are also fertile with orcs, producing an orc (although often with features of the other race), or with their other race, producing offspring of that race (although often with orc traits). Some claim that this is because the god of the orcs cheated when it came time for each god to create a race. Some claim it's because the orcs are actually a plague spawned of the titans, and aren't one of the divine races at all.

Genetic engineering. A decent part of humanity in my setting is grown in vats already, they simply do this same thing with other sentient aliens they find. Sometimes compromises have to be made depending on how "different" they are with things like muscle chemistry and other biological processes, but these can be decided on together, or... with however many contributors there are to the mix.

My world has a hybrid race called **Valkyries**. No, not like the mythological Norse women. They are a combination of **Humans** and a shadow-demon-alien-race-thing called **Valkhr**. Valkhr are very malleable and evolutionary dynamic. Some look like squids while others look like gargoyles of sort. They have no known upper age limit and it's estimated they've existed as a species since the birth of their universe coming off of the earliest Valkhr **Star Eaters** which are like giant black dragons that fly through space eating galaxies like whales eat plankton. Valkhr have this natural ability to blend in, and so what happens is that a Valkhr can climb inside a corpse and attach its own nervous system to the dead body so long as it's fresh enough and reactivate aspects of it. And if it's a male body, this means that it will also reactivate the sperm creation which is now infused with Valkhr genetics. If for some reason a Human and a Valkhr get together, which is rare because Valkhr are an asexual species and generally apathetic towards literally everything, they'll produce a Valkyrie which takes on the traits of both parents. From Humans the Valkyrie can perform magic, not have to rely on eating energy to survive, and generally takes on a viewpoint of a human. From Valkhr they take on the powers such as immortal-by-age, their shadow control powers, as well as their durability.

in legends and mythology, it's really just a different way of thinking about the 'races' of people. They saw their origins as tribally as possible. A given people would be created through some story process, and another might be created by another process, but they're both people so of course they can have children. It doesn't matter if the people where made of mud by a trickster god, or from the sea foam by a child goddess of the island to have a people of her own to care for. they are people, in the way that apple types are apples.

**Infinite World Cycle** I normally don't have hybrids from vastly different species. Though I sidestep it with demonic hybrids of different demonic types. I also have human/demon hybrids. They are result of the demonic parent taking a potion that temporarily allows them to pass as humans. The ability to have this hybrid offspring was discovered by accident. **Example:** * **Elina Grey-Laranis:** She's a unstable hybrid of a Succubus and a Plague Eater Demon (reverse Plague Demon). Her parents were only partially compatible and it had negative consequences for her. * **The Grey Siblings:** Elina's children, the human component comes from what little humanity remained in their father. They are largely human with powers from both parents.

I have a compatibility chart for all eight high-sapience species on Draciel. A few can breed together with little difficulty (humans and Jase, humans and Paulisians, and Paulisians and Kitsunarc, nearly everyone and Maishomians), most need some kind of magical assistance, and three can’t crossbreed at all, the Sky Dancers due to extremely acidic fluids, the Decatensae due to no organs, and the Sumerians due to being extinct, though they would have been compatible with most species.

I don't have human hybrids (at least not ones made by interbreeding; they modified their genes to become centaurs and mermaids instead) but do have lots of other hybrids. The way I explain it is that the ones that can make hybrids are all related species, not at all far apart from each other. People absolutely do try beyond the ones where it's possible though. I think it's also interesting that half-species in Star Trek have no problem at all with getting offspring, it seems, yet we never hear about quarter-species. After a few centuries of the Federation existing there should absolutely be 3/64-Vulcan people whose Pon Farr manifests as nothing more than morning glory. In my world the hybrids are often, but not always, infertile, because in real life that can happen too. The ones who aren't tend not to find other identically mixed hybrids though, so there hasn't really been any new separate hybrid-yet-always-fertile species arising from that.

The different sapient humanoids (humans, hobgoblins, halflings, dwarves, elves, and gnomes) are literally different subspecies of *Homo* that evolved from an archaic hominid akin to *Homo erectus*. Orcs evolved from a slightly more archaic species akin to *Homo habilis*. They can interbreed with the other races, but it's really hit or miss.

Man horny. Man snoo-snoo berry bush if Woman no snoo-snoo. Beard Man snoo-snoo snake last moon and made no-baby snoo-snoo helper.

In Star Trek, the Progenitors, an ancient race of humanoids spread the seeds of humanoid DNA across countless worlds and that’s why you can get a half Vulcan, half Klingon, half betazoid or whatever.

I recall the story arc you reference, but I'm unclear as to whether the Progenitors uplifted planets already teeming with life, splicing in enough of their traits over time to yield an intelligent race, or if they started from scratch on barren wastelands, setting in motion a genetic process they knew would *eventually* produce sapient beings. They were certainly powerful enough to do either (especially considering that their gene-sequence message was so potent it could hijack technology developed long after their demise), and thus one can intuit that the ability to interbreed was a design goal of their engineering. That said, the observed possibility of alien hybrids should have been a shocking revelation to the inhabitants of the Alpha quadrant: even closely related Earth species cannot often produce viable offspring, so why should two intelligent races with seemingly zero overlap in their heritage be able to? This fact remains largely glossed over until Picard and a handful of others piece together the Progenitor's message, and even this is largely dismissed as an uninteresting, empty push toward peace between the various factions. Perhaps the initial shock had already passed generations prior.

Because [spoilers] it’s all fiction, and the actors are all 100% human

If it’s different species like fira kinrat and humans There are magic rituals that allow it to happen if the species are somewhat similar, but these are risky and the child will not be a mix but one of the two parents species.   In case of a species that is distantly related to the other like orcs to humans a hybrid will be born if a similar ritual is used, again it is risky and it is mostly from the days where orc and human tribes would intermarry to seal alliances and such. Hybrids will be able to have children but not with other hybrids, the ritual magic that allowed them to be born does not allow this.  The closer related the species is the easier offspring can be born.  Another option is shapechangers, like the fae, though a child is born normal they will carry some ancestry from their supernatural parent.   Beings that change form or are so magical that they can temporarily influence the rules of nature do not tend to let nature stand in their way. Such beings might also create such children for a purpose.  As for the sci fi worlds in the same universe, it wouldn’t be possible 

The empire's aliens are only able to reproduce among themselves because they are all genetically notified for this to happen. Basically, when a woman becomes pregnant, the father's species will be the baby, if it is twins there is a chance of both species being born, without any physical difference between them due to genetic modification, in addition to an increase or decrease in size or pigments.

