Meet the Anti-Mom. A story of motherhood gone dreadfully wrong, my seventh novel, We Need To Talk About Kevin, has drawn fire from Catholic websites for being hostile to "family", while grotesque distortions of the book's underlying theme ("It's all right to hate your own child, and if they turn out badly it's not your fault") have spored from article to article like potato blight. Devastated mothers send me confiding letters detailing horror stories of offspring just like the wicked boy in my book. Women who'd declined to have children flock to my readings, raising the novel as proof they were right.

Yet even as "Kevin" won the Orange Prize in July, when my role as poster-girl for "maternal ambivalence" jacked up yet another power, something strange was starting to happen. I sometimes departed from script. When a Sunday Times reporter (who clearly thought me a chilly, arrogant creep) asked if I didn't think that declining to reproduce was essentially "nihilistic", I piped readily, "Of course." And when a reporter from Birmingham asked tentatively in a phone interview, "Wasn't refusing parenthood a little ... selfish?" I bellowed into the receiver, "Absolutely!"

The truth is, I had started to feel guilty.

Childless at 48, I'm now old enough for the question of motherhood to have become merely philosophical. Still, I've had all the time in the world to have babies. I am married. I've been in perfect reproductive health. I could have afforded children, financially. I just didn't want them. They are untidy; they would have messed up my flat. In the main, they are ungrateful. They would have siphoned too much time away from the writing of my precious books.

Nevertheless, after talking myself blue about "maternal ambivalence", I have come full circle, rounding on the advice to do as I say, not as I did. I may not, for my own evil purposes, regret giving motherhood a miss, but I've had it with being the Anti-Mom, and would like to hand the part to someone else.

Allusion to Europe's "ageing population" in the news is now commonplace. We have more and more old people, and a dwindling number of young people to support them. Not only healthcare and pension systems but the working young will soon be overtaxed, just to keep doddering crusties like me alive. Politicians sensibly cite age structure when justifying higher rates of immigration, and not only because Europeans so fancy themselves that they refuse to clean toilets. Even if the job appealed, there are already too few of the native-born of working age to clean all those toilets.

Yet curiously little heed is paid to why the west is "ageing". Our gathering senescence is routinely discussed as an inexorable force of nature, a process beyond our control, like the shifting of tectonic plates or the ravages of a hurricane. To the contrary, age structure is profoundly within human control. Remarkably resistant to governmental manipulation, it is the sum total of millions of single, deeply private decisions by people like me and a surprisingly large number of people I know.

We're not having kids.

Western fertility started to dive in the 70s - the same era when, ironically, the likes of alarmist population guru Paul Ehrlich were predicting that we would all soon be balancing on our one square foot of earth per person, like angels on the head of a pin. Numerous factors have contributed to the Incredible Shrinking Family: the introduction of reliable contraception, the wholesale entry of women into the workforce, delayed parenthood and thus higher infertility, the fact that children no longer till your fields but expect your help in putting a downpayment on a massive mortgage.

Yet all of these contributing elements may be subsidiary to a larger transformation in western culture no less profound than our collective consensus on what life is for.

Statistics are never boring if you can see through the numbers to what they mean, so bear with me. The Total Fertility Rate (TFR) is the number of children the average woman will bear over her reproductive lifetime. The TFR required to maintain a population at its current size is 2.1. ( It takes two children to replace the mother herself and her partner; the .1 allows for the fact that, in a fraction of births, the baby will not survive.) Higher than the European average, the UK's TFR is 1.7. Yet that's well below replacement-rate, so the seven million extra Britons predicted by 2050 will almost entirely comprise immigrants and their children.

The figures on the continent are even more striking. Italy, Greece and Spain, countries once renowned for their family orientation, all have a meagre TFR of 1.3, as does Germany, where a staggering 39% of educated women are having no children whatsoever. The cumulative TFR for all of Europe is only 1.4, expected to translate into a net loss of 10% of the population by 2050, by which time eastern Europe is likely to experience a population decrease of 22%. By 2000, 17 European countries were recording more deaths than births, and without immigration their populations would already be contracting.

