Immortal Procreation Clause


 * The fertility of a species is inversely proportional to its lifespan. Thus, as a species approaches immortality, their birth rate approaches zero.

On its surface, being immortal is a pretty sweet gig. You have a lot of time on your hands and usually you never have to suffer the effects of injury or old age.

Now, the wise group of sages known as Queen once asked us, "Who Wants to Live Forever" and here's one reason why: in many works of fiction featuring immortality, not only do they outlive their mortal lovers, but the immortals in question also are sterile or infertile: they cannot have children, since children are considered the "normal" way for mortal humans to ensure their legacy.

In many cases, this is an example of Cursed With Awesome, because, along with some STD Immunity, it means that the teen-looking ancient vampire stud can get it on with the ladies as much as he wants without worrying about consequences of any sort, particularly leaving lovers pregnant with a Dhampyr who will eventually grow up and try to kill him. Or at least demand child support.

Immortals may have methods of making mortals immortal (vampire bite, Applied Phlebotinum, or the like) and they may come to view those that they bring over into immortality as their own children, teaching them the lessons and how to thrive as an immortal. This, however, is not the same as having natural children.

Sometimes the beings in question are perfectly able to have children, but are not allowed to, by the laws of their society, because allowing immortals to breed will quickly lead to overpopulation. This usage tends to be found in hard Speculative Fiction.

Another common aversion is to have immortals that are quite fertile/potent but whose children are completely or near-completely mortal. These examples are also included here because they fit in with the theme that unchecked reproduction combined with immortality is unsustainable.

In a strictly biological sense this trope is fairly logical. Without death, an immortal population would constantly grow and eventually crowd themselves out. As such, childbirth isn't really a necessity for such a species, since the members rarely need replacement. The above formula can (loosely) apply to any given species. Not to mention the little fact that females only have a limited amount of eggs in their ovaries, so one can presume that even if they're blessed with eternal youth, in the end there is no escaping menopause.

This trope includes extremely long-lived characters and species with low birth rates, as they fit on the sliding scale properly. The most common example of this is elves; Tolkienesque elves generally have Type II Immortality and can have children; their population is mitigated by a low birth rate (a typical elf couple can live together for several thousand years and produce only one or two children in all that time), the occasional violent death, and the tendency for older elves to journey across the sea to a mystical land, never to be seen again.

Related to Creative Sterility; this is a focus on sexual reproduction. Can result in a Dying Race.

Anime and Manga

 * In both the manga and anime versions of Fullmetal Alchemist, homunculi, creatures created by alchemy, are stated as unable to reproduce. They exist outside of any ecosystem.
 * is immortal and can reproduce, but his children aren't any different than normal.
 * Played straight in Mnemosyne until a last minute epilogue subversion: bears a child, proving that it is possible.
 * In the Metroid manga it's mentioned that the Chozo are slowly becoming extinct because their lengthened lifespan also made them very infertile.
 * Mahou Sensei Negima averts Immortality Begins At Twenty, causing this problem for pre-pubescent immortals. The vampire Evangeline has been around for hundreds of years, and presumably never reproduced. Although this may have more to do with the fact that she's evil, uber powerful, and scary as hell, as well as the fact that she gained immortality when she was ten years old and has been stuck that way since. It probably applies to vampires, in general, as no other ones have ever appeared.
 * Makie, Akira, Ako, and Yuuna were briefly vampire-ified by Evangeline in volume 3, but they were apparently cured.
 * In the Old Shame manga that Hellsing was based on, Proto-Alucard explains that he kills off vampires who Turn too many humans because if there were too many vampires, there wouldn't be enough any humans left to feed on.
 * He bring this up in Chapter 1 as well
 * Specifically the reason for the Royals killing each other off in Princess Resurrection. Since a fully mature Royal becomes a Phoenix who literally cannot die, There Can Be Only One to become one.
 * The Bounts from Bleach's Bount arc were a group of immortal, soul sucking humans who could summon Bond Creatures, but they were incapable of reproduction. The one Bount that did have the ability to reproduce was killed by her own people as part of some elaborate ritual to summon an army of flying, soul-sucking insects.
 * In Dance in The Vampire Bund we discover that the "True Blooded" vampires can, in addition to turning those they feed on into theoretically weaker ones,
 * Huey Laforet in Baccano! procreated after becoming immortal just to see if this applied. His daughter doesn't inherit his immortality.
 * The Juraians in Tenchi Muyo have vast lifespans (one prominent member of the royal family is over 5,000 years old; she looks 35-40, tops), but their birth rates seem to be quite low. The Juraian emperor, for example, has been married to two women (at the same time) for over 700 years, and only had 3 children between them. His mother-in-law (the above-mentioned 5,000 year old Juraian) has only one biological daughter; while she's raised several other children, they were all adopted.
 * The Juraians in Tenchi Muyo have vast lifespans (one prominent member of the royal family is over 5,000 years old; she looks 35-40, tops), but their birth rates seem to be quite low. The Juraian emperor, for example, has been married to two women (at the same time) for over 700 years, and only had 3 children between them. His mother-in-law (the above-mentioned 5,000 year old Juraian) has only one biological daughter; while she's raised several other children, they were all adopted.