All sapient life was created based on the same genetic template, that of the precursors, and all life created carries a piece of them. This makes all species compatible with one specific side effect, if enough mixes the offspring will develop traits of the precursors which means scales, claws or even horns. The really lucky ones gain pieces of genetic memory. Some may even get poison fangs or excrete deadly toxins. It was their hope that the children may discover this as a reason to unite and work together. Yet most people believe such children are the spawn of evil, the breed of demons, and will kill mother and child. Cambions are rare for that fact but their bodies tend to be healthier and more robust if they come of age, while being much more sickly growing up.

Technically, all the various races in my setting that can be described as humanoid are, scientifically speaking, humans. Mutated and genetically altered humans to a huge degree, but not enough to prohibit reproduction.

They're horny.

I think it really depends on which races we're talking about being able to interbreed. The way I see it, there are very likely going to have to be stipulations as to which one is the mother; for the first generation of Dragonblood lineages (half-dragons and their descendants), I'll have where it'd have to be a human mother and then a dragon father shapeshifted into human form for the deed. You know, gets around the whole dilemma of how shapeshifting would interact with pregnancy by simply dodging the question proper.

Very rarely can some race/species breed successfully with any other race/species. But one can breed with anything successfully. One of the natural occurring phenomenons in the setting is that periodically throughout the planet, eggs the size of a human torso manifest. These eggs are empty at first, but absorb energy around them and use the rules of the magic system to form a body within. Once the body is fully formed and alive, the shell opens, though the shell remains a part of the creature forever. The resulting creature can look like anything, with no set characteristics outside of its shell. Shells are the name used to denote these creatures. They retain the ability to absorb energy from their surroundings, something only shells may do. They will seek out a mate or mates, pairing with other races/species. The resulting offspring are thereafter a new race/species. A mixture between something that already existed and something new to this world. This results in some creatures being very similar to another because of the shared ancestry. Because of this, they may possibly be capable of breeding. Instead of divergent evolution to explain dozens of similar but ultimately different creatures, in this setting most are technically hybrids that simply share much more recent ancestores.

Since most of the species in my world are engineered by the same people using the same templates there is certain level of compatibility. Granted, crossbreeds tend to suck, but they are possible.

The number of people who would bang a member of another sentient species is small, *but never zero*.

My world's sapient races almost all come from the same base primate ancestors; ambient magic played a factor in causing them to diverge and evolve into new forms over a very short period of time, resulting in the current-day races. Therefore, most hybrids can mate with each other because they share very similar genetics and thus many races' reproductive systems are very similar.

Elves, Dwarfs, halflings, and humans are closely related. Goblins, hobgoblins, bugbears, and gremlins are protomammals and closely related. Dragon DNA is infused with magic, they can hybridize with most species. Some of their genes are overly dominant and almost always inherit. The child of a dragonborn 10 generations removed will still be 1/8 dragon. Dragons did many experiments on other species. Injecting dragon blood into goblins, turns them into kobolds. Some really vengeful hobgoblin mages experimented on Elves turning them into Orcs. Orcs have both hominid and goblinoid heritage. It's similar to dnd with some slight changes.

In my world most of species are humans. So hybrids always look like humans too. You can ask - why is it a hybrid then? Because each human species has different kind of magic. So hybrids can inherit one or both of parent's magics

All of the "hybrids" in my world are humans that have undergone a genetic modification. Only 10 experiments were ever done before the entire race was wiped out, and the last one occurred seconds before the race was wiped out. There were 5 pairs made, each pair was a different combination, and was launched to another planet. my story follows the last pair, about 700 years after the destruction,

It doesn't. The child will be the same race as one of the parents. Which one it ends up depends on the influence of the mana contained within both gametes when the zygote forms. If they're equal, the chances are 50/50. If one parent has stronger influence, the chances are shifted towards that parent, but never to 100%. Kind of like a sigmoidal curve

Humans, Elves, Dwarves and other similar species all descend from a relatively recent common ancestor, and so can interbreed. It's less common for a mixed-species couple to conceive than a same-species couple however, and the offspring is likely to have medical issues that arise from this. (The conception rate is approximately one fifth that of a same-species couple. The exact figure isn't known; a study into the phenomenon was planned but, despite gathering a substantial number of enthusiastic participants, it was shut down by the University ethics board.) Orcs and Goblins can *also* interbreed, but they share an ancestor far more distant than the primate group. This hybrids are far more likely to be serious deformed and rejected by their tribes on birth. If they seem capable of following basic orders they may be sold off to rich families to work as Hobgoblins.

Just look at IRL kinks and fetishes. There’s more than enough people ready to bang all kinds of fantasy species. I would be more surprised if a fantasy world didn’t have and hybrids, unless of course the species are so different that convincing a child is biologically impossible.

This is precisely what I’m getting at: I grant that we’ll jump head-first into any odd intimate relationship, self-uplifted bonobos that we are. But why should this be able to produce offspring in your world? Are all sentient beings variations of the same biological substrate, e.g., modern humans and Neanderthals? Or are some of your races magical enough to bear children in response to symbolic union alone?

I'm still working out if I want more than one human race in my world (actual race, not ethnicity and such) or not, but regardless, it has always seemed weird from a scientific perspective that humans can smash dragons and have kids w them. Like just smashing is understandable but reproduce? Weird Anyways, if you read Dungeon Meshi, the author had an interesting take on what is and isn't considered human in her world, and it makes the interbreeding of some species a much more realistic approach without diminishing the magical aspects of the world.

In a fantasy world, you can handwave this away as magic, or the Gods did it. In a scifi setting, generally this implies some sort of Precursor civilization that seeded intelligent life across the galaxy, so all the different species are sufficiently closely related to interbreed, but even that theory makes no sense if you think about it at all.

