Johann Hari: Where have all the strong women gone?

My female friends have to soften their ambition in a way my male friends don’t have to

Precisely a century ago, in a suburb of Boston, a child called Bette Davis erupted into the world. She was not only a woman; she was an electrical storm with skin. With nothing but raw talent and raw determination, she became the most famous woman in the world, taking on the Hollywood studio system, the FBI and the Catholic Church.

For a while, this not-especially-beautiful woman in her forties ruled Hollywood, playing tough women who chose their careers and their own desires over sacrificing for men or children or a picket fence. She never pretended to be dumb, or a little girl. She didn't do soft, or simpering. She had a voice like sour cream, and eyes like a raven. Humphrey Bogart said about her: "Unless you're very big she can knock you down." And she was one of the great events of her time.

She was popular with the mostly-female movie audience - women like my grandmother, who gave me my first glimpse of Bette Davis movies from her lap - in part because her characters will not accept 'their place.' They want more, more, more. It was not easy to be a strong woman then; she said, "When a man gives his opinion he's a man. When a woman gives her opinion she's a bitch." But she fought, and women responded to it. She was only the most shimmering example of a generation of tough Hollywood women whose characters saw the world as a place not to cower from or simper at, but to conquer: Mae West (who made her first film at 40), Lauren Bacall, Katherine Hepburn, Joan Crawford, Barbra Stanwyck, Rosalind Russell, Marlene Dietrich, and more.

Bette was self-confident enough to demand to look bad on camera. On the cast of 'Bordertown', she had a four-hour screaming row with the director because she thought it was ridiculous to show her character wake up in bed with a wig and full make-up; she wanted curlers and cold cream all over her face. In' Marked Woman', she was shown with black eyes and a broken face. In Elizabeth and Essex, she wanted to be shown with a completely bald head - sending the studio into a panic. And she was self-confident enough to be unsympathetic on screen.

But something odd has happened since the reign of Queen Bette: women in cinema have become weaker. If the symbol of 1930s Hollywood was Bette Davis in 'Jezebel', defiantly wearing red to her virgin-white ball, today it is Cameron Diaz in 'There's Something About Mary', rubbing semen into her hair because she is too dumb to realize it's not hair gel.

As women have progressed, the women we idolize - in the movies, on television - have dramatically regressed. Who are our female icons now? Nicole Kidman, whose career is empitomized by her role in 'Moulin Rouge', where she plays a limp, passive prostitute, waiting to be saved. Julia Roberts, whose only iconic role is as a screwed-up prostitute, waiting to be saved. The women of 'Desperate Housewives' - chaotic ditzes, who are either jobless, or have jobs where they merely spread chaos. The women of 'Sex and the City', who are obsessed with shoes and - in the end - have to compromise their careers for men. The popular women are numb blondes or bony little girls with submissive smiles. If a female star becomes too 'tough', she becomes box-office poison: Demi Moore was seen after G.I. Jane as too hard, too 'male.' Even Thelma and Louise had to drive into the Grand Canyon in the end.

The closest we have to Bette Davis-style characters today are found in the films and TV shows of Aaron Sorkin. His dream-girl is a woman talking very fast about foreign policy while putting on her make-up. In West Wing, he found two glorious stars who would have held their own with the 1930s generation: Alison Janney, and Stockard Channing. But what happens to their characters? C.J. has to be given a sick father to humanise her - unlike any of the men - and in the end has to choose between Washington and love. Abigail Bartlett is stripped of her job entirely. Janney and Channing are now reduced to bit-parts in films about teenage girls.

The biggest female stars have contracted in every sense. As they are reduced emotionally to hollow male fantasies, they are reduced physically to skin and bone too. If Bette Davis has screen presence, skeletons like Keira Knightley have screen absence; you stop seeing her even when she is the only thing in the frame. Almost all of the great Hollywood starlets would be considered uncastably 'fat' now: who can forget Liz Hurley's statement, "If I was as fat as Marilyn Monroe, I'd kill myself too"?

The few strong women in Hollywood movies and TV are safely located in an unreal world: Buffy the Vampire Slayer, Xena: Warrior Princess. The closest to an unapologetic feminist is Lisa Simpson - and she is eight years old, and a cartoon. This isn't because Hollywood is especially sexist. Hollywood largely gives us what we want - and we don't want to idolize strong, powerful women today.

My female friends need to disguise or soften their ambition and intellect, in a way my male friends don't have to. A while ago, after writing a column about feminism, I received an e-mail from a reader who said: "I think it's great that you, as a man, write about these issues. But imagine a situation where you were exactly the person you are now, but female. Imagine you were comparably overweight, took comparably little care over your appearance, were comparably aggressive in your opinions, admitted to a history of depression, and were a lesbian. You would not be writing for a national newspaper at all." I think that is undeniably true.

The fear of strong women isn't confined to anecdotes; there's reams of evidence for it. A study by Oxford University psychologists in 2006 found that having a high IQ is a boon for men in finding a partner - and for women, it is an obstacle. For each 16-point rise in IQ, a man is 35 percent more likely to find a partner - while for women, the same IQ bump reduces their odds by 40 per cent. This is why so many clever women mask their intellects, in pubs and offices across the country.

This dynamic spreads to politics too. There's a famous experiment called 'the Goldberg paradigm', where a group is given a speech and asked to rate how effective, intelligent and persuasive. Every time this is run, if they are told it is by a man, they invariably rate it ten to twenty points higher than if they are told it is by a woman.

(There are a thousand-and-one good reasons to oppose Hillary Clinton, but one bad one too: her gender. She fits into this Hollywood pattern. What were the two moments when Hillary - for a flickering second - was actually liked? It was when we found out her husband was cheating on her, and in New Hampshire, when she cried. When Hillary is strong, we loathe her. When she is weak, we warm.)

This rubbing-out of strong, clever women from the popular imagination is part of a subtle backlash against feminism. Women are unimaginably better off than in Bette Davis' hey-day: while she was ruling Hollywood, both my grandmothers were leaving school at the age of 13, told there was nothing for them but the farm, the factory or the altar.

Today, a majority of graduates are female. Yet the culture says - yes, you can have your success, up to a point - but you will have to feel guilty about it. You will have to disguise your skills behind a carapace of self-deprecation and self-abnegation. You will be encouraged to idolise empty shells like Jordan or Victoria Beckham. You will be paid seventy pence to the man's pound for the same work. You will be prompted to inject poison into your face, or have your breasts cut open, to conform to a warped vision of beauty that makes you dislike your own body. Updating Bette's old dictum, the writer Arianna Huffington says, "For a man to be called aggressive, he has to be Joe McCarthy. For a woman to be called aggressive, she has to put you on hold."

The fight against all this need to recapture something of the prehensile spirit of Bette Davis. She faced down these boring old prejudices with a perfectly-modulated snarl. As her biographer Ed Sikov says, "Bette Davis didn't give a goddam. She dares us to hate her, and we often do. Which is why we love her."