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?"

— K, Men in Black

An undervalued human trait is empathy. We can empathize with just about anything (even a toaster!) given the right (or the wrong) conditions. 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. To a point, Heart Is an Awesome Power and humanity has that ring.

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 loses 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 a desire to Become a Real Boy. 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. When Humans Are Bastards, them being infectious would result in worse aliens.

Remarkably, non-humans never seem to leave much of a cultural impression on us. It's as if humanity itself were the perfect condition towards which all things in the universe naturally aspire, although the fact that in most cases humans (greatly) outnumber the non-human individuals may explain this In-Universe. More practically, it is difficult to write stories with alien cultures that aren't based on human cultures, so a story about the impact of an alien culture on human culture might leave the reader thinking 'Is that even really alien?' Stories where the cultural impact goes both ways aren't that rare, but typically have some form of Superior Species, where the non-human culture is naturally (and unarguably) superior. One disturbing inversion is when the alien culture is so alien and incomprehensible in its Cosmic Horror that it warps those humans who come into contact with it into insane monsters.

Compare Humanity Ensues: when a non-human is physically transformed into a human. They need not be happy, willing or even able to integrate. And Love Imbues Life, where the infectious aspect is sentience and (often) the entire human thought process.

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Examples:

• Literature
• Video Games

Anime & Manga

• After God: The real reason why IPOs don't leave forbidden zones isn't because they grow weaker in regular air, but because contacts with humans poison their mentality:
  • Orokapi not only took Obikawa's body, he turned into Obikawa and prefers to stay that way outside of IPO business. Eating Akio also made him think Yoriko is attractive, but friendship with Tokinaga is something he decided himself.
  • Alula seems to have grown attached to Shion just like Waka did and tends to criticize social norms. Her introducing human factors to other IPO was the reason others have decided to seal her away.
  • Despite being savvy regarding Gods being easily affected, Ahu'az ironically uses his cult members to combat own loneliness and only keeps alive people with nowhere to go.
  • Vollof has become a literal drug addict after being introduced to some. Orokapi had to poison him regularly to prevent him going berserk.
• Ronnie Schiatto of Baccano! got entirely bored of being an omnipotent, omniscient Eldritch Abomination after the Advena Avice incident in 1711, so when Elmer asked him to stick by Maiza as a human until the alchemist could learn to smile again, he took the opportunity. Maiza somehow wound up in the Camorra some two centuries later, and Ronnie learns how damn good it feels to be a gangster.
  Maiza: Ours is a demanding business, is it not.
  Ronnie: Do you wish you were still an alchemist?"
  Maiza:...No. No, I don't. There was a time when I regretted ever summoning you on that boat...but I do not for a second regret my place here right now.
  Ronnie: Hah...The same goes for me.
• In Bleach, Ulquiorra, before he dies, begins to understand the human concept of a heart, and maybe even become similar to humans.
• In The Disappearance of Haruhi Suzumiya, the consequences of Yuki Nagato learning to cope with emotions drive the plot.
• Dragon Ball:
  • Son Goku, the protagonist of the original series, would not have been the hero he became had he not been raised by Grandpa Gohan. Him getting Identity Amnesia as a toddler along with inheriting his mother's gentle heart probably helped.
  • Even Vegeta of Dragon Ball Z, the callous alien prince who wiped out hundreds of worlds and cared only about becoming the strongest in the universe eventually softened after he permanently moved to Earth, most notably settling down with a human wife and raising their half-Saiyan children.
  • And then of course there is Piccolo, the former Big Bad who was the solidified personification of Kami's evil and spite, who once wanted to take over the world...
    "Pathetic...to think that Demon King Piccolo would fall...protecting a child...I have been....contaminated...by you...and your father's decency...Gohan."
  • Fat Buu could also count. He started out as a destroyer of worlds and enjoyed nothing better than turning people into his snacks, only to renounce killing because of his friendship with Mr. Satan. True, Buu was told to destroy and kill by his creators and he didn't know better, but it can also be said that Mr. Satan taught him the value of life and gave Buu the moral guidance to become one of Earth's defenders.
  • This was lampshaded by Elder Kai in Dragon Ball Z: Battle of Gods as one of the reasons why Beerus didn't destroy Earth when he had no problem blowing up other planets.
  • In a negative example, the Nameless Namek became corrupted by the darkness of humanity which eventually forced him to split into two beings; Kami and the original Piccolo.
• 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.
• Meruem of Hunter × Hunter, who started out as an unfeeling monster, willing and able to kill anyone and anything for the slightest of annoyances against him. As he spends more and more time playing a fictional board game called Gungi with a blind girl named Komugi, whom he is never able to beat, he noticeably changes his views and takes major Levels In Kindness. In one of his final moments, he expresses the wish that he had been born human.
