History Main / HereditaryTwinhood

* ''WesternAnimation/GravityFalls'': Dipper and Mabel are HalfIdenticalTwins, which foreshadows the reveal that [[spoiler:their Great-Uncle Stan is an identical twin.]]

* ''ComicBook/TheFlash'': Prior to his death in ''ComicBook/CrisisOnInfiniteEarths'', Barry Allen fathered fraternal twins--[[ThemeTwinNaming Don and Dawn]]--with his wife, Iris. It was later revealed that Barry himself had a [[LongLostRelative long-lost identical twin brother]] who had been SeparatedAtBirth and had been raised by the Thawne family, eventually becoming the [[EvilTwin villain Cobalt Blue]]. Since [[SuperpowerfulGenetics Don and Dawn inherited his superspeed]], this led to the line in ''The Life Story of the Flash'': "Twins ran in the Allen family ... literally."

* ''ComicBook/YoungAvengers'': The series has a complex example. ComicBook/ScarletWitch is the fraternal twin of ComicBook/{{Quicksilver}}, and Speed is the reincarnation of one of her magically-conceived identical twin sons. He mirrors Quicksilver's powers; his "brother" Wiccan mirrors Wanda's. In one BadFuture, [[Characters/HawkeyeKateBishop Kate Bishop]] is pregnant with Speed's twins.

* ''Franchise/TheFlash'': Prior to his death in ''ComicBook/CrisisOnInfiniteEarths'', Barry Allen fathered fraternal twins--[[ThemeTwinNaming Don and Dawn]]--with his wife, Iris. It was later revealed that Barry himself had a [[LongLostRelative long-lost identical twin brother]] who had been SeparatedAtBirth and had been raised by the Thawne family, eventually becoming the [[EvilTwin villain Cobalt Blue]]. Since [[SuperpowerfulGenetics Don and Dawn inherited his superspeed]], this led to the line in ''The Life Story of the Flash'': "Twins ran in the Allen family ... literally."
* In ''ComicBook/LegionOfSuperHeroes'', twin births are the norm on Winath, to the point that children born without a twin, like the villain Lightning Lord, are outcasts in Winathian society.
* ''ComicBook/YoungAvengers'' has a complex example. ComicBook/ScarletWitch is the fraternal twin of ComicBook/{{Quicksilver}}, and Speed is the reincarnation of one of her magically-conceived identical twin sons. He mirrors Quicksilver's powers; his "brother" Wiccan mirrors Wanda's. In one BadFuture, ComicBook/KateBishop is pregnant with Speed's twins.

* The ''WesternAnimation/XMenEvolution'' fic ''[[https://www.fanfiction.net/s/5463699/1/All-s-Fair-in-Love-and-War All's Fair in Love and War]]'' has [[RelatedInTheAdaptation Jean Grey and Lance Alvers]] as faternal twins. Jean and Scott Summers's first set of children, Joseph and Monica, are fraternal twins as well.

* ''Series/WandaVision'' uses "twins begetting twins" for a different kind of plot twist. Wanda is a fraternal twin, and gives birth to fraternal twin sons (who have similar powers to herself and her brother Pietro) when she had just been expecting one child. But [[spoiler:seeing her sons reminds her of her brother, who had gone unmentioned since his death -- which in turn causes the fragmented sitcom reality to unravel]].

* ''Series/WandaVision'' uses "twins begetting twins" for a different kind of plot twist. Wanda is a fraternal twin, and gives birth to fraternal twin sons when she had just been expecting one child. But [[spoiler:seeing her sons reminds her of her brother, who had gone unmentioned since his death -- which in turn causes the fragmented sitcom reality to unravel]].

* ''Film/GodzillaKingOfTheMonsters2019'': Dr. Ilene Chen, Monarch's chief mythologist and resident MsExposition, not only has a twin sister, but also twin daughters, her mother and aunt are twins and her grandmother and great-aunt are twins. The novelization takes this even further, confirming that twins run in Ilene's family. WordOfGod reveals that this is meant to settle Ilene and her sister Ling into the roles of the Shobijin, Mothra's twin priestesses, so in this case there's a supernatural justification.

