Now then, time for a little genealogy! If you recall The Massacre Of St Bartholomew's Eve, you'll remember that Steven was none too happy about what happened to the Huguenots- in particular one Anne Chaplet. He was so upset he was on the verge of leaving the TARDIS, but returned after learning of the survival of one of her descendants......
DOCTOR: Oh, so you've come back, my boy!
STEVEN: Yes, yes, I've come back. We can't go into that now. There are two policemen coming over the common towards the TARDIS!
DOCTOR: Policemen? Coming here? Good gracious me! They'll want to use the telephone or something like it.
STEVEN: Oh, that was close.
DOCTOR: Well, tell me, young man, what made you change your mind?
STEVEN: How did you get in here?
DODO: On me feet, same as you did.
STEVEN: Look, do you realise what's happening? We've taken off! We could land anywhere!
DODO: We really travelling? Where to?
STEVEN: But we're travelling in time and space. We're not on Earth any more. We could land anywhere, in any age.
DODO: Tell us another one.
STEVEN: Doctor, how could you?
DOCTOR: What else could I do, dear boy? You don't want a couple of policemen aboard the TARDIS do you? You know, you're the most inconsistent young man? Just now you were telling me off for not having that Chaplet girl aboard!
STEVEN: Ah, that was different! This is no joyride you know. You may never get home again.
DODO: I don't care.
STEVEN: What about your parents?
DODO: I haven't got any. I live with me great aunt, and she won't care if she never sees me again.
DOCTOR: There now, you see? All this fuss about nothing. But don't you think she looks rather like my grandchild Susan?
STEVEN: You forget, I've never met your granddaughter.
DOCTOR: Oh, no, no, no, no, of course not, no. Yes, but she does you know. What is your name, child?
DODO: It's Dorothea, really. Dorothea Chaplet.
STEVEN: Chaplet? Yes, but you're not French, are you?
DODO: Don't be daft. Me granddad was, though.
STEVEN: Doctor, it's not possible is it? Chaplet? Anne's great, great.....
DOCTOR: Yes, yes, it is possible, my boy. Very possible. Welcome aboard the TARDIS, Miss Dorothea Chaplet.
Somehow the Doctor resists the temptation to ask why the devil she'd want to be nicknamed after a now extinct flightless bird, but in his Tenth incarnation he will finally come across one in the Museum Of The Last Ones in the self-explanatory The Last Dodo- while evading capture as the last of the Time Lords, someone determined to make an exhibit of him with echoes of The Space Museum. Mystifyingly he doesn't then offer Dorothea the dodo a place aboard the TARDIS as the newest of his companions. As a younger man, though, he did extend the hand of companionship to the human Dodo, with The Ark marking her first trip in the great space-faring police box!
And its not all sunshine & rainbows. Arriving in the rather ambiguous 57th Segment of Time, presumably a clever way to cover up the fact that nobody, least of all credited co-writers Paul Erickson & Lesley Scott ( in their one & only contribution to Doctor Who), had bothered to work out how time would be measured that far ahead! Dodo's first glimpse of new frontiers was to apparently bear witness to what could be the last days of humanity, as a ship containing its last vestiges makes its way off the planet- which is on the verge of collapsing & falling into the Sun.
If the threat of solar apocalypse weren't enough, Ms Chaplet doesn't feel all that well. But Dodo Gets A Cold is of course a frankly rubbish title for an episode. So The Ark it was/is. But her snotty nose could have dire consequences for these future humans & their odd one-eyed humanoid mammoth-thingy servants the Monoids.
Note their interesting choice of hairdo, as well! I read the news today, oh boy, about the human race, they all got colds...........sadly we never see the true depth of the Monoid branch of the Beatles fan club. So much for Dodo's initial prediction that she was at the zoo, though!
STEVEN: Look, Dodo, you don't know what you might have found out here. No gravity, poisoned atmosphere, all sorts of things. Look, stop prancing around over there. What happens if you get lost?Several other odd features seem to suggest they're nowhere near London, too!
DODO: I catch a bus back.
STEVEN: A bus? Look, what are you talking about? I mean, just where do you think you are?
DODO: Ah! Bet you thought you'd caught me, didn't you? Bet you thought I didn't know. Well, I do.
STEVEN: You do?
DODO: Of course I do.
STEVEN: What, this place? I mean, you recognise it? What, with all these strange animals and flowers and things?
STEVEN: Well, you can't have been here before.
DODO: Yes I have. It's just outside London. I came here once with the school. It's called Whipsnade ( http://www.zsl.org/zsl-whipsnade-zoo).
STEVEN: Just outside London? Look, wait a minute. I mean, it can't be.
DODO: Yes, it is. I bet if you go down that path there, you'll come to the American Bison and the Tea Bar.
STEVEN: Look, we don't even know that we're on Earth.
DODO: Earth? Earth? Well, it couldn't be anywhere else now, could it? Hey, look Steven, that proves it. That's a chameleon.
STEVEN: What this?
DODO: And here's a monitor. Look, that's a Locust. There, what did I tell you?
STEVEN: Look, how do you know all this?
DODO: I learnt it at school. There's nothing you can tell me about nature, simply nothing.
STEVEN: Well?Possible it is, desirable it isn't as a later, colourfully-attired Doctor would remark! But it was, of course, the Ark...
DOCTOR: Well, it's just as I said. It's all very, very strange. That is an Indian elephant.
STEVEN: Yes, I know. What difference does that make? What does it prove?
DOCTOR: Well, that's what I'm trying to find out, dear boy.
DODO: Flowers from America, birds from Africa, a snake from Brazil and now an elephant from India.
DOCTOR: Exactly, my dear.
STEVEN: It's a jungle incorporating things from all over the world.
DOCTOR: Yes, you're quite right, my boy. Yes, and top of everything else, it's a jungle without a sky.
DODO: Hey, look at that then.
STEVEN: No sky?
DOCTOR: No sun, no clouds, merely a metal roof radiating some kind of light.
STEVEN: It's extraordinary.
DOCTOR: Yes, and plus something else.
DODO: What's that?
DOCTOR: The earth, this, this ground we're standing on. It appears to be trembling.
DODO: It is more elephants coming?
STEVEN: An earthquake building up?
DOCTOR: No, it's too regular for that. No, it's more of a mechanical vibration. Yes.
STEVEN: In what circumstances do you get all these things together? I mean, animals and vegetable life from different continents?
DODO: With a metal roof and all this shaking?
DOCTOR: There's only one thing that strikes me. This could be some kind of indoor nature park.
STEVEN: Yes, but on this scale?
DOCTOR: Yes, yes, improbable dear boy, but possible. Definitely possible.
Behind the scenes, The ark was notable for its then-groundbreaking use of out-of-sequence recording. It was the first time in Doctor Who history that a story had been filmed out of sequence - episode four (The Bomb) recorded prior to the previous installment. The Ark also made good use of the forced perspective effect, something which hadn't been widely attempted in Doctor Who to that time. See the Ark above?... Look it's taking off...
The Ark was also the first time a female writer was credited on Doctor Who, although it appears that she didn't actually do any actual work on the script. The co-writing credit came about at the request of her then-husband, Paul Erickson. (Maybe they'd had a row?)
And if you were wondering, Dodo still had her cold going into The Celestial Toymaker, the First Doctor's second encounter with an Old One.