The appearance of Jason Segel’s genitalia in the romcom Forgetting Sarah Marshall had American critics crowing about how the film has courageously broken one of the last taboos in mainstream cinema. Yet Segel’s flaccid member looks pathetic and laughable, especially because it’s attached to a body that is doughy and pallid. It can’t seriously be accused of being capable of anything, let alone of breaking a taboo. So obviously devoid of sexual intent, it symbolises not so much his character’s abject emotional condition at his girlfriend’s rejection of him, but the sorry state of masculinity in American movies today.

Films such as Forgetting Sarah Marshall, Knocked Up and Superbad - all from the production stable of Judd Apatow - show that the young male box-office stars of today’s romantic comedies are goofy schlubs and nerds. As unlikely as it seems, actors such as Segel (Sarah Marshall), Seth Rogen (Knocked Up) and Michael Cera and Jonah Hill (Superbad) now define the paradigm of a Hollywood romantic lead. Cary Grant they are not. They’re not even Hugh Grant. They may know the appeal of sex, but they have no sex appeal.

Yet this is Hollywood, and these pathetic, if well-meaning, losers inevitably end up with the hottest chicks. This is not altogether fanciful, given that the über-schlubby Judd Apatow, who originated this new breed in the short-lived television series Freaks and Geeks, is married to the stunningly beautiful actress Leslie Mann. They represent a kind of wish fulfilment for most men, who can’t imagine scoring so high.

The triumph of the schlub wouldn’t be so significant if the young actors Hollywood is now pushing in dramas and action movies had anything like the masculine heft we have come to expect from our celluloid heroes. It’s hard to think of a male find under 40 who has the innate, old-fashioned ability to project “manliness” as a natural quality without the aid of steroid-boosted biceps. Where are today’s equivalents of the actors Hollywood once offered as symbols of effortless masculinity - John Wayne, Gary Cooper, Gregory Peck, William Holden, Burt Lancaster, Steve McQueen, Paul Newman and Clint Eastwood? Who even is there to step into the shoes of Harrison Ford, Mel Gibson or Bruce Willis? Neither of the two male stars most touted as their successors, Brad Pitt and George Clooney (whom Time magazine recently anointed “The Last Movie Star”), seem to connect with mass audiences. Clooney’s recent period comedy Leatherheads has been a financial disappointment, while Pitt’s last film, The Assassination of Jesse James, barely got out of the starting blocks. Russell Crowe is still flying a lone flag for the macho hero, though he hasn’t had a truly square-cut role since Master and Commander; and Heath Ledger, the great white hope to project complex, Brando-like masculinity, is gone.

Instead, the Hollywood studios are pushing a new generation of actors who are often chosen to star in films in which they are not meant to be the main attraction. Three of last year’s biggest hits were Spider-Man 3, Transformers and Harry Potter and the Order of the Phoenix, but the main draw of these films was the subject, not Tobey Maguire (who perfectly epitomises the geek as superhero), Shia LaBeouf or Daniel Radcliffe. It’s symptomatic of the state of masculinity in Hollywood that the scrawny LaBeouf, who plays the young newcomer in the latest Indiana Jones movie, is being groomed by Steven Spielberg to take over the series from Harrison Ford. If you want old-style beefcake, you have to look to “cartoon” movies such as 300 and Beowulf.

Hollywood has been forced to champion these young actors in part because the slightly older actors touted a few years ago as leading men, including Josh Hartnett, Orlando Bloom, Emile Hirsch, Hayden Christensen, even Leonardo DiCaprio and Keanu Reeves, haven’t maintained their early box-office promise. “They’re all pretty boys,” says one leading talent agent. “They’re kind of safe, not that masculine.”

Of course, the celluloid images of masculinity offered by Hollywood have always been affected by wider social and cultural factors. It wasn’t surprising that the late Charlton Heston - righteous, upstanding, iron-jawed, steel-framed - became such an important screen icon during the early years of the cold war, or that the steroid-enhanced musculature of Arnold Schwarzenegger and Sylvester Stallone defined masculinity as the cold war was coming to a close. As Robert Griswold, author of The Flabby American, says: “Cold wars could not be fought with soft bodies.”

So, what do modern Hollywood’s images of masculinity tell us about maleness today? Some suggest it is a belated response to feminism. Ted Friedman, author of Electric Dreams: Computers in American Culture, suggests that the emergence of the schlub and geek as heroes “has to do with the rising influence of technology”, whereas, he says, “when I was in high school, to be a nerd or a geek was just shameful and not valued”.

Not everyone bemoans the evident lack of masculinity of the emerging stars. “Even Segel’s physique is refreshing,” says Dana Stevens, of the online magazine Slate. “He’s the first leading man in recent memory who’s actually built like most men I know.”