  • In fact, the entire Chimera Ant arc explores how human qualities being injected into a species that previously lacked them would affect it, for both good and ill. Though in this case this trope is somewhat zigzagged as the Chimera Ants haven't infected themselves with humanity so much as they have assimilated its qualities into themselves as part of their biology, which allowed them to gain traits of any creature their Queen consumed which altered their physiology when they are born.
• This is basically what happens to Fafnir in Miss Kobayashi's Dragon Maid. The modern day humans of Japan have rubbed off on him in a way that humans from back home never could have. For starters, humans here have no idea that dragons could exist, so they've been friendly to reasonably nonhostile; and he struck up an unexpected friendship with Takiya after Otaku culture proved to be rather attractive to him.
• In Negima! Magister Negi Magi, we see that this has happened to Fate Averruncus. It does help that he wasn't created to have a one-track mind like the other constructs before him.
• Some of the eponymous aliens of Parasyte start developing emotions, a sense of individuality, and even the ability to feel love after spending time on Earth and learning how to blend in with humans. The most notable example is Tamura Reiko, who spent a long time being an enemy to Shinichi and Migi. Her typical callous attitude towards human life and her alliance with the other Parasites in the area who aim to sustain themselves with human flesh initially leads Shinichi and Migi think she's uninterested in anything but self-preservation, but she displays a distinctly introspective and curious attitude, longing to understand her purpose and the reason she was born as a Parasite. She gets pregnant so she can perform experiments on the baby once it's born, but after her son comes into the world, not only does she never harm him, she actually forms an attachment to him; she quickly kills Kuramori when he dangles him over a steep drop and she dies during a shootout with the police soon after, which she easily could have avoided by fighting back, but chose to shield her son with her body from the gunfire. Before she succumbs to her injuries, she tells Shinichi that she never found the answer to the question of her existence, but she found the answer to another question, implied to be "Can I love?" She hands him her son and asks him to make sure a good human family raises him well — he agrees, and she dies with a smile.
  • Also notable is Migi's development. Although he tells Shinichi that he, as a Parasite, doesn't see the value in things like kindness, self-sacrifice, or love, in the final volume, when it seems that neither of them will survive their encounter with Gotou, Migi shouts at Shinichi to run for his life and leave him behind. Shinichi reluctantly complies, and with the last of his strength, Migi thinks to himself how happy he is that he failed in taking over Shinichi's brain when they first met, allowing the two of them to become friends.
• If you're watching a Pretty Cure season, and the Dark Action Girl decides to infiltrate the heroes' ranks to see why they've been foiling their master's plans, expect this trope to play at full blast by the mid-way point or towards the end, where at that point, they become a Defector from Decadence and join the Pretty Cure team as a Sixth Ranger.
  • This, in turn, makes how Regina is handled in Doki Doki! PreCure all the more interesting. Being the physical manifestation of Princess Marie-Ange's selfish half, she's not used to the feelings of love and selflessness and becomes physically pained whenever she experiences those emotions. So much that she begged her father, who previously disowned her for allying with Mana and the others, to take her back and give her his power just so she wouldn't suffer from those feelings anymore.
  • Likewise, this gets Zig-Zagged in Pretty Cure All Stars F, in regards to that movie's Big Bad. Supreme, wondering how the Pretty Cures were able to survive despite it making sure they were all defeated, split itself into two entities to infiltrate the surviving teams and find out where their strength came from. With Puka on Cure Prism's team, she plays this straight, being so touched by their compassion that she expressed regret in participating in the destruction of the world and helped the Pretty Cures save the day. Meanwhile, Cure Supreme on Cure Sky's team... doesn't, and even after her defeat, she questions why the Pretty Cures refuse to finish her off despite doing everything to warrant death at their hands.
• Queen Millennia: Yayoi Yukino and Daisuke Yamori (real name is Lar Ells Miyoux) are Human Aliens who've been watching Earth for 1000 years. Due to witnessing humanity's growth first-hand, they've eventually decided to oppose La-Metal's secret control over it, who still consider humans animals.
• 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 Space Patrol Luluco, this happens to Alpha Omega Nova, a Human Alien called a Nothingling because he literally has no emotions. Since Luluco loves him anyway, she releases a Care-Bear Stare that allows him to love her back.
• The Zentraedi race in Super Dimension Fortress Macross/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 led 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...
  • This trope is one of the strongest weapons humanity has in both the Macross and Robotech franchises. 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.

