Contraception and new reproductive technologies appear to work wonders, offering new opportunities that fit with modern women's lives. Some time in the future, perhaps human mothers will typically space their children at ten-year intervals - one for every new partner, say - and go on getting pregnant well into the part of their lives that the 20th century would have called "old age".
But if that is what happens, then ironically they will only be doing what their nearest mammalian kin have always done (and will no doubt continue to do): orang-utans, for instance, have babies at eight-year intervals. Human females are unique among animals in their long post-reproductive period of life: first fertility declines, then full menopause follows.
The new resistance to this particular peculiarity of our biology was the main topic at a recent conference at University College London, "Motherhood in the 21st Century". Its specific brief was "to explore the reasons why some women choose to become mothers late in life". The opening address was given by Lord Winston, the fertility expert, and the event drew speakers and delegates from many professions and disciplines (the ape facts came, for instance, from anthropologist Ruth Mace). There was, as the woman sitting next to me put it, an "electric atmosphere".
This is a topic that sparks strong feelings. Media stories and images of women in their 60s, one in India of 70, producing offspring with the help of "donor" eggs (in practice expensively paid for) generate complex emotions that do not occur in relation to ageing male parents.
These are exceptional cases, tabloid exhibits of a modern monstrosity: in reality, very few babies are born to women over 55. But the past decade or so has seen a vast increase in the number of women in the UK and comparable Western countries having babies over the age of 40, while the average age of first maternity is now as high as 30. (Not so long ago, was the age at which a woman was medically deemed to be an "elderly primigravida" - another maternal grotesque.)
Female fertility declines steeply from the mid-30s - that has not changed. In vitro fertilisation has led many to imagine technology as a fallback if they "delay" motherhood, when in practice success rates for older women are very low. They would plan their reproductive lives better if they knew the facts, it is argued. But the would-be rational language of planning (and postponement) has also helped fuel the problem, making it seem as if getting a baby when you want one is a simple lifestyle option.
There is also an issue of parity, at a time when the roles of men and women, and fathers and mothers, are becoming more alike than at any time in history (think of that new and neutral word, "parenting"). Neither nature nor society has ever tried to stop a man of 60 from having a child. The argument is made that the older mother may barely survive into her child's adulthood, but life expectancy has greatly increased, so that 50 may well be the new 30 in relation to mothering as well as much else.
The health "risks" of later pregnancy are often cited, but, as medical ethicist Anna Smajdor pointed out, the risks of contraception and abortion are far lower than for any pregnancy, so if risk is the criterion, then the best insurance policy is simply not to have babies, ever.
Yet the biological differences don't go away. The "fertility business" - it has become one of the biggest health businesses since the birth of the first IVF baby in 1978 - fosters unrealistic hope in women who go on to have cycle after cycle of treatment. But it was a fertility consultant, Peter Brinsden, who argued for better education about the poor chances of post-40 pregnancy, while Winston poured scorn on the new "fertility MoTs" that purport to show the current quantity and quality of women's egg stores. Unscrupulous clinicians are in the driving seat here.
There are plenty of tests and treatments on offer with no scientific basis, Winston argued, and a grave lack of serious research into fertility because there is so much money to be made by working as a practitioner. That's money that women "desperate" for a baby are willing to pay; and the cycle continues.
Rachel Bowlby is a professor in the department of English, University College London.