Mama's Baby, Papa's Maybe

"Telemachus took a deep breath and said: You want the truth, and I will give it to you. My mother says that Odysseus is my father. I don't know this myself. No one witnesses his own begetting."

- Homer, The Odyssey

Prior to the days of DNA testing, it was impossible to verify a child's paternity, and the only evidence besides the word of the mother (who might not know herself in the subtrope Who's Your Daddy?) would be Her Child, but Not His 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," 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 actually wants the heir to be his child. If the mother refuses to tell, only men who have actually slept with her can even guess, and speculation tends to run wild.

Why Luke, I Might Be Your Father is a trope.

A powerful force behind My Girl Is Not a Slut and Nature Adores a Virgin in Real Life, because a man's sexual escapades cannot leave the woman wondering, nine months later, whether she really gave birth to that baby (short of invoking Switched At Birth or, for in-vitro fertilisation, Switched At Implantation). 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.

A trope for historical settings, as Daddy DNA Test is the Trope Breaker, unless identical twins, or clones, are the purported father, or for some reason, testing is impossible.

Ballads

 * In the Child Ballad Gil 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.

Comic Books

 * 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.

Fairy Tales

 * 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 fantasical 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.

Film

 * In The Count of Monte Cristo, Mercédès, the fiancée of hero Edmond Dantes, inexplicably espouses his rival Fernand Mondego soon after Dantes is imprisoned on a trumped-up charge. The paternity of eventually becomes a plot point in the film (which isn't in the original Alexandre Dumas novel).
 * West of Zanzibar: Lon Chaney plays a man whose wife was going to run away with another man and then died shortly after childbirth. He raises his "daughter" to be an alcoholic prostitute. Then the other man shows up, and tells him that his wife never went away with him - the child is his own.

Literature
"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."
 * 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.
 * In Andre Norton's The Jargoon Pard, Kethan is his uncle's heir because as his sister's son, he is his most reliable kin.
 * 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.


 * 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..
 * the issue of both claims is resolved by sequel books, where  and
 * 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 Romance Octavian, the emperor's wicked mother accuses his wife of infidelity and claims her twin children are not his.
 * In some forms of the Chivalric Romance The 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.
 * 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.
 * 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".  This brings about a struggle for succession after Robert's death.
 * 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.

Live-Action TV

 * 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
 * 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 nine 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  Earl also finds out that
 * 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).
 * 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:
 * 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.

Theatre
"Propsero: Thy mother was a piece of virtue, and She said thou wast my daughter;"
 * William Shakespeare
 * In The Winters Tale, Leontes doubts that he is the father of either Mamillus or Perdita.
 * In The Tempest, Prospero tweaks the edge of this trope, explaining the past to Miranda:


 * In Titus Andronicus, he opts for the Her Child, but Not His solution — the child is obviously Aaron's.
 * In The Merchant of Venice, Lancelot argues that Jessica should hope not be Shylock's daughter.
 * 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.

Western Animation

 * In King of the Hill everybody knows that Dale's son, Joseph, is really John Redcorn's child—everyone except Dale and Joseph (and Peggy for an embarrassingly long time), that is.
 * 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  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   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, 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.

Real Life

 * 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.
 * Standing these statistics on their head, however, is the tidbit that in general men only have these tests done if they feel there's a strong probability that they're not the father - but even in these cases where someone's really suspicious, three-quarters of the time they're wrong.
 * Of course, a DNA test is no proof of fidelity, either. If a woman has sex with two men (whether consensually or by being raped) within her fertile period and then conceives, it's a tossup which of the men is the child's father, and the DNA test will resolve it.
 * Commonplace on Talk Shows because of how much drama is stirred up around paternity.
 * 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.
 * 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. However, it was not unknown for a father with a questionable child to exercise his right to kill the infant.