Walking Transplant

Organ donation is a noble thing. Lots of us have little cards that tell the doctors that if we have life rudely yoinked out from under our feet, they can take what's left of us to make sure that the same tragedy doesn't befall someone else. Some forms of donation - like donating a kidney - can actually be done while still alive, which is just as brave, especially since you'll be pottering around the planet for years to come and are still willing to hand over an internal organ so that someone else can live.

Most of us agree though, that it is not something we would want to have forced on us while our hearts are still beating, thank you very much. At that point, the kind act of donation becomes little more than mutilation. Cue fiction.

This character exists for one reason - as "spare parts" for another character. It usually turns up in sci-fi/horror settings, but occasionally makes a guest appearance in emotional drama. They can be raised to cherish their purpose and perfectly content with their (usually fairly short) existence, or they can rage and fight against it. The qualifier is, the only reason they were born is because someone else might need their various body parts at some point. Rather depressing.

This is a pretty legitimate source of angst for the character who's treated like a spare tyre (and usually with about as much consideration for their feelings), but it's also a pretty subtle type of psychological Body Horror. This is their body - the one they were born with, with all their own genetics and personality traits - but as far as the people around them are concerned, the Walking Transplant's very flesh and blood are the exclusive property of whoever they were created to be the donor for.

Fridge Logic begins to creep in once you remember the time and resources necessary to raise a human to adulthood, the incalculable variables that could render their organs unusable, and the difficulty of ensuring that said clone remains in the dark on the until the original needs a new part. That's all bad for drama, though, so it's usually ignored.

Related to, but not to be confused with, Organ Theft. In reality, the idea of a child being a "walking transplant" is often used to argue against the possibility of "Designer Babies" - although there have already been babies screened and selected before birth specifically to donate to an older sibling (usually in the form of some "replaceable" material, like bone marrow and blood). Sometimes combined with Truly Single Parent.

Anime and Manga

 * Pet Shop of Horrors: A rather dark story (even for this series...) reveals that Count D's father engineered a "sister" for D {{spoiler|{she's actually an orangutan)}} to provide him with "spare parts," since D apparently suffers from some kind of Soap Opera Disease that is introduced and then forgotten about. She is eerily proud of her purpose.
 * Adorea of Franken Fran. Under all those bandages is a body covered in zippers for easy access to any emergency spare body parts that Fran might need. Fran replenishes her supply by.
 * Somewhat Tear Jerker example: in Neon Genesis Evangelion, Rei invokes this trope on herself
 * A major plot element in Vandread:
 * A major plot element in Vandread:

Comic Books

 * In the very good but largely forgotten DC Comics early 1990s version of Flash Gordon, the Yellow race of Mongo were acculturated to view their fate as organ replacements for the ruling Grays as the equivalent of going to Heaven.

Film

 * The whole premise of The Island and Parts: The Clonus Horror (the similarity between the two sparking a lawsuit). Just to ram home how inhumane the treatment of the clones is, in The Island we see a baby being removed from its clone mother to be given to the "original" (who couldn't conceive) - after which the clone is "disposed of". For further effect, a clone who wakes up on the operating tables as his organs are removed is harpooned and dragged back so they can finish the job. The "sponsor" (original version) of the main character refers to his clone as "his insurance policy," underlining the fact that the clones are seen as sub-human, and the property of whoever pays for them.
 * It is also mentioned that the other "sponsors" don't know what the cloning process is like. Apparently the guy in charge lied to them all that the clones are brain-dead vegetables, which is the only reason the company hasn't been shut down.
 * In Clonus, the originals know damn well what the process is like - it's implied they're The Illuminati if you pay attention - and they just don't care. The clones are treated somewhat nicer than in The Island, though, up until they're stripped for parts.
 * Never Let Me Go follows the same basic principles, but differs from other movies in that the clones are told about their intended purpose. Not that they're any happier about it, but as the film is quite bleak, they usually eventually resign to their intended purpose and end up dying.