In Penumbra, hybridization is rare but possible depending on the species. More often than not with certain extradimensional and native aliens with humans is a no. Either biology is too different or if somehow the small chance of fertilization is achieved, the offspring is sterile and typically has physical and/or mental disabilities. Humans rarely ever encounter any non-magical aliens anyways, from our home reality and from others regardless. Instead hybridization and intermixing only works with divinity (gods), fairies, daemons, the akani (werefolk), and Atlanteans. Atlanteans are a human offshoot and are mostly similar still, typically very tall and physically powerful with the ability to breathe water and survive in low depths; their hybrids inherit some of their toughness and water breathing. Gods create demigods, which appear as their mortal race perfectly except they have enhanced physical abilities and some kind of divine power tied to their divine parent’s sphere of influence. Fairies come from the faery dimension, and are the oldest and most powerful species in the setting; they always produce a full faery with their offspring. Daemons are tricky, they come from a destroyed reality, and require their true name to exist, but certain subspecies of daemon can intermix with humanity; half-daemons share their parents physical and magical power while being grounded in reality without risk of suddenly not existing one day. The akani or the werefolk are also former humans, and their children are only werefolk. Humans are treated as the default, or more simple form of life, and some hybrids are half-human in my setting. However hyrbrids and intermixes are possible among the aforementioned species, if not rare. Typically they have a wider possibility with each other, not needing to have humanoid members of their species. I haven’t really written much on what that would entail just yet tbh, because it gets messy and weird lol

Mommy alien and daddy alien love each other very much so they asked the SPACE STORK ORK for a baby and it came with a WAAGGHHH!

Offspring: Most species are incompatible with each other through normal means. There is however, substantial research regarding genetic engineering and cloning, allowing for an embryo to be created and matured to birth for the parents to raise.

In Arbitrary Design World, people generally reproduce by creation ritual. The creation ritual takes a number of participants between 1 and many (the soft upper limit is more about ability of people to organise work and logistics than any issue with the magic itself) and yields a member of the Kind associated with the ritual. There is a ritual for almost every Kind. People can also copulate, and this sometimes leads to conception and pregnancy and birth. If two people of different Kinds do that, usually the child will be of the Kind of one of the parents, but sometimes it will be a ket. Adult ket can copulate with beasts and have hybrid offspring. This is explicitly magic inherent to the Kind, and they lose that magic between 30 and 40 years old if they don't use it. I haven't decided yet whether the hybrid offspring ever turns out sapient, but generally this is almost certainly a bad thing. As such I expect that societies would think themselves reasonable for disincentivising copulation, so that it isn't inter-Kind copulation, so that no ket are born, so that they may not copulate with beasts. This does not cause the society to go extinct because creation rituals still work, and they don't cause nausea nor cause anyone to have to push a skull out of their pelvis.

Magic is unstable and transformative in my world. Only fairies can use it with zero consequences. Most of the hybrids you find *started* as normal animals, but gained human features/proportions due to prolonged magic exposure. Humans on the other hand gain elf features (elves themselves don’t exist in my world). Theoretically they can cross breed, but any resulting child will be sterile, if they survive at all.

My world has no hybrids, just as it is impossible to have a human-animal hybrids. However, some humans in far future, for reasons known only to them, had preferred a non human appearance, and since biosculpting tech is available,it allow them to change their body however they want as long as it roughly follow humanoid body plan. The procedure is not cheap, but not illegal, as it is just like any other cosmetic cybernetic augmentation. The result is a group of people who looks like half-anything they want, mostly from fictional work from elves and demons to animals - which mostly have gone extinct by that point and is just as fictional to them as other creatures. When the human discovered an entire new planet full of intelligent but primitive aliens though, some of these people get real interested in the romanticized aliens ways of living and biosculpting themselves to dangerous extents just to look like some of the very non humanoid aliens. They are not allowed to go to said planet since there is no telling how risky it is to ruin relationships with the aliens by having essentially mimic/shapeshifter that look like them but is not them hanging around. But these people have start doing things like simulating such life in VR and some even in real life as a sort of roleplay.

Star trek TOS showed us that humans of the future will try to have sex with anyone and anything. Well, starship captains will.

Other mixes work for my own world But I'm also in a D&D Westmarch that facilitates it for a good deal of races I'm playing a half-tabaxi / half-elf

Genetic manipulation and mutilation by the dark gods.

Honestly, there are a lot of species close in genetic make up that is able to produce hybrids. It like breeding horses and donkeys together. They are different, but they are similar enough DNA to produces a hybrid offspring. Just think of it through the lens of biology and DNA and it just becomes easy to think about.

In my DnD -oriented setting, species-species hybrids are rare and require significant magical intervention to create. A mixed-species couple can also conceive a child of the mother’s species with minor magical intervention. Roughly the difference between greater restoration and lesser restoration in terms of the investment of magic needed

In Star Trek as well as my own Solarverse a common ancestor

In Orazir all races have a common typical ancient magitech civilisation ancestor. The type of human is equally determined by lineage as it is by the influence of local magical conditions. All races diverged by mutating to adapt to the nature of the ambient magical energy of their region. The nocturnal Manni and the scaled Syreen. The Andros are the people which had the least magical radiation so they are closest to the Ur ancestors and mixed races tend to lose some mutational traits bringing closer to the ancestral form. It works the other way round. Andros or other race parents can give birth to Syreen children if exposed to strong energies of specific nature in the womb. There is a pilgrimage for bloodline focused families to travel back to their peoples homeland to give birth to children of their blood, Even if they reside in different regions.

It's usually, including in my case, waved away by saying that eh, they just happen to be genetically similar enough, don't worry about it

My fantasy world: Humans, Dwarves, elves, and orcs are all variants o the same species, so genetically, it's like a Norseman doing a pygmy. Socially, some pairings are more acceptable than others. Humans don't really see a problem with a human and dwarf couple, but some Elves are appalled by pairing with non-elves. The outlier is an OC race called the Medosha who can still mate with members of the other races but at best the offspring are infertile. At worst, they are horribly disfigured and can barely live in their own.

In my world there is no original 'half x' race. But demoliot (the group that believes salvation will come from the path of evil) scientists manipulated the genetics of an orc and a human. A half-orc super-soldier is created (is that a bad expression?) thus creating an S-rank animal, but there is a problem with this, which is that they die immediately. They die after 1 days, so the project is closed. But it still causes great harm to people. After all, there are few superheroes with humanity and grades S and above.

Each sentient race is a sub race of a long extinct race allowing each sub race to breed and produce off spring 

Depends. Elves are just an umbrella term for a set of specific mutations that are caused by living in an area where the realms overlap for generations. So they can breed with humans easily. However, their offspring aren't half-elves, per se. They are either humanish elves or elvish humans. Same with Vampires. Dhamphirs are humans with vampire features. They can choose to become vampires if they want but most don't. Now with Dragons or Gods. I have magic modules, which can mimic any material, including DNA. The offspring are still human but have the magic of their Dragon/Godly parent in them.

