Interbreeding between ethnic groups within a race, or between multiple races in fantasy or science fiction, is a popular activity. But what happens when the resulting babies grow up and start breeding themselves? You might end up with a Heinz Hybrid, or just someone who's mostly A with a little bit of B.
Historically, the One Drop Rule assigned these people to the lower-status group. Someone in the American South who looked Caucasian but had a distant Negro ancestor would be classed as "black". On this wiki, the One Drop Rule expands to cover interracial as well as inter-ethnic lines of descent.
There are two features that must be present for a character to fall under the One Drop Rule:
- The character's "other" ancestry should be distant — a grandparent at the most recent.
- The character should be the target of bigotry/discrimination as a result of the "other" ancestry.
For example, Spock gets a lot of grief from Vulcans due to his 50% human family tree. But he's a Half-Human Hybrid, and would stay on that page instead of moving here. If Spock were to marry another Vulcan, his children and grandchildren note would fall prey to the One Drop Rule.
Compare to Half-Breed Discrimination (when there's more than just one drop) and Uneven Hybrid (when the one drop doesn't result in any discrimination) . Contrast to But Not Too Black. Revealing that a character falls under the One Drop Rule can result in a Pass Fail.
- In Fullmetal Alchemist, Major Miles is one-quarter Ishvalan from his maternal grandfather's side. During the Ishvalan Civil War, when Executive Order Number 3066 came down, stripping any soldiers of Ishvalan ancestry of their commission and imprisoning them, his superior officer Major General Olivier Armstrong disobeyed and kept him with her at Fort Briggs specifically because he offered that perspective. And despite only being a quarter Ishvalan, Miles has the two most distinct physical markers of the ethnicity in his white hair and red eyes, the latter of which he usually hides with tinted glasses.
- A parodic inversion in Blazing Saddles. When the foreman of the railroad gang says he wants "a couple of niggers" to check for quicksand, Bart points out that his grandmother was Dutch and therefore he wasn't entirely Black.
- Ellery Queen's The Roman Hat Mystery. The murder victim had turned blackmail into a career. Which secret drove one of his targets to kill him? The revelation that he had a distant Negro ancestor.
(He) has just a drop in his veins — just a drop, but it would have been more than enough ....
- In the story "The Color of Honor" by Richard Connell, a Klan leader discovers that his grandfather had an affair with a "mulatto" woman, but passed the resulting pale baby off as the child of his lawful white wife. That baby was the Klansman's father, and therefore he himself is a Negro! And as such, he must now fight against the Klan, as is only honorable.
- The original "one drop rule" kicks off the plot of Mark Twain's novel Pudd'nhead Wilson. A woman has enough white ancestry that she could have passed for white herself, but she's still confined to a life of slavery on a Southern plantation. She bears the plantation owner's son, who looks even whiter than she does — then she switches her son with the plantation owner's other, legitimate son, so that her boy can live a life of privilege.
- Brother Paul, the hero of Piers Anthony's Tarot series, is one-eighth black and looks white. Part of his pilgrimage in the Tarot series is a realisation of his black ancestry and how racists blighted the lives of his immediate ancestors - and how his adoptive parents held it against him. It comes to the fore in one surprising way: he finds himself alone and friendless in a black ghetto, facing down people who refuse to believe he has any black ancestry at all and who are prepared to treat him as a white boy in the wrong part of town. He has to prove his credentials, and does so by winning a rapping contest.
- Lampshaded and made a plot point in Sidhe Devil. The story kicks off with Doc being abducted for his seed because he's pure-blooded Daoine Sidhe and his half brother and step-mother, who are in on the plot, secretly aren't due to the one-drop rule.
Doc: I cannot imagine being so devoted to a matter of race that you would lie about it for so many years and suffer to conceal some wayward drop of blood in your ancestry.
- Laura from Sarny is only 1/8th black but has to hide that in order to get anywhere in the post-Civil War era. She's able to pass as white by just covering up her curly hair.
- In Agent Carter, the very white Jarvis is not allowed into a whites only social club because "[his] father was 1/8 Turkish."
- Invoked in one episode of All in the Family. Archie is recruited into a new social club that turned out to be a front for the Ku Klux Klan, and once he learns this he wants out. He eventually tells them he has "black blood"note .
Mitch: There's a whole lot of us, Bunker.
