->''"How come on ''[[Series/StarTrekTheOriginalSeries Star Trek]]'' everybody's private parts are the same? No alien lady ever told Captain Kirk, 'Hey, get your thing out of my nose!'"''
-->-- '''Rajesh Koothrappali''', ''TheBigBangTheory''

In works involving non-humans (whether it be [[FurryFandom anthropomorphic beings]], mythological creatures, or aliens) having sex, there's a tendency for everything to still use a human style sexual system (most visible in the penises). Everything will have sex organs based around humans of a size that allows the owners to copulate with each other as the {{plot}} demands. Often, this manifests itself as a differently colored human penis/vagina, but even when some design consideration is given towards making them look more like the species the creature is based on, they still have a tendency towards human proportions. And human stimulation—it's believed that primates and dolphins are the only creatures that copulate when not fertile.

In RealLife, the genitalia of even closely related species often have significant differences, making cross-species coupling impossible (except for bestiality in some cases), even if they both follow the "Sword and Sheath" model.

Makes the lovers able to consummate an InterspeciesRomance, if humans are involved. Compare NonMammalMammaries. Contrast ExoticEquipment. [[IThoughtItMeant Not to be confused with]] IkeaErotica.

Administrivia/NoRealLifeExamplesPlease
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!!Examples

[[foldercontrol]]

[[folder:General]]
* Rather frighteningly to anyone who accidentally stumbles upon the wrong web link, this is absolutely an area [[RuleThirtyFour Rule 34]] has not missed in RealLife... most commonly with a few specific classes of mammals.
* On the other hand, some ''do'' use physically accurate organs in bestiality or furry porn. Sometimes additionally drawing attention to differences.
[[/folder]]

[[folder:Anime & Manga]]
* Played completely straight in ''{{Macross}}'' (and by extension, the {{Macross}} segment of ''{{Robotech}}''): Humans and Zentraedi can have children apparently without any sort of outside aid, as seen when Max and Milia have a daughter shortly after getting married. Justified in ''{{Macross}}'' {{continuity}} by the fact that both races were created by the [[ThePrecursors Protoculture]]. The same does not apply to [[Anime/{{Macross7}} the Zolans]], who may be RubberForeheadAliens (the Protoculture's influence again) but are also marsupials, giving them a rather different reproductive process.
* ''The Elven Bride'' has acquiring one of these as a main plot point, as Elves and humans have some...mechanical issues. Let's just say this work isn't safe for work.
* Subverted in the short ''Little Wife'' where a newlywed couple (both humans) have direct problems due to... size issues. It's {{NSFW}} naturally.
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[[folder:Comics -- Books]]
* ''ComicBook/{{Ironwood}}'' uses this {{trope}}, although there it is mostly a case of the female genitalia of the fantasy races being compatible with human male equipment. The males occasionally have trouble finding the right spot but, once they do, there are no problems doing the deed.
* ''ComicBook/TankGirl'' routinely gets it on with mutant/genetically engineered kangaroo Booga. His... equipment... is human.
** Probably for the best. Kangaroos have ExoticEquipment.
* ''XXXenophile'' switches between this and ExoticEquipment.
[[/folder]]

