->''"The 'Parallel Worlds' concept is the key to the STAR TREK format. It means simply that our stories deal with plant and animal life, plus people, quite similar to that on Earth. '''''Social evolution will also have interesting points of similarity with ours.'''''"''
-->-- '''Creator/GeneRoddenberry''' (in his pitch for ''Series/{{Star Trek|The Original Series}}'')

While distant planets in fiction are typically different from Earth in many ways (see for example PlanetOfHats, GenericistGovernment, SingleBiomePlanet), they also exhibit astounding cultural similarities: [[AliensSpeakingEnglish aliens tend to speak English]] in the [[OrphanedEtymology idiom of a 21st-century speaker of English]], their written language, numerals and methods of time measurement are conveniently identical to Earth standards or can be easily converted. You might even spot European cars or [[UsefulNotes/{{Vancouver}} Vancouver landmarks]]. All societies will include two genders, which register as very like human categories of "male" and "female," down to females who have Latin-sounding names ending in ''-a'', wear their hair long and their heels high. Expect to come across proper names imported from Earth.

These Inexplicable Cultural Ties are caused by the fact that MostWritersAreHuman and can reasonably expect you, the viewer or reader, to be human as well. Hence, some cultural similarities might be considered AcceptableBreaksFromReality (like a TranslationConvention) or result from a limited budget. Others [[FridgeLogic might strike you as avoidable mistakes]] by the creators of the fictional work.

This trope comes in vastly varying degrees. Sometimes it's just a tiny detail that catches the viewer's eye, maybe a building in the background you recognize from RealLife or a visibly branded over-the-counter prop. On the other side of the scale, the alien planet will exhibit so many implausible similarities with Earth that your WillingSuspensionOfDisbelief is shattered almost instantly. Extreme cases lead to SpaceRomans. Also, the similarities might be HiddenInPlainSight, like a combination of social conventions that are inconspicuous precisely because they are so Earth-like but whose exact re-enactment on a distant planet is completely illogical. As this is an OmnipresentTrope for ScienceFiction, you might have become desensitized to it. And don't expect the characters on screen to spot Inexplicable Cultural Ties for you - odds are they're crazy FunctionalGenreSavvy. Instead, consult your [[FridgeLogic fridge]] frequently.

It's difficult to avert this trope completely in live action settings for budget reasons alone, although good writing can help to pull it off. Actually, as the above quote from the original ''Series/{{Star Trek|The Original Series}}'' pitch shows, use of this trope used to be a selling point to make live action ScienceFiction feasible for the small screen and pull some [[AnAesop Aesops]] in a LikeRealityUnlessNoted setting. Since then, this trope has lost some credibility due to the rise of [[MohsScaleOfScienceFictionHardness harder science fiction]] and better production values and techniques conspiring to change viewer's expectations. It is something of an UndeadHorseTrope, though. Of course, the whole trope is conveniently avoided in case of AliensStealCable or AbsentAliens.

Though [[AnimatedAdaptation Animated Adaptations]] and [[ComicBookAdaptation Comic Book Adaptations]] have the potential to shift a hitherto live-action franchise towards visually more alien settings, they still need good writing and design to avoid this trope. Conversely, [[LiveActionAdaptation Live-Action Adaptations]] of animated works or comic books are likely to introduce more Inexplicable Cultural Ties to a fictional world.

Cultural counterpart to the evolutionary HumanAliens and AllPlanetsAreEarthLike, which refers to planetary properties.

This being an OmnipresentTrope of ScienceFiction, please only mention examples where it is [[PlayingWithATrope played with]], {{averted|Trope}} or employed in a notable way.


[[folder:Anime & Manga]]
* [[ExaggeratedTrope Exaggerated]] by ''Manga/SpaceAdventureCobra: The Animation'', which starts with a story where Cobra eventually has to get into planet Galon, which has been isolated for 1000 years, and stop it from crashing into the sun. 1000 years notwithstanding, it has the same language, same architecture, names like Garcia, dark alleys with brick walls, earthlike clothes including hats with brims and jackets for the crooks, earthlike bars, and English writing everywhere.

* Lampshaded In ComicBook/BuckGodotZapGunForHire. The expository encyclopedia explains that every species has some kind of Ninja and nobody knows why.

