Humanity Is Infectious

""Human thought is so primitive it's looked upon as an infectious disease in some of the better galaxies. That kind of makes you proud, doesn't it? Huh?""

- K, Men in Black

""Being a demon, of course, was supposed to mean you had no free will. But you couldn't hang around humans for very long without learning a thing or two.""

- Good Omens

An undervalued human trait is empathy. We can empathize with just about anything (even a toaster!) given the right conditions (heck, even if they aren't). What aliens should know before coming to invade is that it works in reverse too. Humanity Is Infectious.

The most powerful and dangerous trait humans posses isn't some ineffable 'specialness', but our humanity itself. Frequently, when a non-human critter appears in a story, be it Aliens, Robots, Mutants, spirits or stranger fare, they'll be incapable of emotion (usually love, but good also crops up), creativity/fecundity or individuality. But that all changes as soon as they spend time interacting with humans.

Curiosity Causes Conversion, and by observing and forming relationships with humans, eventually the critter is "infected" with humanity's values and viewpoints, and learns new ideas, philosophies and even to feel. In some stories this can go a step further: a robot might develop a sense of identity, a Hive Queen may learn to love her offspring as family and not just drones, or an immortal elf that not everything has to be pretty or ageless to be beautiful.

Sadly, these beings likely view Humanity Is Infectious as a bad thing precisely because it can 'corrupt' them into thinking/feeling like humans, so any critter who gets infected will likely become an outcast among its people. From a certain point of view, these critters treat humanity as if we were Cthulhu and write us off as dangerously incomprehensible, as if we were Things Aliens Were Not Meant To Know. The greater race is usually out to Kill All Humans, and it becomes this Defector From Decadence's job to either fight or turn their fellows. One variant here is that by becoming infected with humanity, the being somehow is victim to a fall from grace of some kind, and lose their Immortality or magical powers.

This trope usually results in a Heel Face Turn if they were evil, but it may even be a stated goal of those with Pinocchio Syndrome. In fact, the critter may specifically seek out humans to pick up our cooties. For some reason, the more a critter wants to be infected, the harder it is. Often happens to Scary Dogmatic Aliens.

It should be mentioned that Humanity isn't all rainbows and hugs. A critter infected with humanity may become more dangerous now that they can feel anger and hate, or decide they want to 'reward' humanity and keep feeling by kidnapping and harvesting that emotion from people.

Remarkably, non-humans never seem to leave much of a cultural impression on humans; it's as if humanity itself were the perfect condition towards which all thing in the universe naturally aspire. Stories where the cultural impact goes both ways aren't that rare, but typically have some form of Our Elves Are Better, where the non-human culture is naturally (and unarguably) superior. One disturbing inversion is when the alien culture is so alien and incomprehensible in it's Cosmic Horror Story that it warps those humans who come in contact into insane monsters.

Compare Humanity Ensues: when a non-human is physically transformed into a human. They need not be happy, willing or to ever integrate.

Anime and Manga
""Pathetic... to think that Demon King Piccolo would fall... protecting a child... I have been.... contaminated... by you... and your father's decency... Gohan.""
 * Dragon Ball:


 * Slightly more subtle example: Celty from Durarara!! wonders if her time living among humans in Japan may have caused her to adopt some human values, most notably that over time she has come to think of Shinra as more than just a roommate. Of course, we don't know exactly how "inhuman" Dullahans normally are and it seems that Celty was pretty kind in the first place, so even she can't be sure exactly how much it's affected her. Celty herself seems to have just decided to go with the flow and let it happen.
 * In Bleach
 * This is basically the character arc of Deedlit in Record of Lodoss War, especially in the manga, alongside Curiosity Causes Conversion. She becomes fascinated with why humans are the way they are, and eventually, she's even accused by her fellow High Elves as becoming corrupted by human lines of thought.
 * In The Disappearance of Haruhi Suzumiya, the consequences of drive the plot.
 * The Zentradi race in Robotech suffer this after they send infiltrators onto the SDF-1. Being pure Proud Warrior Race Guys, the concept of civilian life, love, music and peace was alien and alluring. In fact, it lead to an Enemy Civil War.
 * In probably one of the largest examples of this trope ever, the introduction of these human concepts led to the defection of over one million starships and countless billions of Zentraedi to the human side. However, the Zentraedi loyalists still have about five times that many ships, so it's not quite the ideal situation...
 * Humanity Is Infectious is one of the strongest weapons humanity has in the Robotech series, and in the parent series Macross. In pretty much each arc, our culture is not only used as a weapon, it allows us to make friends with beings who have Blue and Orange Morality to a terrifying degree.
 * In a recent Mahou Sensei Negima chapter, we see that this has happened to . It does help that