But do we really want our Hollywood movie stars to be like anyone we know?

Where have all the real men gone?

Emile Hirsch Hirsch is one of those young actors who hasn’t yet had a big hit, but who everyone in the Hollywood loop expects will be a big star. He’s believable as a young teen heart-throb in The Girl Next Door, playing an ambitious guy who discovers the girl he likes is a porn star. But Hirsch, 23, is also seen as a serious actor, and made a big impression last year playing the adventurer Christopher McCandless in the critically acclaimed drama Into the Wild, winning a best-actor nomination from the Screen Actors Guild. The 5ft 7in actor lost 41lb playing the part. Next month, he’ll be plastered everywhere as the lead in what is sure to be one of the summer’s biggest hits, Speed Racer, a live-action version of a 1960s animated Japanese series. He’ll follow that with a role in Milk, Gus Van Sant’s biopic of Harvey Milk, the gay supervisor of San Francisco who was murdered in 1978. Hirsch plays a gay-rights activist, while Sean Penn, who directed him in Into the Wild, plays Milk.

Seth Rogen The bearded, bearlike 26-year-old became last summer’s unlikeliest romantic star with the success of Knocked Up, in which he gets the beautiful Katherine Heigl pregnant. Rogen is one of the core members of the Judd Apatow stable, working both as an actor and writer. He got his first break when Apatow hired him for his TV series Freaks and Geeks. After Knocked Up, Rogen wrote the comedy Superbad; later this year, he’ll be seen in Pineapple Express, which he also wrote and co-produced.

Shia LaBeouf LaBeouf has become a big box-office draw in the past couple of years, to the amazement of some. They can’t understand how “the scrappy kid next door”, who looks like a young Dustin Hoffman, could become a Hollywood leading man. Others, however, feel he has the appeal of a younger John Cusack. “I’m not an Adonis, that’s for damn sure,” he admits. “I’ve never really thought of myself that way, and it doesn’t matter to me.” LaBeouf’s biggest supporter has been no less a figure than Steven Spielberg, who was instrumental in getting him cast in his two biggest hits to date: the teen thriller Disturbia and the science-fiction adventure Transformers. The 21-year-old, who grew up in the rougher part of east LA, is set to become an international star next month with the release of Indiana Jones and the Kingdom of the Crystal Skull, directed by Spielberg. LaBeouf plays Mutt Williams, Indy’s motorbike-riding young sidekick. Spielberg sees him as the next Tom Hanks, an everyman who can appeal to everyone.

Jonah Hill If roly-poly, frizzy-haired Hill looks like Seth Rogen’s younger brother, that’s a good part of the reason the 24-year-old was cast as a character called Seth in Superbad, which Rogen wrote. Seth is an academically challenged horndog on the prowl for sex, even if he has to get a girl drunk to make it happen. “The way Michael Cera and I talk in the movie is vulgar,” Hill says. “But, whether people realise it or not, this is how 17-year-old kids talk today.” Like many of the Apatow troupe, Hill is also a writer; as a child, his dream was to join the writing team of The Simpsons. Two scripts he’s written are set to go into production in the next few months, with one to be directed by Harold Ramis. It’s indicative of his star status as lovable schlub who can pull the hot chicks that, a month ago, he got to host Saturday Night Live - with Mariah Carey. Hill attributes much of his success to his looks. “It’s harder to be funny if you’re handsome than if you’re very normal-looking,” he says.

Michael Cera Most people in the UK know the 19-year-old as Paulie Bleeker, the sweet but hapless cause of Ellen Page’s pregnancy in the comedy hit Juno. In America, however, Cera is better known for the cult television comedy series Arrested Development, in which he plays George-Michael Bluth, the engagingly naive, awkward, goofy kid who becomes inappropriately infatuated with his beautiful and manipulative young cousin, Maeby. The Canadian-born actor also became a big Hollywood name last year as one of the leads in the hilarious and filthy teen comedy Superbad, produced, naturally, by Apatow. Cera played the socially inept Evan, who tries to find enough alcohol to get off the geek list and into bed with some “ladies”. Cera has film projects in the pipeline, including a movie of Arrested Development.

Jason Segel Another longtime member of the Apatow comedy team, Segel, 28, got his start on Freaks and Geeks. His big break comes with Forgetting Sarah Marshall, which he wrote and stars in. Not an obvious romantic lead, Segel says his unlikely appeal is because he has “some sort of strange ability to remain likeable while getting extremely close to creepy and pathetic”. He wanted to be an actor, but Apatow told him the only way he’d get to star in a film was if he wrote it.

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