Comics

 * In the Wildstorm universe, the effectively immortal Kherubim suffer from an abysmally low birth-rate. Subverted in that it seems they can breed with humans more prolifically than they can with their own kind.
 * Most elves of Elf Quest can only breed after a "recognition" (which is basically the instincts of two elves deciding the two are genetically very compatible, and forcing them to conceive a child). One of the stories set before the Original Quest mentions that the tribe's Healer tried, and was in one case successful, to break that limitation, because there were worries the tribe was too small. And later on
 * One tribe of elves had no children for millennia, partly because of stagnation (they were hiding from the world in a "fortress" and would not outgrow it).
 * Being a One Gender Race, the Amazons of Wonder Woman in Gail Simone's run suffer from this, being reincarnated from women who were killed by men, including many mothers. They make "Whittle Babies" out of wood to keep themselves occupied, and until Diana was created by the Gods at Hippolyta's demand there were no children born on the island.
 * The Eternals are completely infertile with each other, since they are Nigh Invulnerable, simply regenerate when you do hurt them, and are eternally young. Several of them have sired completely normal baseline human offspring with mortal lovers/spouses over the centuries, but this presents other problems.

Fanfic

 * Justified by a similar lack of desire in Undocumented Features. Humans who have taken the Detian treatment can have children. It's just that the current crop of Detians haven't had very many. For instance, Gryphon has been alive for over 400 years, but only started having children in the last couple decades.

Film

 * In Highlander and its various spin offs, the immortals cannot have children. If you believe the second movie, it's because they're actually from another planet. In the later films (but not in the TV series), Immortals are capable of reproducing until they die for the first time. This is a plot point in the fourth and fifth movies.
 * The Man From Earth fathered many children during his looooong life, but since he is forced to leave his families after a few years, nothing is known about their immortality, apart from one, and he is most certainly mortal.
 * In In Time people can reproduce freely, but to stay alive past the age of 25 you must work to obtain time, which also functions as currency.
 * In the Underworld films, the immortal father of the vampire and lycan bloodlines seems to have stopped reproducing after his original three sons. At least, there's no indication that any other Corvinus bloodline existed for Lucien's agents to hunt down.

Folklore and Mythology

 * While the Greek gods certainly could mate with mortals, the demigod children were, themselves, mortal. A few favored ones like Herakles and Dionysus were later granted full godhood. The gods presumably had kids among themselves less frequently.
 * The Titans, on the other hand, frequently had children among themselves.

