Jonathan Miller's new series about the history of atheism - Brief History of Disbelief - begins with a warning. Unlike recent television histories, he tells us, it will not be drawing on dramatic reconstruction and computer-generated imagery. We should not expect something along the lines of Walking with Atheists, with artful shots of the presenter looking on as the great sceptics of the past extricate themselves from the swamp of ancient superstition.
What's more, there will be no "blurred slow-motion shots of people making leaps of faith, or rather failing to". When heads talk, you simply have to watch them doing it. This, Miller declares from the outset, is dinosaur television in quite another sense - proudly antediluvian in its motion and weighty enough to brush aside anything that gets in its way.
As it happens, the transmission of Miller's three-part series coincides with a perfect example of the mammalian television that replaced his kind of programme in the broadcast ecology. Because if Miller occasionally reminds you of an intellectual diplodocus, thigh-deep in the sea of faith and browsing unhurriedly on philosophical cruxes, then Alan Titchmarsh is unquestionably some kind of proto-mammal. Where Miller moves with deliberation, Titchmarsh scampers. And where Miller ignores the changed climatic conditions of television production, Titchmarsh is perfectly suited to them. He can move from habitat to habitat easily, and he has the adaptability required of the modern television presenter. For British Isles: A Natural History, for example, he has walked down Oxford Street at rush hour in full Neanderthal make-up and climbed into a G-suit to fly in a Hawk jet over the Hebrides. And if you're wondering what either has to do with making the ideas clearer then you've missed the point about mammalian television. It's not about making things clearer - it's about distracting you from the unnerving possibility that you might have to concentrate.
It would be easy to dismiss Miller's preamble as sour grapes - the grumble of a man who in his time has been an ornament of the mainstream schedules and who now finds himself going out on BBC4 - the digital game reserve to which seriousdocumentaries are now almost exclusively confined. His wry lament also chimes oddly with the sense, in his new series, that secularism has passed its apogee - and now needs to reassert itself against a resurgence of fundamentalism.
But when, in another jibe at current television manners, he talked of the "doctrines and dogmas" of modern television, he certainly won a cheer from me. Because if there's anything that's genuinely depressing about modern television, it's not the fungal spread of reality shows or the current melancholy state of EastEnders, but the almost cult-like predictability of the big flagship series.
We perhaps shouldn't be too hard on Alan Titchmarsh. For one thing, there are a lot of people out there who are fond of small furry mammals. For another, his series is on BBC1, and is aimed at a general audience. On the other hand, it is transmitted after the watershed (traditionally the starting whistle for a more adult content) and is a perfect compendium of current factual clichés - from the promise that viewers will be taken "on a journey" to the soaring visuals and the amazing-facts manner of the presentation.
As Miller pointed out, these big-budget extravaganzas are almost invariably required to begin with a trail for themselves - and British Isles didn't shirk the ritual, beginning episode one with a kind of top 10 of the wow-factor moments Alan had up his sleeve. The argument for this style is that the climate genuinely has changed - there are as many competing attractions as in a fairground and you need a vulgar, colourful frontage to pull the punters in.
The argument against it is that it accelerates the very process that it sets out to counter. It presents the world as a set of disconnected facts - and eschews the trickier cultural task of arranging them in ways that make some larger sense. Even more seriously, it allows the attention span to atrophy - an unused muscle which withers away until any extended argument comes to feel almost like an affront, rather than the compliment it actually is.
I'd take money that Miller's approach to his subject will be dismissed as unworkably élitist by quite a few television executives, while Titchmarsh's will be praised for its accessibility. And yet Brief History of Disbelief treats the audience - all of it - as intellectually capable, while British Isles presupposes that most of us are a bit dim. Personally, I'll take the dinosaur any day.
'Jonathan Miller's Brief History of Disbelief' starts Monday 11 October at 9.30pm on BBC4