Elsewhere, couples still heed the Biblical admonition to be fruitful and multiply. Niger, currently suffering from famine, has the highest TFR in the world at 8.0. By 2050, Yemen - a little smaller than France - is projected to have increased its 1950 population by 24 times, exceeding the population of Russia. At 3.0 (3.5 without China), the poor nations' TFR is twice that in the wealthy west, and these countries will provide virtually all of the extra three billion people expected to visit our planet by mid-century.

As for what explains the drastic disparity between family size in the west and the rest, sure, we have readier access to contraception. But medical technology is only one piece of the puzzle. During the industrial revolution of the 19th century, fertility rates in the west plunged in a similar fashion. This so-called "demographic transition" is usually attributed to the conversion from a rural agrarian economy to an urban industrialised one, and thus to children's shift from financial asset to burden. But what is fascinating about the abrupt decrease in family size at the turn of the last century is that it was accomplished without the pill. Without caps, IUDs, spermicides, vaginal sponges, oestrogen patches or commercial condoms. Whether through abstinence, backstreet abortion, infanticide or rhythm, people who couldn't afford more children didn't have them. Therefore the increased availability of reliable contraception around 1960 no more than partially explains plummeting birth rates thereafter. The difference between Germany and Niger isn't pharmaceutical; it's cultural.

I propose that we have now experienced a second demographic transition. Rather than economics, the engine driving Europe's "birth dearth" is existential.

To be almost ridiculously sweeping: baby boomers and their offspring have shifted emphasis from the communal to the individual, from the future to the present, from virtue to personal satisfaction. Increasingly secular, we pledge allegiance to lower-case gods of our private devising. We are less concerned with leading a good life than the good life. We are less likely than our predecessors to ask ourselves whether we serve a greater social purpose; we are more likely to ask if we are happy. We shun values such as self-sacrifice and duty as the pitfalls of suckers. We give little thought to the perpetuation of lineage, culture or nation; we take our heritage for granted. We are ahistorical. We measure the value of our lives within the brackets of our own births and deaths, and don't especially care what happens once we're dead. As we age - oh, so reluctantly! - we are apt to look back on our pasts and ask not 'Did I serve family, God and country?' but 'Did I ever get to Cuba, or run a marathon? Did I take up landscape painting? Was I fat?' We will assess the success of our lives in accordance not with whether they were righteous, but with whether they were interesting and fun.

If that package sounds like one big moral step backwards, the Be Here Now mentality that has converted from 60s catchphrase to entrenched gestalt has its upside. There has to be some value to living for today, since at any given time today is all you've got. We justly cherish characters capable of fully inhabiting "the moment", of living, as a drummer might say, "in the pocket". We admire go-getters determined to pack their lives with as much various experience as time and money provide, who never stop learning, engaging, and savouring what every day offers - in contrast to dour killjoys who are resentful and begrudging as they bitterly do their duty. For the role of humble server, helpmate and facilitator no longer to constitute the sole model of womanhood surely represents progress for which I am personally grateful. Furthermore, prosperity may naturally lead any well-off citizenry to the final frontier: the self, whose borders are as narrow or infinite as we make them.

Yet the biggest social casualty of Be Here Now is children, who have converted from obligation to option, like heated seats in the car. In deciding what in times past was never a choice, we don't consider the importance of raising another generation of our own people, however we might choose to define them. The question is whether kids will make us happy.

However rewarding at times, raising children can be also hard, trying and dull, inevitably ensnaring us in those sucker-values of self-sacrifice and duty. The odds of children making you happier are surely no better than 50-50. A few years ago the New York Times published the results of a study that found the self-reported "happiness" index was lower among parents than the childless. Little wonder that so many women have taken a hard look at all those nappies, play groups, nasty plastic toys and said no thanks.

To illustrate my "existential" explanation for Europe's knee-high birth rate, let's look at three women like me, and why they haven't had children. These are all women (whose names are changed to protect their privacy) whom I admire, and whose company I treasure. In a word, they're my friends. Nevertheless, in sufficient aggregate, we are deadly.

At 44, Gabriella is an accomplished journalist who has written two acclaimed non-fiction books on Africa. She is bright, widely travelled, well educated and physically fetching, with a distinctive acerbity and a candour unusual for her British upbringing. She is half Italian on her mother's side.

