Prior to the days of DNA testing, it was basically impossible to verify a child's paternity. The only evidence, besides the word of the mother (who might be lying, or might not know herself in the subtrope Who's Your Daddy?), would be Chocolate Baby or other forms of Uncanny Family Resemblance, whether to the putative father or the other man. A piece of knowledge embedded in such proverbs as, "It's a wise child who knows his own father," the legal Latin "mater semper certa est" (with an implied: "pater semper incertus"), and "Mama's baby, Papa's maybe."
This can be a source of tension and drama even when the mother is honest, because neither the child nor the father can prove it. The Green-Eyed Monster is very prone to doubt. It can also complicate Heir Club for Men, as the man usually wants his heir to be his biological descendant. If the mother refuses to tell, only men who have actually slept with her can even guess, and speculation tends to run wild.
A powerful force behind My Girl Is Not a Slut and Nature Adores a Virgin in Real Life, because exclusive sexual access to "his" woman used to be the only way for a man to be sure that her children were also his. To what extent there is reason to doubt in real life is not known; numerous urban legends claim a high percentage of babies are attributed to false fathers, but the location of the studies determining this tends to migrate a lot.
Why Luke, I Might Be Your Father is a trope.
A trope limited to historical settings nowadays, as Daddy DNA Test is the Trope Breaker (unless the potential father is one of a pair of identical twins or clones, or testing is impossible for some reason).
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Anime and Manga
In Anatolia Story Lady Güzel, a princess who had once been Kail's lover, insists that he's the father of her child. Because Kail's inline for the throne and having an heir would be beneficial to him, there is a lot of pressure for him to accept the child as his own... but Kail himself knows that it's impossible that he's the boy's father, because he and Güzel haven't seen each other for years. It turns out Güzel had been brainwashed by Kail's Wicked Stepmother Nakia into lying about her child's parentage. Upon being woken up, she readily admits that the father was a wandering ministrel, and that the idea that Kail was the father was preposterous.
Also, Nakia finds herself in such a situation later. As she loses power, people begin to gossip more and more openly about how they think her son Juda is actually Urhi's son with her; the fact that Juda and Urhi have exactly the same hair color and that Urhi is the person closest to Nakia really don't help matters. It turns out Juda really is the king's legitimate son: Urhi is a eunuch and was castrated quite a while before he even met Nakia.
In Fruits Basket, while a young Tohru is at her own father's funeral, she overhears her relatives speculating that Katsuya Honda wasn't really her father, and that her mother Kyouko just had an affair. Their only "evidence" for this was that Tohru didn't particularly resemble Katsuya, and that Kyouko had, years and years ago, been in a biker gang. Hearing this spurs Tohru to begin to speak very formally (something Katsuya was well-known for doing), to try to convince others that he really was her dad.
The female shogun Yoshimune from Ooku invokes this trope in pondering what a patriarchal Japan would look like. She thinks that matriarchy has a distinct advantage because of it. This may influence Yoshimune's later choices in how to handle her Royal Harem: she spends equal time each week with her primary male concubines, interspersed with one-night-stands with servants. Thus, when she becomes pregnant, none of them can argue when she names the most malleable candidate as the father.
In one story of Tomie, the baby of a family grows up to be a creepy child version of Tomie, who naturally resembles and acts like no one in the family. The father accuses the mother of having an affair because of this, especially when he finds out that a wealthier family apparently has a child who looks the same. The mother, meanwhile, maintains that the child is his and that she did look like him when she was an infant. Actually, there are several child Tomie's running around because a creepy guy injected the babies with Tomie's blood.
In the Child BalladGil Brenton, the hero accepts the heroine's story of how he got her pregnant, but the ballad ends with magical writing on the baby's body affirming that he is in fact the father, to doubly avert this trope.
The Basque ballad Pello Joxepe tells of a man refusing to acknowledge his son as such.
"Johnny Be Fair" is a joke that got turned into an Irish ballad. Buffy Saint-Maire and Debra Cowan both sang versions of it. The song tells of a girl who wants to marry, but all of the young men who propose to her turn out to be her father's bastard sons. In the end, she goes to her mother in despair, and her mother sets her straight:
My mother said “If your father knew,
It’s me he’d surely kill,
For your father’s not your father,
So marry whom you will.”