Literature

 * The Tucks from Natalie Babbitt's Tuck Everlasting cannot change; they don't age, they don't die. Mrs. Tuck was past childbearing age when she drank from the spring, so it isn't an issue for the elder Tucks. However, the eldest Tuck son got married in the years after they drank from the spring and before they realized its effects; he had children, but his wife eventually thought he'd made a Deal With the Devil and left him.
 * Brought up in one of Joanne Bertin's The Last Dragonlord. Dragonlords, the people who shapeshift between dragons and humans, have exceedingly long lifespans; as of the first book, the youngest is really six hundred years old, still looks the same, and is still called "little one." They cannot have children with ordinary humans, and while that does not apply between Dragonlords, they voluntarily do not have children, since when they do reproduce their offspring are very nearly always human. The same Dragonlords who enjoy their human friends and grieve and let go when they age and die have a lot more trouble with it when it's their own children.
 * In CJ Cherryh's Cyteen, it is mentioned in passing that rejuvenation drugs have a side effect of making the user sterile.
 * In Mercedes Lackey's Urban Fantasies and Historical Fantasies, the immortal sidhe can reproduce, but it happens extremely infrequently. As a result, children are treasured by both the Unseighlie and Seighlie Sidhe, although only the Seighlie expand this love to human children and try to save them from unpleasant fates.
 * For the elves in the Obsidian trilogy, children are also very rare and precious.
 * Vampires from Meyers' Twilight were believed to be infertile, but it turns out that that only applies to the females. So the guys can still get it on with a human girl, but it's incredibly dangerous for the human woman.
 * The same for wolves (though they're really only immortal so long as they shape shift). While there's only been one female wolf, she appears to have become menopausal after she became a wolf. The males can all still have children, a fact which is publicly known because of imprinting. Um...yeah.
 * A similar situation holds for the werewolves in Patricia Briggs's Mercy Thomas novels. The werewolves don't age (and if they were old when they were turned, they'll revert to looking adult, but permanently young and fit). Male werewolves can have children with ordinary women, but they'll be born mortal, and there's a high risk of miscarriage. Female werewolves can get pregnant, but inevitably miscarry when they change, which they must do at full moon. The only exception is Charles, the son of the Marrok, who is the offspring of two werewolves and was born one; his Native American mother used magic to hold off the change, but the effort depleted her strength and she died in childbirth. It's often a plot point that older werewolves often become unstable because they have outlived too many partners and children - in the Briggs 'verse it's dangerous to try to become a werewolf, as you have to be savaged to the point of death and not many survive the process, so they can't automatically turn their wives and children.
 * Vampires in Briggs's 'verse seem not to reproduce in the usual way as they're not so much immortal as undead; they're literally dead during the day. They remain the same age as when they were turned. However, many of them assume a parental responsibility for new vampires that they have turned, and a vampire seethe acts very much like a big dysfunctional mafia family.
 * Fae, on the other hand, can have children with mortals or with each other, and how "immortal" the children are seems to vary. There are lots of different kinds of fae and not very many of them in total.
 * Used in Terry Pratchett's Strata, in which the universal currency is a life-extension treatment. One of the main characters, who is several centuries old, wonders what life would have been like had she been a "short-lifer" and thus able to have children.
 * In Mickey Zucker Reichert's The Renshai Trilogy and its sequel The Renshai Chronicles, it's remarked that the Norse Gods are almost completely infertile, and that many of them had a human parent. In the second trilogy, the life cycle of Elves becomes an important plot point: a new elven child can only be born if one of the currently existing elves dies (freeing their soul for Reincarnation), so the Elven population can never grow beyond its current numbers. Furthermore, the elf needs to have died of natural causes - any violent death permanently reduces the maximum elven population.
 * There is a cultural mandate against reproduction by immortals in Jitterbug Perfume by Tom Robbins.
 * Averted in JRR Tolkien's legendarium, as Elves live forever but are perfectly capable of having children. They simply don't choose to do so very often; by the time of The Lord of the Rings, Elves are near the end of a very long-term emigration, sailing away from Middle-Earth when they've grown weary of it, so overpopulation isn't a problem. In the stories set in the earliest time periods, though, there are frequently several generations of a single family living and ruling together, making a mental picture far more difficult than the two-generation Hugo Weaving/Liv Tyler pair in the films! There is also the implication that having children can be very spiritually draining for Elves, restricting them from having too many. One Elf was so diminished by giving birth that she essentially lost the will to live. The endless lives of Elves also means that after a relatively short time, sex becomes boring to them. In his notes at one point Tolkien indicated that elves do not have children after a certain age. (So, menopause?) Also that Feanor had the most children that any elf ever had, whereas seven children would be, if anything, low for most fertile human couples if they both lived through the women's child-bearing years in most eras.
 * The Cracked article 6 Horrifying Implications of Awesome Fantasy Movie Universes discusses this: "no one in the Elfish kingdom is getting any, anywhere."
 * Also averted with hobbits, who often have large families despite living longer than humans.
 * But played straight with Ents, who live nearly forever but are all male and thus can't reproduce. Presumably wherever the Entwives are they have the opposite problem.
 * Roger Zelazny's Book of Amber series: as the books themselves comment on, the immortal lords of multiverse have been around for millennia, but are not particularly fertile: the first book is Nine Princes In Amber, not Nine Hundred Thousand Princes In Amber.
 * There is reference to several older princes who died "For the good of Amber" though.
 * The immortals from The Company Novels, though
 * In Poul Anderson's The Boat of Million Years, the immortals are perfectly capable of reproducing. Unfortunately, the children are never immortal, even when both parents are.
 * Completely ignored in Robert A. Heinlein's Time Enough for Love. Many near-immortals live throughout the galaxy and reproduce like bunny rabbits, even if they're 20 centuries old. Their children may also be effectively immortal, depending on what genes they picked up and whether they have access to a rejuvenation clinic. They solve the overpopulation problem by continually colonizing new planets. Justified as reproduction was the entire point of the Howard Families. They were an experiment in human longevity that worked spectacularly well.
 * It is worth noting that Tellus Secundus, the planet where the story begins, has an unusually high population of near-immortal "Howards" and in consequence has instigated population controls. The planet's chief executive mentions to Lazarus Long that he'll grant an exception to any woman Lazarus feels like having a child with. Lazarus himself is a special case as, being over two thousand years old and born at the start of the Howard experiment, he can claim over 80 percent of the galactic population and over 99 percent of Howards as his descendants to some degree or another.
 * Sort of the case in the universe of the novels American Gods and Anansi Boys with two notable exceptions. In the former, Wednesday (Odin) tells Shadow that people like him generally "shoot blanks" . We are also informed in American Gods that Mr. Nancy (Anansi) has a son, Charlie, who is the protagonist of Anansi Boys and is seemingly completely normal.  . Charlie ends up having children, who seem to be human.