Literature

 * Jodi Picoult examined this in My Sisters Keeper. Anna is a designer baby, genetically engineered to save the life of her older sister, Kate. When Kate's kidneys fail, Anna's parents expect her to hand over one of her kidneys. She sues them in order to gain control of her own body . The attitude of her mother, in particular, can be pretty chilling - at the best of times, Sara is hugely insensitive and so obsessed with Kate that she fails to see the dire straits Anna and older brother Jesse are in...but at worst, there is something downright creepy in her tendency to break Anna down into her component physical parts. Two examples stand out: Even at Anna's birth, Sara totally fails to mention her newborn as she rushes off to oversee Kate's treatment thanks to Anna's umbilical cord. Still creepier is when she denies Anna a chance to go to hockey camp in case something happens to Kate - since when the next crisis strikes "we will need Anna - her blood, her stem cells, her tissue - right here."
 * In the novel and 2010 movie Never Let Me Go by Kazuo Ishiguro, the students of Hailsham are all . They develop their own Gallows Humor to deal with the horror of their situation, but overall it's a more melancholic/tragic, rather than horrific, take on the subject.
 * In the Vorkosigan Saga, on Jackson's Whole, there's a trade in creating beautiful, aged-up clones of the powerful and rich and then scooping out and replacing their brains with those of their progenitors. Mark, who is a clone for other purposes, was raised amongst these clones and has set out to destroy the industry. At first he tries to do so physically, but when that doesn't work set about to do it economically, by obsoleting the procedure or otherwise making it unfeasible.
 * Let's stress this point. Old, rich degenerates have clones made of themselves and make the clones undergo different body-morphing procedures until the time comes when their brains are scrapped and the old geezer's brain is transplanted in. All the while, the kids they are in an exclusive boarding school and all of them are told that they are heirs of VIPs. Then, when they reach physical maturity at the age of 10, they are called to "meet their parents", and they are never seen again...
 * The "Unwinds" in Neal Shusterman's Unwind. There was a war between the pro-choice and pro-life people in America. A compromise was reached when the government decided that anybody from birth to 13 could not be killed, but from 13 to 18, they could be retroactively aborted, or "unwound". All their body parts (not just organs) were taken away from them and given to other people. The main characters of the book are volunteered for this process for different reasons. Connor is a troublemaker. Risa, who is a ward of the state, has reached the peak of her musical ability so she is going to be unwound to save costs. Lev is volunteered because his parents are strict Christians who give 10% of everything to God, including children, and Lev is the tenth child.
 * That is psychotic!
 * That is the point.
 * The kids' book Clone Catcher, by Alfred Slote, centers around the use of clones for this purpose; the rich have clones created and then raised in secure compounds until their organs are needed.
 * House of the Scorpion features entire People Farms for this purpose. Those used are all clones, which "aren't human" anyways. And as a rule they're deliberately brain-damaged shortly after birth so as to make sure they don't seem human. The main character is a rare exception,
 * This is the basis of Spares by Michael Marshall Smith.
 * In The Patternist Series by Octavia E. Butler, the immortal soul eating Body Surfer Doro attempted to create a new race of human telepaths through a selective breeding program extending from the early ages of human history towards the present so he can have new bodies to possess. He is eventually Hoist By His Own Petard as one of his group of eponymous network telepaths struggle beyond his control and absorb him instead.

