"Doctor Who doesn't have alien races. It's got monsters instead. There's no pretence at realism, there's no desperate attempt at "alien culture." Daleks don't have a culture, they're just monsters, they're symbols of things that are scary and violent and destructive. Which means, like I've said before, that Doctor's got more in common with folklore than with Science Fiction." - Lawrence Miles
Science fiction often tends towards the extremes of the utopian (in this case, faith in the ability to overcome evil or in science as a progressive force) or the dystopian (in this case, technological dehumanisation, environmentalist comcerns, religious bigotry or fears of foreign invasion), with little time for the no-man's land between that the present is invariably composed of. In that sense, it often has the purity of a fairy tale, where variations on similar patterns are endlessly repeated and counterpointed. Although Doctor Who had almost limitless possibilities in terms of locations, themes and characters open to it, it never quite escaped the persistence of then genre it started with (as well as, a cynic might suggest, hardly ever escaping the South of England). On the one hand, it puts forward an idea of benevolent intervention, on the other, it is postcolonial enough to denounce imperialism and military aggression. The series shows an eccentric gentleman who defeats his enemies with intelligence and ingenuity, but nonetheless often with force, (albeit often wielded by others, whether companions like the Jamie or the Brigadier). On the one hand, the very genre of science fiction reflects an interest in science, as does its lead character's status as a scientist, but science is frequently characterised as a destructive and dehumanising force. On the one hand, its genre commits it to themes of alien invasion, but it often resists this totalising description of other species; even the inhumanity of the Daleks is often shown through the lack of a 'human factor' in characters like Maxtible. The worst monsters are frequently human.
The period with the First and Second Doctors ranks high as one of my favourites. This was when the series tended to be strongest as a drama, as in the early episodes wherein Ian and Barbara must humanise an alien Doctor who abducts them from Earth in An Unearthly Child (and where they find themselves to be as primitive as the neanderthals in the same story). One of the most notable aspects of these early episodes of Doctor Who was the way in which it was intimately connected to the apocalyptic trend in contemporary British science fiction (for example, in the cosy catastrophe of Wyndham's Day of the Triffids, The Kraken Wakes, or Christopher's The Tripods). As Susan Sontag put it The Imagination of Disaster "Thus, science fiction film is concerned with the aesthetics of destruction, with the peculiar beauties to be found in wreaking havoc, making a mess." For example, The Daleks is set on a Skaro decimated by nuclear warfare (with the Daleks later decimating all life on the planet Kembel in The Dalek Masterplan) essentially reprising the Eloi/Morlock split of The Time Machine by HG Wells, The Ice Warriors sees the Earth facing environmental disaster and a new ice age while The Dalek Invasion of Earth is set against the wartorn ruins of London (this at a time where memories of the blitz were comparatively fresh; the model here is War of the Worlds).
Even in historical episodes like The Aztecs Barbara's inability to change history and bring civilisation to the Aztecs in the face of the impending Spanish invasion presents a decidedly austere outlook. That said, the story reverses the normal theme; in a sense Barbara is the invader here and inverts the Doctor's normal role. The Doctor's benevolent imperialism fails here, as much as in the later The Time Meddler (is the Monk's desire to advance Earth that different to the advice the Doctor gave to the Thals?). In fact, the themes of the historical stories, where the travellers are caught up in events beyond their control and manipulated by others (as in Marco Polo, The Reign of Terror, The Romans and The Highlanders) seem to diverge from the futuristic stories where the Doctor increasingly finds himself resisting alien invasion.
Similarly, many episodes showed unease about the ideal of industrial and scientific progress that had been established in post-war Britain, a theme exemplified by the Robomen in The Dalek Invasion of Earth (or 'dalekisation' in the much later Revelation of the Daleks), the cloned Drahvins in Galaxy Four, The War Machines and the Cybermen in such episodes as The Tenth Planet and Tomb of the Cybermen (and especially the cyber-conversion in the later Attack of the Cybermen and audios or novels). The progress of The Savages is built on the exploitation of the primitive tribes. Environmental themes emerge early on also, with Salamander's environmental damage in Enemy of the World, the sabotage of the weather control systems in The Seeds of Death and The Moonbase, altered plants in The Keys of Marinus the polluting herbicide in Planet of Giants and the drilling in Inferno and Fury From the Deep (though here, it is equally true that for both of these the threat is from the inhuman aspect of nature), not to mention the mining in The Dalek Invasion of Earth. But equally, the Doctor's scientific knowledge is vaunted throughout this time and usually proves invaluable, as in The Ark.
One of the other principal 'narratemes' of the series was the theme of humans as the aggressors, (and apparently aggressive aliens as benign) as opposed to the more traditional theme of alien invasion. This particular theme was first developed in The Sensorites, The Rescue, Galaxy Four or The Ark, and persisted through to Third Doctor and episodes like The Silurians (where the Doctor's attempts to negotiate a peace treaty are thwarted by both sides) and The Ambassadors of Death. Nonetheless, the nature of the genre requires the inhuman to be a threat; The Power of the Daleks shows a human colony fooled into believing the Daleks to be benevolent, for example. The failure to recognise threats of this kind is as much a recurring theme (e.g. The Macra Terror) as that of seeing them where they are absent, with pacficism being condemned as strongly as it elsewhere advocated in The Daleks and The Dominators.
