Regeneration




 * This article is about the Time Lord physiological process. For the non-fiction book see Doctor Who: Regeneration

Regeneration is the process by which the Time Lords maintain their centuries-long lifespans. It is generally described as a "genetic reshuffling" which a Time Lord may go through if his or her body is worn out by age or has suffered some life-threatening injury or infection. Time Lords may even regenerate at will.

The regeneration process
During regeneration, the body of a Time Lord is reconfigured into a new form; the new form is generally physically younger and healthier (in human terms) than the Time Lord's previous incarnation. After each regeneration there is a marked change in a Time Lord's appearance and personality. During the process of regeneration there are the genetic equivalent of 'bit errors' appear in the DNA of the regenerated cells. This is what causes the appearance of the Time Lord to change; because even the cells of the brain regenerate as well, their brain chemistry and organisation will change. Although the aspects of their personality caused by "nurture" will not change, the "nature" contribution to their personality will change. (BFA: The Sirens of Time)
 * ''However it has been hinted that, at least in the Doctor's case (in multiple Doctor stories), regeneration comes with the cost of gaps in memory and intelligence as the First Doctor is often shown to be wiser, more intelligent, and quick witted than his future incarnations. This may be due to the changes to the brain caused by regenerations, although it is possible they may gain other skills as the Tenth Doctor has demonstrated a level of skill in piloting the TARDIS none before him have.

The actual regeneration is a painful process as bones and tissue settle into their new forms. (DWN: The Power of the Daleks) During the first few hours of the regeneration, the Time Lord will often suffer from confusion, erratic behaviour and memory loss. (DW: Castrovalva, The Twin Dilemma, The Christmas Invasion) If they are knocked unconscious, the whole process might be started all over again. (DWN: The Power of the Daleks) After a while, the Time Lord's body will have settled down, though they can regrow limbs within the first 15 hours of the regeneration due to having enough residual energy. (DW: The Christmas Invasion) The presence of a TARDIS helps the regeneration process. (DWN: The Power of the Daleks) Some Time Lords, however, may regenerate with little or no overt complications, for example, Romana. (DW: Destiny of the Daleks)


 * ''Since the series revival, every seen regeneration has had a similar violent fiery effect, only differing with The Master, which had a similar though multi-coloured effect. This is due to Davies wishing to identify the regeneration as a 'time lord process', though fans often theorise that the time war (and the assumption that the Eighth Doctor regenerated in the explosion that destroyed Gallifrey) was so violent that it has had an adverse effect on how regeneration occurs, perhaps being more violent due to the war.

On two occasions (regenerating in his Ninth and Tenth incarnations), the Doctor warned his companions away. This would seem to imply that the energy released during the process poses some level of danger to Humans, and possibly that them being too close may pose a danger to the Time Lord. (DW: The Parting of the Ways, The Stolen Earth) However at least one regeneration occurred with other individuals seen in close proximity (DW: Logopolis), but other on-screen regenerations have occurred with the Doctor either by himself or with onlookers standing away from the Doctor.


 * It is possible the concept of the regeneration energy posing a danger is only a recent addition to the show, or is potentially a result of a linger effect of the Time War on regeneration.

Limitations
Though Time Lords can regenerate after severe injuries, regeneration does not seem to be guaranteed. The Doctor, for example, was at one point convinced that he was going to die at the hands of the Gelth (DW: The Unquiet Dead), although it is possible he meant the particular incarnation, and there have been numerous occasions in his lifetimes where survival -- including regeneration -- was not assured. A very sudden death may also make it impossible to regenerate. (DW: Turn Left) As well, the interference of some medications, such as anaesthesia, may disrupt or destroy the regenerative process. (DW: Doctor Who: The TV Movie)

It was established that a Time Lord can regenerate successfully twelve times before permanently dying. (DW: The Deadly Assassin) As with most such "rules" there were occasionally exceptions to the twelve regeneration limit and it may be circumvented through unorthodox means. The Master, after taking over the body of a Tremas, is offered "regeneration: a whole new life cycle" as an incentive to rescue the four Doctors from the Death Zone. (DW: The Five Doctors)


 * Alternatively, this might just imply that a cycle of regenerations can be given to non-Time Lords.