Live Action TV

 * There is an episode of CSI where a girl is found dead in the desert; turns out she was conceived as a bone marrow donor for her older brother. Older brother felt bad about this and so, in a total failure of logic, killed her.
 * He was a staunch Catholic and she was so depressed by her life she was considering suicide. His first plan was to make the parents agree to stop using her as his donor and let him die. They went back on their promise when he had kidney failure, stating that they had only agreed to stop treating the original cancer, not the side effects and were going to force her to donate a kidney. He killed her, confessed to a priest, then planned to die from his disease, thus ensuring both went to heaven, instead of her going to hell as a suicide.
 * The question of why he didn't just run away, if he was sufficiently at liberty to dump a body in the desert, is where this troper's Insane Troll Logic-tolerance ran out.
 * This troper had the same reaction initially, but it made marginally more sense after realizing that given their treatment of the "donor sibling" up to that point, the parents would probably treat her even worse should her brother, her "reason for living" in the first place, run away for her sake.
 * Star Trek Enterprise cloned Trip so Dr. Phlox could get certain brain parts for replacement. The problem was that the clone retained Trip's memories and didn't want to die...
 * An episode of Private Practice has a mother, six months pregnant with the walking transplant, have her terminally ill son need a blood transfusion within the week or the son will die. Their baby girl has not developed enough, so what does the mother do?
 * That show loves this trope. One episode featured a couple with a walking transplant baby who was intended to save his twin sisters with leukemia. When he turned out to have only enough cord blood for one sister, the parents were asked to choose their favourite to treat!
 * Used in an episode of Sliders, which has our Quinn as this for the world-of-the-week's Quinn.
 * Another episode features a world where all people or a certain age are considered potential organ donors, whether they want to or not. Each receives a non-removable tracking bracelet that activates when a compatible organ is needed. Then a special police unit arrives to take the "donor" into custody. The doctors behind the program are shown to be corrupt, often using the system to get what they want (i.e. if you don't do what I say, I'll activate your bracelet and take your heart or liver).
 * In Law and Order Criminal Intent, there was this one guy who goes around literally giving away pieces of himself since he had given away pretty much everything else.
 * Done in the original Law and Order when a doctor is revealed to have been implanting IVF patients with his own sperm, which screws up one couple's plan to save one child by conceiving another. McCoy briefly considers indicting the doctor for the child's death.
 * One of the reasons the Goa'uld System Lords take their lo'tars (trusted human servants; literally means "you, human") everywhere with them is to have a spare host in case their current one expires for any reason. In this case, the lo'tars are donating their entire bodies. However, most are brainwashed into believing it to be an honor. They are also expected to be knowledgeable about Goa'uld politics in order to avoid any faux pas.
 * Mohinder was conceived to be a blood donor for his sister. Although by the time he was born she was too far gone and was always a point of contention between him and his father.
 * On Neighbours Nicola was conceived for the purpose of saving her sister Miranda's life. This is a major factor in her psychotic break shortly before she left the show.

Video Games

 * Producing these is revealed to have been the original purpose of the laboratory where 1213 takes place.

Western Animation

 * The Venture Brothers: Dr. Venture has this as a partial purpose for his sons. Season 2's premiere reveals why this is okay.
 * Played for laughs in Futurama; the Professor keeps Amy around because she is of the same blood type.
 * He views all his employees this way: "Damnit, Hermes, just jump already. Stop hogging that healthy liver!"

Real Life

 * Well on its way to aversion in Real Life. With the rapid advancements being made in tissue engineering, The Island-style cloning people for parts makes absolutely no sense. The method of building organs discussed in 2057, by using a "cell-jet" printer, is actually being worked on.
 * I wouldn't be so sure. While it is true that scientists all over the world are researching ways to create artificial tissues to replace damaged ones (especially heart and nerve tissue which lacks any significant regenerative abilities) However, most, if not all of these procedures require human stem cells - and the easiest way to get them is to harvest them from human embryos. To avoid the immune system attacking the transplanted tissue, some scientist have actually mentioned the posibility of cloning the patients and harvesting the stem cells from the embryos before they get any chance to get angsty and turn against their creators.
 * You can harvest stem cells from the umbilical cord of newly born babies. This avoids all the previous problems.
 * ( Along the same veins, some scientists are also trying to use the stem cells that can be found in an adult's body (like, for example, in the bone marrow, or in certain skin layers) for these purpose, allthough this is slightly harder as those cells can only turn into certains types of other cells. Some scientists are trying to reverse them to their pluripotent state, tough.
 * I suppose that one could also do this in the future for other reasons - i.e. seeing the effects of drugs on whole humans (rather than just cell cultures or animals).
 * Unlikely; the ethical violations in raising a human being solely to test drugs on are incredible. All said this trope is well and truly averted in real life and will be for the forseeable future. It's just smart business planning too; why raise an entire human being if you need a heart transplant, when you can just make one from scratch.
 * Advances in genetic engineering may eventually make it possible to breed domestic pigs with human-analog histocompatibility traits. Most internal organs are similar in pigs and in humans, so such animals would be ideal four-legged examples of this trope, with few ethical constraints and much faster turnaround-time to grow them to adult size.
 * To be clear, there is no record of a successful xenotransplantation. Organs grown in the pigs would need to be nearly identical to the recpients' genes to not be attacked by (and attack) the former, and the pigs' own immune systems would be likely to attack any alien organs growing within them. Once again, growing transplants from scratch may be more plausible.