[[folder:Films -- Animated]]
* The aliens in ''WesternAnimation/{{Planet 51}}'' live in what is essentially [[{{Eagleland}} 1950s suburban America]], and they [[AliensSpeakingEnglish even speak English.]] The only thing that distinguishes them as aliens is their appearance, as they are otherwise exactly like humans.

[[folder:Films -- Live-Action]]
* ''Franchise/StarWars''
** Inexplicable Cultural Ties is often played with in the blatantly [[MeaningfulName Meaningful Names]] some characters are given, one of the worst offenders being Separatist general Whorm Loathsom. Sith names like Maul and Bane apply, too. The implication is that these names just happen to be meaningful in English or Latin by chance, while the in-universe language "Basic" just ''appears'' to be English on account of a TranslationConvention.
** Likewise, different accents and dialects of English are used to distinguish characters' affiliation, background or species to the point that a British actor in ''Film/TheEmpireStrikesBack'' was given an American accent in post to conform to the Rebel-American, Empire-British pattern. In universe it is explained that British accents are from the core worlds, while the Rebels generally game from the outer rim.
** [[AvertedTrope Averted]] by OrwellianRetcon in a ''Film/ANewHope'' where the Death Star's English tractor beam controls have been translated into [[CypherLanguage Aurebesh]] for the current release.

* Often played straight in classic ScienceFiction novels and short stories, where LikeRealityUnlessNoted is in effect, for example in ''Literature/{{Nightfall}}'' by Creator/IsaacAsimov. Old advice on writing science fiction usually encourages this; it might seem more exotic for alien characters to say "[[CallARabbitASmeerp The podnaug is chatnik forgs away, we'll take the whekk]]", but that's just going to [[WillingSuspensionOfDisbelief break the reader's immersion]] as they have to pore over your glossary. As you're [[TranslationConvention translating the rest of the words anyway]], you'd be better off just writing "The airport is fifty miles away, we'll take the car."
* Creator/PhilipJoseFarmer's ''Dayworld'' books have a minor example of this: he writes in the foreword that the future world depicted has universally adopted the [[TheMetricSystemIsHereToStay metric system]] and the twenty-four hour clock, but Imperial measures and 12-hour time are used for the convenience of the (American) reader.
* {{Deconstructed}} in Creator/UrsulaKLeGuin's novelette ''The Pathways of Desire'', where more and more suspicious resemblances to American stereotyped notions of "primitive" tribes turn up in the HumanAliens' culture. In the end [[spoiler:the adolescent fantasies of a boy back on Earth turn out to have [[RealityWarper created the entire planet]]]].
* One of the footnotes in ''Literature/TheHitchhikersGuideToTheGalaxy'' mentions that every intelligent species independently came up with a drink whose name sounds like "Gin and Tonic". Of course the drinks themselves vary widely, from water served slightly above room temperature to being able to kill a cow at two hundred paces.
* Consciously invoked, then explicated, in ''Literature/TheLordOfTheRings.'' Samwise Gamgee's name is deliberately chosen to remind the reader of a working-class Englishman, but in Appendix F Tolkien tells us that it's [[TranslationConvention just a translation]]. Sam's real name is Banazîr Galbasi (which, oddly, sounds more like Persian or Pashto, or perhaps Turkish).

