Accidental incest is incest that is committed by two partners who do not know they are biologically related. It can occur when two people who are unaware of their biological relationship become sexually intimate. When two related people meet as adults, and become sexually attracted, it is known as genetic sexual attraction. When a biological relationship is suspected, DNA testing may be used.
Artificial insemination with donated sperm may result in accidental incest. Since sperm donation is often anonymous, many people conceived in this manner are usually unaware of any biological half siblings they have. The likelihood of accidental incest is kept low with doctors limiting the number of times that each donor's sperm can be used. Some countries have laws limiting the number of children a donor can father in order to reduce the likelihood. Taiwan allows those conceived by artificial means to receive testing to determine if they are related to a person they are considering marrying.
Other causes may include:
- Children separated from their family at birth
- Child abandonment
- Sexual exploration
- Alcohol abuse
- In 2008, it was reported that a British brother and sister who were twins separated at birth married without knowing of their relationship. According to the report, the relationship was discovered soon after their wedding, and the marriage was annulled. The case has raised the issue regarding whether adoptions should be kept secret. Concerns have been raised however about whether the story is in fact true.
- Although not exactly accidental, a famous German case has opened doors to the legalization of accidental incest. Patrick Stübing has had four children with his sister Susan Karolewski whom he met as an adult, serving prison time in Germany where incest is illegal.
- An engaged couple in South Africa who had been together for five years and were expecting a child when discovered that they are brother and sister just before their wedding. They were raised separately and met as adults in college. Just before the wedding, their parents met and they came to realize that they were siblings. The couple broke off the relationship after the discovery.
Mythology and fiction
- In the classic Athenian tragedy Oedipus Rex by Sophocles, Oedipus, king of Thebes, is told by a prophet that he will murder his father and marry his mother. Oedipus considers the possibility ridiculous and argues vehemently with the prophet. His wife Jocasta, widow of the former king Laius, urges Oedipus to ignore the prophet, reminding Oedipus that Laius was actually killed by bandits at a crossroads on the way to Delphi. It is eventually disclosed to Oedipus that as a baby he had been given up for adoption in an attempt to evade the prophecy that he would one day kill his own father. Oedipus suddenly realizes that the prophecy had indeed been fulfilled: he had quarreled with some travelers at a crossroads and slain them. One of them, he realizes, was Laius, his biological father whom he had never known, and that by marrying Laius' widow Jocasta, he had married his biological mother. Jocasta hangs herself and the despairing Oedipus also intends to commit suicide, but eventually takes pins from the dress of his dead wife and uses them to poke out his eyes.
- King Arthur was seduced by Morgause, his half sister and fathered Mordred. Since he did not know Morgause was his half sister at the time (Arthur was raised away from his parents by Sir Ector), it can be considered accidental.
- Moll Flanders unknowingly marries her half-brother, and has children by him.
- In the play Andorra by Max Frisch, Andri falls in love with his half-sister (whom he then thought his full sister) Barblin. His mother tells them upon finding out, according to common belief at the time, that he is a rescued Jewish boy from the country of the Blacks and merely adopted, whereupon the two get engaged. The father, teacher Can, forbids their getting married, not giving any reason, because the rescue story is a disguise and Andri really is the fruit of an affair of his with a Black woman. Thus, to Andri he becomes implausible in his tolerance for the Jews and causes a crisis of identity in him, triggering a good part of the plot.
- In Os Maias by Eça de Queirós, the main character (Carlos da Maia) falls in love with Maria Eduarda and maintains a secret affair until he is told by a friend she is his sister (Carlos supposedly never had a sister). At last, Carlos informs his newfound sister that they are siblings and that they cannot live like this anymore.
- Túrin Turambar and Niënor Níniel in The Lay of the Children of Húrin (Narn i Chîn Húrin) by J. R. R. Tolkien
- In the original Star Wars trilogy, the early relationship between twin siblings Luke Skywalker and Princess Leia Organa (who were separated in order to hide them from their father Darth Vader and his master Emperor Palpatine) has the potential to becoming accidental incest but Leia's relationship with Han Solo prevents this. However, because of the implications, it has become subject to both fan fiction and parody. Robot Chicken parodies the idea in a sketch in which Luke and Leia are seen in a bed after apparently having sex, with Leia saying "This is so wrong." In Family Guy's parody of Return of the Jedi, when Lois/Leia tells Chris/Luke she always knew that they were siblings in response to Luke's admission they are siblings, shocked Luke questions her further she replies saying "I'm from Alderaan, its kinda the Mississippi of the galaxy."