The Third Doctor is a rather less favourite period of mine (largely due to the more predictable format and an increased tendency towards sexism after Liz Shaw's departure). This saw the Doctor working for the military (a somewhat dubious pairing in light of the show's antipathy to violence; this was also the period that saw the Doctor engaging in fights with his enemies), alternately denouncing them as The Cave Monsters but relying on them precisely to use force elsewhere. Environmental themes recur, as with The Green Death (which also reprises the theme of electronic dehumanisation with almost as little subtlety as in The War Machines, The Keys of Marinus and The Ice Warriors), The Mutants and The Claws of Axos but environmentalism is severely critised in Invasion of the Dinosaurs. Episodes such as The Curse of Peladon (where the previously belligerent Ice Warriors prove to be innocent in the face of human mendacity) and Frontier in Space continue the theme of unjustified suspicion of other species, but there is again too little suspicion in The Claws of Axos. The Baker era saw a much greater emphasis on the misuse of technology rather then seeing it as an ill in its own right, in The Robots of Death and The Face of Evil (it's interesting to compare The Face of Evil and The Invasion of Time with previous stories showing advanced and primitive societies; the focus is much more on differing civilisations than on the noble savage; neither side are accorded a monopoly on the true society). For every allegory on environmental destruction like Planet of Evil, Terror of the Zygons or Nightmare of Eden there is a story like The Ark in Space where the disasters prove to be entirely natural (and with nature even viewed as a threat in stories like The Seeds of Doom and development being advocated in The Creature From the Pit).
The most famous episode of this time, Genesis of the Daleks, revisits the theme of nuclear devastation; in spite of its second world war costumes and references to Nazi eugenics (a theme repeated in the later Remembrance of the Daleks), Genesis of the Daleks depicts what is essentially a cold war. Here, the complicated aspect of the Doctor's benevolent imperialism is most problematic, as the Doctor concludes he has no right to snuff out the Daleks at their becoming, since to do so would be to deprive other races all of the good that came out of their own struggles against the Daleks; later in Resurrection of the Daleks the Doctor sees this decision as wrong. Within The Leisure Hive much of David Fisher's scriptwriting comes from the same background as stories like Genesis of the Daleks. The taste for political allegory is marked to say the least; two races, the Argolin and the Foamasi, and a war that left the surface of Argolis radioactive and barren. Although much of the earlier and later allegories used an obvious Cold War metaphor, this follows Genesis of the Daleks in taking its metaphor from Nazi Germany, showing the rise of fascism against a largely passive populace and with eugenics as a prominent theme. The scene where Romana is the only one to try to stop the destruction of the Foamasi ambassador shuttle while all others stand by is one of the most disturbing things the series ever did (not least because it represents a horrifying failure on the part of the Argolin to learn from history). Equally, the script reflects Chris Bidmead's grounding in science, and the achievements of Argolin science are seen as much as their legacy to civilisation.
By this point, the series has become much more diverse in terms of its style, possibly due to the introduction of Blake's Seven, which had little ambiguity about its dystopian character, and accordingly portrayed its idealist hero as little better than a fanatic, whose obstinacy caused the death of friends on numerous occasions and where the President of the totalitarian defence of the Federation is easily able to articulate a coherent defence of the Federation against the anarchy represented by Blake. The true hero of the series was clearly the amoral Kerr Avon, contrasted to the heroic idiocy of characters like Tarrant. With the Davison era, much of the traditional thematic ambiguity is preserved in this period; in Kinda man is the invader and science gives way to mysticism, in The Visitation man is invaded and superstation gives way to rationality, while Four to Doomsday foregrounds themes of environmental destruction and dehumanisation. Equally, Warriors of the Deep presents a cold war allegory bluntly foregrounding the theme of mutually assured destruction (and reprising the narrateme of stigmatisation of the alien last seen in the likes of The Cave Monsters and Frontier in Space) and Planet of Fire returns to the theme of blind religious faith in false gods first explored in Face of Evil.
Later, In The Curse of Fenric, the theme of environmental destruction is a standard one, but the handling of religion, if unorthodox in theological terms is also unusual for the series; it must be the only occasion a church as setting is not destroyed. Equally, Ghost Light casts a narrative of alien invasion in the style of the supernatural, but unusually for the series, there are no concerns at the fallibility of superstition when set against reason; instead, the scientific penchant for exploration and classification is seen as both sinister and comic by turns. Possibly this is because of the extent to which Josiah and Redvers are both alternative images of the Doctor, with Josiah's husks even being equivalent to regenerations (in a story that eschews pure narrative in favour of symbolism, with even a telephone representing technological evolution), just as the Rani and her experiments on humans provided another version of him. Although the story tends to reject the supernatural in favour of the material (presenting Light as both an angelic figure and as a vampiric one, rather resembling Dracula, especially when he casts his cloak over a a maid he is about to dismember. The normal associations of light and dark are inverted), much of its details are nonetheless not susceptible to being explained in this way (from the light in Redver's snuff box to why no-one questions the Doctor's presence. During this period, the Doctor becomes more alien, a manipulator that is unconcerned for his companions, bringing out the full ambiguities of his benevolenent imperialism to an extent rarely seen in the series, excepting perhaps Evil of the Daleks, where the Doctor consents to experiment on Jamie as part of a plot against the Daleks and accordingly uses precisely the same ruthless tactics as the Daleks themselves.