For men the holy grail is within reach – you just need to get fit, and then you'll be fine; then you can think about something else. But the messages aimed at women are much more complex and confusing. As the American social commentator Warren Farrell has pointed out, women's magazines often contain articles about being Superwoman, which are next to adverts about being Cinderella. (来源：英语杂志 http://www.EnglishCN.com)

In other words, the words tell women how to be independent and in control. But the adverts, where the money is, tell them they have to be beautiful.

Farrell said this more than two decades ago – and, shockingly, nothing has changed. There's a solid pulse running through everything our culture aims at women – be beautiful, be beautiful, be beautiful.

But being beautiful, it turns out, is a near-impossible task. It keeps getting harder and harder. Everybody knows that it entails being slim – and every year the ideal gets slimmer and slimmer. In 1960 the average model weighed 10 per cent less than the average woman. Now she weighs 25 per cent less. Soon she will weigh 30 per cent less. But she doesn't have the breasts of a skinny woman – nor, as Susie Orbach has recently pointed out, the bottom. To achieve the ideal is vanishingly impossible.

And it's getting worse. Orbach believes that we are exposed, on a weekly basis, to several thousand images that have been digitally manipulated. And this, in turn, makes more women opt for cosmetic surgery – which, of course, moves the goalposts even farther away.

When lots of people have surgery to make themselves look more beautiful this has the effect of making everybody else feel less beautiful. And this is happening on a global scale – in 2007 people spent £9 billion on cosmetic surgery; the vast majority of them, of course, were women.

So: men are told they should aspire to fitness and strength, and women are told they should aspire to something more nebulous. But that still does not explain, in terms a man could understand, why the female message is so much more powerful and disturbing.

It doesn't explain why a tenth of women are anorexic, why a growing number are bulimic, why almost half of women, at any given time, are on a diet. It doesn't quite explain the meltdowns. And it doesn't explain why women want to be so skinny. Why they think they are fat, when they are not. It doesn't explain why, when a woman's body is perfectly attractive, she often thinks it isn't, and can't be persuaded otherwise.

In short, it does not explain why a man can look at an advert featuring a six-pack and laugh at it, whereas a woman might look at a picture of Gisele Bündchen and feel a sense of unease that hangs around for days.

John Updike once said that the female body is the world's prime aesthetic object – we look at it more than we look at anything else, including landscapes, gadgets, cars. In fact, cars and gadgets are often designed to resemble the female body, and landscapes can be painted to remind us of it. When we talk about 'the nude' in art we are almost certainly referring to the female nude. As far as nudes are concerned, the male nude is a distant runner-up.

I once wrote the introduction to a book of male nudes by the photographer Rankin; it was a sequel to his previous book of female nudes. One thing struck me above all – male nudes were a much, much harder thing to portray than female ones.

That's because the female body carries with it a huge weight of iconic significance – thousands of years of being looked at. The female body has meaning. Pictures of the female body can be profound, serious and complex. For thousands of years they have been depicted with reverence. Now imagine having one of those bodies. It puts a bit of pressure on, doesn't it?

Now I'm beginning to see why women might be so addicted to perfection. They have a lot to live up to – a couple of thousand years of art history, and a couple of thousand airbrushed boobs and bums to deal with every week.

But what started this off in the first place? Why aren't there so many airbrushed pictures of men around? Of course, these pictures do exist, and their numbers are increasing. But why are women so much more vulnerable to pictures of perfect bodies than men?

In his book The Evolution of Desire, the American psychologist David Buss goes some way towards explaining why this should be so. Since the Stone Age, he explains, men and women have had different attitudes towards sex. Men can pass on their genes with very little risk – all they need is a fertile woman.

But it's different for women, because pregnancy is incredibly risky. What women need is a man who looks like a good provider – better still, who looks like a proven provider.

So let's think about our Stone Age man and woman. If he's going to settle down, and stop playing the field, he wants one thing above all – a woman who looks fertile. More than that, he wants a woman who looks as if she'll be fertile for many years to come. In other words, he might consider being a provider and protector, as long as his mate looks young, fertile and unblemished.