In Savage Dragon, Dragon's then-girlfriend was pregnant. Since she was a past prostitute and there was a subplot at the time indicating that she might've been cheating on him (she wasn't), the first words out of his mouth were "Is it mine?," which upset her a great deal. He ended up apologizing, she ended up forgiving him, and the baby ended up being his, leading to the boy becoming a hero years down the line.
In Watchmen, Laurie is aware that her mother's husband is not her father, but her guess at the actual father is off, and when she finally realizes the truth, she's shocked and horrified.
In Peter the Fool, the king goes to investigate how the princess came to be pregnant. The baby recognizes the man responsible — by wishing her to be pregnant.
In the folktale The Snow Child, the husband claims to be taken in by the fantastical story his wife tells about how the child came to be conceived without a father, always involving snow. Then, later, he sells the boy as a slave and tells his mother that he melted.
In The King of Erin and the Queen of the Lonesome Island, the queen of Tubber Tintye finds herself with child, and has to hunt around to find out who the father is. When she tracks down the father, she forces the knowledge from the queen of Erin that her sons were in fact the sons of the gardener and the brewer.
In The False Prince and the True, a youth on trial for striking the prince reveals that he is actually the king's son from a secret marriage, whereas the prince is actually a quarryman's son, passed off as the king and queen's because the queen feared the king's wrath.
This trope is averted/inverted in Dodes'kaden by Akira Kurosawa with a local woman who has five children. The children tearfully ask their mother’s husband, their alleged father, about the rumours saying they’re not his children; he tells them he is if they say he is.
The Painted Veil (2006): "Am I the father?" "I don't know."
The blonde discovers she's pregnant and goes confront her husband: "Are you sure it is mine?"
In the Odyssey, Telemachus wonders about this — a doubt that no one else expresses — because he wonders if he is a worthy son of such a father.
In Jane Eyre, Mr. Rochester's ward is the daughter of his one-time mistress, who sent him the baby after he had dismissed her when he learned she was unfaithful to him. She said the child was his; he assures Jane he has his doubts.
In Sharon Shinn's Jenna Starborn, a retelling of Jane Eyre, Everett Ravenbeck also has a ward of unknown paternity born to an erstwhile mistress — he tells the title character that he never had the child DNA-tested, much to her surprise.
In Madeleine L'Engle's The Love Letters, Charlotte fled to Portugal because when she told her husband she was pregnant, he had asked her who the father was when he was.
The Jungle has, as part of Jurgis's Trauma Conga Line, his wife Ona tell him that she was raped by a businessman and she's been going to him for conjugal visits to ensure financial security for the family and also that she is pregnant. From what is narrated of their miserable bedtime experiences, they are most likely not having sex and if they are, then it is not very often. Therefore, there is the chance that Ona got pregnant from her visits with Connor. However, Jurgis never makes any comment on the paternity of the child.
Becomes an issue for two characters in Larry Niven's The Integral Trees and The Smoke Ring. After one female character is used as a Sex Slave, her husband can't accept her child as his until learning that the child inherited a respiratory problem from Mom's husband/his true father.
In Edgar Rice Burroughs's Beyond Thirty, the British Isles have "retrogressed" — there are tribes that did not have a word for father, and other tribes where they are aware of fatherhood, but practice matrilineality because of this trope. The heroine tells the hero not who her father is, but whom her mother once told her was her father.
It appears that the line of descent is through the women. A man is merely head of his wife's family—that is all. If she chances to be the oldest female member of the "royal" house, he is king. Very naively the girl explained that there was seldom any doubt as to whom a child's mother was.
Inverted in Wicked, in which Elphaba isn't sure if Liir is her son or not, because she'd been unconscious at the time he was born and no one would tell her if she'd given birth during that time or not.
Although Played Straight with her sister Nessarose, who her father suspects is not his. Turns out it's true about Elphaba, too, with a different father than her sister, though.
the issue of both claims is resolved by sequel books, where Liir's daughter turns up green, confirming Liir's parentage at last and the family tree confrims that Nessarose is indeed Frexspar's child
In L. Jagi Lamplighter's Prospero's Daughter trilogy there is considerable speculation about Caliban's father. At the end, he has one question, and uses it to confirm what the evidence points too.
In Angie Sage's Septimus Heap novel Magyk, Sally is convinced that this trope explains why Jenna doesn't look like her family. Fortunately. In reality, Jenna's a foundling, and they must hide her origin.
In the Chivalric RomanceOctavian, the emperor's wicked mother accuses his wife of infidelity and claims her twin children are not his.