 * Possibly on purpose, considering that the mother-in-law lives within spitting distance of them.
 * Played straight so hard it hurts in Fragment. When the protagonists discover the
 * In Three of Heart, One of Blood, the Legacies are incapable of breeding, though the systems still work. This is a fact that Doryn uses and exploits. A lot.
 * In the sci-fi The Declaration by Gemma Malloy, immortality has been made possible. Unfortunately, nobody who "opts-in" is allowed to have children because of this. Any children, or "surpluses," born to people who opt in are sent to group homes and taught that they are worthless beings that do not deserve to exist.
 * Fairies in Artemis Fowl (who are not immortal but very long-lived) can only have one child every twenty years; humanity's faster reproduction is actually the main reason it was able to more-or-less take the world from them.
 * Witches in Phillip Pullman's His Dark Materials trilogy live roughly a thousand years. They take human men for lovers and bear children; if the children are girls, they're witches and if boys, human and short-lived. Presumably, they don't have children especially often. One character suggests that a witch dies when her heart is so broken from watching her lovers and sons grow old and die that she can't go on.
 * Straightforwardly stated in C.S. Friedman's The Madness Season. The vampires of that book are only fertile when they subsist on a diet of willingly provided human blood. This is explained in-text as an evolutionary mechanism to keep them from reproducing in an environment that isn't willing to support new vampires.
 * The Marra, as well, are subject to this. Energy beings who are not able to die but can also not create new Marra (or, if they can, they have forgotten how)
 * The Culture generally discourages having more than a few children but no one stops those who wants dozens. Given that they have unlimited resources it's not really a problem.
 * Averted in Wen Spencer's "Tinker" series. The Oni are immortal and breed like mice. Famines are common in the Oni's overpopulated world. The Elves on the other hand are just as fertile as humans but don't feel the need to have as many children since they are immortal. The population of Elfland has dropped by 50% over the last two thousand years due to war, accidental death, and suicide.
 * Unicorns in The Last Unicorn (immortal but can be killed) live solitary lives in separate forests and mate very rarely.
 * In Aleksandr Zarevin's Lonely Gods of the Universe, the Human Aliens from the planet Oll arrive to Earth in distant past, escaping from a power-hungry official. They plant some seeds they bring with them to grow food, and the seeds of a salad plant known as ambrosia grow practically overnight. After eating a salad made from ambrosia, they suddenly fall ill and wake up young and immortal. Somehow, an alien plant has acquired entirely new properties on Earth. They make a few locals immortal as well and establish themselves as gods on the island. While the females who become immortal are incapable of conceiving a child, this is absolutely not the case for any immortal male who sleeps with a human woman. That is, in fact, the cause of the many hair colors modern humans have. The original humans all had dark hair, while the Olympians (yes, those Olympians; they also call their island Atlantis after Atl, their home country on Oll) are all redheads. Immortality can only be achieved through consuming a sufficient quantity of ambrosia, which withered and died soon after blooming.
 * In Niven/Pournelle's The Mote In God's Eye series, the Moties invert this - if they don't have children, they die young and horribly. Oh, and the most likable group, the ones who learn English and talk to the humans of the series? They're sterile hybrids. They die after 25 years or so.
 * In L. Jagi Lamplighter's Prosperos Daughter trilogy, since the immortality comes from an external source, they are fertile and most have had dozens of children. But the source is not extended to the children or spouses, and so some swore off it.
 * The Elves of Katherine Kerr's Deverry series usually live around 500 years, looking young until the last year or two of this, but have very few children during this time.
 * In The Witcher cycle the Elves breed much slower than humans, because their women ovulate once in a couple of years (or even tens of years). Not to mention that after a hundred or so years, the sex gets boring. It's also mentioned they're only fertile at young age, but as later in the books a girl is bred with an elf over 500, it's probably only the women.
 * In Mikhail Akhmanov's Arrivals From the Dark books, Paul Richard Corcoran, being a Half Human Hybrid, and his descendants have unnaturaly long lifespans (150-200 years). However, this also means they are highly unlikely to have children until they are well in their 40s or even 50s. This could indicate a slower rate of maturity.
 * Averted in The Dresden Files as well. Wizards are mostly immortal (they can be killed, but left to their own devices and otherwise unmolested, they'll go on for centuries), and they can reproduce. Molly Carpenter and  are wizard children.
 * Georgie Kincaid, succubus, is unable to bear children since she became a succubus.
 * In the Tide Lords Tetrology, the immortals cannot interbreed with each other (The union of an immortal egg and an immortal sperm would become immortal at age -9 months and thus never come to term), but they can and frequently have interbred with mortals (There are four entire species who are descended entirely from the mortal offspring of immortals). Said children are always born mortal, but.
 * Goes beyond this with the "glorifieds" in the Left Behind book Kingdom Come, since they won't even have the desire for sexual intercourse.
 * That's canon. There is no marriage between humans in Heaven. With no marriage and no sin nature, there is neither sex nor the desire for sex, because there is no licit means for sex to occur, nor a desire for anything illicit.
 * So much for free will.
 * In Isaac Asimov's story The Last Question, one person states that their supercomputer has solved a lot of problems, but all the solutions were virtually undone when it solved the problem of aging and death.
 * The Kantri of Tales of Kolmar can live around two thousand years and are considered mature at two hundred fifty. About two hundred of them fled to the Dragon's Isle five thousand years ago and never increased their numbers. One observes with frustration that they should have increased, but the species seems demoralized and getting more so. There are fewer mated pairs and even fewer births happening all the time. It's mentioned with great concern that there have been only three births in the past eight hundred years - and the Kantri with their huge claws are helpless in the face of complications of birth. If a human hadn't stepped in and midwifed during Song In The Silence, the first birth in three hundred years would have ended tragically. Also, Kantri only feel the desire to have sex a dozen or so times in their long lives, and the act is difficult and painful, not fun. Mated pairs enjoy 'joining souls', but this gets no one pregnant.
 * The Kantri of Tales of Kolmar can live around two thousand years and are considered mature at two hundred fifty. About two hundred of them fled to the Dragon's Isle five thousand years ago and never increased their numbers. One observes with frustration that they should have increased, but the species seems demoralized and getting more so. There are fewer mated pairs and even fewer births happening all the time. It's mentioned with great concern that there have been only three births in the past eight hundred years - and the Kantri with their huge claws are helpless in the face of complications of birth. If a human hadn't stepped in and midwifed during Song In The Silence, the first birth in three hundred years would have ended tragically. Also, Kantri only feel the desire to have sex a dozen or so times in their long lives, and the act is difficult and painful, not fun. Mated pairs enjoy 'joining souls', but this gets no one pregnant.