Archie: Well let me tell you there's a whole lot of us.
Mitch: "Us" who?
Archie: Us blacks.
- Mixed-race Bette and fully black Yolanda on The L Word discuss racial politics, and at one point Yolanda brings this up to tell Bette why Bette is still considered 'black'. Bette retaliates by asking if she's going to let White America define her identity.
- Dungeons & Dragons:
- AD&D's second edition went there with half-elves right in the Player's Handbook, where the children of a half-elf could only ever be a half-elf themselves or else essentially human with some cosmetic elvish features depending on the other parent, but never an actual 'proper' elf. This isn't even presented as prejudice (which could vary by setting), but just as biological fact.
- In 4th edition, the ancient, decadent Empire of Bael Turath made a collective Deal with the Devil that transformed them into the first generation of tieflings. While tieflings can interbreed normally with humans, the children are always tieflings, no matter how small a fraction of Turathi blood is in their ancestry; and those children get to experience the full gamut of distrust and prejudice that their "devil-tainted" pedigree attracts.
- In a more positive example - the sorcerer class. It requires one to have some sort of magical ancestry, but not necessarily to a degree of being a distinct "race" such as dragonblooded or aforementioned tieflings. One drop is enough to be able to get magical powers.
- Invoked in Show Boat. Steve is white, and his wife Julie is mixed-race, passing for white — their marriage was a crime in the South at the time. When someone tips the local sheriff off and he comes to arrest them, Steve quickly cuts Julie's hand and swallows her blood; when the sheriff arrives, he asks, "You wouldn't call a man a white man that's got Negro blood in him, would you?" He swears to having that blood in him, letting the sheriff assume this trope is in effect and Steve has been passing for white; the two are able to leave the boat, and the South, in peace.
- In the Dragon Age universe, the offspring of an Elf and a Human is always a human. There is absolutely no difference between an "Elf-blooded" human and any other human being, but being Elf-Blooded is considered a major shame. So much so that when it's discovered that an Empress's personal Champion is Elf-Blooded, she exiles him before the scandal can damage her political career.
- And as revealed in one of the novels, this is also one of the reasons it was considered important enough to cover up Alistair's maternity. His real mother is not only an elf but Mage and a Grey Warden, none of whom are liked in Ferelden, so he was raised to believe his mother was a castle servant who suffered Death by Childbirth. Especially since he can potentially become the King of the entire country, since his father was none other than King Maric.
- In Not Tonight, Britain is under the rule of a xenophobic far-right nationalist party, and large portions of the population have had their UK citizenship revoked because they have at least one non-British citizen as their parent or grandparent.
- In Fire Emblem: Path of Radiance and Radiant Dawn, anyone with even a single Beorc/Laguz relation in their ancestry can be born a Branded, who are looked down on by both races.
- In Gunnerkrigg Court, Antimony Carver stopped being considered a human when it was revealed she had a fire elemental in her ancient ancestry. Subverted, though, since both "sides" want to claim her instead of rejecting her. Furthermore, the waters are a bit muddied between this trope and Half-Human Hybrid as that ancestry doesn't get diluted - the fire passes wholesale from the mother to the (always only one) child.
- Virginia's "Racial Integrity Act of 1924" split Virginians into "white" and "colored". And then the lawmakers realized they had a problem on their hands — many of the Virginia elite claimed descent from Pocahontas, and as written this law would have redefined them as "colored". In the "Pocahontas Exception", a person who was 1/16th American Indian was legally considered white. (The same fraction of any other ethnicity classed you as colored.)
- Under Nazi Germany's Nuremberg Laws, a person with one Jewish grandparent was Mischling Second Degree, with limited legal rights. The SS was even stricter — if you wanted to join, you had to prove that all your direct ancestors going back to 1750 were non-Jewish. Depending on how long one considers one generation to be, this could involve proving Aryan ancestry back 8 or 9 generations. (But, given that the records used contained religion and not ethnicity, one could even have had completly Jewish ancestry and be classified as full "Aryan", if all your (distant) ancestors were converts).
- Northern abolitionists took advantage of this trope in the antebellum period. They would stage mock "fancy girl slave auctions", and gradually put lighter-skinned women on the "auction block" until finally they were showing off women who were outwardly pure Caucasian but had the necessary one drop of black ancestry to be classed as black in the slave-holding South.