Comicbooks

 * In a Pre Crisis Flash story, the intelligent apes of Gorilla City revealed their existence to humanity, only to regret it after the concept of "leisure time" was introduced into their society, turning many of them into couch potatoes. Their solution? Brainwashing the entire human race into forgetting they existed, so they could go back to hiding! (this was a pretty ham-fisted way to retcon them back to their original Status Quo.)
 * An X-Men story had a nurse infected with an parasite from a race of evil aliens (obviously a Captain Ersatz for an Alien Queen) but her Christian faith and love for people were so strong that neither she nor the people she'd infected fell to The Corruption.
 * The third Blue Beetle, Jaime Reyes, has formed a sort of symbiotic bond with a piece of alien AI that was meant to take complete control of him. By the time he's done with it he's taught it free will and heroism, among other things, and there are hints that these things have been spread throughout the entire alien infiltration program.
 * The Reach commander Big Bad stubbornly refuses to believe that Jaime's simple heroism and good nature changed the Scarab and wastes valuable time and resources trying to find a more concrete explanation. His Dragon is able to believe it, and criticizes his boss for being in denial.
 * Subversion: all the aliens and powerful beings who have tried to "fix" Superman's silly humanistic tendencies have found that humanity is really, really hard to cure.

Fan Fiction

 * In the Buffy the Vampire Slayer fanfic Difficult to Fight Against Anger, after Anya confesses to Xander that she nearly did the vengeance thing on him, but couldn't bring herself to do it, Xander says humanity's rubbing off on her, to which her response is, "Yeah. Kind of sickening."
 * This is thoroughly explored in Claymade's Dark Lords of Nermia.
 * In Kyon: Big Damn Hero, this is the reason for the Integrated Sentient Data Entity's planned deletion of Yuki.

Films -- Animated
"Amalthea: I can feel this body dying all around me!"
 * The Last Unicorn uses this trope to horrifying effect by showing exactly what happens when you put the mind/soul of a pure, immortal unicorn in a base mortal human body.


 * Used again in a less horrifying and more tragic fashion when she falls in love for the first time. She almost considers giving up on her quest and marrying the guy. He convinces her that giving up isn't an option and that the quest must be seen through to the end.
 * Played tragically at the end. Despite rescuing the other Unicorns and returning to her true form, the ending is given a bittersweet twist as it's revealed her time as a human has left her with the unique (among Unicorns) ability to feel regret. Being the ageless kind of immortal, that means she'll have to live with the pain of her regrets and losses for a very very long time.

Films -- Live-Action
"T-800: I know now why you cry. But it's something I can never do."
 * The T-800 in Terminator 2: Judgment Day. Originally coldly robotic, its neural net processor ("learning computer") picks up human slang and attitudes from the Connors.


 * Even the T-1000 picks up a few mannerisms. At first, it's only using a personality in the process of better infiltrating humanity in order to kill John Connor. By the end of the movie, it likes to silently mock the protagonists' futility via Finger Wag and taking its sweet time to attack Sarah Connor for no other reason than For the Evulz.
 * Note that the T-800's chip had its ability to learn from its surroundings turned on by the Connors. In the director's cut, at least.
 * Starman doesn't quite make it all the way to human. His gait and mannerisms remain stiff and quirky, but emotionally, he gets it.
 * In Teenagers from Outer Space, reading a single human book is enough to convince the alien Derek to turn against his space-Nazi brethren and side with humanity.
 * Daybreakers does this literally:.
 * This is the entire premise of the film The Nines, wherein the protagonist
 * Avatar is an inversion: Jake finds that Na'vi-ness is infectious, and turns against his fellow humans to save the native population. The movie follows the structure of alien-invasion plots, but with the roles of human and alien reversed.
 * RoboCop is about a police officer who loses his humanity by becoming a cyborg only to later gain it back.