Live Action Television

 * In Stargate SG 1, The Asgard are not capable of sexual reproduction; they lost the ability due to extensive genetic alteration. To achieve immortality, they upload clone bodies with their memories when their old bodies die. Eventually even this tactic fails.
 * The Goa'uld, as a parasitic race, is only very rarely capable of sexual reproduction, and the resulting child is very dangerous; thus the practice is proscribed. The normal life cycle of Goa'uld includes the spawning of new parasites by extremely rare slug-like queens, with Jaffa specially prepared to incubate the larvae; this almost always happens off-screen.
 * More specifically, procreation between two Goa'uld hosts is forbidden. Such a child, known as a Harcesis, would be born with all the genetic memories of the Goa'uld. Exactly why this would be a bad thing for the Goa'uld is never spelled out but it's probably to prevent Goa'uld secrets from falling into the hands of enemies like the Tokra or the Asgard.
 * In one episode an alien race weaponized this trope. After making contact with Earth they offered a treatment that would cure all diseases and drastically (though not infinitely) extend our lifetimes. After everybody on the planet got the treatment SG-1 found out that, of course, it causes sterility and would lead to the extinction of humanity. This was that civilization's way of taking over planets without a fight, just a bit of patience. Fortunately, the main characters were able to cook up some time travel gimmick to warn their past selves to not allow this to happen.
 * The Aschen treatment didn't itself cause infertility; the Aschen used it on themselves to create the wonderful society Earth was so eager to ally with. They added something else along with the treatment to make Earth infertile.
 * With one important exception, the immortal vampires in the Buffy Verse cannot create natural children. Even in that one exception, the vampire mother could not bring the child to term the normal way, and the child was mortal anyway.
 * Mortal in the age-and-eventually-die way, but he had all the strength, speed, and super senses of a powerful vampire with none of the weaknesses (sorta like Blade, but white and with puppy-dog eyes)
 * Averted in New Amsterdam, where it has been established that John Amsterdam has had several children, who, unlike him, are mortal. One of these children, Omar, looks older than John himself, and knows about John's immortality.
 * One episode shows that John keeps records of his descendants, so he can keep track of them and avoid dating female descendants.
 * Captain Jack Harkness, from Torchwood, is another aversion. He's immortal, but can have children. The children, again, are not immortal, thereby preserving the intent of the Clause.
 * The fourth series, Miracle Day, is set to involve a thorough subversion of this trope; humanity mysteriously becomes immortal and one of the immediate problems is an impending overpopulation crisis.
 * The Cylons from Battlestar Galactica are immortal due to their resurrection technology. They are also near-universally infertile, with only a single half-human child born to the entire race.
 * One notable exception exists, but
 * An episode of The Twilight Zone features a movie actress who remained remarkably youthful despite starring in films from the Silent Age (this taking place in the 1960's). She was accompanied by an old woman who acted as a maid.
 * An episode of The Twilight Zone features a movie actress who remained remarkably youthful despite starring in films from the Silent Age (this taking place in the 1960's). She was accompanied by an old woman who acted as a maid.

