How many regenerations does the Doctor have left?

[Pharaoh Atem]

he has 46 in all

[jameshawking]

That depends, really.

How many millions of people are watching?

[/thread]

Really though, this is kind of a silly thread, is it not?

[ringwraith]

It's 12 regenerations, so ultimately a Time Lord has 13 forms... I guess really depends on "Journey's End" (season 4) making David Tennant regeneration 9 and 10.

This assessment is correct. The regeneration energy left over from David Tennant's self-healing exercise was powerful enough not only to turn Donna into a demi-doctor, but also to generate an entirely new, albeit human, body for the Doctor with it's own mind and will. This "metacrisis" as it is called in the series was then left on the parallel earth with Rose to live out his remaining human-length years, giving Rose her much coveted human-style relationship with the Doctor. And Donna's enhanced, self-destructive, demi-doctor mind was suppressed by the Doctor for her own good. But that regeneration energy was full, complete, and total. It was all used up. David Tennant is the tenth Doctor and both ninth and tenth regenerations. Thanks to this event, we no longer have to draw a distinction between the form number, tenth Doctor, and the regeneration number, ninth regeneration. Matt Smith is now both the eleventh Doctor and the eleventh regeneration.

But that having been said, it still doesn't in any way close the book on the limit of the number of regenerations the Doctor can have. Even without delving into the annals of Doctor Who history, we can gleen some very promising plot-line openings that will allow the Doctor to break the established 12 regeneration limit.

First let us establish that regeneration is a biological, not supernatural, phenomenon for time lords. The original allotment is 12 regenerations. We have become accustomed to the use of the term "regeneration energy." This energy, seeing that it has a biological source would have to come from cellular mitochondria, an organelle in the cytoplasm of cells that functions in energy production. For time lords, their cellular mitochondria are physically capable of generating enough energy to produce 12 complete regenerations. Human beings age and die because each time our cells divide, they lose telomere length. Finally, cell division becomes corrupted because the segment of DNA that occurs at the ends of chromosomes reduces to a point where it can no longer guide the cell in accurate replication. I postulate that the cellular mitochondria of time lords experience a similar reduction after each regeneration ensuring that only 12 regenerations can occur without some type of intervention. It would not be necessary for another time lord to "pop up" upon the death of the final form to prevent the dying time lord from regenerating further. Simply put, the time lord has run out of regeneration energy.

We are offered some evidence that this line of thinking is reasonable from the episode called "The Doctor's Daughter." In it, Jenny is created when a progenation machine removes a few of the Doctor's cells and extrapolates a female genetic construct. She has two hearts like the Doctor, and after a fatal shooting, it appears to be the Doctor's sincere hope that Jenny will regenerate as he does. However, the Doctor, Martha Jones, and Donna Noble all leave disappointed, thinking that Jenny has died the true death. We as the audience, however, are privileged to learn that Jenny experienced a mild form of regeneration that did not have nearly the intensity of a full on time lord's regeneration. When a time lord regenerates, the regeneration energy is so powerful that it reorganizes his genetic structure into some other possible combination. It is alluded to in "Let's Kill Hitler" that the time lord may have some small influence over the final outcome of the new form when Melody Pond, during her regeneration says, "...I'm concentrating on a dress size." But other than that, the time lord's form succumbs to this overpowering structural reorganizational principle. The fact that the cellular mitochondria of a progenated time lord would have substantially less energy for regeneration is logical and accounts for the delayed resurrection of Jenny, the Doctor's daughter. I would even go so far as to postulate that a progenated time lord would have 12 "regenerations" as well, but given the much milder form, it would probably be more appropriate to refer to them as resurrections since the genetic structure of the being does not undergo violent reorganization.

Now, having well established the line of thinking that the regeneration energy of a time lord is fixed and has a biological source, I bring up the plot-line opening that I mentioned before. We know that regeneration energy can be transferred from one being to another as an act of will on the part of the time lord himself. We saw it with David Tennant utilizing only a part of the regeneration energy and then sluffing off the rest into his severed hand. The leftover energy of that regeneration was enough to accomplish only a certain number of odd effects, the "metacrisis" of Doctor Donna and the second, human, Doctor. We also know that during the regeneration time period, time lords can heal themselves rapidly, even regenerating limbs as the Doctor himself did for his severed hand. In the episode "Let's Kill Hitler," Melody Pond absorbed the bullets of serveral machine guns at once and used the regeneration energy to disable the nazi soldiers. If you will recall, in that same episode, she also poisoned the Doctor with the poison of the Judas tree, which apparently not only would have killed the Doctor, but disabled his remaining regeneration as well. The Doctor died in this episode, died for real. It was Melody Pond after she was made aware that she was to become River Song, the Doctor's one true love, who resurrected the Doctor. Because she was still regenerating herself, she was able to control the regeneration energy and channel it into the Doctor.

Later we learn that she "used up all her remaining regenerations in one go," to bring the Doctor back to life. It was never made clear whether her using all her regenerations in one go was because it was actually necessary to bring the Doctor back or whether it was just due to her inexperience with controlling the redirection of regeneration energy. But I would venture to say it was the later, not the former. First the Doctor had only been "dead" a minute. The leftover energy from her own regeneration should have been enough to "heal" him back to life. I believe her inexperience with the process coupled with her own newly discovered love for the Doctor caused her to relinquish all of her regeneration energy into his form. It was more an act of desperation, to undo the damage she had done. She just kept channeling until there was no more energy to channel.

Having become the beneficiary of all her future life force, the Doctor then became obsessed with saving her for all time, which is why he kept the com link from her space suit attached to and hidden inside the sonic screwdriver that he gave to her. If you recall, when River encounters the Doctor for his first time, he is David Tennant at the library with Donna Noble. Then in the episode "Forest of the Dead" River commits suicide to save the computer core allowing all the people within it to be rematerialized. Even though the David Tennant version didn't know all that was to come, he knew himself well enough to realize that he must have figured out some way to save River. And he did. Finding her com link saved inside the sonic screwdriver that River had brought with her, the Doctor was able to upload her consciousness pattern into C.A.L. and therefore, save River, albeit in a virtual world.

Now this brings me to the crux of my point. Melody Pond's first form was the girl in the spacesuit. When she regenerated the first time it was in a New York alley with a homeless man back in 1969 / 1970. The form she took then was the young Mels that Rory and Amy grew up with. It is conceivable that the Silence brought her new young form forward in time, placing her in the same area as the young version of her parents so she could grow up with them and have the best possible chance of encountering the Doctor again. Her second and final regeneration occurred in the episode "Let's Kill Hitler," where she assumed the form of actress Alexandra Kingston. This is the form she kept until her later/earlier (timey, wimey) death in "Forest of the Dead." So only having used two of her twelve potential regenerations before bequeathing the rest of them to the Doctor would have allowed the Doctor to become the beneficiary of 10, count 'em, 10 unused regenerations. Along with his final remaining regeneration, this would afford our hero 11 remaining unused regenerations. He's almost as good as new!