Control over regeneration
Generally, regeneration is initiated when a Time Lord has been too badly injured to survive. However in some cases Time Lords have been known to exercise control over the process. Romana appeared to regenerate on a whim, (DW: Destiny of the Daleks) while Azmael initiated a thirteenth regeneration in order to end his life (DW: The Twin Dilemma). The process can also be stopped with some difficulty (DWN: The Power of the Daleks), as the Master did in order to spite the Doctor (DW: Last of the Time Lords).

The degree of control that Time Lords have over their end appearance is unclear. The Master was able to make his next regeneration as young as the Tenth Doctor. (DW: Utopia) Although it is possible this was merely a coincidence, as most regenerations result in a physically younger form. Romana seemed adept enough at the process to custom design her new appearances, trying several bodies before finally deciding on a copy of Princess Astra. The Doctor criticized Romana for taking on the form of another person, suggesting such things were not unheard of (DW: Destiny of the Daleks). In contrast to Romana, the Doctor did not appear to have much control over his post regeneration appearance; after his fourth regeneration he commented "that's the problem with regeneration, you never quite know what you're going to get" (DW: Castrovalva), and would restate this immediately prior to his ninth regeneration (DW: The Parting of the Ways).
 * It is possible, given Time Lords are 'born' from looms, that Time Lords of the Doctor's generation are not able to control the appearance their regenerated form will take while later ones are. Equally it may be that the next incarnation's form can be controlled more easily when regeneration is voluntarily triggered but not when caused by more violent circumstances, this seems somewhat plausible given in the Doctor's case most of his regenerations have taken place because he sustained a mortal wound.

The Time Lords were apparently capable of controlling the regeneration of individual Time Lords, either forcing a regeneration (DW: The War Games) or removing later regenerations (DW: The Trial of A Time Lord).

Aborted Regeneration
Occasionally, a regeneration will fail and the regeneration will abort. Though Time Lord technology can treat this, in some occasions the damage will be too severe to fix.

After being shot by the War Lords, the War Chief was barely able to survive. While being taken back to the War Lords' planet, his body attempted to regenerate. Due to the massive injuries and the lack of medical care, this regeneration aborted. The result was that he turned out looking like two individuals poorly fused together. (NA: Timewyrm: Exodus)

Meta-Crisis
A Time Lord can prevent death and regeneration by focusing the regenerative energies into a severed appendage. The severed appendage siphons off the excess energy while the Time Lord uses just enough of it to heal wounds. This results in the appendage storing enough energy to actually grow a nearly identical Time Lord if it comes in contact with living tissue. As a consequence he healed but did not change. After Donna touched the hand, it grew into a one hearted version of The Doctor, owing the "human biological metacrisis" her DNA caused. (DW: Journey's End)


 * Due to the fact this has never been seen before, and it is rare for a Time Lord to have a severed appendage, it is unknown if this used up a regeneration or not.

Science
The exact mechanism that makes regeneration possible has not been stated, though many theories have been made. These varying explanations may or may not be compatible with each other.


 * One explanation was Cardinal Rassilon had been investigating a method of regenerating decaying and diseased tissue via a series of permanently carried self-replicating biogenic molecules. The cells of a Gallifreyan body could be repaired, restored and reorganised. This would result in a wholly new physical form. The brain cells would similarly be rearranged, though to a lesser degree, thus ensuring the new incarnation will replicate the memories and personality of the former incarnation. Cardinal Rassilon intended for this mechanism only to be used upon the Gallifreyan elite. He also inputted a parameter of 12 regenerative cycles to avoid decaying biogenic molecules. (BFA: Zagreus)


 * Another theory attributes regeneration to a "nanomolecular virus" that rebuilds the body much like the "self-replicating biogenic molecules". (EDA: The Gallifrey Chronicles)


 * A third theory is that Time Lords have triple-helix DNA: the third strand was added by Rassilon to make regeneration possible. (MA: The Crystal Bucephalus)


 * One partial explanation of the process links it to the release of massive amounts of a hormone known as lindos at moments of extreme trauma, with the hormone triggering the regeneration itself. Recently-regenerated Time Lords can be identified by the raised levels of lindos in their system. (DWN: The Twin Dilemma, BFA: Unregenerate!)

The Doctor's Regenerations
Following is a list of how each Doctor has regenerated, thus far.