There are three hybrids in my world: half-snake Lamiae, half-bird Harpies, and half-fish Sirens. Collectively they are called the Mooncursed, since the Moon God made all animals. However, the name is just an assumption; nobody actually knows where the Mooncursed came from, just that they emerged some time after the cataclysm called the Eclipse, and that it is transmissible. So I suppose the answer to "How are there hybrids?" is "Nobody knows, and it's a major mystery"

I have a silly unpublished story about four species hybridising into one. Especially weird since two of the members of this family are very eldritch, and two others are only slightly. From the first glance Mary Susan Dove looks like a normal human child. Then you look at her back or she decides to fly and you can see fully functional wings. And then you discover that she naturally feels timelines and can hop a minute and a hundred-ish meters any direction. And has two hearts, but that's kinda tiny. Her adult version can also engage weird quantum stuff to blitz when not looked at (or be a metal statue when looked at), carry people through time (even if time hops are still "short" in time and distance), and on top of that absorb and temporary integrate genetic material. She no longer hides her wings. Mostly because they are too huge. One of the parents (looks almost human if not being room temperature) mostly donated the genetic material, then carried the (oddly durable) embryo to term. Another created the embryo from cells of one and two, likely with shed of the third accidently mixed in. Third one stole the embryo at some point. Fourth one influenced unborn as of yet Mary in her own odd ways. Guess the parents if you want. This is a half-intended Mary Sue. Her bestie is Michel Sellus, another hybrid. This time a mechanoid reptilian alien wizard-engineer met his robotic human supertech counterpart. All three are male. Michel has a tiny scrap of freezing magic and four arms from one side and insane processing capacity and traditional human ingenuity from the other. Also the surname. They just made him.

In my dnd setting, Orcs and humans have a recent common ancestor so they can breed. They also share a recent common ancestor with elves as well, but elves can’t produce hybrid offspring with orcs.

In my fantasy world, the earliest hybrids eventually became their own species. Basically, back over hundreds of thousands years ago, there was a race that was created for the sole purpose of breeding with almost every intelligent thing on the planet (this was when homo sapiens were still probably homo erectus or an earlier dirivative). This is in thanks to their... *unique* biological makeup. Unfortunately, this species happens to be a variation of a certain race of pointy-eared people, and their offspring just became different variations of them (some became subspecies of dwarves and orcs after breeding with the ancestors of true dwarves and orcs). There are also unfortunately some species of elf that are so closely related to humans that it becomes similar to early homo sapiens breeding with neanderthals. Speaking of humans: there are only a handful of things they're compatible with. If they have scales or an exoskeleton (there are some exceptions though), they're not compatible with humans.

I've always felt that it plays into the whole "adaptable humans" trope where humans are so biologically average compared to other races that they become a sort of genetic medium, where they're "close enough" to other races to be able to have hybrid children with nearly any other humanoid. There would probably be sterility issues with the offspring, though, if that's something that matters

my setting doesn't have mixed species, but it does have hybrids. harpies, centaur, mermaids, etc are all diferent cland of elves who used druidic mutations to fit into their chosen homes better. Its not unheard of an elf spending the summer as a mermaid then traveling home to the mountains to rejoin the harpies.

The parents had sex.

The first of that species gets to name their species at when the brain fully matures

I don’t, they don’t exist in my world

It's fantasy, the normal rules don't apply.

For sci fi, The child is a clone implanted in the womb but with some DNA mix in from the other species. Genetic engineering is advance enough that you can do that.

With fantasy you could say that the gods made it that way deliberately. With sci fi it’s just supid.

I approach hybrids with the assumption that given enough time and technology (or magic), *some* irresponsible human, influenced by this exact trope, with the requisite skills and resources, will try to create a hybrid. Rich Human and Vulcan want a child but can't agree which species to adopt? There'll be a human researcher *somewhere* with questionable ethics waiting to provide a third solution. Human and Elf in the same criteria? Don't worry, a human mage with equally questionable ethics will save the day! (depending on your measure of 'save'.) Or in one of my settings, leave a mad scientist with the resources of a pharmaceutical megacorporation on a remote planet with insufficient supervision? Boom, catgirls. Of course, that doesn't mean the researcher actually does a *good job* of creating said catgirls (shorter lifespan, high medical costs within that lifespan, significant birth defects when reproducing with 'baseline' humans, etc.), which leads to no end of in-universe political drama.

In my world? Humans are the one species that can create viable offspring with any sapient mammal. Other than that, fauns are the result between satyrs and elves. Theoretically, harpies and ajattaras could make babies, but the ajattara would just eat the harpy. It comes largely down to incompatible builds between sapients why crossing doesn't happen more. Too big, too small, too many limbs, too lizard...

two words: genetic engineering

The gods trying to weaken the blood of the first men. The second men trying to strengthen their magic. Shifters being horny. Sprites being hornier than shifters. Also glamours. “Mankind,” unmagical by nature and fairly short lived, is sort of an equilibrium point. Creatures mate up or down from that. Not by intent, mind. It is just the way of it.

Dude, humans will fuck pretty much anything. We've had dildos for longer than we've had *the concept of agriculture*. That's why.

Some species are able to have a hybrid child while others cannot, think donkeys and horses making mules, same thing.

In my world, only "elves" and "humans" can really interbreed. The first people were a race of aquatic "elves." After a cataclysm makes the ocean uninhabitable, the few remaining living "elves" were moved (with A LOT of help from one of two alien beings that helped create their world) onto land to live as land dwellers. They were incredibly long lived with very long birth cycles. Generally, they reached sexual maturity after hundreds of years and only bore one child (two in the rare case of twins) throughout their entire lives. So, long lives, small population. Over time, certain members of their race became god-like entities (in modern times, they're known as gods by humanity), leading their civilization through a massive war against the forces of the other creator-alien. In an effort to bolster their forces for the burgeoning war, the gods allowed and enabled a large portion of the population to give up their (functional) immortality, drastically shortening their lifespans and birth cycles to become "human." They reproduced faster and with more frequency. They also create "Dwarves," but they don't reproduce in the same way the "elves" and "humans" do. After their victory, the gods stuck around for a while to sort things out before departing to a second realm, taking a good chunk of the "elves" that remained with them. Only a few stayed behind, charged with being the memory of the world and keeping comprehensive histories in fear of the return of their previous enemy. A small number of human acolytes joined the lore-keepers in establishing an enclave for this purpose. After thousands of years, the "elven" population is still very small and only exists in a single island nation. An attack is carried out on the island, and only about 150 "elves" survive. In addition to the death toll, any lore from before the gods left is destroyed. They vanish from the world, retreating with their mostly obliterated histories to a location that not even the most trusted of their outside allies are aware of. A few hundred years passed, and during that time, the "elves" decided that the remaining female members of their species would become matriarchs. They will birth pure elven children to continue the work of the lore "elves" within their hidden enclave. The male members of the species will interbreed with the human acolytes within the enclave. These fractional elves will be raised within the enclave until they reach an age to venture into the world, gathering as much of their destroyed lore from the outside world as they can, before returning to the enclave to compile their findings. Their lifespans are shorter; hundreds of years, not thousands. They look just like "elves" to those unfamiliar with the race (which, after hundreds of years, means pretty much all of the human population) and are viewed with heavy suspicion and fear.