[[folder:Live-Action TV]]
* ''Franchise/StarTrek''
** The original ''Series/{{Star Trek|the Original Series}}'' is very aware of this trope (as evidenced by the opening quote) but plays it straight most of time. The episode [[SpaceRomans "Bread and Circuses"]] actually [[HandWave handwaves]] it, citing something called "Hodgkin's Law of Parallel Planet Development", an alternative title for this trope.
*** Interestingly, two episodes feature what ''had'' been somewhat extreme cases of this... until the subtle differences to Earth ran head-long into apocalypse, leaving society devastated and the cultural similarities somewhat hidden to the casual observer: "Miri" (seems to have been very much like Earth, even physically, but developed a life-prolongation project that went [[GoneHorriblyWrong disastrously wrong]], leaving kids and teenagers as the only survivors) and "The Omega Glory" (There was a bacteriological war between two factions. The descendants of one are called Kohms, the other are Yangs -- and the Yangs maintain garbled versions of the [[MeaningfulName United States Pledge of Allegiance and Constitution]]).
*** The above two examples, plus the episode with the Roman planet, were actually retconned/handwaved/explained in much later released reference materials, where a scientist determined that sometime in the distant past, the Sol system passed through some kind of NegativeSpaceWedgie that caused the entire solar system to be duplicated at the subatomic level. One "nearly perfect" duplicate was created in the form of Miri's planet, and two less-perfect duplicates were created in the form of the Omega Glory planet, and the Roman planet. All ended up diverging from the original Earth, but the latter two diverged a lot more than Miri's planet, which was identical until the mid 20th century. It should be noted that Voyager encountered a NegativeSpaceWedgie just like this (only smaller) in the Delta Quadrant, and it caused a nearly perfect duplication of the ship. These anomalies go a long way to explaining the "parallel planet development" law posited in the original series.
*** Another later retcon occurs in the ''Literature/StarTrekDepartmentOfTemporalInvestigations'' novel ''Forgotten History'': Miri's Earth is actually from a parallel universe, and the Yangs were ''given'' their US symbols by an Earth ship a mere hundred years before Kirk visited.
** ''Series/StarTrekTheNextGeneration'' has the episode "Who Watches the Watchers", who would be an excellent example of this trope... except the Mintakans aren't inexplicable human-like, they're inexplicably ''Vulcan''-like. Given their comments in that episode and the above mentioned handwave, the cultural ties evidently aren't quite so inexplicable to 23rd and 24th century Federation science as it would seem to us 20th and 21st century viewers.
** Whereas by the time of ''Series/StarTrekDeepSpaceNine'', the cultural assimilation of the Federation has become so great that even the Ferengi on a space station owned by a non-federation government quote Human literature with some frequency, especially Quark, and the Trill, aside from some very central differences due to their biology, seem culturally human to an almost egregious extent.
*** Though Series/StarTrekDeepSpaceNine did have some of this in reverse. Bashir and Garak would regularly trade commentary on the literature of each other's race and their bafflement by it. Garak doesn't believe that ''Theatre/JuliusCeaser'' was a tragedy so much as a farce [[ValuesDissonance because the Cardassians find the idea of a ruler not anticipating treachery to be ludicrous]] (although he apparently revised his opinion once he came to better understand the cultural context), and he believes that the lesson of the "Boy who Cried Wolf" is "never tell the same lie twice" though this may be more Garak than his society (He does seem [[WhatDoYouMeanItsForKids quite alarmed that this passes for a children's story among humans.]])). Conversely, Barshir finds the "The Neverending Saga", a tale of generations of one family all dutifully working for the state and their family and a Cardassian great work of literature, to be boring because of the conformity, which is not something admired by humans. Later he expresses his disdain that modern human literature is largely adapting alien works to human settings, rather than creating their own unique works.
** KlingonsLoveShakespeare! Though they tend to miss the meaning in some works. ''Theatre/RomeoAndJulliet'' is a tragedy because the two children let their love come before their family feud and died for their treachery. Hamlet is not well liked because Hamlet is very hesitant to seek rightful vengeance.
* All over the place in the new ''Series/{{Battlestar Galactica|2003}}''. Even though it's [[HandWave handwaved]] by repeatedly stating that[[spoiler: all of this has happened before, all of this will happen again]], the similarities are glaring, with the skyline of UsefulNotes/{{Vancouver}}, vintage Earth dresses, cars and army trucks, a Myth/ClassicalMythology identical to our own, the Latin alphabet, Western names, Music/BobDylan... [[spoiler: and all of this supposedly repeating itself 150,000 years later down to the details on our Earth without any explanation whatsoever.]]
** Website/AlternateHistoryDotCom gets its name for this trope from a specific instance of this: The [[https://www.alternatehistory.com/wiki/doku.php?id=alternate_history:citroen_ds_incident "Citroen DS Incident"]], after a user criticized the show's use of this trope by pointing out that apparently the Battlestar Galactica humans have, well, the [[https://en.wikipedia.org/wiki/Citroën_DS Citroen DS]].
* Mostly [[AvertedTrope averted]] on ''Series/BabylonFive'': the various RubberForeheadAliens' home worlds are usually pretty alien, especially Minbar, and the aliens have distinctly alien cultures.
** The Centauri, however, qualify as [[SpaceRomans European nobility in space]] (with the occasional bodyguard, attendant, and courtesan thrown in), blending the elaborate costumes of pre-Revolutionary Bourbon Frenchmen and late 18th century Prussia with the intrigue-heavy culture of Renaissance Italians and/or Early Imperial Romans, down to freakishly Italianesque names such as Londo Mollari, Vir Coto, Cartagia, and the eye-roll-inducing name of Antono Refa.
** The hat of the Minbari is tradition, and much of their behavior could be compared to a somewhat idealized (discounting that whole KillAllHumans thing, of course) version of several human cultures. It is their architecture that is alien rather then their culture.
** Lampshaded when G'Kar mentions that, with no explanation that he has ever been able to determine, every sentient race in the galaxy has, apparently independently, come up with a dish that looks, smells, and tastes identical to what the Narn call "breen" and humans call "Swedish meatballs". He says that if he could discover the reason behind this, he would likely know a great deal more about how the universe works. He's right, if he means that he would know that he's in a television show written by someone who felt like giving a ShoutOut to ''Literature/TheHitchhikersGuideToTheGalaxy'' and its nigh-identical gag with gin and tonic.[[note]]Technically, the ''Hitchhiker's'' gag was about many very different drinks having the same name on every planet rather than many very similar dishes all existing under different names in every culture, but same point.[[/note]]
* [[JustifiedTrope Justified]] in the Franchise/StargateVerse by means of an AncientAstronauts premise.
** Although rather less justified when you consider that the [[PuppeteerParasite Goa'uld]] had been thrown off Earth some time during ancient Egyptian times, yet many planets had cultures from much later times on Earth even though the humans transplanted there could not have actually been from those cultures. Similarly, the Ancients, and planets they had influenced, were generally portrayed as similar to Roman, Greek and Arthurian cultures which only existed long after they had [[AscendedToAHigherPlaneOfExistence disappeared]].
* ''Series/DoctorWho'' often ''references'' many very different and alien worlds, but the ones we usually see seem pretty Earth-like, [[BBCQuarry mostly due to budget reasons]]. Particularly of note is the Doctor's home world of Gallifrey, and the species seen in "Voyage of the Damned"; for a group coming to visit Earth's "strange and foreign culture" they certainly seemed like the British upper class. The original series is rich in examples of cultures who are impossible to distinguish from humans but don't appear to be actually descended from Earthlings.
* ''Series/FarScape'' The Peacekeepers (and therefore the human character who has borrowed their uniform as casual dress) wear DM boots, or biker boots. Presumably someone invented motorbikes at some point, but Docs?