Literature

 * Terry Pratchett is fond of this trope.
 * In the Book Thief of Time,  has been a person for so long that she got a personality and joined the Good Side fighting her former "comrades".
 * Death himself has been shown to be particularly susceptible to this, going so far as to getting fired once for being too empathetic (by adopting Susan's mother), and almost turning human himself.
 * In the co-authored book Good Omens, this happens to the angel Aziraphale and the demon Crowley as well: Aziraphale becomes a little more lax about rules and when to follow them, while Crowly develops a bit of a conscience and takes a liking to humanity.
 * Mort shows that the inverse is also true for Death-
 * Men At Arms describes dogs as being wolves that have been "infected" with human traits, the good and the bad.
 * Throughout the series, many creatures are described as "almost human, really", such as a Troll who lends at 300% interest per month, or Dragons fighting to death rather than submission.
 * From The Dresden Files we have Lash,
 * In Proven Guilty, the Winter Lady Maeve expresses concern that her late counterpart in Summer, Aurora, fell victim to human concepts like "hearts, good, evil."
 * In Liz Williams' Inspector Chen series, one of Chen's friends is a demon who's developed a conscience from being around people too much. In the scene where this is first mentioned, he describes it as if it were literally something infectious he'd caught off humanity, and claims that the only reason he hasn't had it seen to is that as a minor public servant his health insurance doesn't cover it.
 * Literal (and quite unpleasant) variant in Isaac Asimov's short story Hostess.
 * A nastier-than-usual version in the Star Wars Expanded Universe: when the Killiks inadvertently assimilate Raynor Thul into their Hive Mind, they begin to value individual life—even though individual Killiks aren't particularly sapient and reproduce extremely fast. Next thing you know, they're trying to expand their territory like crazy, nearly precipitating a war with the Chiss.
 * In Animorphs novel Visser we learn that Visser One very nearly fell into this trap when she discovered Earth. And she had a partner, Essam, who fell into it completely. In varying degrees, there are any number of Yeerks in the main series who start acting and identifying more "human" than the Yeerk Empire would want them to.
 * This was the strategy used to defeat the Tyr in C.S. Friedman's Madness Season. The Tyr were a Hive Mind alien race incapable of knowing fear, since the individual lives were worthless, or compassion, since it was unable to comprehend sapience outside of itself. However, during one stage of Tyrrish development, it becomes separated from the overmind. The humans manage to get hold of one such adolescent Tyr and teach it the notion of individuality—even going so far as to give it a name, Frederick. The winning strategy is then to get Frederick into a position where he becomes the new Overmind, infecting the entire race with fear of individual mortality and compassion for outsiders.
 * In the Codex Alera, the Vord Queen starts to slide into this, ending up as an almost-Cute Monster Girl from the Uncanny Valley. It is strongly implied that the reason that she is acting so "human" is because Tavi accidentally bled all over the mound she was incubating in, resulting in an integration of human genetic material with Vord.
 * Morning Light Mountain over the course of Pandora's Star and Judas Unchained as an accident of uploading Dudley Bose's personality into its brain to learn about humans. Turns out this is a bad thing because Morning Light Mountain's inherent urge to expand get's augmented with things like hatred for all things not Morning Light Mountain.
 * This is a significant theme of Robert A. Heinlein's novels dealing with intelligent computers. It occurs first in The Moon Is a Harsh Mistress, when the computer Mycroft Holmes learns to be human (and enjoy it) through observation of those around him. Similarly, in Time Enough for Love, Lazarus Long expresses the opinion that the thing that turns a computer from merely a powerful machine into a fully sapient AI is The Power of Love—specifically, being loved and paid attention to by a human. This can then develop into full-blown Pinocchio Syndrome.
 * The Man Who Fell to Earth, both novel and film, plays the idea of an alien becoming more human as a tragedy: Thomas Jerome Newton starts as an innocent humanoid alien and ends up  thanks to human pastimes and relationships. The story averts Humans Are Bastards, but we don't come out looking too hot...
 * Averted in C. J. Cherryh's Foreigner series. The alien atevi experience no emotions which are forms of affection, and they never will, because which emotions an organism can experience are determined by neurological hard-wiring, and atevi don't have the hard-wiring for those emotions. Similarly, the atevi do have the alien emotion manchi, an emotion that humans will never be able to experience, no matter how much exposure they have to the atevi.
 * The Worldwar series by Harry Turtledove has cultural infectiousness going both ways. While we adopt lots of The Race's technology, and their practice of not wearing clothes and instead wearing body paint, and even their practice of calling things "hot," (similar to slang for "Cool,") we managed to introduce the Race to The Oldest Profession, drugs, and marriage. It's more difficult to see the contamination of the Race's culture, though, because of how slowly their society moves.
 * In the Starfleet Corps of Engineers stories, P8 Blue, an insectoid alien, finds that her belief systems are influenced by the humans she works with. She begins to find an interest in history where her people usually ignore it, and even feels slightly maternal towards her larvae, being a little sad when she drops them off at the childcare centre, never to see them again.
 * Deliberately averted in Isaac Asimov's Robot stories. Asimov disliked what he called "robot-as-pathos" stories, preferring to see robots as just highly complex and intelligent tools.
 * However, Asimov's novella The Bicentennial Man and the movie based on it arguably fit this trope.
 * In Ray Bradbury's The Martian Chronicles the Martians (who have psychic abilities of some kind) gradually become infected with human memories to the extent that their entire culture goes insane and is pushed to the point of extinction.