Tabletop Games

 * Most of the various immortal races in the Old World of Darkness are like this. Only the weakest 14th or 15th generation vampires in Vampire: The Masquerade can have children, who end up as dhampirs, only extremely yang-imbalanced Kindred of the East can have children (their version of dhampyrs), and that's made increasingly complicated by the fact that a female Kuei-Jin has to remain yang-imbalanced throughout the pregnancy, and demons from Demon: The Fallen might possess human bodies, but they lack the spark of life to create true progeny.
 * The original mummies were sterile too. However, their successors, the mummies of Mummy the Resurrection, are fertile, capable of having mortal children (justified, as the mummies' immortality is the result of the Spell of Life).
 * It carries over into the new version; a vampire can only give birth to a Dampyr through the use of certain dark rituals and curses, and the True Fae of Changeling: The Lost are described as immortal, all-powerful, and utterly sterile.
 * In Dungeons and Dragons, the lifespan of elves has decreased somewhat over the various editions (from a maximum of two thousand years for grey elves in 1st edition to a handful of centuries now); perhaps this is appropriate, considering that they've become more and more common in their game worlds, suggesting higher levels of procreation. Okay, fine, they're still supposed to be majestic, long-lived, and rare, but Rule of Cool sometimes dictates otherwise.
 * They say now that Elves do reproduce, but it's a long pregnancy, and that they need to wait 5 years to get pregnant again. But, of course, Your Mileage May Vary.
 * Another example is the 3.5 edition Elan, a race of psionically enhanced and modified humans who are functionally immortal. They can no longer procreate with humans due to their modifications (they are classified as aberrations, not humanoids), and the only way to make more Elans is by modifying an existing human with a mixture of psionics and an alchemical conversion process.
 * In Warhammer 40000, the same procedure that turns humans into near-immortal, superhuman Space Marines also renders them sterile.
 * Possibly it could just be a result of the degeneration inherent in certain chapters' methods or traditions. The Salamanders chapter is known to raise families of their own, and the Space Wolves are renowned for their, ahem, voracious appetites when it comes to the pleasures of the flesh. But most chapters do indeed not have children, whether because the process that made them Space Marines is corrupt or they are simply forbidden is left up in the air, which, given Warhammer 40000 canon, is completely intentional.
 * Most likely Space Marines remove their... umm, you know.
 * Space Marines are genetically and surgically modified. Even assuming that they are fertile (seems unlikely) and not poisonous, the children wouldn't be Space Marines, and might not be normal humans either.
 * Space Marines are largely infertile for three reasons. One, the God Emperor of Mankind did not want a race of immortal super warriors to replace mankind, but to defend it. Thus there are no female space marines and those that presumably can breed just produce regular humans. The second reason is that their extensive genetic and surgical alterations completely change much of their bodies structure. Since preserving reproductive capabilities is low on the list of priorities for the transition process, most marines likely do come out sterile. The third reason is that marines devote themselves entirely to war, they are either fighting, training to fight, or praying. Marines are only mandated 30 minutes of free time a day, and many chapters don't allow even that. Few chapters give a marine the chance to even find out if they're fertile, rendering the question of their fertility irrelevant.
 * Similarly, the Eldar combine a low birth rate with a natural aversion towards any sort of extreme emotion; to the point where their population is likely below sustainability levels.
 * Spycraft has a setting, 'World on Fire'. One faction is the Eternals, which are Exactly What It Says On the Tin. They can have children, but these are very very mundane.
 * Invoked by Tzeentch in Warhammer Fantasy. The ancient race of Dragon Ogres asked the Lord of Change for a boon, to make them immortal. He did, but also rendered them sterile. Most of the still-living Dragon Ogres consider this to be Tzeench's idea of a joke.