Comic Books

• Blue Beetle: 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.
• The Flash: 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.)
• Galacta: Daughter of Galactus: Galacta could be like her father Galactus and devour everything in sight, but she has too much compassion for the humans she lives alongside.
• Invincible: Viltrumites seem to be particularly susceptible to some kind of infectious humanity. Nolan Grayson/Omni-Man, the first envoy the Viltrumites sent to Earth to prepare it for annexation, quickly learned during the course of his heroics that while humanity can collectively be very brutal and monstrous, outstanding individuals can be endearing and amicable. He came to love one particular human woman and married her, and found that he could not deny his feelings for his wife even when he tried to suppress them in accordance with Viltrumite tradition.
  • When the remaining Viltrumites immigrated to Earth to breed and replenish their severely depleted ranks (because human and Viltrumite genetic code is so similar that the offspring of a human and a Viltrumite has complete Viltrumite powers), Grand Regent Thragg expected his people to maintain their imperious culture and not form attachments to the humans the Viltrumites took as mates. As he remained isolated on the Moon, Thragg noticed that more and more of the Viltrumites who mingled with humans began to accept human culture and behave in ways that showed attachment and care for their unwitting human partners and lovers. In issue #101 Thragg gives a dressing down to three Viltrumites who explicitly go against his repopulation plans; two of them, General Kregg and an as-yet unnamed male Viltrumite, explicitly express affection for their human mate or mates, explaining "To have someone care for you…to be able to think about them…the bond that forms [is] amazing. It changes everything, Thragg." (The third dissident Viltrumite, Anissa, both never wanted children in the first place and also thought the humans she had encountered to be inferior and dissatisfactory, so it's no wonder she would refuse to have a child with one of them.)
• Monstress: For thousands of years, Ancients had been having sex with humans and there had never been any resulting children. However, all that contact with humanity had been reducing the differences between humans and Ancients until a baby boom of Arcanic hybrids happened. Also, being with humans so often may be leading to the Ancients becoming weaker — the Sword of the East tells the Queen of Wolves that the Ancients have been losing power for 1000 years and are almost mortal now. Meeting a half-human Arcanic centuries ago is also a factor in Zinn being so different from other Old Gods.
• Spider-Man: The Lizard has always had loathing of humans as his hat, even all the way back to the '60s. And even HE found out that humanity was infectious when storyline events first destroyed his human alternate personality Curt Connors (leaving just "The Lizard") and then turned the Lizard back into Connors' human form (done to try and restore Connors, all it did was trap the Lizard in Connors' human form for the first time). While at first the Lizard was filled with complete loathing and disgust and went about the usual evil plans, being exposed to the different perceptions, vices, and interactions of humans made him slowly start to change his mind; by the end he wanted to remain human just so he could keep enjoying things like potato chips. It didn't give him any actual EMPATHY, but it made him realize that humans were not innately inferior scum.
• Superman: 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.
• X-Men:
  • One story had a nurse infected with a 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 first Nimrod (an extremely advanced Sentinel robot) was capable of shapeshifting and took up a human persona in between trying to eradicate mutants. It seemed to gradually be growing towards appreciating that life more than following its preprogrammed task. However, the character's trajectory shifted drastically after a change in writers.