Live-Action TV
"Quark: I want you to try something for me. Take a sip of this. Garak: What is it? Quark: A human drink; it's called root beer. Garak: I dunno... Quark: Come on. Aren't you just a little bit curious? Garak takes a sip, wincing as he tastes it. Quark: What do you think? Garak: It's vile! Quark: I know. It's so bubbly, cloying...and happy. Garak: Just like the Federation. Quark: And you know what's really frightening? If you drink enough of it, you begin to like it. Garak: It's insidious. Quark: Just like the Federation."
 * In the Doctor Who episode "Dalek", this happened to the Dalek upon exposure to Rose.
 * The situation with the Dalek was kind of this trope with a dash of Humanity Ensues, since the Dalek started growing emotions as a result of having physically assimilated Rose's DNA, as opposed to just of hanging out with humans for awhile.
 * It has been theorised that this trope has happened with the Doctor to some extent, although given that his personality changes with each regeneration it's a bit hard to pin down exactly how much humanity has rubbed off on him.
 * Note that the above
 * Inverted when Rose's mother Jackie worried that Time Lordiness is infectious in Army of Ghosts, when she suggested that after she'd died that Rose would never return to her home time or planet and continue to travel with the Doctor forever having completely lost her humanity in the process.
 * This has actually happened to Daleks a couple of times. The first was the serial The Evil of the Daleks, in which they try to isolate the "human factor" that allows humanity to continually resist and defeat the Daleks. Those Daleks that are exposed, however, perform a Heel Face Turn and a civil war errupts.
 * More recently, the Cult of Skaro tried to do something similar and hybridize themselves with humans to discover why we are such great survivors, while their race is on the brink of extinction. The first Dalek to do so, Dalek Sec, also performs a Heel Face Turn, and is exterminated by his brethren.
 * Both Cat and Kryten did this in Red Dwarf.
 * Star Trek: The Next Generation - Hugh from "I, Borg" seems to fit this one to a degree.
 * Not just him. After he's returned to The Collective, his acquired humanity spreads to every drone on his ship, which is quickly severed from the rest of the hive-mind lest it cause a Galactic BSOD.
 * Seven of Nine from Voyager was also assimilated by individuality.
 * The holographic Doctor from the same show got encouraged, usually by Kes, to become more human, to the point where he's eventually more human than quite a few real humans.
 * In Star Trek: Deep Space Nine, Quark and Garak remark on this:

"Spock: At the moment, that is all we can do, except hope for a rational explanation. McCoy: Hope? I always thought that was a human failing, Mr Spock. Spock: True, Doctor. Constant exposure does result in a certain degree of contamination."
 * In Star Trek: The Original Series, Spock, as the Token Non-Human, occasionally makes reference to this:


 * There's a lot of this in Star Trek. After the normaly selfish "omnipotent" being Q from Next Gen spends some time as a human, he ends up sacrificing himself to protect the crew - and is given back his powers because of it. He then becomes more of a Trickster Mentor to Picard then an outright antagonist.
 * The whole premise of V is that the aliens, when living among the humans long enough, become disillusioned from their leader Anna and rebel.
 * Battlestar Galactica: The humanoid Cylon-models. At least, some of them.
 * Stargate Atlantis: Todd the Wraith became considerably more human during his imprisonment by the Genii.
 * Illyria from Angel has this as her main storyline, including the fact that she seems to feel that the ways of humanity are literally an infection. Angel and Spike, as well as Anya from Buffy the Vampire Slayer, are examples as well.
 * The longer Castiel hangs out with the Winchesters of Supernatural, the more human-like he becomes. Recently he was watching porn, which is especially odd considering he's an angel.
 * Delenn in Babylon 5 gets some of this after at the end of the first season/beginning of the second. She's eventually kicked off the Gray Council for exactly these reasons, even though there hasn't been a demonstrable change in her behavior at that point.
 * This is actually part of the reason that Humans Are Special in Babylon 5: Humans are empathetic, and therefore weave disparate groups into communities, with a common purpose. Babylon 5--a place where many species gather to live and do business with each other in (relative) peace and harmony—to say nothing of discuss their differences in a permanent, neutral forum—would have been literally unthinkable to another species. The smartest aliens are the ones who get this concept and sign on to it as much as circumstances allow: G'Kar for the Narn (who writes the Constitution of the Interstellar Alliance) is the greatest example, but Vir and even Londo, for the Centauri, come to accept it to a degree.
 * Stargate SG 1 has a great deal of this, most evidently seen with Teal'c. He eventually gets an apartment, trades in his Goa'uld-issued Staff Weapon for duel-wielded P-90s, and adores Star Wars to a somewhat unhealthy degree. When asked to come up with an example of virgin birth, the audience thinks of Jesus. His immediate answer? "Darth Vader."

Tabletop Games

 * An interesting example lies in the True Fae from Changeling: The Lost. One of their defining elements is that they cannot understand empathy; if they adopt emotions, it's merely the mask of an emotion, not something deep seated. Any True Fae that actually learns how to think like a human becomes a Charlatan, losing all memories of their existence in Arcadia and a good chunk of their powers as well. Problem is, such a state can easily be reversed...
 * Any emotion works, incidentally. Love does the trick, but one sample character became a Charlatan on connecting with the madness of a Serial Killer, and one spent so much time stalking his brother's killer with a knife, fueled by hatred for him, that he became a Charlatan and forgot why he wanted him dead. All he remembered was that the man did something terrible to him, so he just keeps stalking.
 * If by "Infectious," you mean that humanity is likely to virus-bomb your world until no life forms remain, than yes, Warhammer 40000 humanity fits. Otherwise, no. This humanity is not infectious.
 * Or looked at another way, humanity was infectious, but now the galaxy has been vaccinated.
 * Chaos actually pulls this off a little straighter, oddly enough.
 * A similar effect with the Alchemical Exalted, in that they typically start out with a relatively human outlook but become steadily more icy, ruthlessly efficient, and generally computer-like as their Clarity rises, until they become closer to machines than men. What's one of the easiest ways to bring Clarity down again? Simple. You interact with humans.