Video Games

 * In Creatures games, there are many "immortal" third-party breeds; the majority of them are infertile by default, because immortal creatures capable of breeding would overpopulate the world pretty quick.
 * But the Fast Ager Norns, who tend to evolve spontaneously in many C3/DS wolfing runs, avert this hard. Maturing within seconds, very fertile, and immortal, they will easily max out your population no matter what population limit you choose. They're basically the cancer of the norn population.
 * In the Fallout series, the two types of creature that are biologically immortal, Super Mutants and Ghouls, are both unable to reproduce. The former due to sterility as a side effect of FEV, and the latter... radiation sterility and, well... rot?
 * Van Buren would have had "born ghouls," children born into ghouldom. To Drs. Sebastian and Clark, the masterminds of the breeding program, the born ghouls represent the future of the ghoul "species."
 * Averted in Lost Odyssey: the five immortals can and do have children, but their children, even when both parents are immortal are not themselves immortal. This prevents any potential overpopulation problems.
 * The krogan in Mass Effect were infected with a virus that devastates their birthday (1 out of 1000 is live, the rest are stillborn) in order to prevent them from taking over to galaxy on sheer numbers due to a combination of being one of the longest-lived species in the universe and being able to breed like rabbits, which is necessary on the harsh environment of their home world but not so much on the colony worlds they were given as a reward for their help in the Rachni War. And even with the high mortality rate, they're still capable of maintaining a population equilibrium if not for the species wide fatalism that followed the Genophage (kind of hard to keep you chin up when your allies annihilate a fundamental aspect of your biology and society).
 * The asari, who live for one thousand years, don't seem to have a problem with this trope though. They happily breed all they want to.
 * The asari, of course, are an entire race of Blue Skinned Space Babes, which probably rejiggers their place on the immortality vs. fertility continuum.
 * Most of the time the asari don't choose to procreate before they pass their 300th birthday and become Matrons, and generally don't have that many children in their whole lifetime; nearly 1000-year old Matriarch Benezia only has one daughter, for example. Aethyta, who's as old, is implied to have had a good number, but then her father was a krogan.
 * This may have something to do with the fact that the asari do not reach adulthood until they are 80, 40 years of which are the equivalent of being a human teenager.
 * Asari under three hundred years old generally like being out in the galaxy and doing dangerous things, and they are also much easier to kill than krogan, not having multiple redundant organ systems. Therefore adventurous lifestyles are more of a check on their population than for krogan.
 * True Ancestors in Tsukihime are noted in supplementary materials to have been rather on the decline. They did not even have enough children to replace the members they lost, so the birth of Arcueid itself was pretty big news even before people knew how powerful she was. Possibly tied to the fact that they were almost entirely all male.
 * In Golden Sun II, the ancient lost civilization of Lemuria has a grand total of two children, both of whom comment on how lonely it is being surrounded by ancients. (Lemurians aren't strictly immortal, but they slow down their aging process to live many centuries.)
 * Averted in Dwarf Fortress, with interesting results. Elves mature and reproduce at the same rate as humans, but have no upper limit to their ages. This results in massive populations; they would have taken over the world by sheer dint of numbers if it weren't for two weaknesses: they are poorly armed (having only wooden weapons and armor) and they are cannibalistic maniacs who start wars over the way other species treat plants, resulting in them warring with pretty much all of their neighbors. Battles with thousands of elves fighting (and losing to) less than a hundred dwarves are not uncommon.
 * World of Warcraft has the Draenei, who live for at least tens of thousands of years (and may be immortal), and very rarely have children.
 * Also, now that Night Elves are no longer immortal (their natural lifespan is still probably pretty long, but not infinite) they're starting to have kids more, as evidenced by some of their quotes.
 * Played straight and Averted in The Sims 2. Zombies and Servo robots are immortal but cannot have children, while Vampires can reproduce, but any children born will be completely normal.
 * In Runescape, the Dragonkin are nearly immortal, living for thousands of years at least, but can still be killed, and can't reproduce. This has lead to them becoming very afraid of death.
 * The Trow in Bungie's Myth series were created as an entire species by the god Nyx at the begining of the world. They have no natural causes of death, are eighteen feet tall, and have bodies that are as tough as stone. For many thousands of years they dominated the world, but entropy and a series of costly wars took its course, and now there are only a few hundred Trow left, if that. The ones that remain tend to keep to themselves, though prey you never have to run into one on the battlefield.
 * A female dwarf in Divine Divinity mentions that she is pregnant, but she's only in her tenth month, so she's not showing any visible signs yet.
 * In novels for Starcraft, the Xel'Naga were incredibly long-lived but couldn't reproduce.
 * In Aselia's ending for Eien no Aselia and have a child together. This is apparently completely unheard of and they're a bit nervous about how they're going to explain it.
 * In The Elder Scrolls, the Elven races live considerably longer (how long is undisclosed), but have far fewer children. However, their chance of having children if they have a non-elven lover.
 * In-game documents and supplemental materials for the Myst series reveal that the D'ni, whose lifespans could run into a fourth century, reproduced very slowly due to the narrow window (30 hours every 72 days) in which their women could conceive.

Web Original

 * As a demonstration of why this trope is often necessary, the site Grudgematch had a hilarious take on the disastrous consequences of James Bond winning immortality in the grudgematch: massive inbreeding due to James' libido.
 * Elves in Tales of MU are true immortals in terms of lifespan, and generally quite sexually potent as part of their being better than everybody. They keep their birth rate low by doing things that don't produce children.
 * The alien race known as the Silent Ones in Orions Arm use a treatment that completely halts aging but severely stunts the development of their larvae, so they keep small groups of mortals to replace the few immortals that die. However most Terragen (human-derived and/or created) sophonts are effectively immortal and decidedly not infertile, the population being in the quadrillions about 10500 years in the future.
 * Word of God (pun intended) has this as being the demographic issue with the angels in The Salvation War -- "angelic females simply are not very fertile and the chance of conception is extremely low," so the reason for the war being fought on Earth is to put off or prevent any human incursion into Heaven. Whereas the daemons tended to be killed en masse in generally horrible ways during the Curb-Stomp War, their birth rate will allow them to eventually recover, whereas angels dying off in those numbers might actually cause them to go extinct.
 * Although as of Chapter 83, it seems that the low birth rate of the angels was at least partially due to Yahwehh's obsession with controlling sex and sexuality and now that  there's been a rash of pregnancies among the angels.
 * Dissected (and arguably deconstructed) by the Writerium (and its successor the Writer's Workshop).
 * This blog post hilariously suggested that romances like the one in Twilight prevent vampire from population problem.