Gabriella was negative about childbearing from the get-go: "I was someone who loathed the onset of sexual maturity. Menstruation, pregnancy - all these biological processes that you couldn't control, which caught you unawares and seemed designed to embarrass you in public - felt like a baffling, humiliating negation of my existence as a thinking, reasoning adult." By her 20s, her hostility had hardened. "As a young woman I remember being astonished to meet contemporaries who had decided to have children within years of leaving university. It seemed nonsensical. Here we were, just emerged from the tedious constraints of a seemingly endless education, financially independent for the first time, tasting our liberties at last, and the first thing they decided to do was to enter the prison of childrearing, with all its boring routines and dreadful responsibilities. Having children in my 20s would have spelled the end of everything I had spent my life working towards and was about to really enjoy: the ability to spend my money the way I wanted, travel where I wanted, choose my partners, live as I wished."

By her late 30s, however, Gabriella had misgivings. Friends were having children, and she felt left out. Encountering other people's children, she realised "there were great joys to be had from the process" and that "watching something [to non-parents, children are often mistaken for objects] growing and changing each day was also an intellectually intriguing process". Ergo, kids just might be interesting and fun. Yet Gabriella's then-partner was an older man averse to parenthood partially on (sound) medical grounds. At no point did her pining for children become a make-or-break matter in her relationship, from which we can construe that the pining was either mild or theoretical. For the most part, "the issue was ignored, avoided, allowed to slide or used as a bargaining chip when things got difficult." Indeed, when that relationship hit crisis point and her partner did a U-turn on fatherhood, his offer of a family was insufficient to salvage it for Gabriella. Happiness, in this case the romantic variety, trumped motherhood, full stop.

Gabriella is now resigned to the fact that she will not have children. "Could I now cope with the sheer exhaustion of the early sleepless years? Could I accept, as my friends have, that for the first five years I would stop having interesting conversations with adults my own age and settle for the glaze-eyed exchanges I've witnessed as an outsider?"

When I ask what she believes redeems her life in the absence of children, her answers are unhesitating. "Firstly, my work. Not in the sense of ambition and earning power (ha ha), but in the sense that the only imprint I can leave on this earth is my work. My motto, as the years go by, has become that of Voltaire's Candide: 'Il faut cultiver notre jardin.' We need to tend the garden. Do it as well as you can. Writing is my only skill; I apply it to the best of my abilities." Secondly, "I live for friendships and family. I have friendships that have gone on for so long and have been so close that I suppose they constitute a form of marriage."

On her own account, she has no regrets. "Had I had children, I would have written no books, nor would I have been a particularly successful journalist. I certainly wouldn't have gone off to Africa. I'd rather pine for children than die saying to myself, 'I could have been a contender.' I was a contender."

Nevertheless, in the larger social picture, Gabriella concedes, "If people like me don't reproduce, civilisation may be the worse for it. On both my mother's and my father's sides, I come from generations of academics, historians, diplomats - thinkers and doers - and as the years go by I begin to see that, far from being an exception or maverick, I am, in fact, the very obvious carrier of a certain genetic inheritance. I am a typical product of my family; I can see the thread stretching back through the generations. Do I think it's a shame that this genetic inheritance won't continue? Yes, I do. I'm arrogant enough to think that the world will be a poorer place without my genes in it. But the fact is that I don't care enough to do anything about it. There wasn't time to do that and the other things on my list."

When I press her on the implications of a contracting European population, she readily concurs that "many western cities will be largely black/ Hispanic/Asian in 50 years' time. Does that bother me? Well, I vaguely regret the extinction of gene lines that in their various ways played a part in the establishment of western civilisation. But the gene lines coming in from the developing world will have their own strengths, energies and qualities."

Last, and this is the sort of statement that many a childless woman - or man, for that matter - of my generation might honestly make, but that you will rarely read: "I'm an atheist. I'm a solipsist. As far as I'm concerned, while I know intellectually that the world and its inhabitants will continue after my death, it has no real meaning for me. I am terrified of and obsessed with my own extinction, and what happens next is of little interest. I certainly don't feel I owe the future anything, and that includes my genes and my offspring. I feel absolutely no sense of responsibility for the propagation of the human race. There are far too many human beings in the world as it is. I am happy to leave that task to someone else."