Fan Works

• Invoked almost word-for-word in the Godzilla fanfiction Abraxas (Hrodvitnon) by Vivienne when assuring several of her human friends of San's Heel–Face Turn. Indeed, Vivienne acts as San's Morality Pet and possibly the first being in his Time Abyss-long life who's reciprocated his craving for approval from a sibling, and she sates his curious tendencies. San's telepathic voice is gradually changing with his Character Development, as seen with him picking up Vivienne's British accent.
• This is thoroughly explored in Claymade's Dark Lords of Nerima.
• In Demon In Fodlan, Goetia not only becomes a human at the start of the story, but his continuous interactions with the people at Garreg Mach Monastery and getting attached to a few characters has him starting to slowly developing emotions and empathy—something he was unable to do when observing humanity at a distance in the past. The problem is that for someone who was an immortal Demon, these new-found emotions start to conflict with his alien views that he has live by for so long. As a result, Goetia attempts to distract himself in order to avoid these conflicting feelings, to little to no success.
• In Deserted Distractions, Yami Bakura laments that this is the reason he's attracted to Tea; since Ryou is his host and likes Tea, he does too. This also comes into play when the group is sent to the Shadow Realm and a demon nearly overwhelms Bakura due to him retaining human senses and form.
  The trouble with being embodied was that it was so damn addicting. A paltry five years sharing some teenager's skinbag and he was already forgetting how to be spirit, how to be pure, undiluted essence. Physicality was a habit that was hard to break.
• 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 revealed to be the key plot to the real Big Bad in the Ben 10 fanfic series Hero High: Sphinx Academy. Where Alex revealed that she wanted it to turn it into a weapon to eradicate all of the aliens species that were created like they were in an attempt to "cleanse" the universe".
• In Kyon: Big Damn Hero, this is the reason for the Integrated Sentient Data Entity's planned deletion of Yuki.
• In the Mork & Mindy fanfic Mork and Mindy's Twenty-Fifth Anniversary, Mearth tells Mork that his Earth reports are changing Orkan society. The Orkans are becoming more accepting of emotions and Mearth expects that a motion to make marriage legal again may succeed.
• Played with in Silly but Killy where humans are replaced by Orks. The non-Ork crew of the Normandy come to act and think more like Orks over time. Except Wrex, but Krogans are rather similar to Orks to begin with.
• In Snippets of Sirin Shariac's life a recurring theme in chapters that focus on Bella or Kurikara, two Honkai beasts given sentience, is their desire and struggles to better understand human behavior and customs and slowly adapt to them.
• Suggested in A Thing of Vikings when Toothless observes that the dragons have begun to learn compassion from the humans, as if the dragons were still wild he would probably have been abandoned by the rest of his kind after the loss of his tail-fin as opposed to life on Berk where he has been given a chance to fly again. After over two years living with humans, Eret notices dragons developing a taste for ornamentation, such as Stormfly getting carvings on her horns in a similar style to human tattoos or another Nadder getting gold gilding on its horns after its rider started wearing earrings.
• In What You Already Know, at one point, Jacob Carter explicitly asks Selmak if he’s been influencing the symbiote to favour Earth; Selmak clarifies that he has, but only in the sense that bonding with Jacob has given him an insight into the Tau’ri that the Tok’ra as a whole lack.
• This is more or less Ulquiorra's view of the ponies in A Hollow in Equestria as he often regards them as being a corrupting influence on himself. With it being implied he's actually concerned by the possibility he might start to act like them if the corruption goes on long enough.
• In What if the Yeerks Were the Good Guys?, Temrash wonders if he's gone native; he started considering himself male after infesting Tom and keeps using human expressions.

Films — Animation

• Kubo and the Two Strings has the main antagonist, the Moon King, look down on humanity and human nature. When his daughter fell in love with and married the human samurai Hanzo and had a child, the Moon King went into a rage and his other daughters saw it as a betrayal of their godly aloofness. The Moon King then wanted to pluck out his grandson Kubo's eyes, this so he'd be unable to look into any other human's eyes and thus won't be able to empathize with them. Being blind himself, the Moon King thought that without human concerns, this would allow Kubo to become a fully immortal god despite his half human heritage. When Kubo rejects the Moon King, he retorts:
  Moon King: You want to be human? Then share their weakness. Suffer their humiliation. Feel their pain!
• 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.
  Amalthea: I can feel this body dying all around me!
  • 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. Yet oddly enough she feels she's gained something and actually thanks Shmendrick when he tries to apologize for what he's done to her.
• WALL•E has an odd variation where the humanity comes from the robot. Eve, the deficient robots, and even the human captain get more and more human-like by interacting with Wall-E.

