Why are we seduced by the freak show of the TV age?

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In Big Brother, the audience is part of the problem: collaborators in the crassness and cruelty of the humiliation-game - the tasteless watching the talentless. For Press and pundits, analysing our fascination has become part of the routine. In between the on-screen entertainment - the nightly news from nowhere, the weekly climax of expulsion from trashparadise - Brotherhouse junkies pay to peer through the webcam into the inmates' tawdry lives.

Thousands of punters gamble on the outcomes of their dreary dramas. The tabloids report it as greedily as any saga of sex and crime. They scream editorials and invent smear campaigns in an effort to influence the vote, as energetically as in any General Election campaign. It is the triumph of the trivial. Inside the house is a bunch of nobodies. Outside, everybody seems to be watching.

Anyone who isn't watching is watching the watchers, trying to explain the success of the show. But all the theorising has missed what really makes Big Brother work, mistaking it for a new kind of entertainment. Really, it is just an updated version of one of the most primitive, basest amusements in the world: mocking the afflicted, a form of psychological bullying, in which you make people vulnerable, then taunt them for it. In the history of British showbusiness there are two glaring precedents: the Victorian freak-show, and the 18th century abuse of the mentally sick for fun.

Up to 1770, a visit to the "madhouse" was a regular item on the tour of London amusements. At the asylum known as Bedlam, strollers could ogle the freaks for an admission charge of a few pence. Paintings of Bedlam are stunningly like glimpses into the Big Brother House.

Dim-witted inmates loll among rubbish, picking at each other's sores and scabs, near-naked and behind bars, fancying themselves as kings and "persons of fashion", just as the Big Brother contestants fantasise about stardom and celebrity-status. In Bedlam, the standards of the world are suspended, its values turned upside-down. Big Brother's Jade - whom the tabloids tease as ugly - was caught by the cameras praising her prettiness.

The audience is in the Bedlam scenes, eyeing the inmates pruriently. It was a favourite outing for titillation: men took mistresses, because they hoped to see the poor crazies do something sexually uninhibited. Tom Rakewell - the anti-hero of Hogarth's famous series of pictures of London life - ends up in Bedlam. Nowadays, he would be just the sort of young person Channel 4 selects for Big Brother: lazy, shameless, uncritical, unintelligent, selfcentred, exhibitionist, he just "wanna have fun". Drink and sex are all he thinks about. His place in Bedlam, like a stint in the Brotherhouse, is the reward of a shallow character.

If Bedlam was a human zoo, the freak show was a human circus. In late 18th century Soho, you could see an Essex girl "seven feet high" and "an Ethiopian link between the Rational and the Brute Creation". The big attraction of 1824 was a Sicilian dwarf 20-inches tall: pay an extra shilling and you could touch her "particulars not mentionable to ears polite".

The Big Brother house contains nothing as exotic as the hairy hermaphrodites and elephant men beloved of the freak-show impresarios. But when Channel 4 selects specimens for its human menagerie, it goes for trendy forms of the grotesque: female body-builders, unbelievably dumb blondes, aggressively bald men of selfhumiliating repulsiveness, and a youth who boasts "I have really nice teeth for someone who doesn't brush that often". To get on the show, you have to be willing to take off your clothes and probably fornicate - if you get lucky enough - in public.

The C4 house has, its seems, a filleting effect on inmates' intelligence, and a brutalising influence on their behaviour. They live - literally, to judge from some residents' complaints at the smell - in an animal atmosphere, talking about the size of nipples, dreams of sex, whether menthol cigarettes cause infertility and whether anyone has "done a poo". People look like pigs and behave like dogs, or is it the other way round? The freak-show tradition is not dead. It thrives in television.

We have abolished cockfighting and bear-baiting. Why do we still torture Big Brother's dumb critters for our sport? Hundreds of thousands of otherwise decent, normal people are relishing the prospect of seeing Jade tonight, smuggled out of the house to avoid a gauntlet of cheap hatred. I know what people say: the victims of Bedlam had no choice, whereas Big Brother's little siblings volunteered for selfexhibition. It's their own fault if they end up over-exposed.

But there are two reasons why we should worry. First, Channel 4's claims about the care with which it selects robust, emotionally secure applicants are unconvincing. Some of them seem too stupid, too shallow, too scarred to cope. Tonight's favourite for expulsion is an intellectually challenged young woman from a broken home with a disturbed history, whose former teacher has expressed real fear for her.

And even if the inmates' fate is their own moral responsibility, I worry about the rest of us: about the inward effects of lapping up squalor. Voyeurism isn't the worst sex-perversion Big Brother inspires: much creepier, much more disgusting, is the sadism of the hundreds of thousands of Britons who make a phone call every week to inflict a spasm of humiliation. I think back to Bedlam. The spectators were worse than insane: they were corrupt. Gawping at unfortunates sapped their sensibility and stoked their self-satisfaction. They should have looked into the madhouse and seen reflections of themselves. Usually, however, they didn't. "From so humbling a sight," wrote a London visitor to Bedlam in 1753, "we may learn to moderate our pride." It's a lesson we ought to learn from Big Brother.