[[folder:Video Games]]
* Zigzagged with ''[[Franchise/MassEffect Mass Effect]]''. Turians are pretty blatant SpaceRomans, down to using Roman names like Septimus, with even their racial name being a play on 'centurion'. Similarly, the asari possess a CrystalSpiresAndTogas aesthetic, prefer life in city-states, boast about being the inventors of democracy and worship of a wisdom goddess named Athe'''m'''e, making them obvious Space Greeks (specifically Athenians). The universe is also filled with locations named after Myth/ClassicalMythology, even where it does not make much sense, like buildings on alien homeworlds. However, all communication in ''Mass Effect'' happens through the medium of a UniversalTranslator and your PlayerCharacter is human, so it is very likely that this is mostly the result of an in-universe CulturalTranslation in order to make the alien races seem less, well, alien, to humans.

[[folder:Web Comics]]
* In ''Webcomic/{{Homestuck}}'', the [[AllTrollsAreDifferent troll]] civilization of the planet Alternia displays a staggering similarity to ours, notably in culture--they even have [[Series/TheFreshPrinceOfBelAir the same TV shows]] and a Creator/WillSmith. Justified, however, in that [[spoiler:our universe (and thus Earth) were actually created by trolls, implying that the similarities are a result of humanity having vague memories of their makers' civilization and replicating them.]]

[[folder:Western Animation]]
* ''WesternAnimation/{{Futurama}}'' plays with every kind of ScienceFiction trope. This one is no exception:
** PlayedForLaughs with the Yiddish-using Decapodians.
** [[InvertedTrope Inverted]] by Creator/GeorgeTakei's George Takei in "Where No Fan Has Gone Before": "I've done enough conventions to know how to spell ''Melllvar''." ''Franchise/StarTrek'', of course, is possibly the chief TropeCodifier.