ROSE: Well, he's got two hearts.
JACKIE: Oh, don't be stupid.
ROSE: He has.
JACKIE: Anything else he's got two of?
(The Christmas Invasion, 2005 Christmas special)

So is there anything else he's got two of? Or to put it more generally, what are the physiological differences between a human and a Time Lord, other than the number of hearts? How can you tell, just from examining a Time Lord's body, that he - or she - is a Time Lord?

Let's say you can't kill the person to see whether they regenerate, nor can you wait hundreds of years to see whether they die of old age. All you can do is a one-off examination of their body. You have all the equipment you need: stethoscopes and so forth. So that you can see the whole of their body (as well as to exclude the possibility of identifying a Time Lord by their dress sense), let's assume they're naked:

naked Doctor

  • 8
    Kill him. If he regenerates, he's guilty of being a Time Lord. If he stays dead... then he was innocent.
    – Omegacron
    Commented Jul 15, 2015 at 19:01
  • 3
    @Omegacron What if he's in his final regeneration (and doesn't have a handy bunch of Gallifreyans behind a crack in the sky to give him a new regeneration cycle)?
    – Rand al'Thor
    Commented Jul 15, 2015 at 19:08
  • 2
    Easy, by their eccentric dress sense. Commented Jul 15, 2015 at 19:10
  • 2
    @Wikis I've edited to make it clearer what I'm asking. I hope Matt Sith's naked torso isn't considered too NSFW for this site?
    – Rand al'Thor
    Commented Jul 15, 2015 at 19:40
  • 2
    "Matt Sith" ... I'm picking up Star Wars knowledge by osmosis on this site! :-O
    – Rand al'Thor
    Commented Jul 15, 2015 at 19:40

2 Answers 2


This is from Wikipedia so take it for what it is, but the main differences are:

Physiological differences from humans include two hearts which normally beat at 170 beats per minute, an internal body temperature of 15 degrees Celsius (59 degrees Fahrenheit) and a "respiratory bypass system" that allows them to survive strangulation. Time Lords can also survive full exposure to the vacuum of space with no ill effects, though when in a vacuum for an extended period, a Time Lord must take a supply of air along or suffocate. Time Lords also seem to have an increased resilience to higher frequencies of sound, as seen in "The Christmas Invasion" and "Partners in Crime". If severely injured, Time Lords can go into a healing coma which lowers their body temperature to below freezing.

So according to this, a simple temperature test will do. If you're still not sure, throw him to outer space and see how long it takes him to suffocate.

Some of these facts are marked as "citation needed". Others are referenced to different episodes of classic Who and new Who.

  • 2
    Does anybody have a source for that body temperature statement? Wikipedia page itself lacks that particular citation.
    – Viniter
    Commented Aug 15, 2015 at 16:59
  • 1
    “Time Lords can also survive full exposure to the vacuum of space with no ill effects” — weeeeell, sometimes they go blind. Commented Feb 14, 2018 at 9:28
  • They can also survive freezing temperatures way below human range "DOCTOR: Stasis chamber. You've got to take it below minus two hundred. Freeze it out of me! It'll use me to kill you if you don't." Season 3, Episode 7 (42 minutes)
    – Matt
    Commented Jan 8, 2020 at 14:21
  • There was a 2nd Doctor story that mention the body temp, but I don't recall which. Also, the novelization of "Mark of the Rani" mentions it as well. (It was how the Rani recognized the Doctor as a Time Lord.) Commented Feb 2, 2022 at 21:31

Assuming a brief (relatively) non-harmful physiological examination with commonly available 21st century human medical tools ...

Aside from the 2 heartbeats... which might not be unique to Gallifreyan physiology, heck even one our own species has had 2 hearts!

Also assuming they haven't had a "dodgy" regeneration and are missing a head or have a dog's nose (according to comments by the 9th Doctor)....

If you stuck a light down their throat you might see evidence of their "Respiratory bypass system".

  • I've always taken that "missing a head" thing to be a case of Rule 1: The Doctor Lies.
    – Rand al'Thor
    Commented Jul 15, 2015 at 22:04
  • The tricky bit is that the Doctor sometimes tells outrageous truths. Commented Aug 15, 2015 at 15:13
  • When you have eliminated the impossible, whatever remains, however improbable, must be the truth. - Sherlock Holmes
    – Rand al'Thor
    Commented Aug 15, 2015 at 15:14
  • 1
    Missing a head is very common. Some Time Lords have as few as one head. These tend to be overrepresented in the military and political arenas of Time Lord society. Commented Mar 29, 2016 at 14:04

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