In some forms of the Chivalric RomanceThe Swan Children, a woman taunts another woman with infidelity because she had given birth to twins; later, she gives birth to seven children at once, and her mother-in-law taunts her with the same "proof" and exposes the children, although she has not been unfaithful.
In Marie de France's Le Fresne, a woman taunts another woman with infidelity after she bears twins; then she bears twins herself, and unable to prove her innocence, exposes one daughter.
In L. M. Montgomery's A Tangled Web, a woman never named the father of her illegitimate baby. When one couple separated the night of their wedding, some of the speculation was that he confessed to being the father.
In Ovid's Elegy XIII, he invokes Isis and Lucina to save his mistress, Corinna, after an attempted abortion; during the course of it, he admits that the child may not be his.
Jacky invokes this trope in Under The Jolly Roger. She knows she's shortly to be deflowered by Captain Scrogg, so she decides to sleep with Robin. Her reasoning is that if she becomes pregnant, whoever the father is, she'll be able to tell herself it's Robin's baby and be able to love it the way it deserves. It doesn't work, but neither does Captain Scrogg's Attempted Rape, so it all works out.
From the start there is speculation as to whether the father of Isabelle's children is Charlie or her husband in The Thirteenth Tale.
This is the backstory of one of the characters in Mercedes Lackey's Magic's Promise; when the kid was born early and looked like neither his mother nor his father but exactly like his maternal uncle, his father assumed the very worst, and took it out on both mother and child. Particularly awful because there was a way to check; the father just didn't want his suspicions confirmed. The boy was simply born prematurely, and wasn't the uncle's.
In Gene Stratton Porter's The Song of the Cardinal, with some Fridge Logic. The father cardinal suspects an egg was laid by an interloper and the mother knows it for her own. Except, of course, her actual egg could have been tipped out of the nest by a brood parasite — avian mothers would not have the certainty of a mammalian one.
This could be said for George R. R. Martin's A Song of Ice and Fire. There is a succession struggle after the current king's death due to this trope (His wife Cersei having indulged in Twincest but nonetheless claiming the children are her husband's).
A lesser, but telling, example can be found with another Lannister. Genna Very-Reluctantly-a-Frey née Lannister may have pulled this as a protest, if her two nephews are right in their suspicions. A family tradition with Lannister girls when unhappily married off, perchance?
Also inverted in the person of Jon Snow. Though he is an Heroic Bastard, his father, Lord Eddard Stark, adopted him and raised him alongside his trueborn half-siblings. Additionally, it has not been revealed who Jon's mother is; though a number of characters have provided Wild Mass Guesses of their own, none of them line up with the fanon conjecture, and the sole character who can confirm any of these preductions, Howland Reed of Greywater Watch, has yet to appear "on-screen."
In Robert A. Heinlein's Time Enough for Love, Lazarus Long time-travels to his own childhood, with a story about having been a foundling. The family resemblance, combined with the backstory Lazarus (going under the name "Ted Bronson" at that point) provides, leads his mother Maureen and her father Ira to conclude "Ted" is the illegitimate child of Ira's late brother. Later on, Maureen admits to Lazarus that her father thinks it a good deal more likely that "Ted" is Ira's own son.
In Poul Anderson's The Man Who Counts, one set of aliens holds another in contempt because they breed in a blind frenzy after their migration, and children's fathers are unknown. (The other set holds the first in contempt for breeding all the time, like fish.)
Aunt Dimity: This figures in the Backstory of Kit Smith, but it isn't revealed until many years after the fact. The truth his father was neighbour and family friend Christopher DuCaral is actually something of a relief, since Kit thought insanity ran in his genetic heritage and refused to marry anyone to avoid passing it on. On confirming the news, he goes to his long-time love Nell Harris, helps her down from her horse at the riding school, and kisses her.
Barrayar in Lois McMaster Bujold's Vorkosigan Saga is only acquiring the tests in the middle of the saga. Early, Cordelia shocks her father-in-law by pointing out that paternity is uncertain; a major plot in A Civil Campaign revolves on the revelation of, several generations earlier, a count's heir actually being another man's child — a Cetagandan's child — and in Captain Vorpatril's Alliance, Ivan observes that testing is turning up more and more Cetagandan blood, people being only human.
In Dorothy L. Sayers's Lord Peter Wimsey novel Strong Poison, a servant talking about the infamous aunt and actress, says that her marriage was just a sham, and there's no knowing who the father of her two children were.
