Not long ago Harvey Mansfield took a call from a journalist. She wanted a comment on a former colleague. Mansfield, a 73-year-old professor, said: “What impressed all of us about him was his manliness.”

There was silence at the other end of the line. Finally the female voice said: “Could you think of another word?” It was then that the professor realised that manliness has become a dirty word. And if “displaying qualities considered admirable in a man” (as the dictionary has it) has become unacceptable, then presumably being a man is unacceptable, too. Wondering how this could be, he concluded that a prolonged period of social engineering — kick-started by feminists who refused to let men open doors for them or carry their bags — had resulted in the virtual abolition of manly virtues.

Honour, bravery, self-restraint, zeal on behalf of a good cause, and feelings of delicacy and respect towards loved ones: all had become meaningless. And the men Mansfield grew up to admire, who most vividly manifested those virtues — including Humphrey Bogart, Ernest Hemingway, and Tarzan — meant nothing any more.

Horrified, Mansfield did what a professor at Harvard does best: he wrote a book. And that book, entitled Manliness, has quickly driven feminists potty. One, Naomi Wolf, says it made her “froth at the mouth”.

Mansfield’s thesis is that we live in a society that takes no account of differences between men and women. “Women today want to be equal to men, equal in a way that makes them similar to, or virtually the same as, men. They do not want the sort of equality that might result from being superior at home if inferior at work.

“We are in this great experiment, and it seems to be going along without much awareness of how radical it is. But the gender-neutral society can’t simply let nature take its course, because there are no gender-neutral human beings.”

Social psychology and evolutionary biology have proved that there’s substance behind the sex stereotypes. Notably, Mansfield observes, there’s a likelihood that men, rather than women, will be promiscuous, spatially aware, dyslexic, tongue-tied, aggressive and given to abstract ideas — though not necessarily all at once. Male athletes, he adds, are more likely to spit than women.

To speak of innate difference between the sexes is a dangerous business, and nowhere more so than at Harvard, one of America’s great universities. Another of Mansfield’s former colleagues, Lawrence Summers, was obliged to resign in February as president after claiming that women’s brains are less well suited to science and maths than men’s. “I have never been close to Larry Summers,” Mansfield says. “But I have been a partisan defender.”

Of course, not everybody thinks we live in a gender-neutral society. The UK Resource Centre for Women in Science, Engineering and Technology was established in 2004 to increase the participation of women in science, engineering and technology — women like the ones Summers deprecated.

A spokeswoman, Ros Wall, argues that women can be just as good as men in these disciplines, but commonly find themselves unwelcome in the workplace.

Despite this, Mansfield contends that “the entire enterprise of modernity could be understood as a project to keep manliness unemployed”. Sounding more than a bit like Don Quixote, he says professionals are unmanly because they treat each other with courtesy but never with chivalry. Meritocrats are unmanly because they think the system should recognise their merits, rather than claiming or fighting for honours themselves. And commerce is unmanly because it’s materialistic and willing to settle for gain rather than victory.

Even the modern obsession with health is unmanly, because it seeks a longer or less troubled life rather than a life that’s short and eventful “in the noble manner of Achilles”.

If you pin him down, Mansfield will tell you that manliness is “confidence in risk”. By that definition, any drunken hooligan breaking windows is manly. He agrees, but there are many levels of manliness, he adds. “Higher levels include risking life for a cause.”