Web Comics

 * Dan and Mabs Furry Adventures: Cubi Clans are led by a Tri-winged Succubus or Incubus, who are as close to immortal as one can get with a an ungodly long lifespan and are so powerful very few dare to challenge them. The catch is they cannot have children of their own. The character Fa'lina shows how this can be bad, being a clan leader and being the last surviving member of said clan.
 * In addition to Cubi, no new members of the Fae race may be born until living members willingly and deliberately die. They can have children with just about anything, but, well...
 * Destania's clan leader Cyra is in a similar boat as Fa'lina. Destania is her last surviving "child" and she can't even speak with her anymore since Destania has given up dreaming -- and Cyra mostly communicates in dreams..
 * The elves of Errant Story previously had an extremely low fertility rate, which is part of the reason why taking on human lovers was so popular among them; as Sarine put it, elves could "try for centuries to have an elven child with no success, or they could go fuck a human and have the next best thing." In the wake of the Errant Wars, the elven fertility rate seems to have dropped from "low" to "zero," as the last elven child born is now some 1,500 years old.
 * Parodied in Irregular Webcomic's "Fantasy" storyline, where it's pointed out that Elven longevity also means that young Elves take centuries to grow past adolescence. As a result, the Elves invented prophylactics before they discovered how to use fire.
 * The Bradicor of Ghanj-Rho in Schlock Mercenary have, individually, survived millions of years and watched the evolution of intelligent life forms, but are indifferent to the gradual extinction of their species.
 * Our heroes end up accidentally flattening their last female during first contact and dooming them to extinction. The Bradicor react more with annoyance than anything else.
 * In Jack there are some people who have missed their chance to die for some reason, their biology is frozen at the point where they should have died and they can't reproduce as a result.
 * And now it appears that sterile immortality was intentional.
 * The fae of Drow Tales have a version on this, in that they're type II immortals and have very low fertility rates in even the best of times. Diva'ratrika Val'Sharen is over a thousand and has only had five (surviving) daughters and one son, while her daughter Zala'ess has had many more and her sister outright that she's had to do a lot of screwing around to get that many. Word of God is that female fae do not get periods, which probably explains why the birthrate is so low and why even very old fae like who is a dark elf and over 1,000, can still be having children since they do not have an equivalent of menopause.

Real Life

 * Averted with amoebae, and other single celled organisms that reproduce by binary fission. When you split in half (as opposed to budding off a daughter cell), you can consider both resulting amoebae to be an extension of the life of the parent. In short, every single amoeba on the planet is the very first amoeba. They're immortal and reproduce like crazy. Good thing they're fairly low on the food chain, so their hypothetical immortality isn't much of a problem.
 * Throughout history people have attempted to discover the secret to eternal life and Audrey De Grey is probably the most famous example in modern science. He has come up with his own theories and has even gone so far as to speculate that once humanity has stopped, and reversed, the ageing process; people will have to file a form to have children and then wait for other people to die (through natural causes or requested suicide) to be given the go ahead.
 * Thought experiments on population growth rates suggest that extending lifespan needn't necessarily produce an Explosive Breeder, as it's really the age at first reproduction that determines how fast a population grows. Mathematically, having a breeding female live forever will do less to increase birth rates than having her produce a daughter (who'll breed early in turn) slightly sooner.
 * This idea is truth in television in human communities insomuch as the childbirth rate of a country appears to be inversely proportional to its average lifespan. However, this applies only to communities, and is attributed to things like education and not seeing everyone around you die young (which tends to cause survivor lust).
 * More likely it's a consequence of development. Good healthcare improves lifespans but also reduces infant mortality, meaning people don't need to have as many children to guarantee some survive. More developmed countries also tend to have less of a primary-industry focus meaning children are a net drain on assets rather than a source of income. State welfare and wealth in general also means parents aren't as reliant on children to support them in their old age.
 * Because human oocytes (eggs) are produced by a woman's ovaries before she, herself, is born, an immortal woman's capacity for natural reproduction would inevitably expire when her supply runs out, even if she never goes through menopause (assuming the science at some point won't be able to reboot the ova production mechanism, of course). She could, however, give birth to a baby conceived in vitro from a donor egg.