Films — Live-Action

• Hinted at in Alien Nation. George Francisco's take on humanity:
  "You humans are very curious to us. You invite us to live among you in an atmosphere of equality that we've never known before. You give us ownership of our own lives for the first time and you ask no more of us than you do of yourselves. I hope you understand how special your world is, how unique a people you humans are. Which is why it is all the more painful and confusing to us that so few of you seem capable of living up to the ideals you set for yourselves."
• 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. The traits that convert him to their culture are actually the same ones used by humans in straight versions of this trope; the corporate suits and mercenaries he's surrounded by in the beginning are the ones who are callous and disinterested in the natives.
• Daybreakers does this literally: the best cure for vampirism is the blood of an ex-vampire.
• In Death Takes a Holiday, Death ends up liking the land of living, and would've probably stayed if he didn't have to go back and reap souls.
• Disturbingly deconstructed in Guardians of the Galaxy Vol. 2. Ego the Living Planet is a mighty celestial being who saw mortals, with their finite lifespans and mundane forms, as utterly disappointing. However, when he met Meredith Quill-Star-Lord's mother-he began to feel and understand mortal emotions like love for the first time. So he killed her by using his powers to induce a brain tumor. He feared that her making him think like a human would cause him to abandon his plans to assimilate all life into himself, and he couldn't allow a mere mortal to derail his life's work.
• This is what happened, more or less, in a negative sense, to Agent Smith in The Matrix series. Even in the first one, he should just be a program performing a function, but his behavior (negatively assessing humanity, seeing himself as 'trapped' in the Matrix with them, showing rage and sadism) is far more in line with a human villain, something, of course, he doesn't grasp in the least.
• In My Favorite Martian, Uncle Martin doesn't have a high opinion of Earth or humanity at the start of the film, but the longer he stays on the planet and interacts with Tim, the more he starts to embrace his own emotions and see the beauty around him. He finally realises something is up when he seduces Mrs. Brown to get the ship back.
  Martin: Feelings for an Earth woman? I need to get off this planet.
• This is the entire premise of the film The NIN9S, wherein the protagonist turns out to be a demigod who created the local universe and the humans in them, fell in love with his creation, and has been slumming it among them ever since to the point of even forgetting that he is a god.
• RoboCop (1987) is about a police officer who loses his humanity by becoming a cyborg only to later gain it back.
• 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.
• Terminator 2: Judgment Day:
  • The T-800. Originally coldly robotic, its neural net processor ("learning computer") picks up human slang and attitudes from the Connors.
    T-800: I know now why you cry. But it's something I can never do.
  • 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.
• Thor remarks during The Avengers that while the Asgardian people are Sufficiently Advanced Aliens, humanity has much to teach them about becoming a mature society.
• Inverted in the low budget British horror movie Xtro, which features a family man who gets abducted by aliens and converted into one of their species. The conversion process gives any human victim who undergoes it enormous powers over mind and matter, but also gives them a sense of Blue-and-Orange Morality which allows them to exploit and kill their formerly fellow humans.

