Doctor (Doctor Who) - Physiology

Physiology

Although Time Lords resemble humans, their physiology differs in some key respects. For example, like other members of his race, the Doctor has two hearts (binary vascular system), a "respiratory bypass system" that allows him to go without air, an internal body temperature of 15–16 degrees Celsius (60 degrees Fahrenheit) and he occasionally exhibits a super-human level of stamina, and the ability to absorb, withstand, and expel large amounts of certain types of radiation (the Tenth Doctor stated they used to play with Röntgen bricks in the nursery, after absorbing the radiation from an x-ray of significantly magnified power). This ability would seem to have limitations which have yet to be fully explained, as he is harmed by radiation in The Daleks, Planet of the Spiders, and The End of Time. Additionally, he has withstood exposure to electricity deadly enough to kill a human with minimal damage (Terror of the Zygons, Genesis of the Daleks, Aliens of London, The Christmas Invasion, Evolution of the Daleks, spin-off audio Spare Parts). Certain stories also imply that he is somewhat resistant to cold temperatures. To counter extreme trauma, such as exposure to the poisonous fungus in The Seeds of Death and after being shot in Spearhead from Space, he can go into a self-induced coma until he recovers.

Additionally, he has shown a resistance to temporal effects and has demonstrated some telepathic ability, both the ability to mentally connect to other incarnations of himself he encountered (The Five Doctors), and an ability to enter into the memories of other individuals, similar to the Vulcan mind meld portrayed in Star Trek ("The Girl in the Fireplace"). He can apparently reverse this process, sharing his memory with another, as seen most recently in The Big Bang. Some humans can also enter the Doctor's memories after he enters theirs, as demonstrated by Madame de Pompadour (much to the Doctor's surprise) in "The Girl in the Fireplace", when she explains, "A door, once opened, may be entered from either direction." In "The Fires of Pompeii" the Doctor reveals that he is able to perceive the fabric of time, discerning "fixed points" and "points in flux"- moments when history must remain as it was originally versus moments when he can change or influence the original course of events-, as well as all past, present and possible future events. It is revealed in the episode "The Unicorn and the Wasp" that if he has the right vitamins and minerals in the right order he can stop himself dying from a dose of cyanide.

The Doctor also exhibits some weaknesses uncommon to humans. For example, according to The Mind of Evil (1971), a tablet of aspirin could kill him. In Cold Blood, a process meant to decontaminate him of bacteria from the surface of Earth causes him intense pain, and he says it could have killed him if allowed to proceed to completion. In the Eighth Doctor Adventures novel The Adventuress of Henrietta Street the Doctor lost some of his biological advantages over humans when his second heart was surgically removed when it appeared to be poisoning him, resulting in him losing the ability to metabolise drugs in his system and his respiratory bypass system, but these are restored to him when he begins to grow a new heart after his old one 'dies' (Camera Obscura). Events from the novels may or may not be canonical.

In his final serial, the Second Doctor states that Time Lords can live forever, "barring accidents." When "accidents" do occur, Time Lords can usually regenerate into a new body. However, it is stated in The Deadly Assassin that Time Lords can only regenerate a total of twelve times, giving a theoretical final total of thirteen incarnations. It may be possible to exceed this: in The Five Doctors the Time Lords offer the Master, who is inhabiting a Trakenite body, a regeneration cycle as reward for his help and cooperation, and at some point during the Time War they resurrected him, with his new body having at least one regeneration of its own. Regeneration is apparently optional, as in "Last of the Time Lords" the Master refuses to regenerate despite the Tenth Doctor's pleading. In addition, there are ways of killing a Time Lord that do not permit regeneration; for example, more than once it has been implied that stopping both the Doctor's hearts simultaneously would accomplish this. In the events of "The Impossible Astronaut", it appeared that shooting the Doctor during his regeneration into a Twelfth Doctor killed him permanently. However, "The Wedding of River Song" revealed that this was not actually the Doctor, but the Tesselecta robot pretending to be him, so the efficacy of a mid-regeneration killing has not been confirmed.

In an October 2010 episode of the spin-off series, The Sarah Jane Adventures, when asked by Clyde how many times he can regenerate, the Doctor (Matt Smith) flippantly replies "507". Whether this is true or just a joke is unclear, but the writer of that episode, Russell T. Davies, said it was "...too good an opportunity to miss."

Other skills include his mental communication with other Time Lords, in some cases over a galaxy's distance. His skill with hypnosis is such that he requires only a second's glance into a subject's eyes to put him/her under his spell. The Doctor can read an entire book cover to cover in a second by thumb-flipping the pages before his eyes (City of Death, "Rose", "The Time of Angels"). Though any medical skills he shows early in the series are rudimentary, by Remembrance of the Daleks he can perform sophisticated medical diagnoses merely by touching someone's ear. He is an excellent cricket player (Black Orchid) and in "The Lodger" he proves to be a prodigiously talented footballer despite unfamiliarity with some of the game's basic rules. Though reluctant to engage in combat against living opponents, this is not for any lack of skill in doing so; the Doctor is conversant with both real and fictitious styles of unarmed combat (most obviously the "Venusian Aki-Do" practised by the Third Doctor), has won several swordfights against skilled opponents, and is able to make extremely difficult shots with firearms and, in one instance (in The Face of Evil), with a crossbow. Thanks to exposure to many of history's greatest experts, including those from the future, the Doctor is a talented boxer, musician, organist, scientist, singer (able to shatter windows with his voice), and has a PhD in cheesemaking (The God Complex).