Irish-born Nora, 46, is an events planner who lives in London. She enjoys her work, in which she is renowned for her effectiveness and good humour, but she places equal emphasis on after-hours. She maintains a large, lively set of friendships, and regularly partakes of the city's concerts, films and plays. She's sharp, droll and quick-witted.

Astonishingly, Nora and all five of her Irish siblings have neglected to reproduce: "Each of us is quite independent, with goals that were more immediate and career-oriented than children."

Unlike Gabriella, through young adulthood Nora always assumed she would have children. Yet she is romantically fastidious and wilful. Though she admits, "I went through a phase when I was coming up to 30 when I got very depressed because it appeared to me highly unlikely that I would have children", motherhood "was never so important to me as to compromise on the man". As smart, appealing women, both Nora and Gabriella might surely have had families were they willing to marry Mr Not Quite Right, but kids weren't important enough. Once again, personal happiness trumps kids.

Nora grants she's "a bit" regretful, although "as I grow older, I feel a greater need for solitude, and for 'me-time'. Perhaps it's work that does it - being responsible for 10 staff and having a fairly 'open-door' policy makes me delight in going home, closing the door and relishing the peace." A holiday to Canada with her godson was sobering. "Yes, he's great - funny, intelligent, well-mannered, interested - but I felt that the responsibility of taking him into bear country was huge. A metaphor for life, perhaps?"

Nora's maternal regrets are skin deep. "I think I have a lovely life. I can see myself continuing to have fun, to enjoy my job, to meet interesting people, to go on great holidays, to read interesting books, to support my family and friends." (Note that I did not plant the words "fun" and "interesting" in my interviewee's mouth.) When I ask what she sees as redeeming her life, she balks. "I think that's a very Protestant question! I'm not sure my life needs redemption. Maybe I'm too much of a hedonist."

Still Nora sorrows, "I think my parents came from an excellent gene pool, and it's a shame that, to date, that hasn't been passed on." Though she has many cousins, the loss of the combined heritage of her particular parents is "a sadness". As for perpetuating her ethnicity, her parents both taught Irish, and she has "a mother tongue that is under threat. But in the wide scheme of things, I am conscious that languages disappear every year." We are of a generation grown accustomed to loss - of habitat, wilderness, biodiversity, fish. Why not Irish, too?

Be that as it may, at the end of our exchange Nora declares fervently, "You and I should have had children!" - hastily appending that she meant not for our own sakes, but in social terms. "We're blessed with brains, education and good health." She admits that the longer our discourse has continued, "the more I think I am a squanderer of my gifts and my heritage. But I live in a decadent age where that doesn't seem such a problem. Anyway, devoting my whole life to promulgating my ethnicity is a big ask."

At only 26, Leslie will have to stand in for the staggeringly numerous younger British women who have shared with me their lack of enthusiasm for the familial project. Leslie is a publicist for a small literary publishing company, to which she is devoted. She's very good at her job. Her sunny, perky quality provides a welcome counterpoint to my jaded older friends, and she's optimistic about the future - hers, that is.

Leslie does not want children. "When I think about my future, I envisage the fulfilment of ambitions such as travelling and furthering my career, not having babies. I can't imagine I will be able to give up the lifestyle I lead to become a parent. I would like to spend time working and travelling abroad. Financial independence is very important to me, as is retaining my own independence in any relationship. Something would have to give in order to properly care for a child, and unfortunately it's most often the mother who has to forego some aspect of her life."

When I ask her, an only child, if it matters to her whether she carries on the family line, she says, "It's not really something I've thought about."

On the other hand, Leslie offers evidence that Be Here Now - living for the present - is not always morally arid. "I certainly don't see my purpose as being to perpetuate the human race. What makes my life worth living for me - and what, I think, redeems my life - is my relationships and interaction with others, be they family, friends, lovers, colleagues, total strangers. I think what redeems individuals is their acts of humanity."

Like most of her generation, Leslie isn't concerned with maintaining the Anglo-Saxon identity of Britain. "Is there any true British race now, anyway? I think it's far too late to start worrying about its preservation at this stage." She has embraced multiculturalism, and faces the prospect of western cities going majority-minority with cheer. "Most of my friends are from different ethnic backgrounds, and I feel lucky to live in London, a city full of such diverse cultures, religions and races. I think diversity adds to British culture rather than destroys it."

