Megan Fox is the sexiest woman alive. Last year she wasn't sexy at all. In 2007, the 21-year-old starlet didn't even make the top 100 in FHM's annual ranking of the world's women. In 2008, she's number one. The obvious reason for her sudden rise up the charts is the popularity of Transformers and its key scene in which she appears in a short skirt bent over a 1976 Camaro. But she couldn't have entered the list at all if she hadn't made the wise career decision to change her last name from "Foxx" to "Fox." One more x and she's a porn star; one less and she's an object of aspiration – perfect for FHM.

For Him Magazine, and the other lad mags like Maxim and Umm, occupy a strange, liminal place in the territory of contemporary male desire. They exist to allow men to look at women's bodies sexually but not pornographically. With the emphasis on suggestion rather than revelation, the women in their pages are slick materialistic ideals, as current in their smooth plastic forms as the Prius or iPhone.

The downside to such manufactured people is that they're all the same. If you were mugged by any one of the women in the top 10, you couldn't pick the perpetrator out of a lineup. They're all white. They all have long hair and they're almost all blonde. They all have the same high cheekbones. They all have the same nose. Each woman is allowed exactly one deviation from the norm, and the deviation is immediately remarked on – her tattoos or her extra-dark eye makeup or her curves. The girls of FHM are obviously products of a fundamentally icky consumerist objectification, but their engineered homogeneity also reveals an incredibly limited imagination.

In some ways, it's a surprising development. If the lad mag is the latest chapter in the long, toxic and ancient book called "Men Staring at Women," it's very different than anything that's come before. The nude throughout the history of art offered a social expression for forbidden sensuality, which is why the women, sprawled on exotic beds or on picnic lawns, emerging from the bath or from the sea foam, are always sexually available. In FHM, the women are totally unattainable – "too good for you, buddy" – and their way of dressing, in the context of a world in which seemingly every celebrity has a home sex video on the market, is comparatively modest. The subjects of nudes were womanly – whether the plump nymphs cavorting in pastoral scenes of Rubens or the cubistic chest-thrusting models in Picasso's Demoiselles D'Avignon. Their womanliness reminded male audiences of their manliness. The women in FHM's top 100 are almost all rail thin, with whittled down bodies and faces. Every year there is less and less to them.

Naomi Wolf in The Beauty Myth complained that women in the media were "mock-ups of living mannequins, made to contort and grimace, immobilized and uncomfortable under hot lights, professional set-pieces that reveal little about female sexuality." She was right and she's still right. But the women in FHM are an equally false representation of male desire. FHM is not a men's magazine like GQ or Esquire. It's a magazine for lads – for 15-year-olds. It serves adolescent boys with the fantasy that there is something or someone out there who is the "sexiest," a comforting norm of male desire which does not exist and has never existed.

If only it were so simple. Men (as opposed to boys) know that male desire doesn't fit any pattern; it changes unpredictably, sometimes over years, sometimes over an afternoon. Male desire is particular – some men like women in tutus, others like women who are morbidly obese. Who can say what men are attracted to? It could be the second joint of the middle toe, or green eyes, or a certain ineffable way of walking.

Shakespeare found the world's sexiest woman in Cleopatra, but her sexiness was a shifting bizarre mass of contradictions and complications: "She makes hungry where most she satisfies; for vilest things become themselves in her." The appeal of FHM's list of sexy women isn't the women so much as the list: It imposes order on what is inherently chaotic. It's a false order of course, but the lads reading FHM can pretend for a while.

How this ranking of the parade of gleaming pneumatic women will affect young men isn't clear. Will it terminally limit their budding libidos or only provide a kind of temporary simple-minded refuge from the gathering deluge of sexual complications they're about to face? As with everything when it comes to male desire, nobody knows.

The great Victorian art critic John Ruskin, a man who spent half his life among pictures and sculptures of naked women, was nonetheless shocked to discover on his wedding night that his bride Effie had pubic hair. On coming into contact with a real woman, the poor man actually went into spasms. We can only hope there's a better fate for the lads whose first image of womanhood is Megan Fox with one x.

Stephen Marche is the author, most recently, of Shining at the Bottom of the Sea.