In I Shall Wear Midnight, Tiffany's father attributes the abusive Mr. Petty's anger towards Amber (without excusing it) to this trope.
In Julie Kagawa's The Iron King, Meghan is deeply distressed to learn that her mother's husband, who vanished when she was six, was not her father. (Though her father knew.)
In Ladylord, the baby Sen-Ya is believed to be the long-desired son and heir of First Lord Yassai, but is not actually Yassai's son. Yassai is mostly impotent, and to get pregnant, the concubine who gave birth to Sen-Ya visited the dungeons as an anonymous lady of the court and had sex with one of the prisoners (as the guards seem to indicate ladies of the court not infrequently do). Yassai assumes that the second part of Sen-Ya's name is to honour him, but it's actually from the prisoner.
The Last Dragon Chronicles: When Liz starts to explain all about Arthur, the first conclusion is that he is Lucy's father. Wrong. Liz quickens an egg, it hatches, Arthur comes home and she's nursing a newborn. His conclusion? She cheated.
A non-human example in Harry Turtledove's Worldwar series. The Race have a mating season, during which their females start producing pheromones that drive males crazy. A male's mating display (raised crest) drives a female crazy, and they proceed to do it anywhere they happen to be at the moment. The concept of family does not exist, and hatchlings are raised (or, to put it better, domesticated) communally by females. Any other time of the year, they don't think about sex at all. The same is true by the other two races conquered by the Race: the Hallessi and the Rabotevs. They are disgusted when they learn that humans mate year-round and form permanent bonds. However, since ginger causes females to temporarily produce pheromones, some members of the Race have also started to have regular sex, and normal male-female friendships evolve into permanent bonds and raise their own hatchlings, although this practice is considered obscene by the majority. On the other hand, The Emperor has a harem of females kept away from any other male specifically for the purpose of having an unbroken dynastic line. This has worked for over 50,000 years.
Mentioned in Anne Rice's The Queen of the Damned in relation to the Great Family that descends from Maharet, who had a daughter before being turned into a vampire. Maharet has spent millennia tracking and protecting her descendants. However, she only tracks the matrilineal descendants due to this trope, even in modern times when DNA testing can be done (the book was written in 1988).
Live Action TV
Happens practically Once an Episode on Maury. "You are/are not the father!" is a preferred Catch Phrase of the titular host, who invites couples on his show to do DNA tests to see if the man in question is the father of a child or not. It gets to the point where women have had to come back several times to try and find out, including one woman who came on the show eighteen times without success.
An episode of Sanford and Son has an old friend of Fred's claim that he had a one night stand with Elizabeth and that he's actually Lamont's father. Another friend of Fred's actually says the trope name verbatim. In the end it turns out that the guy actually slept with Aunt Esther, and thought it was Elizabeth in the dark.
On Two and a Half Men, Alan's ex wife Judith had a daughter with her current husband Herb. Alan, however, suspects he might actually be the father, after he and Judith had a brief tryst while she and Herb were separated.
On My Name Is Earl, this comes up more than once. The first time is when Joy is pregnant (for the second time, having been visibly pregnant already the night she met and married Earl), and Earl thinks the baby is his...but she has been sleeping with Darnell, and the truth comes out 9 months later. It comes up again with her first child, Dodge. In what turned out to be the final episode, Earl learns that Joy has never told Dodge that Earl is not his biological father, prompting Earl to seek him out on Dodge's behalf. After discovering a likely candidate (a man whose wealth and connections could improve Dodge's life if they were to develop a relationship) , Earl has Dodge's DNA tested and finds out that he himself is Dodge's biological father. He just didn't remember Joy, whom he had casual sex with at a costume party when she assumed he was the other man. Earl also finds out that Earl Jr. isn't really Darnell's, as was previously thought.
An episode of House plays with and lamp-shades the gender double-standard of the trope when the title character tries to do a Daddy DNA Test on Taub's kids (from simultaneous pregnancies with the two woman he had been seeing). After a moment of weakness, Taub shreds the results without looking.
The Doctor Who episode "A Good Man Goes to War" plays with this trope, repeatedly and rather clumsily attempting to cast doubt on the paternity of Amy's baby.
The answer: it IS her husband Rory's, but because the baby was conceived in the TARDIS, she is also a Time Lord.
