It is almost midnight in Beverly Hills. Outside the extraterrestrial-looking Prada boutique on Rodeo Drive, the 20-year-old actress Lindsay Lohan is twirling and air-kissing under the heat of several dozen flashbulbs. A line of black T-shirted valets welcomes the Aston Martins and Maybachs as they pull up outside the party. Standing behind the black velvet rope is the well-known nightlife correspondent for a newswire service.

“Who the hell are these people?” she complains, as yet another flock of teenagers, all bad hair and preppy blazers, climb awkwardly from a car the price of a Venice Beach apartment. “They look as though they should have been put to bed at least an hour ago.”

The correct question is not “who are these people?” but “who are their parents?” — for these teenagers are the winners of Hollywood’s gene-pool lottery: the product of every on-set romance in deepest NmubuOoboo, every ill-advised quickie in the Club World bathroom, and every between-take latte with the Key Grip’s daughter.

If the members of this Hollywood über-class had a catchy, media-friendly acronym (they don’t, but I’m willing to offer one), they would be the Sados: the “sons and daughters of . . .”

All of which matters little — an invitation to join Mary-Kate Olsen in the smoking section of a Prada party is hardly consolation for the blight of celebrity parents — until they get a job in Hollywood. And then the world sees green. Consider the reaction of the British tabloid press to photographs of 16-year-old Lorraine Nicholson out on the town with her 69-year-old movie star father, Jack Nicholson. “Jack the lad out with a teenage blonde!” sneered the Mail, noting with palpable distaste that the snaps with Daddy could only help Lorrie’s acting career (she has a cameo in the widely derided Adam Sandler blockbuster Click, due out in September).

But how prevalent is nepotism in Hollywood? And does it matter? Should we care that Tori Spelling is Aaron Spelling’s daughter; that Sofia Coppola’s dad directed The Godfather; or that Liv Tyler was going to Aerosmith concerts before she was going to pre-school? Haven’t Jeff Bridges and Nicolas Cage proved themselves enough to end the jibes about their A-list relatives (in case you’re wondering, Cage is part of the Coppola clan). How much more money does Ben Stiller have to make — and how many more on-screen credits must he give himself (he managed six for Zoolander) before he is more than Jerry Stiller’s boy?

I put this question to Andrew Breitbart, professional troublemaker for the news website The Drudge Report and co-author of the anti-celebrity tirade Hollywood, Interrupted. He begins to hyperventilate almost immediately. “Someone like Tori Spelling is the average girl on the street,” he rages. “Yet she’s cast as one of the good-looking chicks in Beverly Hills 90210 and we’re not supposed to notice? Clearly, Hollywood is not a meritocracy. There are no checks and balances against nepotism that, in any other industry, would result in people rolling their eyes. Can you imagine being told at the hospital: ‘Actually, Dr McDonald’s son is going to perform this surgery today’? In just about every industry less sexy than Hollywood there are rules against this kind of thing.”

Breitbart makes a strong case, but isn’t this just the ranting of an embittered outsider? What do those who actually work in the business think? I call an A-list screenwriter who would rather lose a kidney than be named in a Times article about nepotism.

Squirming, he offers this: “Nepotism is a lot like narcissism in Hollywood. It’s so pervasive, it’s actually hard to identify.” He cites under-the-radar examples such as Christian Slater, whose mother is the legendary casting agent Mary Jo Slater (Ms Slater did not return my call, thus no light was shed on her role in her son’s acting success). Yet family is not the only enemy of equal opportunity, he says. Many stars, such as Adam Sandler, tend to employ only their closest buddies. In one possibly apocryphal incident, an A-list actor even insisted on casting his own horse.

To Susan Jansen, who created the hit television show and movie Lizzie McGuire (which helped to launch the mega-brand that is Hilary Duff), no one should be ashamed of the N-word. Unlike many in Hollywood, she concedes openly that her first break was the result of family contacts. “I’d just got out of film school,” she remembers. “My mom had been talking to my uncle Howard about how miserable I was, so he called me up and said “do you want to write comedy? It’s a nice life”. Uncle Howard was a business affairs lawyer for Paramount, and he did things like negotiate the contracts for Cheers. Anyway, uncle Howard got me a meeting with the head of TV at Paramount — a meeting I probably wouldn’t even be able to get today.”

Not that the meeting with Mr Paramount went smoothly. Says Jansen: “We sat down and he asked me what TV shows I liked. I told the truth: I didn’t watch TV, I didn’t own a TV and I grew up without a TV. He looked at me like I was the biggest idiot who ever walked the planet. But I was there because of uncle Howard, so he said ‘Why don’t you go out, buy a TV, watch some of our shows and, if you feel like it, you can write a script for me’.”

Four days later, she did just that. The Lizzie McGuire movie alone went on to make almost $60 million (£33 million). These days Jansen lives in Bel Air, in the former estate of the aviation pioneer Howard Hughes.

Of course, Jansen would never have achieved so much without her considerable talent. The same can be said of Jeff Bridges, who landed his first movie role at the age of six months (his father was Lloyd Bridges, the blond heart-throb star of the longrunning television series Sea Hunt). Nevertheless, the knowledge that so many beneficiaries of nepotism are unburdened by ability can result in paranoia.