The Spectator's cover story this week is another re-examination of the changing face of the gender pay gap - somewhat provocatively titled "the Richer Sex".

Needless to say, women are not actually the richer sex. Their median wage remains 11 per cent below men's in the latest comprehensive study [2] by the ONS, from 2007. Instead, the piece's author, Liza Mundy, touches on two trends which she sees in the UK.

The first is that, as the pay gap narrows (and it is narrowing – it is down from 16.5 per cent in 1997), the number of women earning more than their male partners will inevitably increase. Mundy highlights the apparently devastating effects that has on these "pursewhipped" men (a word apparently "slowly entering the English language", though not slowly enough):

I interviewed a woman I'll call Felicity, who married a gregarious salesman earning a third of what she did, But while he enjoyed the lifestyle her money could buy, he came to resent it. He started working less, playing golf more and watching TV instead of coming to bed with her. She wasn't surprised when she found his stash of online porn, but was still shocked. She ended up going into therapy.

Much the same argument was made, reduced to its barest essentials, by Tony Parsons on Woman's Hour in May [3], when he told Jane Garvey "my penis would literally fall off [if my wife earned more than me]. Literally, Jane, it would literally fall off."

Thankfully, this epidemic of shrivelled members is still a long time coming, because the gender pay gap has more structural reinforcement than Mundy makes out.

She correctly points to the fact that, in the first third of their lives, women – particularly educated, middle-class women – have largely closed the gap. Take the continued better performance of girls at GCSE, or her example of university education:

Women receive 58 per cent of all undergraduate degrees. Half of trainee barristers and 56 per cent of medical students are women, compared with 25 per cent in the 1960s.

And the increased success of younger women has paid off: between the ages of 24 and 32, the pay gap is negative. Younger women earn more than younger men.

But therein lies the rub. Munz optimistically assumes that this will continue; as that cohort ages, the gender gap will disappear, and women will actually become the richer sex. But the evidence points to a different outcome. The gender pay gap hasn't disappeared, it's just become a baby pay gap [4]:

The pay gap between women and men with no children is 8.0 per cent. The pay gap between women and men with four children is 35.5 per cent. (For one child, it's 12.3, two is 14.9, and three is 19.0).

The pay gap between men and women who are married, cohabiting or in a civil partnership is 14.5 per cent; the pay gap between single men and women is -1.1 per cent. For the purposes of the point I am making, of course, one can read "single" as "unlikely to have a child any time soon".

It's not even enough to not have children, either. Once a woman reaches an age where potential employers think she might have children, the pay gap starts to widen.

The problem is that we have a legal system which emphatically reinforces the idea of women as carers, and from that we get the society we deserve. With the discrepancy between paternity and maternity leave, it's made unfairly difficult for a family to fight traditional gender roles. And so while I hope that Munz is right, and that we will start "calling into question the old notion that women are 'hard-wired' to seek providers", we can't just hope that a generation of smart girls will do it for us.