- In the Family Guy episode, "Halloween on Spooner Street" while playing spin-the-bottle at a Halloween party, Meg (dressed in a sexy kitty costume) and Chris (dressed as Optimus Prime) accidentally make out in a pitch black closet. When the closet is opened and can see each other, they become repulsed at what they had done, saying they had already done so much. In Valentine's Day in Quahog, Stewie travels back in time to the 1960s to see what love was like and falls for a baby girl. Opening up, he kisses her but is repulsed when he discovers she is in fact Lois, to the point of vomiting.
- In All My Children, Erica Kane nearly seduces her half-brother Mark Dalton until she discovers the truth from her mother Mona.
- In a third season episode of House, the team treats a married couple, Jeremy and Tracy, for similar symptoms. During treatment, the couple likens themselves to Romeo and Juliet, as Jeremy's father had forbidden him from becoming involved with Tracy, citing various reasons. When the team is able to diagnose both Jeremy and Tracy of a rare hereditary condition, it is revealed that the true reason Jeremy's father was opposed to their union was an affair he had had with Tracy's mother, which resulted in Tracy's birth, thus making them half-siblings.
- In the sixth season of NCIS, the "Heartland" episode begins with a savage assault on two corporals, killing one and leaving the other, Corporal Ethan LaCombe, seriously injured. The NCIS investigation takes the team to Stillwater, Pennsylvania, which happens to be Gibbs' home town. A powerful local industrialist, Charles Winslow, has been strongly opposed to LaCombe's interest in his daughter, Emily, which suggests that he might be in some way connected with the assault. DNA tests intended to help identify his assailant disclose a shocking fact: LaCombe is actually Charles Winslow's biological son. He opposed LaCombe's love interest with his daughter because, as only he knew until the NCIS investigation found it out, they were actually brother and sister.
- On the American television series Perception, the fourth episode of the second season, "Toxic", features two teenagers who were revealed to have been having an affair, against their parents wishes, due to the fact that, unbeknownst to them, they were half siblings. The girl being the result of an extramarital affair between her mother, and the boys father. The series main character, neuropsychiatrist Doctor Daniel Pierce, explains the situation as being the result of Genetic sexual attraction by name, and implies that the Westermarck effect, which he does not name, would normally prevent it.
- In the Dollanganger series by V. C. Andrews, Christopher and Corrine, the parents of the main character Cathy and her three siblings, are revealed to have been half-uncle and niece, but never learn that they are also half-brother and sister. Corrine's father, Malcolm, is Christopher's older half-brother by the same father. Christopher's mother, Alicia, was later raped by Malcolm and became pregnant with Corrine. To prevent a scandal, Corrine was passed off as the child of Malcolm and his wife, and told that she is simply Christopher's niece. When they met for the first time as teenagers, they fell in love and eloped after their relationship was discovered. They eventually married and had four children together by the start of Flowers in the Attic.
- In King of the Hill Joseph Gribble is revealed to have a half-sister, due to his mother, Nancy Gribble's, affairs with John Redcorn, who also cheated on her around the time with another woman, thus giving birth to his half-sister Kate, the two share a brief relationship, although do not share anything sexually.
- In the series The Mortal Instruments by Cassandra Clare, Jace Wayland and Clary Fray fall in love before their father tells them that they are brother and sister. They continue to have a romantic interest, though they do not sleep together. Later, Clary's mother reveals to her daughter (in City of Glass) that Jace is, in fact, somebody else's son but raised by Clary's father. However, as a friend points out, Clary did kiss her biological brother, who had shown a romantic interest in her – knowing full well he was her brother.
- In the film Oldboy, Dae-su Oh is tricked into have sexual relations with his daughter, whom he had been separated from for 15 years and had not recognized.
- In the Konami RPG Shadow of Memories, it is implied in Ending E between protagonist Eike Kusch and his romantic love interest Dana, as the pair are secretly long-lost biological father and daughter who were separated since Dana was an infant in the Middle Ages and then serendipitiously reunited in the present-day due to the time-travelling machinations of the malicious djinn Homunculus.
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