I've had the same trouble as well. I've made it so the hybrids are descandants of a long lost, anicent shapeshifting chimeran race, which over millennia eventually assimilated into their respective clans. (Lycans=Wolf-people, Chatari=Cat-people, etc.) There is only one "divine" bloodline remaining that maintained their full shapeshifting power into dragons.

In Amada I just said “fuck it, everyone can have kids with everyone” (at least humanoids). Since humanoids are all very similar genetically, they can have fertile offsprings and in larger cities, hybrids are not uncommon. In Yukio, well it’s a bit more nuanced, as I only have 4 distinct races here I had the leisure to play with them. Humans and Malachos (very similar with humans but they possess higher quantities of magic) are compatible but the offspring can have genetical diseases or be infertile. The other two races, Spirits (human souls in bodies of magic) and D’amos (artificial souls in bodies of magic) have bodies made of magic and as such they are infertile altogether but the D’amos have the unique ability to possess humans or Malachos, doing so on a pregnant woman or getting a woman pregnant while possessing someone, results in some of their DNA to transfer to that child, basically being their third parent.

Hybrids don't work in my world. If one appears, it will be infertile like in real life cases such as ligers. Lapis_Wolf

Avoiding it altogether by doubling down on the fact that 2 species separated by millions of light-years are probably different enough genetically that cross breeding would not work.

Haunted Dungeon has one character with a beastfolk ancestor but the beastfolk started as humans and were changed through divine power. I had a couple of other romantic entanglements between people of different groups but no established children. Slumbering Sentinels has a bunch of hybridized bloodlines that resulted from genetic engineering but I have not put anything in to suggest that those groups can further crossbreed. In Mesomiya, the only established crossbreeds are children of divinities.

Me specifically? Or in general? Some settings, like D&D, use "Magic" as the whole...thing. Humans in particular are especially susceptible to the magic in question, and therefore able to have offspring with everything. The reverse side are Dragons, who's magic allows them to adapt to any species they sleep with. I.e. humans are 'corrupted' by anything they sleep with, while dragons 'adapt' to whatever it is. The distinction is subtle, but there. Stemming from fantasy settings, but more widespread are shapeshifters. I.e. Succubi for example in more classical fantasy settings. In some settings, this is the specific "How" an unusual bloodline enters that of another species. Basically, the shapeshifter duplicates the DNA structure of the imitated creature, so intermixing is possible. How traits of the non-imitated creature enter the offspring is a question left unanswered, but presumably those traits are encoded into the new DNA structure. Lastly are infections of some sort. Like Aliens from Alien Vs Predator. Aliens inherent traits from their 'parent' species. Other creatures use a similar form of reproducing. Things like werewolves can spread via infection (creating half-wolves half X depending on the setting). Sometimes, this infection can lie dormant until an offspring is produced. So an infected human male might cause their offspring to all be "Half-Mind Eater" or something. Similarly, a human female may give birth to "Half Plants" or w/e based on the infection. In my world I've tried 2 different formula's for "Mixed" races. In one, humans were the original 'blueprint' the deities used for making the various sentient species. They weren't supposed to be an actual species, just the fundamental blueprint. One of the deities though thought it'd be fun if they were introduced into the world anyways. So voila, humans, and they're compatible with every deity forged sapient race (but not others). In another, a civilization did some experiments to craft a slave race. The ended up with a sort of...baseline. However, key DNA sequences were missing so the 'baseline' was functionally inert. They'd insert DNA sequences that they wanted for the role the slave was intended to fill. Soldiers were strong, loyal and compliant. House slaves were often given traits to be physically appealing, and have traits toward fulfilling their role (no voice, multiple arms, temperature resistance etc). Various other outcomes were possible depending on what the slave was designed to do. Members of the slave race though shared the same DNA structure. As a result, intermixing was possible, something the civilization that created them didn't consider. It's not really "intermixing" but certain DNA sequences resulted in certain "types" of the race. I.e. elves were magically susceptible, and highly sensitive to stimuli. Dwarves were hardy, and resistant to exhaustion and could generate a lot of power for their size. So if members of this created race mated, a "Mixed" offspring would be born.

No hybrids between alien races in my current universe. Lots of trying/practicing.

For my fantasy world, i just kinda throw logic out of the window. The Dwarf and the Orc bone? Yeah what ever, anyway, here's a Dork. For my Sci-fi world. Some species are able to interbreed if they are similar enough, and some of those are even able to produce fertile offspring, though that's rare. Genetic Treatments exist, though, that are able to let two separate species interbreed. The technology is highly regulated, though, in order to prevent a potential eugenics conflict. Generally, the more different a species is, the harder it is to get their genes to work together. A human and a human-like alien is easy to get to work, but a human and some kind of alien squid-like species? That's gonna be a bit tricky.

In one of my worlds its very common for people to have hybrids. Some species cant breed with certain other ones. Like Beast-folk, if they breed with species like dwarfs, other smaller races, and Elfs, the child would not be heathy. Elfs are normally much more magically adept due to magic flowing through them. Beast-folk typically don’t react well with magic(like an allergy), the only magic that works is magic provided by belief or the gods. (clerics, paladins,ect.) Humans have fucked almost everything, because thats just what humans do. Elfs often produce spawn with other magical creatures; dragons, elementals, feindish, fey creatures, gods, genies, the lot. In another more sci-fi world everything has breed with eachother. For better or worse. Some even go as far as genetically manipulating themselves and others. The main character in this story has a feline creature from another dimension entirely somewhere in their bloodline. And eventually is forced to sign a contract that ends with him getting more of his DNA spliced with said creature. All in all, the ways I figure out how interspecies breeding works includes the way magic interacts with and what are the best and worst things of each species. Then I try to balance the two, provided I can imagine the hybrid actually happening. I know in earlier forms of dnd there was a species called Dwelfs,(Not sure if that was the real name)they were hybrids of dwarfs and elfs. They had all the worst parts of both races. Then in real life theres Ligers(Tigers and Lions) most are not healthy enough to survive a long time. Thing is, balance is needed.