Videogames

 * A possible example occurs in World of Warcraft in Ulduar, where the raid group beats the tar out of Algalon the Observer and, in doing so, effectively cause him to feel empathy for the first time. He enters a recall order to a prior order he'd sent to have Azeroth scrapped by the Titans.
 * The Big Bad of Persona 3 grew empathetic to humanity through his time and, though he couldn't stop The End of the World as We Know It, offered SEES the chance to live out their lives in ignorance of it, so they wouldn't be afraid.
 * Also Aigis, who develops human emotions during her time with SEES and through her Social Link plotline with the protagonist.
 * A common occurance in Super Robot Wars, but most notably in Original Generation 2, where it happens to no less than four characters across two (and a half) different factions:
 * Lamia Loveless is both The Mole and a Ridiculously Human Robot. Since the protagonists don't know she's an Artificial Human, they treat her with a level of affection and familiarity her creator never did, and she starts to develop feelings for them that contradict her programming. In a rare case of the "infected" not being rejected, her villainous creator actually sees this as a miracle, repairs her after her Heroic Sacrifice, and helps her escape back to the heroes. Her "siblings" Echidna Iisaki and Wodan Ymir follow the same pattern of developing human traits,.
 * Einst Alfimi is an Eldritch Abomination in human form. She was created to be a soulless, emotionless replacement for mankind once they were wiped off the face of the universe. Unfortunately for the Einst, she was created from a sample obtained from the local Bottle Fairy and Manic Pixie Dream Girl, Excellen Browning. After several fights with the protagonists, she abruptly switches sides after hearing Excellen's love interest deliver a Patrick Stewart Speech to her boss.
 * The Elves in Dragon Age Origins were immortal, but became mortal literally through exposure to humans. Or so they say.
 * In Prototype, As he consumes people, he gains access to their memories and skills, but also appears to develop admirable qualities like compassion and love.
 * The Materials of the Magical Girl Lyrical Nanoha As Portable games are Humanoid Abomination created from the remnants of the Darkness of the Book of Darkness. They were supposed to be Omnicidal Maniacs like the Darkness of the Book Darkness was, and in the first game, they were. However, thanks to their interactions with the characters in said first game and their own budding sentience, they returned in the sequel a lot more human than before. Not only did they gain their own Dark Pieces, which are only formed when someone has their own hopes, wishes, and regrets, but they've also become individual enough for two of them to reject their original Omnicidal Maniac goal as something that is both obsolete and runs contrary to their new goals in life (i.e., making friendly rivals out of their former enemies).
 * The Puyo Puyo series has Ekoro, a Spacetime Traveller. In his first appearance, he only sees humans as silly and as something that gets in his way of crushing all exsistance in Puyo. By the time 20th Anniversary rolls around, thanks to a case of amnesia, he starts to learn about how to act and what is and isn't considered "fun". The hidden unlockable costume for him shows that he has a case of Humanity Ensues.

Webcomics

 * In Homestuck, the Trolls' first contact with humanity is conducted by sending death threats and harassing messages to the protagonists over the internet, but as both groups realize, several Trolls quickly and unconsciously begin adopting human mannerisms and figures of speech, even forming

Web Originals

 * One forum post on 4Chan was about how an alien race uses Memetic weapons, that is, weapons of ideas. It's considered a very serious weapon of war. They are outright horrified when they hear that not only is it legal on earth, but it's considered a game: whoever can spread ideas, or "Memes" the furthest wins. That's right, humans managed to weaponize their infectiousness. And they did it by accident.

Western Animation

 * Ben 10 Alien Force has this happen when he's stranded alone with a Highbreed in an Enemy Mine situation. The Highbreed ends up becoming less xenophobic than the rest of his kind, and ends up the Supreme in charge.
 * That Highbreed initially believies that due to this "infection" he no longer belongs with the rest of his kind, and opts to stay on that hostile planet.

Real Life

 * Domestication is essentially applying this to animals.
 * It's amazing the range of pets that show more self-awareness than non-pet members of their species. There are even reports of a pet crustacean showing playfulness uncharacteristic of its species.
 * This is not, however, the only mental difference between dogs and undomesticated wolves. Dogs are wolves that have been selectively bred to be a Slave Race.
 * Reports of children who've been Raised by Wolves suggest that this even applies to humans – being members of the species ''Homo sapiens" helps, but much of what makes us human is being raised by them.
 * But being infectious appears to be an inborn instinct, apparently evolved for childrearing but also incidentally applied to pets.