Live-Action TV

• 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.
• Delenn in Babylon 5 gets some of this after literally becoming part human at the end of the first season/beginning of the second. She's eventually kicked off the Grey 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: Other than Delenn (who, besides becoming part-human, marries the very human Captain Sheridan as part of a (successful-in-the-long-run) project to join the Minbari to the human project of empathy), 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.
• Battlestar Galactica: The humanoid Cylon-models. At least, some of them.
• Buffy the Vampire Slayer: In the penultimate episode of Season 5, Glory freaks out when she realizes that the powers separating her and Ben are breaking down, causing her to gain his emotions and humanity. She pleads with her High Priest minion to remove Ben from her body for this reason, outright describing Ben as "infecting" her.
• Doctor Who:
  • 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.
    • Inverted when Rose's mother Jackie worries that Time Lordiness is infectious in "Army of Ghosts", when she suggests that after she dies Rose will never return to her home time or planet and will continue to travel with the Doctor forever having completely lost her humanity in the process.
  • This has happened to Daleks several 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 erupts.
    • "Dalek": This happened to the Dalek upon exposure to Rose 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 a while. It freaks out and self-destructs.
    • "Daleks in Manhattan"/"Evolution of the Daleks": 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.
• Farscape: John Crichton has this effect on most aliens who come into contact with him. The change is most pronounced in Defrosting Ice Queen Aeryn who notes after Talyn!Crichton's death, "He made me better."
• Kamen Rider:
  • Kamen Rider OOO: Ankh is initially quite mad over being forced to hang out with group of quirky people who won't leave him alone. He warms up to them over time, going from Token Evil Teammate to a Jerk with a Heart of Gold. When he rejoins the Greeed later on he finds them disgusting and empty.
  • Kamen Rider Ex-Aid: Working with her human colleagues at CR allows Poppy Pipopapo to evolve past her programming as a video game character, most obviously shown when she is able to ask what the Bugsters will do once they exact their revenge on humanity. Neither Graphite nor Parado are able to answer that.
  • Kamen Rider Build has an example of this trope backfiring spectacularly. Late in the series, The Hero Sento uses the power of Build Genius Form to "infect" Big Bad Evolto with human emotions. While he's overwhelmed at first, once Evolt gets used to them it actually makes him stronger, since the Rider System in this series is driven by emotions — and considering he was a Planet Eater before that happened...
    • The deconstruction continues with the fact that said emotions end up completely screwing over Evolt; more and more he prioritizes his sadism over his pragmatism, the latter being the reason he was so successful for so long earlier in the story, with it all accumulating in his final and total defeat.
• In Lexx, His Divine Shadow's means of prolonging his life by transferring his essence to human hosts ran the risk of permanently altering that essence. The risk was minimized by cleansing the hosts' brains before the transfer. His Shadow's latest host being improperly cleansed was a major plot point.
• Lucifer seems to not-so-subtly imply this of the divine beings who remain on Earth for a time. Lucifer, Mazikeen, even Amenadiel aren't immune to the charms of humanity. The longer they stay, the more their personalities develop outside of their former position in the heavenly hierarchy.
• Both Cat and Kryten did this in Red Dwarf. Interestingly, Cat, as an evolved housecat, started as utterly self-centred, but being around humans taught him to (occassionally) have compassion for others. Kryten, as a service mechanoid, started as utterly selfless, but being around humans taught him to think of himself sometimes.
  Kryten:Don't you think I'd love to be deceitful, unpleasant, and offensive? Those are the human qualities I admire the most!
• On Resident Alien, an alien kills a doctor named Harry Vanderspeigle and then assumes his form. As he begins to interact with humans, he starts feeling a range of human emotions that he never felt as an alien, as his people don't have those emotions. He comes with a secret mission to Kill All Humans and spends most of the first season searching for his lost device to do so. However, by the finale when he's recovered it, he finds he's having problems bringing himself to activate it, and is taunted by a hallucination of the corpse of the human Harry, who tells him he's been infected with humanity. When he then uses a targeted form of the device's effects to vaporize the corpse, a bit of it comes into contact with him as well and gets messed up. He realizes that if he remains on Earth when the device goes off, then he will die as well.
• Stargate:
  • Stargate Atlantis: Todd the Wraith became considerably more human during his imprisonment by the Genii.
  • 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."
  • This also happened to Selmak, the Tok'ra Jacob Carter played host to. While once their most respected member, the other Tok'ra started to reject him out of the belief that Jacob's influence was making him more sympathetic to the Tau'ri than his own people.
• Star Trek: The Next Generation: Hugh from "I, Borg" seems to fit this one to a degree. And 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 Star Trek: 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 the Star Trek: Deep Space Nine episode "The Way of the Warrior", Quark and Garak remark on this:
  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.
  • It even becomes obvious in later seasons that constant exposure has made Quark a much... softer Ferengi, who then transmitted the disease of humanity to the Grand Nagus (by way of Quark's mother), who then spread it to the rest of the Ferengi by the end of the series.
    • Quark's brother Rom spreads it even further when he becomes Nagus himself.
• In Star Trek: The Original Series, Spock, as the Token Nonhuman (well, half-human), occasionally makes reference to 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.
• There's a lot of this in Star Trek. After the normally 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 than an outright antagonist.
• The longer Castiel hangs out with the Winchesters of Supernatural, the more human-like he becomes. In one episode he was watching porn, which is especially odd considering he's an angel, who in their true forms are Energy Beings with No Biological Sex. Although when he becomes human (a few times) he is unhappy to be Brought Down to Normal, he never loses his love for humanity and his admiration for them to the point where he no longer fits in with his own kind.
• The whole premise of V is that the aliens, when living among the humans long enough, become disillusioned from their leader Anna and rebel.