In season 9 of Stargate SG-1, Vala, while trapped in the Ori galaxy, gets married to cover up the fact that she got pregnant out of wedlock. The truth does eventually come out, though: the Ori impregnated Vala with the Orici, who is basically the in-universe version of the Antichrist.
A major plot point in the first season of Veronica Mars. Hinted at a little, then kicked into high gear with the bombshell "I told him I'd get a paternity test and take him for millions."
Subverted in The Fresh Prince of Bel-Air. On "Mama's Baby, Carlton's Maybe", Carlton's ex-girlfriend Cindy comes back with a baby. After passing out a few times, Carlton accepts the baby as his and plans to elope with Cindy. It turns out that the baby can't be his because he never had sex with her.
Tim and Corrine get married, and Corrine quickly becomes pregnant. She's 5 months pregnant when they've only been married for 3 weeks. She assures Tim that she hadn't had sex with anyone during that time before they got married but Tim doesn't believe it. A week or two later she has the baby and it's possessed, which is why it grew so fast.
Burt gets Abducted By Aliens and replaced with an alien double. After that plot is resolved, his wife Mary learns she's pregnant. At first she's thrilled, but then realizes that the baby could be Alien!Burt's rather than Human!Burt's.
On Rome, Antonia's paternity is unknown. Agrippa asks Octavia whether he or Antony is the biological father, though how he expected her to be able to answer that isn't expounded on. Toddler Antonia's very brief appearances give no clues. She's blonde, which could imply Agrippa is the father; however, her maternal uncle, Octavian, is also blond, and many white children do have blond/e hair that becomes much darker over the years. Historically, Antonia's paternity was never debated.
Religion and Mythology
One Jewish legend states that when Sarah finally got pregnant, gossip claimed that the father was not Abraham but Abimelech—after all, she had lived with Abraham for decades without conceiving and had been taken into Abimelech's house right before the pregnancy happened. God gave Isaac and Abraham a Strong Family Resemblance just to stop the rumors.
Plays into the differences in stigma between illegtimate children in the Scarlet Dynasty; a woman's child is definitely the child of a Dynast, meaning they have to be raised according to the usual (expensive) standards regardless of how their uncertain parentage makes their chance of Exalting less likely (as well as their unknown bloodline making them a poor marriage prospect), while male Dynasts can opt in or out of claiming their bastards (although there are still strong pressures to claim and financially support them from the outset). The concern there is less about who the parents are, and more about management of the Super Breeding Program.
In Much Ado About Nothing, Don Pedro asks Leonato if he is Hero's father and his response is basically "Well, that's what my wife tells me!" It's clearly meant to be a joke, though. (His wife may actually be standing right there as he says it, though she's a ghost character.) However, men's fear of being cuckolded is played rather seriously as a theme throughout the play.
Also, right after this line, Benedict asks if Leonardo was in doubt when he asked his wife, and Leonardo responds with "Senior Benedict, no, for you were but a child then."
In Euripides's Ion, Apollo exploits the difficulty in telling: his oracle tells Xuthus that Ion is his son when in fact, he is the son of Xuthus's wife Creusa who was raped by Apollo before meeting Xuthus and abandoned her child in the woods. Xuthus and Creusa married but never had children, so Xuthus went to Apollo's oracle for help. The oracle told him that the priest outside talking to his wife was his son, and Xuthus himself wondered if this was his biological child by some other woman or a "gift" from Apollo. Only after he leaves does Athena appear, explaining that Ion is the child Creusa bore Apollo but who will now he considered Xuthus' instead.
Eventually John Redcorn wants to reveal the truth to Joseph, but Nancy (the boy's mother) refuses to allow it based on the strong bond Joseph and Dale share. As she puts it "Joseph already has the only father he'll ever need".
Indeed, Dale and Joseph even discover that Dale was out of town the night Joseph must have been conceived but convince themselves that she was simply abducted by aliens and impregnated with her husbands genetic seed (for some reason) that night.
Another episode involved a former lover of John Redcorn's (a single mother with a darker-skinned daughter about Joseph's age) moving into the neighborhood and beginning to date resident loser, Bill. While Joseph and the daughter develop crushes on each other, Dale discovers via covert DNA testing that they are half-siblings. After convincing himself this means he is the father (via alien abduction and impregnation once again), he reveals the test and results to his wife, who confronts John Redcorn over this infidelity during their affair. Fortunately, Redcorn ends up taking some responsibility and the mother and daughter end up moving in with him, separating the girl and Joseph (without alerting them to their blood relation) before anything actually incestuous occurs.