[[folder:Films -- Live-Action]]
* ''Film/{{District 9}}'' mentioned, but didn't show, "interspecies prostitution". One wonders as to the mechanics, as the Prawn are naked for the whole movie and don't have visible external genitalia. They are shown to reproduce by laying eggs.\\\
One assumes, given how grossed out ''everyone'' is by the idea, that it is just about as natural and comfortable as having sex with a chicken (which people actually ''have'' been known to do). In other words, it's taboo even amongst deviants but there's some people who are just too damned kinky and/or curious not to try.
** A deleted scene mentions that they're hermaphrodites.
* In ''Film/GalaxyQuest'' The human-looking aliens are actually some sort of squid thing under their holograms. Chen and Laliari don't seem to care.
-->'''Guy:''' That ain't right!!!
* Lampshaded in ''Film/StarTrekVITheUndiscoveredCountry'' when Kirk fights an alien in the penal colony. Lying on his back, he kicks the alien in a jointed area in the middle of his legs. The alien immediately keels over groaning. When [=McCoy=] says "It's a good thing he had knees," Martia, [[spoiler:the Chameloid]], says, "That was not his knee. Not everyone carries their genitals in the same place." Cue shocked look on Kirk and [=McCoy=].
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[[folder:Literature]]
* SF author Creator/JohnVarley absolutely ''loves'' this {{trope}}:
** The ''Literature/GaeaTrilogy'' has the Titanides, an alien species who are sexually compatable with humans because they were deliberately engineered to be sexually compatible with humans.
** ''Literature/SteelBeach'' has the ULTRA tingle system, which gets around the whole genital compatibility issue entirely by using wireless modems for sex.
** [[TheProtagonist The actor protagonist]] of ''Literature/TheGoldenGlobe'' equipped himself with a penis that can be turned inside out for use as a vagina, primarily because it doubles his chances of getting roles.
** Finally, the novel ''Literature/TheOphiuchiHotline'' has literal [[MaleToFemaleUniversalAdaptor male to female universal adaptors]] that allow characters who go in for radically modified genitals to "dally" with their more conservative counterparts.
* In ''[[Literature/DreamPark The California Voodoo Game]]'', two conspirators meet at a sleazy hotel called the Mate & Switch. Each room is equipped with sensory-simulation bodysuits that let the wearer experience the sensations of being the opposite gender, making each a '''literal''' MaleToFemaleUniversalAdaptor.
* Simply glossing over this (very Edwardian, of course) doesn't mean it's not there; JohnCarterOfMars and his red Martian princess Dejah Thoris. Would not her biological equipment for laying ''eggs'' cause at least a bit of a shock for our Earthly hero?
* An interesting version occurs in the SuperHero novel ''SoonIWillBeInvincible''. [[TheHero The heroine]] Damsel is the daughter of a human male and a GreenSkinnedSpaceBabe, however, she was bred in a laboratory because her parents were ''not'' compatible with each other. Her mother wasn't even a mammal.
* Played with in James Patrick Kelly's ''Look into the Sun'': The protagonist is sent on an interstellar trade mission that requires him to be transformed into an alien species that just happens to use sex as a bonding and bargaining tool. Fortunately, he's also been equipped with a neural AI that can translate all of the alien physical sensations into the human ones he's familiar with... until the AI gets pettish mid-screw and refuses to translate any further, leaving him to cope with his new BizarreAlienBiology on his own, such as the sudden realization that his delicate, flower-like genitalia means the females have been taking the dominant role during copulation all along.
* In ''Literature/WestOfEden'', Yilanè have reptilian genitalia, including hemipenes on the males (who also function as MisterSeahorse). However, the female genitals are compatible ''enough'' with human equipment that Vaintè and Kerrick are capable of having plenty of sex while the latter is the former's personal slave. It should be noted, however, that Vaintè is insane both by human standards and [[BlueAndOrangeMorality those of her own race]], and Kerrick was raised by Yilanè and has (at this point) an incomplete and screwed-up understanding of human sexuality. When Kerrick returns to humanity, he starts looking back on his time with Vaintè in [[{{Squick}} disgust and horror]].
* In ''Literature/{{Spellsinger}}'' by Creator/AlanDeanFoster looks like all [[PettingZooPeople sentient mammals]] including humans are compatible, if not able to crossbreed. Jon-Tom [[{{Squick}} decides not to investigate any further]], when he gets a chance.
** In another novel, ''Quozl'', the eponymous aliens are human-sized marsupial rabbit-squirrels, who copulate for recreation 20-60 times a day.[[note]]Which isn't as much as you'd expect. In a time for a human "quickie" Quozl can do it more than a dozen times.[[/note]] For some reason their scientists are shocked to learn they are compatible with humans and decide to keep it a secret from the rest of the population. (Preventing humans from going OutWithABang probably wasn't the reason. [[spoiler:And it didn't happen when the truth was revealed.]] More likely it was done to prevent Quozl from experimenting and to stay hidden.)
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[[folder:Live-Action TV]]
* In the ''Series/BabylonFive'' {{spinoff}} ''Series/{{Crusade}}'', Captain Gideon accidentally acquires a data crystal containing Pak'ma'ra/human porn. The ship's doctor walks in and comments that this shouldn't work. (The Pak'ma'ra are humanoid, but closer to StarfishAliens than RubberForeheadAliens with tentacles around the mouth and a hump that is the female of their species) Then they [[HeadTiltinglyKinky bend their necks ninety degrees]] with a look of horror on their faces. Gideon remarks that technology is a wonderful thing.
* ''Series/BabylonFive'':
