LAST NIGHT Thomas Sutcliffe

The title of The Really Useful Show (BBC 1) suggests a kind of hierarchy of utility - there's ordinary-grade useful, and then there's a four-star premium version - really useful. And while you know that this is just standard titular hype, it still provokes some itchy thoughts about what daytime television actually considers to be of service to its viewers.

The answer would appear to be cosmetic improvement. Without the make- over, the revamp and the new do, daytime broadcasting would barely make it to the mid-morning coffee break. Sometimes whole programmes are devoted to the cult of transformation, such as Style Challenge, in which various chirpy punters are redecorated by make-up experts and celebrity hairdressers (though why anyone would take style advice from Nikki Clarke, a man who looks as if he is on his way to a Seventies Disco costume party, is a continuing mystery). At other times, the suggestion that external show is the quickest route to inner happiness is less explicit but no less fundamental.

To call such programmes superficial is not simply a casual insult - it is a precise account of the universe of appearances they inhabit (the Greek word kosmos, meaning appearance or order, is the root for both "cosmetic" and "cosmos", a useless fact which seems oddly appropriate to daytime broadcasting).

On Monday, The Really Useful Show included a feature on mountain bikes, so it may be that yesterday's programme was not entirely representative in its concentration on outward show. But the first item, about what it claimed was a new trend for dental braces, was typical of daytime television in taking it for granted that a perfect smile was a necessity, not a luxury - "50 per cent of children need or badly need their teeth straightening," said Jacinta Yeo, the programme's dental adviser. Why do they need their teeth straightening? Because their teeth are so snaggled that they can't eat? Because they are in constant pain? Unlikely, I would think, given that previous generations have somehow managed to survive the horror of misaligned incisors. They "need" them straightening because dentists want to earn more money and because programmes like this contribute daily to the terror of not looking quite right. Improvements in appearance are almost always associated with an increase in self-confidence, an entirely self-fulfilling prediction given that "letting yourself go" is presented so consistently as an act of moral delinquency.

I'm not sure that Seven Wonders of the World (BBC2) could be described as useful either, not if you had any strict idea of practical application. But what an inspirational and pleasurable programme it can be when it's done well (I watched it immediately after The Really Useful Show, so you will have to allow for the slightly intoxicating effect of sudden decompression). Steven Pinker's programme was exemplary, not just because his choices mixed the humble and the arcane, but also because he talked with a limpid fluency that persuaded you that even complex mysteries were just within your grasp.

He began with the bicycle, passing on the elevating information that while a person on foot is less efficient than a horse or a jet aircraft, a person on a bicycle is more energy efficient than any known animal or any known machine. I wouldn't have believed it possible to turn such a bathetic piece of machinery into an idealised object, but I will cycle home tonight in an aura of virtuous calorific economy; and while I pedal I will be thinking about some of his other choices - either the camera, which has extended the range of our vision way beyond the possibilities of biology, or combinatorial systems, by which a finite number of elements can deliver an infinity of statements. I will also listen more carefully to my children, alerted by a dazzling explanation of one childish error to the fact that every verbal mistake offers a clue to our possession of speech. If I had to choose a list of my own wonders of the world I think it would have to include the BBC, which can pass so effortlessly from the mind-numbing to the mind-expanding in a single day.