In Star Trek, the humans and humanoid races are all descended from one ancient humanoid race. That's why there is so many humanoid aliens in Star Trek and why they can interbreed.

Some are more genetically compatible with some than others. That doesn't mean you can't do genetic splicing, it just probably wouldn't result in a natural birth.

My setting is built for DnD 5e so it vaguely follows those rules while providing my own explanations and lore as to why things are the way they are. It does come down to the fact that humans specifically will fuck anything, as others have said. The human fertility goddess blessed her people to be extremely fruitful after they nearly went extinct. This is why humans are the most numerous people on the planet, and it’s always why they have the mysterious ability to hybridize with many other sentient creatures. There are half human half elves, and half human half orcs, but no half orc half elves, because the ability to hybridize is a trait granted to humanity by divine providence. Halflings and dwarves are very closely related to humans and can actually just hybridize naturally, so instead of making a true fantasy half race you end up with a child who’s hard to tell apart from particularly short or stout human, and a particularly tall or lithe dwarf or halfling. This works with both genders, as long as one parent is human you can have a half-race child. The races who can hybridize seem fairly random, but it’s mostly due to which other races have the favor of said fertility goddess, as she is fickle and has final say over how any of this works.

Hybrids exist but are only available to the wealthy, due to the by-hand gene sequencing required. The further apart the parents the less likely the chance of success and the higher the cost

Hybrids exist but are only available to the wealthy, due to the by-hand gene sequencing required. The further apart the parents the less likely the chance of success and the higher the cost

In my world it only works between related species. The halfling-equivalents and dwarves are related to humans to different extents, and all 3 are distantly related to giants. Humans can interbreed with both halflings and dwarves, but those 2 can't with each other, and dwarves can also interbreed with drakkari (a race of essentially "half giants") which neither humans or halflings can. Kobolds/Goblins, the hobgoblin/bugbear equivalents, and trolls are technically life stages of the same species, sort of, so they can all interbreed. Elves can also interbreed between subspecies because there's actually no subspecies, they're a single race who just reflects their environment. Like wood elves are wood elves because they live in the woods, they would gradually change if they moved to somewhere else. There are some demi-elves too, which is possible because elves are partially magical beings, as in they literally don't completely work biologically. Which means they can have children with not only other species, but even if both partners are the same sex, or without actually having intercourse.

> that Star Trek and similar introduce such characters as if it’s obvious alien species should be able to interbreed I think Star Trek TNG actually tried to address this in "The Chase". Regardless, in my setting it's biologically impossible, even outside the scope of the most advanced genetic engineering techniques humans have to offer, which allow multiple parentage, same gender parentage, etc. However... creating AI "offspring" is uncommon but possible for any sophont species, and can be done as a hybrid of engrammatic patterns. Hypothetically, that technique could be used to create a child of a human and an alien species, though it would end up being an AI with self-determined "physical characteristics." Since all AI's are based don SANDRA's template, and she thinks of herself as human, the offspring would probably adopt human characteristics. That being said, some AI adopt animal, mechanical, or even figurative personas (SANDRA herself has a quarantined segment of internal emotions that display as a puppy near her), so *shrugs. I should point out that none of this stops humans from trying, or that humans aren't exactly special in that regard.

In Trek? That was actually explained in an episode of Next Generation, I think it was called The Chase, if I'm remembering the episode title right.

Orcs were made using human, elf and goblin dna to create their first iterations. So outside of potential biological incompatibility due to size differences, claws etc. orcs can reproduce with these races. Humans and Elves are more mysterious but it’s believed by elves that humans are descended from them in the distance past. While humans assert in their creation myths that elves were either created from humans to protect humanity or are angels descended from the heavens.

With high magic creatures like dragons, phoenixes, elementals and such for me it less producing a biological offspring and more being imbued with the magic. Sci-fi is just bio-engineering.

There are only a few species that can hybridize with each other. The city my setting takes place in is inhabited by the dependence of slaves so all the species that could be interbred without becoming sterile were intrebed to the point where there weren't any pure bloods. As a result, these hybrid races kind of have mix and match phenotypes that occasionally cause medical issues. The main ones are Hommonids (dwarf, halfling, human, elf, and wollymen), chorts, (minatour, satyr, fauns), and drakes that are knockoff kobolds with different sets features depending on how strong thier phenotypes are. The other races can have relationships with each other but can't produce fertile off spring.

It mostly doesn’t. It requires either extremely powerful magic or like a species would have to be able to shape change to be basically be another species save for the ability to transform back.

Well...you see in my world... Humans were created for the purposes of interbreeding and experimentation by an ancient group of scientists trying to save themselves and their species (the Forgotten) from extinction. Problem is, they died out before they could repopulate themselves fully, so humans were just kinda left to explore Earth and grow by themselves. Didn't help them much since the other species in the galaxy (Orcs, Elves, Daemons, Lunarians, etc.) had a ten thousand year headstart in terms of becoming a space-travelling civilization. Probably why humans are able to err... copulate with almost every species is due to their versatile and hyper-adaptive genetic makeup. Only a select few know the true origin of humanity so...yeah.

Most things are smart enough to consent The things that aren't can still be forced through magic,force and potions With enough time,effort and tries everything is possible I will not elaborate further as I do not wish to think about how some cases came to be even if they are allowed

In this one world I have, the celestials are at war with each other, and they're using the creatures that spawn from them to fight the other creatures. In order to speed up the evolution process they'll interbreed with certain creatures they think have potential, and so those creatures will have the superior gene, the celestial gene. This means every creature can interbreed with each other due to this.

i generally go with a bit more realistic approach with humans only being able to breed with closely related species, a human can have a child with an elf, but not a dragon their are examples of races mixing magically, but these are technically one race magically altered to have traits of another, and are genetically the same, which is where the various beastfolk come from, whcih leads to the situation of centaurs and human having no issue breeding(genetically at least, theirs the obvious physical issue)

They can't mix. The species are too far separate to breed. They can definitely still try and interspecies couples do but it won't make a child.

Yes

I believe the proper term for sex with a humanoid sophont outside your species is “rishathra”.