** The series unexpectedly describes Centauri genitalia quite explicitly and as being mostly (if not entirely, barring near-perverse levels of creativity) incompatible with comparable human anatomy. Although looking like they should be just simple RubberForeheadAliens (they look like sharp-toothed humans with strange hairdos), genetically they have nothing in common with us. To the point they have 6 tentacles on the male and 6 vaginas on the female's backs. Their equivalent of kissing is penetration with just 1. Oh and the tentacles are prehensile and Londo gets caught using one to cheat at poker...
** G'Kar ([[spoiler:before his [[CharacterDevelopment spiritual transformation]]]]) ([[spoiler: and after: remember the removable eye on the wedding night]]) is seen as being also a bit of pervert, being into Human women as well as at least one Centauri female. His species, although looking reptilian, are marsupials, including keeping their young in a pouch. As Na'Toth said in her first appearance, "Far be it from me to ask how ''anything'' gets in ''your'' bed..."
*** He also propositions to Lyta, but only in order to re-introduce the telepathic gene into the Narn gene pool, implying that not only is it possible for a human and a Narn to have sex, but that viable offspring may result from it.
** A throwaway line about "what are these cramps I'm getting" when [[spoiler: Delenn]] becomes a half-human hybrid implies that her species, at least, has a rather different reproductive system than humans. On the other hand, that could just mean that her species' females don't menstruate... which is true of most mammals here on Earth.
* Most alien species, at least those encountered by Starfleet, seem to be sexually compatible with humans in the ''Franchise/StarTrek'' universe. Even those that shouldn't be, like the Cardassians (which, according to {{canon}}, supposedly evolved from reptile-like ancestors, but are capable of mating and reproducing with mammalian humanoids). In an unexpected subversion of this, it is noted that Klingons, Vulcans and humans, while sexually compatible, have a difficult time producing hybrid offspring "without help".[[spoiler: In the Next Generation episode "The Chase" it is revealed long before humans, Klingons, Vulcans, Cardassians, and other races came into being, there was a dying race who spread their genetic material to developing worlds in hopes of their legacy continuing. This is likely the reason why there is such genetic compatibility.]]
** Implied in the ''Series/StarTrekVoyager'' episode "The Disease", when Ensign Harry Kim has a passionate affair with beautiful humanoid alien Tal.
-->'''Kim:''' I've got to be honest, I wasn't expecting something so different.\\
'''Tal:''' Neither was I. Our species look so similar... well, at least on the surface.\\
'''Kim:''' I would've never guessed when it came down to the basics. Well, let's just say the birds and bees will be very confused.
* Subverted in the 1980s miniseries ''Series/{{V}}'', in which a reptilian humanoid is required to undergo surgical alteration (and make no mistake, even the simple act of implying as much was pretty racy for early 1980s primetime!) before mating with a human female. The novelization goes a little further than the TV show did, noting that the human subject of the experiment -- although unaware of ''how'' alien her lover is -- senses that something is ''wrong''.
* In ''Series/{{V 2009}}'', it is perfectly possible for a Visitor to have sex with a human, as evidenced by two of the show's interspecial couples. One of them, in fact, results in a HalfHumanHybrid, something the aliens thought impossible given the two race's diverse origins.
* Subverted in ''{{Lexx}}'' with Stanley and Lyekka. Although they would have sex if given the chance, Lyekka is a highly evolved plant and has no genitalia. There's also the issue of Lyekka's entire raison d'etre being to seduce other species by appearing in a form desirable to them for the purpose of [[ImAHumanitarian EATING THEM]]. Despite her affections for Stanley, she is still just a plant that might just eat him if they ever tried doing it.
* Hilariously {{conversed}} about in ''TheBigBangTheory'': After the gang speculate on how Amanda and Sarek concieved [[TheSpock Spock]], considering their difference in species, Raj muses on how in ''Franchise/StarTrek'' everybody's private parts seem to be the same: "No alien lady ever told [[TheKirk Captain Kirk]] 'Hey, get your thing out of my nose!'"
* Presumably the case in ''Series/{{Farscape}}'', at least most of the time, though you never actually see the genitals. Implied by Chiana and D'Argo, for instance, given that their sexual positions seem very human-esque and even though they are very different species explicitly stated as not genetically compatible, they still manage to have lots and lots of sex.
** D'Argo (a Luxan) had a hybrid son (Jothee) with his Sebacean (augmented human) wife. Jothee also lots of human-like sex with Chiana. Zhann (a blue humanoid plant) at one point states that Luxans 'make excellent lovers', implying the two can have sex, but not necessarily reproduce.
** Aeryn (a Sebacean) has a child with Crighton (a human), even though she details many large differences in her reproductive biology.
*** Sebaceans do originally come from basic human stock, but were genetically altered by the Eidelons in order to serve as their Peacekeepers.
** Apparently, Sebaceans are also ''technically'' genetically compatible with ''Scarrans'', who are, more or less LizardFolk (although their females look more human). Scorpius is the result of a female Sebacean being raped by a male Scarran (in fact, he was at first told it was a male Sebacean who raped his female Scarran mother, while in truth he was the only viable offspring produced by Scarran research into genetic compatibility between the species). He does have many health issues and can only survive with cooling rods inserted ''directly into his brain'' because his Scarran physiology produces tons of heat which his Sebacean physiology is especially vulnerable to and unable to deal with.
*** That said, it's hard to say how ''physically'' compatible a Scarran would be with a human or a Sebacean. For example, their [[PardonMyKlingon mivonks]] are internal, as one character found out after a GroinAttack utterly failed.
[[/folder]]