 * 1) First Doctor: apparently succumbs to old age and/or possibly from the energy draining effects of the planet Mondas (DW: The Tenth Planet)
 * 2) Second Doctor: a forced regeneration and exile to Earth by the Time Lords. (DW: The War Games)
 * 3) Third Doctor: radiation poisoning from the Great One's cave of crystals on Metebelis III. (DW: Planet of the Spiders)
 * 4) Fourth Doctor: falls from the Pharos Project radio telescope. (DW: Logopolis)
 * 5) Fifth Doctor: spectrox toxaemia. (DW: The Caves of Androzani)
 * 6) Sixth Doctor: injured as the Rani attacks the Doctor's TARDIS (DW: Time and the Rani)
 * 7) Seventh Doctor: dies on the operating table while undergoing exploratory heart surgery. (DW: Doctor Who: The TV Movie)
 * 8) Eighth Doctor: unknown as of yet, possibly as a result of the Last Great Time War.
 * 9) Ninth Doctor: cellular degeneration caused by absorbing the energies of the time vortex from Rose Tyler, which she in turn had absorbed from the heart of the TARDIS. (DW: The Parting of the Ways)
 * 10) Tenth Doctor: Begins regeneration soon after being hit by Dalek fire, (DW: The Stolen Earth) aborted by redirecting the energy to his severed hand (DW: Journey's End) It is not yet known whether this constituted an actual 10th regeneration. The Tenth Doctor's anticipated full regeneration into the Eleventh Doctor has yet to be chronicled.


 * The Eighth Doctor unofficially regenerated into the Alternative Ninth Doctor; the circumstances of this are not revealed. An unofficial regeneration from the Third Doctor into an alternate Fourth Doctor was also depicted, again with the cause unrevealed (Doctor Who and the Daleks in the Seven Keys to Doomsday).

Other Time Lord's Regenerations

 * The Doctor's arch-enemy, the Master was able to extend his life past his 13th regeneration. He first attempted and failed to use the Eye of Harmony on Gallifrey to renew himself, though he was able to absorb enough energy from it to extend his life for a time. (DW: The Deadly Assassin) He was finally able to gain access to the Source on Traken, and used some its powers to steal the body of Nyssa's father Tremas. (DW: The Keeper of Traken) When this body was finally destroyed by the Daleks on Skaro, the Master's essence entered that of a human on Earth, and in this body the renegade Time Lord tried to use the powers of the Eye of Harmony's dimensional link on the Doctor's TARDIS to steal the Doctor's remaining lives. (DW: Doctor Who: The TV Movie) Though he was fatally wounded in the attempt, he was later resurrected by the Time Lords to fight in the Last Great Time War, (DW: The Sound of Drums) complete with a new set of regenerations. He was only seen to use one such regeneration, after having been shot by the Malmooth Chantho (DW: Utopia) but may have used others prior to that.


 * Rassilon was said to have achieved a cycle of perpetual regeneration, becoming immortal. It was for this secret that Lord President Borusa sent four of the Doctor's incarnations and their companions into the Death Zone, where Rassilon lay in eternal sleep in the Dark Tower. (DW: The Five Doctors)

Behind the Scenes
Regeneration was first introduced when the First Doctor (William Hartnell) changed into the Second Doctor (Patrick Troughton) in the closing moments of The Tenth Planet. Tradition has it that Hartnell himself thought up the idea of the Doctor being able to change into a new body as a means of keeping the series going after his departure. In The Power of the Daleks (the first story featuring the Second Doctor), the Doctor described himself as having been "renewed", and also said that the change was "part of the TARDIS."

The change in the Doctor's appearance was meant to occur several stories earlier, during The Celestial Toymaker, with the Toymaker capriciously changing the Doctor's appearance out of spite (the Doctor is invisible for most of the story and would have reappeared in the final episode played by a different actor). The reason for the change of plan is unknown - either it was decided to retain Hartnell in the role for a few more stories, or the actor was accidentally issued with a new contract by mistake, making it impossible to recast the Doctor at that moment in time.

The process was not actually referred to as "regeneration" until the end of Planet of the Spiders, when the Third Doctor (Jon Pertwee) changed into the Fourth (Tom Baker). Prior to this, the Doctor was simply described as having "changed his appearance."