In American Dad!, when excessive partying with an old friend of her mother's causes one of Hayley's kidneys to die and the other to begin failing, necessitating a transplant, Francine is forced to reveal to Stan that he may not be Hayley's father. Three days before their marriage and subsequent consummation, Francine cheated on him in a moment of cold-feet-fueled weakness at her bachelorette party largely caused and galvanized by the same hard-partying girlfriend who wrecks her daughter's kidneys twenty-some-odd years later. Unsure of Hayley's actual paternity, Stan demands a test while Francine insists on finding the other man just in case Stan isn't a match for Hayley's transplant, and along this adventure Stan struggles with the idea that he's raised Hayley and devoted so much time and love to her and yet may not be her father. Eventually Stan comes to realize that regardless of her paternity, Hayley is still his daughter, and when the results of her paternity test are presented to him he declines to read them.
On multiple occasions throughout the episode, when asked by Francine if he can forgive her infidelity, Stan holds her tenderly in contemplative silence before calling her a slut and then remarking off-handedly in bewilderment on his body language, and the mixed signals it must be giving her.
On Archer, the titular protagonist has at least three potential fathers, including the heads of the KGB and a rival spy agency. Much is made of his mother's promiscuity, which hasn't slowed down in the slightest.
The use of DNA testing. In about three-quarters of the cases, the purported father finds he is the real father — which means, of course, that in a quarter, he finds he's not. Influencing these statistics is the fact that generally, a paternity test will only be performed in cases where there is both doubt about parentage and access to testing.
Commonplace on Talk Shows because of how much drama is stirred up around paternity.
Maury gets a special mention because one person quoted the trope name. The guest who said it was a woman named Rachel, the mother of her two sons who were getting tested to prove whether or not they fathered their wives' children (and if so, making them her grandchildren); she was a real skeptic about the paternity and wanted confirmation from her friend "D.N.A." (It was the first of her two appearances on the show, and you can see/hear her say the trope name in this clip here on YouTube, not oncebut twice.)
Literature/Real Life: In Conn Iggulden's epic stories of the Mongol Empire, a recurring plot-theme concerns Genghiz Khan's uncertainty over the paternity of his eldest son Jechi (at the time of conception, his mother Borte was a prisoner of the Tartars and was known to have been raped). Because he half-believes in the "this is a Tartar's bastard" stories, Genghiz repeatedly shuns and blanks his oldest son, or else gives him punitive or seemingly impossible tasks to complete that he would not dream of imposing on the favoured younger sons. This had consequences that stretched down the generations and caused the Mongol empire to collapse prematurely.
The whole reason Queen Isabella the I of Castille took the throne of her dead brother instead of his daughter is due to the uncertainty of her parentage; the king was rumoured to be "more interested in his guards than his queen" and the queen had many lovers and even several illegitimate children. DNA tests on their remains have proved otherwise.
At the Oneida colony, the practice of "complex marriage" caused onlookers to wonder about the children knowing their fathers. The leader retorted that the children knew their fathers the way children outside the colony did: on the word of their mothers.
Victorian anthropologists hypothesized that matrilineal systems were more primitive than patrilineal systems, stemming from before the organization of marriage, so that only a child's mother could be known. This has not been borne out by subsequent research — but not before it had been imported in many historical novels, and Two-Fisted Tales.
The practice in Egypt of the Pharaoh marrying his own sister was taken to be evidence of this, but since the Pharaoh's heir would be his own son even if he was not born to the sister, it appears to be a matter of regarding only his own sister as his social equal and so an appropriate wife.
Also a matter of getting the strongest royal blood possible for the offspring—the stronger an heir's claim, the less likely a coup becomes, so getting it from both sides helps.
This factored into the inheritance snarl around Hatshepsut and the Thutmoses. (Thutmose III was her nephew, and her husband's son, but not her child; her only offspring was a daughter. Thutmose II was her sickly half-brother, to whom she was queen, and who left her regent to his heir when he died young. Thutmose III's reasons for attempting to write her out of history have lately been suspected to be as much about downplaying the fact that he was only royalty on his father's side for his son's benefit as about resentment for the semi-usurpation thing, considering his timing.)
Thutmose III was six foot two and has been called the Napoleon of Egypt for his conquests. Hybrid vigor oi!