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.
• 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.
• Akash'Bhuta in Sentinels of the Multiverse spends most of human history alternating between murderous rampages with an end goal of killing all of humanity and spending decades or centuries recovering from her defeats, but once she's forced by circumstances to reincarnate in the more humanoid shape of Akash'Thriya and spend time with the Naturalist, she rapidly moves into more antihero territory, even being willing to sacrifice herself to help the people of Megalopolis - the kind of big city that she would usually attempt to obliterate.

Theatre

• In Pokémon Live!, thanks to Ash's memories, MechaMew2 gains sentience and the ability to talk.

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 they have to work together against a common foe, several Trolls quickly and unconsciously begin adopting human mannerisms and figures of speech, even forming romantic obsessions with the kids. This gets flipped around later on when the humans also start to take on troll mannerisms after a while.
• A peculiar variant occurs in Kevin & Kell: When the animals think too much about humans (most of them not even believing in humans), they lose touch with their instincts. In that sense, they become more humanlike. But this may be significantly less true now that the two worlds have their population balance restored, most of the time.
• In Ow, my sanity, Nancy experiences human emotions once she takes human form. Her distastes (such as jealous feelings towards someone making a move on David) and her desires quickly start to mould her behaviour.
  Nancy: I want to 'like' more things.
• In The Sanity Circus, one of the Scarecrows forgets what it is and associates with humans instead, given its (seeming) human form. Not only do they act like a human in practically all ways,butwhen reunited with the other Scarecrows they tell them that they don't trust them and see them all as monsters.
  Ah. What a very... human answer.
• Saturday Morning Breakfast Cereal: Invoked and inverted in the comic for 2013-12-05, where a boy is supposed to teach a robot humanity but instead decides to emulate its emotionlessness to escape the sadness of his life.
• In General Protection Fault, the Gray Euler says that the fact Planck and Pi are considering defying the Great Skaboola shows they've been tainted by contact with humans and their ideas of individuality. Pi retorts that every Gray who has come into contact with humans has become more of an individual, Euler included, and this is a good thing. (It's worth noting that Euler's insistance on obeying the heirarchy is based on the assumption that the Skaboola is himself unquestioningly following the orders of the Grand Protruberance, who himself is obeying the Supreme Fu. In fact, the Skaboola has also been "tainted" to some extent, being quite prepared to bend the rules to acquire Earth cheese, and the Protruberance thinks he's incompetent.)

Web Original

• 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 (and valid method of advertising): whoever can spread ideas, or "Memes" the furthest wins. That's right, humans managed to weaponize their infectiousness. And they did it by accident.
  • On a slightly different note one of these "Humanity Fuck Yeah!" stories — one of the few that doesn't involve fighting as these were collected from the tabletop games section of Reddit — has humanity becoming the cultural center of a galactic alliance: we meet some aliens, we like their style, and soon the aliens are wearing the human-versions of their own uniforms and the rest of the galaxy looks to Earth to tell them what's hot and trendy.
• Happens in The Salvation War, (chronologically) first with Michael (yes, the archangel), and later with the demons, once we beat them up hard enough that they're ready to sit there and pay attention.
• Prevalent in The Jenkinsverse, in which human customs, language, and even inventions prove to be popular among the other races, especially the Gaoians. Among other things, human terminology is very commonly found among those who interact with humans.

