The book was - as Friedan was - a flawed advocate of women's rights: Friedan had little apparent interest in women who were anything other than white and upper middle-class. Her homophobia became an embarrassment to the women's movement. Her egotistical paranoia about being ousted as the face of the women's movement was captured with wince-inducing brilliance by Nora Ephron in her 1972 essay Miami.

The feminist movement never did and never will run smoothly. But Friedan's book, as Stephanie Coontz writes in her recent book, A Strange Stirring, rescued ''a generation of intelligent women, sidelined from the world''. Whatever its flaws, the publication of The Feminine Mystique remains as much of a landmark in the history of feminism as Emily Davison's death 50 years earlier at the 1913 Epsom Derby.

And so, 50 years on from Friedan, it pleases me to announce we have a new face to the feminist movement. That face belongs to none other than Beyonce Knowles.

Last week, the new issue of American GQ was published and it neatly encapsulated where Western feminism is today. Inside, Knowles gives an interview that will probably be studied by future generations for lessons in both the loopiness of the 21st-century celebrity world and how hilariously far American magazine interviews have fallen since the days of, say, Gay Talese and Lillian Ross. In this typical piece of puffery, Knowles shows off her ''temperature-controlled digital storage facility that contains virtually every photo of her'', including one video diary entry in which she informs herself that she is going to listen to one of her own songs before having sex with her husband, which is one way to get in the mood, I guess.

But there is, the GQ journalist assures the reader, more to Knowles than raging narcissism - she is a powerful woman with a defiant feminist streak. ''Equality is a myth, and for some reason everyone accepts that women don't make as much money as men do,'' she rails. ''I truly believe that women should be financially independent from their men. And let's face it, money gives men the power to run the show. It gives men the power to define value. They define what's sexy. And men define what's feminine. It's ridiculous.''

Knowles is right: it is ridiculous that American women earn 77¢ cents to every $1 earned by men. This is almost as ridiculous as, say, a self-professedly powerful female celebrity (''I'm more powerful than my mind can even digest,'' announces Knowles) complaining about men defining sexiness in a men's magazine in which she poses nearly naked in seven photos, including one on the cover in which she is wearing a pair of tiny knickers and a man's shirt so cropped that her breasts are visible. These photos, incidentally, were taken by the bafflingly successful American photographer Terry Richardson, a man with a penchant for highly sexualised photos of women and who has been repeatedly accused of sexual exploitation and misconduct by young female models, which Richardson has denied.

To complain about the sexualisation of women in men's magazines may seem like complaining about the weather. But as Knowles rightly says in relation to the pay gap, the status quo should not just be shruggingly accepted if it is wrong. I never fail to be amazed at the high profile, often A-list women who celebrate their professional success by posing near naked on the covers of allegedly classy men's magazines, such as Esquire and GQ, and these covers are, to my eyes, becoming increasingly close to porn.

In the past four months alone, we've had Cameron Diaz bending over in a pair of mesh pants; topless Mila Kunis in leather trousers (while inside she writhes naked on a bed); Rihanna naked save for a mini leather jacket; Lana Del Rey also naked except for some jewellery (that was on GQ's October issue, which had four alternative covers featuring men. All of these men, funnily enough, were clothed).

It's one thing to submit to this attention-seeking nonsense if you're a C-list reality TV desperado trying to get on the cover of British weekly lads mag Nuts; it's another if you are professedly one of the most powerful women in the entertainment business who has no need of such tactics. Knowles rightly hates the fact women are humiliated by being paid less than their male counterparts. But they are similarly humiliated by being fed the message that it doesn't matter how successful, powerful or smart you are - all that matters is how sexually available you are willing to make yourself look.

I should feel happy, I guess, that Knowles is willing to speak about equality, considering how notoriously few young women in the public eye are willing to identify themselves as feminists. That her Dworkin-ish call to arms comes served up with photos of Knowles jumping on a bed in a bikini, well, that's the deal these days, apparently, in which famous women can sing about ''independence'' and ''girl power'', as long as they're wearing next to nothing. The feminist movement never did run smoothly. But half a century after Friedan, it should be running better than this.

Hadley Freeman is a columnist and features writer for Britain's Guardian.