According to one leading demographer the most consequential announcement last week relating to future tax revenues and demands on the NHS was not to be found in the budget. It was instead a statistic released by the Office for National Statistics: the average fertility rate is now 1.44 children per woman - the lowest figure since records began.
For Paul Morland, author of No One Left: Why the World Needs More Children, it's just the latest milestone in a long term and worrying trend. "We've had a below replacement level fertility rate now for 50 years," he says. "We now have more deaths than births, and we are not alone."
Most countries in the world have below replacement fertility - which in the UK is about 2.1 children per woman, and slightly higher in countries where infant mortality is a greater threat. The exception is sub-Saharan Africa, where high fertility rates are still common, though dropping.
The pattern is well established. As societies grow wealthier and more secular, and woman gain greater agency, birthrates come down.
Morland believes the world is teetering on the edge of a population collapse. But to those concerned about overpopulation, increasing human consumption and climate change, pro-natalism is alarmist, nostalgic for women's domestication, and indifferent to the effect ever-expanding humanity has wrought on the planet.
"The World Wildlife Fund says that we've lost 73% of our wildlife population in the last 50 years," says Amy Jankiewicz, chief executive of Population Matters, a campaign group in favour of sustainable human population. The plunging fertility rate, she says, is "cause for celebration". As she points out, the current UK population is about 68.3 million and is expected to reach 78 million by 2050. "It's not sustainable," she says.
But behind those headline figures, another picture emerges. The demographic makeup of the UK and the rest of Europe, not to mention North America and most of Asia, is radically changing. And it's this factor that is central to matters of fiscal revenue and public expenditure. Not only is the fertility rate going down, but longevity is going up. We are getting older as a nation and a global society.
This ageing can be seen in what is known as the old age dependency ratio (OADR), which is the number of people of retirement age versus the number of people of working age. Or to put it another way, the number of people paying tax versus the number of people receiving pension support, as well as a disproportionate amount of NHS and care services.
In the UK the OADR was below 20% in the 1950s - there were more than five workers for every retiree - whereas it is more than 30% today (or just three workers for every retiree). Morland notes that by the end of the century it "will be approaching 60%", which would be 1.7 workers for every retiree. That, too, is likely to be unsustainable.
Just look at the NHS. When it was established, writes Morland, there were around a quarter of a million people in Britain in their late 80s or older. Members of this cohort require six to seven times as much health spending as those in the prime of their lives. Today, he says, there aremore than 1.5 million in that age group and by the end of the century the figure is predicted to be almost 6 million. Here's another statistic to conjure with: in Italy in 1950 there were 17 under-10s for every one person over the age of 80. Today, writes Morland, "the two groups are matched roughly one-to-one". It's no coincidence, he says, that the countries with the most ageing populations, such as Greece, Italy and Japan, have the worst levels of government debt to GDP.
Europe's solution to this growing shortfall in the labour force is immigration. The UK's population would now be in decline if it wasn't for the massive number of immigrants that keep service, health and care industries going. But to sustain this policy, argues Morland, almost half the population of the UK would have to be foreign-born by the end of the 21st century.
Jankiewicz counters that the good thing about immigrants is that they don't add to the world's population, but merely shift its distribution. Large-scale immigration, however, has been cited for the rise of right-wing parties in Europe, Brexit in the UK, and the popularity of Donald Trump in the US.
Moreover, says Morland, the developed world routinely strips the developing world of its brightest and most dynamic people in what amounts to a post-colonial raid on those economies. In any case, it won't be long before sub-Saharan Africa moves, like India and China, to similarly low fertility rates, adds Morland.
So what's the answer? There is no doubting the effects of the Anthropocene epoch, and it stands to reason that the world's population can't keep growing indefinitely. But unlike with almost every other vital aspect of the economy, democratic governments have almost no involvement in the fertility rate, either in its move up or down.
The decision to have a child is rightly a private one, usually made between two people. It's extremely doubtful that any couple has ever set about trying to have a baby to solve a future labour shortage - that really would be a passion killer. Thus any governmental attempt to influence the parenthood decision could appear intrusive, and has in the past been draconian.
China famously implemented a one child policy between 1979 and 2015 to halt the country's population growth. It was a flagrant curtailment of its citizens' human rights, and yet now that all restrictions are lifted, economic development has left China with a fertility rate of 1.0. Recently its government has been accused of pressuring women into having more children.
When the fertility rate drops, the number of girls born obviously drops (even more so in countries like China, where female foetuses are more often aborted than male). That means that there will be fewer women of child-bearing age, which in turn means that the fertility rate required to maintain the population goes up even higher. Rapid depopulation is the inevitable outcome..
For Jankiewicz, this can only be a good thing. "The fewer people the better is what we stand for," she says. Even a pro-natalist like Morland, who describes himself as "unapologetically rightwing", accepts that humanity must have a population limit. But he argues that its decline needs to be better managed and should be delayed until AI and robotics can replace labour.
He calls for a "cultural revolution" in which the idea of having larger families is seen as desirable or even cool. After all, he notes, "women in the UK and the US have about three-quarters of a child less than they say they want". He emphasises that any cultural change would have to entail an equitable sharing of childcare duties between parents.
But while a man with many children might be viewed as a potent paterfamilias figure or someone, like Elon Musk, with many willing partners, there aren't many have-it-all role models for women - mother-of-six investment banker Nicola Horlick with her nanny-back-ups, or perhaps the Yorkshire Shepherdess Amanda Owen, with her nine children? The point is they're well known because they are such striking exceptions.
The paradox of fertility is that it is highest in poor countries, but in the developed countries people cite high costs as one of the main reasons for limiting or not having children. Some governments have attempted to alleviate the problem by subsidising childcare, offering extended parental leave and various tax breaks for families.
Yet while there are signs such measures may have small effects, they are not of the kind that will reverse current trends. Hungary, for example, is estimated to spend 5% of its GDP on pro-natal policies.
As a result the fertility rate has climbed from 1.25 to 1.5, yet that is a long way from replacement level. And given that the Hungarian government is right-wing, populist and anti-immigrant, it has helped foster the belief that pro-natalism is really just another form of pro-nationalism.
There aren't any easy answers to this problem, and even the questions are complex. But some kind of public debate is required because the implications of population decline (or indeed increase) are too great to be left to just happen.
The British government is right to avoid advising citizens on their procreative choices. But it should be clear about what the consequences are for the generations to come.