Researchers in evolutionary psychology have noted that when a young child's resemblance to its parents is brought up in a family setting, it will nearly always be the mother's relatives commenting on the child's resemblance to the father.
In some cultures, men may act more paternal to their sister's son than to their (alleged) own, as they can be sure they're related to the nephew in question.
Roman law neatly averted this trope, at least in theory; "the father is he to whom marriage points." In other words, legally speaking, biological parentage was irrelevant; the mother's husband was responsible for the child, period. This led to strict enforcement of "My Girl Is Not a Slut"-style customs, and it was not unknown for a father with a questionable child to exercise his right to kill the infant.
Even today, there is a (rebuttable, meaning it can be disproven with DNA testing) legal presumption that the husband of a woman is the father of any child she has. The "psychological parent" doctrine also states that after a child bonds with the man they believe is their biological father, if it turns out to not be the case this man will still be treated legally as their father and have the obligation to pay support, for the child's mental health. Of course, if the man is proven not to be their biological father that may put a crimp in their relationship after that point anyway.
This continues: one of the few cases in which Justice Antonin Scalia has written the opinion of the court is Michael H. v. Gerald D. (1989), which holds that for the purposes of family rights under the Due Process Clause of the Fourteenth Amendment to the Constitution, the "tradition" of recognizing the mother's husband as the legal father of a child trumps any biological arguments unless the state in question has statutory provisions to the contrary. (The case involved a girl proven to be the biological child of the plaintiff; he petitioned for visitation rights, arguing that as the biological father he had a constitutional right to see his daughter, but as California did not at the time provide for visitation rights for the biological father of a child born to a woman married to someone else and who had never been married to him, his petition was denied.) This particular opinion caused a stir in the legal community, and Scalia, although joined in the holding by a majority of justices, was only joined in the whole opinion by Chief Justice Rehnquist.
One less fortunate case: a woman still married to a man who had been in prison three years got pregnant and wanted to divorce him and marry her boyfriend before the baby was born, but an old law prevented divorce while a woman was pregnant, under the assumption that the baby *had* to be her husband's. That it obviously was not in this case was irrelevant; the baby would still be recognized as his.
In the 6th book of his Histories (chapters 62-70) tells the problems faced by Demaratos, king of Sparta. When he got the news of his birth, the father, King Ariston, at first suspected that he had been fathered by the mother's first husband because Demaratos was born before ten months had passed since the wedding (for the Greeks, pregnancy lasted ten months) and he had had no children from his first two wives. So he rashly said "this cannot be my son" in the presence of some Ephors. Later he decided that Demaratos was his son after all and after his death Demaratos succeeded to the throne. However he got into an intense rivalry with the other king of Sparta, Cleomenes, who then accused Demaratos of not being Ariston's son, used Ariston's rash words as evidence, and called for him to be deposed. Since there was no DNA test, the Spartans decided to consult the oracle of Delphi, which confirmed Cleomenes' accusation. So Demaratos was no longer king. However it later emerged that Cleomenes had bribed the priestess of Apollo (who was subsequently stripped of her office), and Herodotus notes that Cleomenes himself came to a bad end because of this blasphemy. In some desperation, Demaratos asked his mother if he really was Ariston's son or not. Her answer: In the third night after the wedding a man came to her who looked just like Ariston, who slept with her, left wreaths with her and left. And then Ariston came and was surprised to see her wearing the wreaths. So it must have been a god who had taken Ariston's shape. (The wreaths turned out to have come from the temple of the heros (demigod) Astrabakos). So Demaratos' father was either Ariston or a god.
Inverted by DNA testing in one case, where a woman was seeking benefits for her children. DNA could prove her boyfriend was the father, but indicated that another woman was the mother—something that made no sense to the woman nor her doctors. Eventually, it was discovered she was a chimera—her reproductive organs had different DNA than the rest of her.
This trope is the reason why, in the past, it was considered perfectly acceptable for a man to be unfaithful on his wife and have mistresses. But if a woman cheated on her husband, she was evil, vile, wicked, a demon, a witch, a whore, etc, etc and could face serious punishment. Like losing her head.
Some female mammals, such as lions, chimpanzees, and rats, tend to mate promiscuously within their social group, many more times and with many more partners than is necessary for conception. This may be a countermeasure to prevent infanticide by the males of the same group, as a male which has mated with any particular mother can't be sure her offspring aren't his.