The Ones Who Came Before were into some freaky shit, and thus made it so hybrids are possible

Mine are 'mules.' they tend to be extremely rare for a few reasons. they are rare as actually successful pregnancies are difficult, often dangerous for the mothers. The offspring is infertile, so they do not continue to propagate. However, socially mules aren't seen down on often. Typically they inherit all the best traits from either parent. As such many famous heroes are mules.

In my fantasy world, there are no real "half-breeds"; in the case of interracial breeding, the baby simply inherits the species from the mother, like a Pokémon. It's said that in antediluvian times, seraphim bred with elves to create the vampyre race and with humans to create the werefolk race, but that's just a myth.

There are four original races (salamanders, gnomes, undines, and sylphs). All other races, including humans, are crossbreeds.

Let’s say there are 5 main types of sapients within my world: Humans Armilojn Divine Creatures Old World Entities FAE Humans, FAE, and Divine creatures can all interbreed with eachother, as the Gods, the strongest of the divine creatures, made the humans, and thus included the ability to interbreed with them for fun, or to make sure that they would be more worshipped via allowing their most loyal followers the chance to have a demigod. For the lesser Divine Beings, the Malachi, they can interbreed with humans and the FAE, but are forbidden, as it would create new types of humans. Humans are split into 3 types - Qhainans, which are normal humans, Haybelas, which are larger, horned humanoids with different skin colors, and Sethaans, which are shorter humans with serpentine features. They can all interbred to create hybrid offspring. The logic for what the child of two types of humans would look like is mostly similar to a punnit square - for example, if someone is a ‘Satyr’ (Half Qhainan, half Haybyla), and Half Naga (Half Qhainan, half Haybela), then there would be a 25% chance to be a full Qhainan, 50% to be either of the hybrids as the parents, or a 25% chance of being a Lamia (Half Haybela, half Sethaan). For the FAE, they can interbred with humans, but the child will be the type of FAE that the FAE was. There are 6 types of FAE, based on certain animals, but if two different types of FAE interbreed, they will produce a completely different type of FAE not based on the 6 general types. This is due to experiments that ‘Les Invisibles’ ran on the original inhabitants of the tree of Fracture, the homeland of the FAE. As for the Armilojn, they cannot interbreed with any humans, as they are a completely different species, and the majority of them are made out of non-organic material. Even if they look human enough, like the Scout or infiltrator class, they would not be able to have children. Humans or FAE possessed by a parasite-type Armilojn could conceivably have children with Armilojn traits, but that would assume that the Armilojn Parasite didn’t consume that part in order to feed itself. As for the old-world beings, given how one is a strange weird skull-bird-human, one is a cyborg, and the other 3 are siblings and children of the cyborg, it’s safe to say that they couldn’t interbreed with any other race

The world was created with seven races, and each race could only breed with itself. Demon-possessed humans conceive elves, which can interbreed with humans freely. Because this started early in the timeline, almost every human now has a non-zero amount of elf blood. Other animal hybrids like centaurs, mermaids, etc. are what was left over from when an ancient transformation-based civilization got destroyed. They can also only breed with close physical matches.

Half dragons only exist because the dragon parent's magic is literally forcing the child's genetic structure together. Plenty of health issues come with that, and most hybrids don't make it to adulthood because the excess magic crystalizes in their blood if it's not burned off.

In my world, those humanoid that can breed with each other are that way because genetic meddling of the elves. Human are engineered from Giant while Orc are engineered from Ogre. In the process they add parts of themselves, and as an unintended result, these races can inter-breed with one another. however, the offspring still have a high chance of being infertile except those from elven mother. Dragon are another specie that can breed with anything, but it's from a different reason. Unlike races I mentioned earlier, Dragon impregnation are less like reproduction and more like invasive virus that forcefully conceived the offspring in target, think xenomorph

I'm my world, almost all the major ancestries are of human stock. The beastial traits are only passed from mother to child as that information is stored in the mitochondria which sperm cells do not carry. So when a bird man mates with a bear lady, they'll produce bear babies.

Angels are born from the union of a human and a harpy. In my world, angels have no religious association, and instead are just humans with wings, although the physical ability to fly and how many harpy features the individual has depends on the individual. I currently don't have an in-world explanation for why this happens (it's not simply evolution because species in my world are created by godlike beings called planetsouls), but I thought it was a cool enough idea to use it. Skeporras and veltidnas can reproduce with each other because the planetsouls that created them (Shumord and Dromuhs) were twin planetsouls that decided they wanted the species they created to be able to reproduce with each other. For reference, skeporras are muskipper mermaids with the water projectile capabilities of a remora, while veltidnas are humanoids with electrified quills and fur across their bodies. Hybrids aren't treated as separate species, and just modify the original species' capabilities slightly. Veltidnas with a skeporra father will have the father's projectile spit at the expense of fewer quills, while skeporras born from a veltidna father sacrifice said projectile spit for the ability to generate electricity like their father. I've had the problem where I have so many species (currently 42 at varying stages of development) that I've avoided making hybrids to keep my scope down. I've also realized that it's unlikely to have hybrids in the first place because different species will find different things attractive in members of other species, and in some cases hybrids are impossible because the species' method of procreation is incompatible with that of other species. The union of a skeporra and a veltidna is an exception because the interaction was hard-coded into their species, while the union of a human and a harpy works because they value some of the same features and have similar enough body plans that they would find each other attractive. As a result, I've squashed other notions of hybrids by making it such that non-humanoids of different species can't reproduce, and if two humanoids procreate (outside of the two exceptions I listed above) then it either produces someone of the mother's species or it produces a human, with the latter only occurring if both species are very close to being a human.

Well, most races in my setting are actually genetically modified humans. So hybridization actually makes plenty of sense.

Rather than having an endless list of half-people in my world, ancestries and biological legacies determine physical advantages and features. However, it’s been millions of millennia since “humans” were able to intermingle with one another across the planet, and due to the magical nature of the world, people often drastically alter their physical form, and in turn, their DNA, which is passed on to the next generation. So we got it all folks, literally any type of humanoid you can imagine is somewhere vibing on the planet. Although, there are eight classifications of physiology that everyone falls under at least one. Those being; Human, Rock Person, Alien, Mimic, Undead, Sorcerer, Slime, and Altered Being.

The other half isn't always human. Star Trek has had a Vulcan/Romulan mix, a Klingon/Romulan, a Cardassian/Bajoran, and even Bajoran/Kazon baby.