As for whether she worries that she might regret giving motherhood a miss, Leslie would subject the decision to one test only: whether she might be "discontented" in future. "But then who's to say that I would feel more content if I did have children?"

Contentment. Happiness. Satisfaction. Fun. There's nothing, strictly speaking, wrong with these concerns, but they are all of a piece. They fail to take into account that our individual lives are tiny beads in a string. Our beloved present is merely the precarious link between the past and the future - of family, ethnicity, nation and species. We owe our very contentment - which Hurricane Katrina reminds us heavily relies on potable water and toilets - to the ingenuity of our ancestors, yet it rarely seems to enter the modern childfree head that proper payback of that debt might entail handing the baton of our happy-happy heritage on to someone else.

There is no generalisation in this article, no matter how harsh, that would not apply to me. I care about my own life in the present. I think I should be, but - doubtless because I don't have children - I'm honestly not very fussed about what happens after I die. I'm proud of the Shriver family, but not enough to help to ensure that it outlasts me. As Nora pointed out, my genes are swell. But like my friends', my sorrow at not having passed them on is vague, thin and abstract, and no match for Be Here Now. I fancy I work very hard; in socially crucial respects, I am lazy. Like Gabriella's, my stunted progeny are eternally 8in high and made of pulped trees, and if they keep me up at night I can quiet them by rewriting a lousy chapter in the morning. If I feel, oh, a little wistful about the fact that my country of birth, the US, will within my lifetime no longer be peopled in majority by those of European extraction (I'm German-American on both sides), that passing dismay has never been considerable enough for me to inconvenience myself with giving lifts to football practice. Frankly, if I can't be arsed to replace myself with a reasonable facsimile, immigrants willing to nurse sick little boys through their fevers have truly earned the right to take my place.

Of course, that "wistfulness" is political dynamite. Yet maybe the multiculturalism debate is sufficiently matured for us to concede that white folk are people, too. We encourage minorities of every stripe to be proud of their heritage - Jamaicans, Muslims, Jews - as well they should be. We don't assume that if an immigrant from China cherishes his roots and still makes a mean moo shoo pork he is therefore bigoted toward every other ethnicity on the planet. So can Italians not champion Italianness? Or the British their Yorkshire pudding? Indeed, the tacit consensus - that every minority from Australian aboriginals to Romany should be treasuring, preserving and promulgating their culture, while white Europeans should not - is producing a virulent, sometimes poisonous rightwing backlash across the continent, and a gathering opposition to the immigration that Europe sorely needs if it is to maintain itself economically. In the interest of civil, rational thinking on this matter, we should at least allow ourselves to talk about it. The long-dominant populations in most of Europe are contracting, and maybe by the time they're minorities in their own countries they will have rights, too - among them at least the right to feel a little sad.

Meanwhile, as the west's childless have grown more prevalent, the stigma that once attached to being "barren" falls away. Women - and men, too - are free to choose from a host of fascinating lives that may or may not involve children, and across Europe couples are opting for the latter in droves. My friends and I are decent people - or at least we treat each other well. We're interesting. We're fun. But writ large, we're an economic, cultural and moral disaster.

There has to be something wrong when spurning reproduction doesn't make Gabriella and me the "mavericks" that we'd both have fancied ourselves in our younger days, but standard issue for our age. Surely the contemporary absorption with our own lives as the be-all and end-all ultimately hails from an insidious misanthropy - a lack of faith in the whole human enterprise. In its darkest form, the growing cohort of childless couples determined to throw all their money at Being Here Now - to take that step-aerobics class, visit Tanzania, put an addition on the house while making no effort to ensure there's someone around to inherit the place when the party is over - has the quality of the mad, slightly hysterical scenes of gleeful abandon that fiction writers craft when imagining the end of the world.

Not to disparage old people, but "senescent" is not a pretty word. Large sectors of western population have broken faith with the future. In the Middle East, birth rates are still sky-high, whereas Europeans, Australians and many European-Americans cannot be bothered to scrounge up another generation of even the same size, because children might not always be interesting and fun, because they might not make us happy, because some days they're a pain in the bum. When Islamic fundamentalists accuse the west of being decadent, degenerate and debauched, you have to wonder if maybe they've got a point.