[[folder:Tabletop Games]]
* ''{{Exalted}}'' averted this trope with an April Fools sex supplement. One of the artifacts in the PDF is called the Many-Stalked Flower of Delights, which allows beings of incredibly different physiology to enjoy the pleasures of each other's company. The creator of the artifact was an Eclipse who apparently '''fell in love with a mountain'''. Not the god of the mountain, the mountain itself. The first use of the item caused a [[SomethingElseAlsoRises volcanic eruption]]. Of course, the Many-Stalked Flower of Delights is a Male-to-Female Universal Adaptor, but it's the opposite of this trope.
[[/folder]]

[[folder:Video Games]]
* Apparently in ''Franchise/MassEffect'' human and Quarian genitals are similar enough that sex can occur normally once you get around the problems inherent in cross-species fluid contact.
** Don't forget the other races; heck, Mordin has ''pamphlets'' on cross-species intercourse for whatever RomanceSidequest you pursue. Drell, turian, quarian, he's got you covered. It's not made clear if all the parts line up precisely. The pamphlets are necessary to achieve proper positioning and to hit the right erogenous zones. All we really know is that the respective parts are in the same general area on the humanoid species. It's also for health safety. Quarians with their atrophied immune system are only an extreme case. There are also all kinds of allergies to the body chemistries of other species. There can also be mechanical issues. One pairing has ''chafing'' as a specific risk.
** Asari do not appear to have this problem, mostly because nothing needs to be, ahem, inserted. All you need is a nervous system and they can initiate melding at a touch, although this doesn't stop them from engaging in physical intercourse.
[[/folder]]

[[folder:Web Comics]]
* In ''{{Drowtales}}'', because dragons are descended from elves who were mutated or changed into the four legged lumbering beasts they are today, they are able to mate with[[note]] Dragons are the ''size of small elephants'' [[/note]] and produce offspring with normal drow.
** Zhor, a giant purple spider is able to mate with and knock up [[spoiler: Mel'arnach]] to produce [[spoiler: ''Ariel'']].
* The {{webcomic}} ''[[http://www.klinefx.com/DreamwalkJourn.html Dreamwalk Journal]]'' does this with human-insect/arachnid hybrids, although everything seems to be scaled up quite a bit, even for visiting humans.
** Justified in that, according to WordOfGod, the hybrids and their sexual customs were all created by human genetic engineers centuries or millennia in the past.
* Averted in ''Webcomic/TheOrderOfTheStick'' with {{lizardfolk}}s, who have [[http://www.giantitp.com/comics/oots0738.html a genital sheath and hemipenes]], like most reptiles. Though this doesn't seem to stop [[http://www.giantitp.com/comics/oots0676.html interspecies prostitution]], at least with the females.
* Undead seem to be able to breed in both ''GrimTalesFromDownBelow'' and ''Dungeon & Denizens''; detailed explanations on what male "biophiliacs" (including skeletons with no flesh) do for sex and procreation: [[http://dungeonsanddenizens.com/d/20060417.html]] [[http://grim.snafu-comics.com/?comic_id=033]]. So while it goes unmentioned, they MUST use some adaptor, right?
** Spoiler for ''GrimTalesFromDownBelow'': [[spoiler:Yes. It's called another dude, and an abortion clinic. Think about that for a minute -- how else did you think a skeleton would have a dead baby?]]
* Creator/JayNaylor varies use of this trope. Sometimes male organs are human-like, other times (mostly with equines and canines) they are anatomically close to the RealLife animals. Females, however, universally have human-like vaginas.
[[/folder]]

[[folder:Western Animation]]
* The title trio of the American animated series ''WesternAnimation/AquaTeenHungerForce'' have all displayed sexual interest in and claim to have had sex with human females at one point or another, despite the apparent lack of genitalia (and the fact that all three are a giant, anthropomorphic foods -- a box of fries, a milkshake and a meatball, respectively). And yet two have vaguely phallic appendages and the third can change his form a bit...
** However, it should be noted that Shake is a huge goddamn liar, and Frylock mentions at several points that Shake doesn't have a penis. When Shake claims to have had sex one time, Frylock's response is "When? How? With ''what''?" It's repeatedly mentioned that Frylock is a virgin, but this seems to be attributed more to his nerdiness than any physiological shortcomings. Finally, any claims Meatwad makes are probably made without any understanding of what he's talking about, just parroting things he overheard from Shake, Frylock, or Carl.
* In ''WesternAnimation/Ben10AlienForce'', the main source of superpowers is revealed to be having alien ancestry, which includes, among other things, energy beings (although granted said energy being could assume human form) and an alien made out of living fire (which is a bit harder to explain). Plus there's the whole human marrying Mud Monster story from the previous series....
[[/folder]]
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