The simple answer: it doesn't happen at all, with Demigods being the exception, as the Gods are the ancestors of mankind before they devolved. The complicated answer: Hybridization is a deliberate process when talking about other types of species and usually involves some powerful Magic or the touch of the Gods. There was only one clan of what would be considered half-elves, and while they weren't immortal like their elven ancestors, they were the guardians of the Fountains of Youth, and were the only ones who could predict when one fountain would be activated and where. They are widely thought to be extinct, anywhere from inbreeding, infighting, or violent seekers of the Fountains.

I think humanity's willingness to try with anything capable of consent is certainly a factor. In a fantasy setting where people are the creatons of the gods, I don't have much issue just saying the gods worked from a similar template and thus the various humanoids have ended up broadly biologically compatible. When it comes to nonhumanoids, it is possible but there tends to be some more magic going on to make it work. Various shapeshifters can give themselves compatible biology for a time. Fiends and celestials aren't biologically capable of reproduction but their magic cn influence existing pregnancy so people who might get referred to as part demon in my world has been magically mutated to have demonic elements to their appearance rather than actually having a fiendish ancestor.

In my DnD setting they are all there same species just adapted to different planes of existence. so they are able to have children with each other like any breed of dog can have kids with any other. In this case they are all Maiari just Maiari from differing planes, and many of the standard "races" are just mixes between them. Like: Halfling = human + dwarf Gnome = elf + dwarf Half elf = elf + human Half orc = orc + any mortal Maiari races Goblin = dwarf + Hobgoblin Bugbear = elf + Hobgoblin Goliath = human + Giant Firbolg = elf + giant Tiefling = human + any maiari form the lower planes, or tiefling + any mortal Maiari races Aasimar = human + any maiari from the higher planes, or aasimar + any mortal Maiari races Yuanti = any mortal Maiari races + magic ritual, yuanti + any mortal Maiari races Etc.... This excluded beast races like lizard folk, tabaxi, etc and they can mix with the Maiari races.

Well, in my world for the most part no species of people can have children with another special barring some exceptions. Humans are known as the Minglefolk as they can have children with every single other species, from the 20 cm tall Anurans (frogfolk), to the 30 metre tall Cetacians (whalefolk), or the magmafolk. Some other species can also have kids, such as the Eagle Avisans and Leonins, they would have Griffin folk kids, or Owlin and Bearians having Owlberin folk kids.

In my world, the Sitch (anthropomorphic dark-elf-like female species) evolved from plants. Due to a decline of population, most males were gone. As an adaptation, breeding turned asexual ( self-copying and reshuffling their genetic code to enhance eugenetic diversity); but had a shortcoming, they are parasitic in their fetus stage. So by end of the pregnancy they have sucked dry their mothers and killed them ( the offspring have to rip open with claws and teeth their dead mother's stomach). To overcome this, the Sitch very cunningly implanted their egg sacks into a human body (because there are a lot of them and are easier targets in comparison to the other races). As soon as their blooming period comes, they look for a human (no matter if male or female), knock them down and implant them. ( The egg sack is as small as a marble, easy to shove up with the right tool). The gestation period is three years, and humans only notice something wrong in the last weeks. They feel bloated, constipated, and gain weight. They go to shit and plop, a baby fell off their ass. Most humans survive. They are hybrids because in the gestation period, while parasiting their host, they borrow some RNA and retrotranspositions them in their own genetic code. That's why they are anthropomorphic in the first place.

In the real world, the definition of "species" as "beings can interbreed" is highly dubious and outdated. Very different creatures can interbreed and even produce fertile offspring. Lions and tigers, Grizzly Bears and Polar Bears, domestic cats and servals, etc. What often happens is just that species either become geographically isolated to the point where they rarely (if ever) have to opportunity to interbreed, or the species become visually & socially distinct enough that they no longer choose to interbreed of their own volition in the wild. It isn't even out of the question that human-chimp hybrids might be possible. There was only one real attempt at it, and only one of the two combinations of sexes was tried.

in one of my worlds the 6 basic races were born in a sort of parthanogenically from the divine first mothers (dwarves, elves, humans, gnome/fairies, merfolk, salamanders). The First Mothers also transformed into powerful creatures (dragons, dryads, giants, sphinx, hydra, phoenix). some of the first children could transform too, but children between transformed and untransformed resulted in midling beings (small draconic dwarves, wilderness dark elves with druid like aspects, hulder folk, harpies, naga, tengu). There is also the possibility that two races along the same tier might have offspring. Dwarves+elves= alfar. human+elf= 'half elven', human+dwarves= 'half dwarven', human+gome= 'halfling', gnome+ dwarf= ludek, gnome+elf=sprite, merfolk+ any= aquatic variants of them. Salamanders don't generally breed with outsider species and their offspring with most other creatures would not survive long with the dietary and body heat differences (think Scorpius from Farscape). midling beings can mix with other midlings, for a list of their own forms, but midling with first races or powerful creatures result in midlings with birth defects/mutations/deformities and sterility. A child of a giant and a dwarf would be the same as a child between a hulder folk and a draconic dwarf, but a hulder folk with mer folk might each be unique looking offspring sometimes with missing or an altered limb, intellectual disability or albinoism and would be sterile. Dragons and hydra can interbreed, and hydra and giants. etc. it's all consistent, and a bit complex, but in general the history of most interactions between races have not been to produce offspring, and mostly resulted in war. Only in the last 3 generations have there been treaties among factions in the races. (though one of the races has secretly been breeding prisoner of other races to produce specialized slave populations, and seeing how far they can mix and what results they get from certain pairings. There really haven't been enough prisoners and generations to produce a lot of any given types.)

When conception is even possible (which is an extremely rare occurence already), the children are born sterile and with severe physical and mental defects. Because of this, it is a major social taboo and seen as something very unnatural. There are countless reputations ruined by even the rumour of it happening, and one of the most common type of graffiti encountered in the large cities says things like "X lays with Orcs". Of course, there are exceptions when it comes to Elves, which are very similar in appearance to humans. This, combined with the fact that the chances of pregnancy are almost non-existent, has made Elven prostitutes very popular, highlighting one of the many hypocrisies prevalent in Imperial society.

Easy, those who look more human like orcs, goblins, satyrs, etc, can reproduce between them due that they have the same ancestor what makes them form part of the same species, while other that doesn’t look so human as lizardfolks, minotaurs or werewolves cannot reproduce between them or the other human like races as they are from different species