Hell hath no fury like an American feminist. If you've ever met the professional variety, you will learn that soon enough. You will discover as well that any attempt at rational dialogue with such a person is enough to prompt a torrent of abuse that is now one of the mainstays of the American left.

I say this as someone who believes wholeheartedly in equality of opportunity for men and women. You name a political and civil right, and I think women should have it. But my sin is to persist in the naive belief that men and women are actually constitutively different beings, with different biological and psychological profiles that may sometimes demand different treatment.

For the better part of two decades now, this belief has been anathema among American elites. Single-sex education is close to illegal. The American military has been turned into an institution in which male aggression has been usurped by female input at every turn. Under the guidance of Justice Ruth Bader Ginsburg, the Supreme Court has slowly rendered any different treatment for men and women in any public place unconstitutional.

And under the tutelage of an academic establishment wedded to the notion that gender itself is a cultural construct, American education and even medicine have been rendered relentlessly anti-male.

At Harvard, a group of sociologists is hard at work developing new school curricula to erase any behavioural differences between boys and girls from early childhood on.

The result? Well, the results are in the papers every day. Delinquent males, denied effective discipline in school and forced into female-friendly environments, are dropping out of educational establishments at higher and higher rates. The college population is now 55% women, 45% men.

The American department of education reported in 1998 that the reading proficiency gap between boys and girls in school is now close to one and a half years of schooling - with girls way ahead. According to the medical profession, there is an epidemic of "attention deficit disorder" among American boys.

There is a crisis of American manhood going on. The bad news is that American men seem to be getting dumber, meaner and poorer as the years go by. The good news is that some people are getting brave enough to say so. A new book, to be published next month, The War Against Boys, by Christina Hoff Sommers, lays out plenty of horror stories of the new educational consensus.

Boys are essentially being told that what comes naturally to them - rough-and-tumble play, confrontation, physicality, mischief - are psychological disorders. In one school, boys were disciplined for making guns out of their fingers and pretending to shoot at one another. Seven-year-old boys found kissing or teasing girls are sometimes expelled on sexual harassment charges.

Another recent book to tackle the feminist orthodoxy of gender-as-culture is John Colapinto's moving study of a Canadian infant boy who was the victim of a botched circumcision at eight months and had his penis burnt off.

He was born in the mid-1960s and, following the doctrine of gender-as-cultural-construct, the doctors advised his parents to remove the boy's genitals altogether and make him into a little girl.

By a fluke, the boy had an identical twin who grew up as a normal boy while he - given the name of "Brenda" - was dressed in girl's clothes and reared as a member of the female sex.

At the time, the medical establishment hailed the surgery as a brilliant success, and cited Brenda as proof positive of the cultural origins of gender. Then, mysteriously, Brenda disappeared from the scientific literature. Intrigued, Colapinto tracked her down and found "him" working in an abattoir in Winnipeg.

It turns out that Brenda was beyond miserable as a little girl. Although denied the truth about her real gender until she was 14, she insisted on wearing boy's clothes and playing rough sports. It was only when her parents thought she might commit suicide that she was told the truth.

She subsequently took testosterone, had a double mastectomy, married a woman and now has three adopted children. Call her David. That's who he is. As Nature Made Him, as the book title has it.

The unique nature of this story - with an identical twin as a control group - should persuade any reasonable person that gender is something buried deep in human biology. It is about as culturally constructed as the colour of your eyes.

From the minute the Y chromosome triggers testosterone in the womb, boys and girls are programmed differently.

Because this difference was used in the past to justify male oppression does not mean it can be denied. And its persistence is testimony to its power. Nature cannot be foiled, merely derailed.

What is happening now in America is the slow crumbling of an ideological edifice that was constructed with perfectly good intentions on the basis of a lie. Too bad that several generations of boys and men have been the victims of that lie. And too bad that few people until now have had the courage and intellectual honesty to expose it.

Andrew Sullivan