* WesternAnimation/GravityFalls future timelines commonly have at least one of the Pines twins parent twins (or occasionally, triplets) themselves.

* ''Literature/HeraldsOfValdemar'': The main characters of the books are identical twin girls with an older brother. Of the past five generations of their mother's family, three have consisted of identical twin girls with an older brother.

* ''Literature/TheBelgariad'': At the end of the Malloreon, Polgara (who had a twin sister) has twins; Belgarath says it's a family trait.

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The presence of established twin relatives, identical or fraternal, can often set up the birth of more twins or a [[LongLostRelative long-lost twin]] showing up. If one of the parents is a twin, having twin children is often used to bring their story full circle (especially if the children are [[UntoUsASonAndDaughterAreBorn a male/female pair]]). Often, the newer or younger set of twins parallels the older one in some way: they bear [[GenerationXerox strong similarities]] to the [[StrongFamilyResemblance previous set]] that can extend to [[InTheBlood personality and behavior]], take different life paths, or have an entirely different sibling relationship. In other words, the twin children are used as not so subtle {{Foil}}s or {{Mirror Character}}s to the parents.

In real life, there is no scientific proof that twins skip a generation, and as far as scientists know, identical twins are a spontaneous, random occurrence that doesn't run in families. Fraternal twins can run in the family, but only through the ''mother'': some women are genetically predisposed to hyperovulation[[note]]Fraternal twins are caused by two separate eggs being fertilized by two separate sperm, while identical twins are caused by a previously-fertilized ovum splitting in half. Men always release multiple sperm, but women most often ovulate one egg each month. If a woman has a hereditary predisposition to ovulate more than one egg at a time, her chances of having fraternal twins will be higher, whereas the father's DNA obviously won't affect how many ripened eggs his partner has available for his sperm to fertilize[[/note]]. Artificial insemination and a previous birth can also increase the chances of a multiple birth. Fiction, however, will often treat [[AlwaysIdenticalTwins identical twins and fraternal twins similarly]].

* ''Literature/WolvesOfTheCalla'': in Calla Bryn Sturgis, the main setting of the story, almost all births are twins, with having just one child being a rarity. It is lampshaded however that this is not a natural phenomenon, and the abundance of twins is what makes Calla a target for the Wolves, who want 1 child of each pair of twins every 23 years in order to drain them from the innate material responsible for TwinTelepathy.

* ''LIterature/HeraldsOfValdemar'': The main characters of the books are identical twin girls with an older brother. Of the past five generations of their mother's family, three have consisted of identical twin girls with an older brother.

* In ''Literature/LordOfTheRings'' and its expanded universe twins Eluréd and Elurín had a sister,
Elwing, whose sons were twins Elrond and Elros, and Elrond in turn has two sons named Elladan and Elrohir, who are never explicitly identified as twins in the text but were born in the same year and look so alike people can't tell them apart.

* In ''Literature/LordOfTheRings'' and its expanded universe Elrond Half-elven had a twin brother named Elros, and he in turn has two sons named Elladan and Elrohir, who are never explicitly identified as twins in the text but were born in the same year and look so alike people can't tell them apart.

* ''WesternAnimation/GravityFalls'': Dipper and Mabel are HalfIdenticalTwins, which foreshadows the reveal that [[spoiler:their Great-Uncle Stan is a identical twin.]]

* ''WesternAnimation/GravityFalls'': Dipper and Mabel are HalfIdenticalTwins, which foreshadows the reveal that [[spoiler:their Great-Uncle Stan is a fraternal twin.]]

* ''Literature/WolvesOfTheCalla'': in Calla Bryn Sturgis, the main setting of the story, this is taken UpToEleven as almost all births are twins, with having just one child being a rarity. It is lampshaded however that this is not a natural phenomenon, and the abundance of twins is what makes Calla a target for the Wolves, who want 1 child of each pair of twins every 23 years in order to drain them from the innate material responsible for TwinTelepathy.