Western Animation

• Ben 10: Alien Force has this happen when he's stranded alone with a Highbreed in an Enemy Mine situation. The Highbreed, Reinrassic III ends up becoming less xenophobic than the rest of his kind, but ends up believing he has been literally "infected", and opts to exile himself on the planet.
  • He eventually ends up realizing the error of his species' way, and becomes their leader, playing a major factor in their Heel–Face Turn.
• Swap "human" with "pony" and you've got what happened with Discord in My Little Pony: Friendship Is Magic. Just being befriended by Fluttershy was enough to make this otherworldly monster of chaos to try his earnest ("most of the time") to be a good guy because he had come to value their friendship and, in turn, began to understand empathy and affection. The other villains even comically miss the point by describing The Power of Friendship as some manner of Mind Virus, reminiscing about how great of a villain he was before "friendship ruined him."
• Scavengers' Reign plays with this trope. Robot Buddy Levi starts the series as a nonsentient appliance that's little more than a smartphone with arms. But interfacing with a mould species native to Vessna makes it slowly gain sentience. By the end of the series, Levi is significantly more human-like, but this change is not because of humanity's influence.
• Solar Opposites: Subverted, Korvo wants to get off Earth as quickly as possible while Terry at least tries to assimilate with humanity. Both are still learning and are quick to misunderstand basic human mannerisms or use their technology in the wrong way.
• Parodied in the South Park episode "Trapper Keeper". A robot named Bill Cosby is sent back in time to hinder Cartman's Trapper Keeper from destroying humanity. He seems to succeed by explaining the situations to the protagonists and destroying the Trapper Keeper. However, Cartman decides to let his mother buy him a new one. This time, he decides to shoot him but Stan, who would have liked to do that, is stopped by the robot for this reason:
  Robot: I'm afraid I can't. I'm starting to actually feel what you humans call compassion. It's an amazing feeling.
  Boys: [disappointedly] Awww...!
• Happens eventually to Peridot on Steven Universe, and presumably happened to the Crystal Gems millennia ago. In this case, it wasn't just humanity but the appeal of Earth in general that's infectious.
  I think you're all insane!
  But I guess I am too.
  Anybody would be,
  If they were stuck on Earth with you.
• Fixit from Teen Titans (2003) decides to "help" Cyborg by removing his human parts which he perceives as weak points on his mechanical body. It's not until he downloads Cyborg's memories and sees life through the eyes of a human that he realizes how wrong he is and releases Cyborg.
• Just like in the comics, this happens with Blue Beetle in Young Justice (2010). However, it's implied that Jaime was able to spread humanity to the scarab because the scarab malfunctioned and couldn't communicate with the rest of the scarabs.

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 Servant Race.
    • Interestingly, there is a theory among some scientists that the fact the humanity domesticated dogs so early in our development had a significant impact on our evolution, so it's possible that the inverse of this trope may also be in effect, albeit to a lesser extent.
    • Research suggests though that 'friendly to humans' behaviour is actually genetic, rather than learned.
    • To what extent? Bears, raccoons, wolves, and other species have been known to show such behavior without any genetic domestication. Though there's been divergence since then, modern dogs originate with the practice of keeping tame wolves.
  • Dogs do not naturally give or receive social cues with their eyes, relying instead on body language and vocalizations. Domesticated dogs have learned to watch the eyes of humans for social cues, and might even be learning to give eye-based social cues themselves.
    • Despite this, it can be shown that many dogs aren't as smart as wolves because they never learned to hunt and, thus, never learned to be creative or adaptive. Being trained and being taught skills are two different things. However, seeing-eye dogs, drug hounds (and some attack dogs pulling double duty), certain show dogs, and some hunting dogs are probably more quantifiably intelligent than even the most wily of wolves as these animals are taught how to make judgment calls instead of just blindly obeying orders, so it balances out.
  • For a specific example, meet Christian the lion. His human owners hugged him so he learned to hug back. After being released to the wild Christian would hug the other lions, a behavior not normally seen in the species.
  • 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.
  • Adult cats in the wild almost never meow at each other or other animals. Domesticated cats, however, learn very quickly that humans are more responsive to sounds than body language and are thus far more vocal than non-domesticated cats.
  • Related to domestication is neoteny, in which humans have bred animals to retain juvenile characteristics, including cats and dogs. Another example where humans also seem to have done this to themselves through sexual selection: Modern humans never develop the heavy brow ridges and thicker skulls that earlier hominids grew as adults.
• The idea behind memetics (as in Memetic Mutation) is that ideas are infectious.
• Washoe was a female chimpanzee raised in captivity and one of the first to be taught hand signs. Later, other chimps around her learned some of the signs from her.

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