Societies do collapse, sometimes suddenly. Nevertheless, prophets of doom might keep in mind that their darkest predictions have been, on the whole, a little premature. In 1968, Paul Ehrlich, a lepidopterist, and his largely uncredited wife, Anne, published a best-seller called “The Population Bomb.” For centuries, economists had worried that the world’s food supply could not possibly be expected to keep pace with the growing mobs of people. Now there was no postponing our fate. “The battle to feed all of humanity is over,” Ehrlich wrote. “In the 1970s the world will undergo famines—hundreds of millions of people are going to starve to death.” This was the received wisdom of the era: a decade earlier, an only slightly flippant article in Science estimated that in November, 2026, the global population would approach infinity. Ehrlich prescribed a few sane proposals—the legalization of abortion, investments in contraception research, and sex education—but he also floated the idea of spiking the water supply with temporary sterilants. Americans might protest such extreme measures, he allowed, but people in foreign countries should have no choice. It was only reasonable that food aid be conditioned on the developing world’s ability to exhibit civilized restraint. Nations that tolerated a free-for-all of unrepentant copulation—he singled out India—would be left to fend for themselves.

“The Population Bomb” transformed regional unease into a global panic. India, in less than two years, subjected millions of citizens to compulsory sterilization. China rolled out a series of initiatives—culminating in the infamous one-child policy—that included punitive fines, obligatory IUD insertions, and unwanted abortions. Ehrlich can hardly be blamed for the most coercive incarnations of population control. He might, however, be accused of impeccable comic timing. By the time “The Population Bomb” was published, the population-growth rate had already peaked. For hundreds of thousands of years, we had gone forth and multiplied. This epoch was coming to an end.

The “total fertility rate” is a coarse estimate of the number of children an average woman will bear. A population will be stable if it reproduces at the “replacement rate,” or about 2.1 babies per mother. (The .1 is the statistical laundering of great personal tragedy.) Anything above that threshold will theoretically generate exponential expansion, and anything below it will generate exponential decay. In 1960, the tiny country of Singapore had a fertility rate of almost six. By 1985, it had been brought down to 1.6—a rate that threatened to roughly halve its population in two generations. As the economist Nicholas Eberstadt told me, “For two decades, the leaders of Singapore said, ‘Oh, uncontrolled fertility has terribly dangerous consequences, so the rate has to come down,’ and then, after a semicolon, without even catching their breath, said, ‘Wait, I mean go up.’ ” The nation’s leaders launched a promotional campaign: “Have-Three-or-More (if you can afford it).” Singaporeans were known to be good national sports, but, despite the catchiness of the slogan, they proved noncompliant. From one nation to the next, the nightmare of too many descendants turned into the nightmare of too few. In 2007, when Japan’s total fertility rate hit 1.3, a conservative government minister referred to women as “birth-giving machines.” This didn’t go over particularly well with anyone, including his wife.

Today, declining fertility is a near-universal phenomenon. Albania, El Salvador, and Nepal, none of them affluent, are now below replacement levels. Iran’s fertility rate is half of what it was thirty years ago. Headlines about “Europe’s demographic winter” are commonplace. Giorgia Meloni, the Prime Minister of Italy, has said that her country is “destined to disappear.” One Japanese economist runs a conceptual clock that counts down to his country’s final child: the current readout is January 5, 2720.

It will take a few years before we can be sure, but it’s possible that 2023 saw the world as a whole slump beneath the replacement threshold for the first time. There are a couple of places where fertility remains higher—Central Asia and sub-Saharan Africa—but even there the rates are generally diminishing. Paranoia has ensued. In the past year, hundreds of men in the Central African Republic have reported the presumably delusional belief that their genitals have gone missing. In Nigeria, where the fertility rate has fallen from seven to four, a widely read tabloid blamed a conspiracy of perverts in the French intelligence services who had been “using secret nanotechnology innovations to steal penises from African men in order to reverse the extinction of Europeans unwilling to bear children.”

The phenomenon exerts a peculiarly deranging force, and until recently Americans remained oblivious. In the past two decades, however, the American fertility rate has dropped roughly twenty per cent, to 1.6. The right wing sees depopulation as a greater threat than climate change. Elon Musk describes it as “the biggest danger civilization faces by far,” and is trying, in his quiet way, to compensate on his own. He has sired, at least in a technical sense, thirteenish known children, and has reportedly offered the dispensation of his sperm to friends, employees, and people he met once at a dinner party. (Musk denies this. Skeptics of the strategy, though, might recall that Genghis Khan, according to legend, had more than a thousand offspring.) Vice-President J. D. Vance has blamed this “catastrophic problem” on the “childless left.” Liberals more often dismiss the issue, not without reason, as scaremongering in service of the Republican assault on reproductive rights. Some go further: a dwindling population is a more environmentally sustainable one.

Anyone who offers a confident explanation of the situation is probably wrong. Fertility connects perhaps the most significant decision any individual might make with unanswerable questions about our collective fate, so a theory of fertility is necessarily a theory of everything—gender, money, politics, culture, evolution. Eberstadt told me, “The person who explains it deserves to get a Nobel, not in economics but in literature.”

The global population is projected to grow for about another half century. Then it will contract. This is unprecedented. Almost nothing else can be said with any certainty. Here and there, however, are harbingers of potential futures. South Korea has a fertility rate of 0.7. This is the lowest rate of any nation in the world. It may be the lowest in recorded history. If that trajectory holds, each successive generation will be a third the size of its predecessor. Every hundred contemporary Koreans of childbearing age will produce, in total, about twelve grandchildren. The country is an outlier, but it may not be one for long. As the Korean political analyst John Lee told me, “We are the canary in the coal mine.”

In Seoul, an endless, futuristic sprawl of Samsung- and LG-fabricated high-rises, an imminent shortage of people seems preposterous. The capital city’s metropolitan area, home to twenty-six million citizens, or about half of all South Koreans, is perhaps the most densely settled region in the industrialized world. When I visited, in November, I was advised to withdraw my phone from my pocket on the metro platform, because it would be impossible to do so once on board the train. Fuchsia metro seats are reserved for pregnant women. Those who aren’t yet showing are awarded special medallions as proof of gestation. A looping instructional video reminded passengers of the proper etiquette. Even amid the rush-hour crush, these seats were often left vacant. They seemed to represent less a practical consideration than an act of unanchored faith—like a place for Elijah at a Seder table.

Portents of desolation are everywhere. Middle-aged Koreans remember a time when children were plentiful. In 1970, a million Korean babies were born. An average baby-boomer classroom had seventy or eighty pupils, and schools were forced to divide their students into morning and afternoon shifts. It is as though these people were residents of a different country. In 2023, the number of births was just two hundred and thirty thousand. A baby-formula brand has retooled itself to manufacture muscle-retention smoothies for the elderly. About two hundred day-care facilities have been turned into nursing homes, sometimes with the same directors, the same rubberized play floors, and the same crayons. A rural school has been repurposed as a cat sanctuary. Every Korean has heard that their population will ineluctably approach zero. Cho Youngtae, a celebrity demographer at Seoul National University, said to me, “Ask people on the street, ‘What is the Korean total fertility rate?’ and they will know!” They often know to two decimal places. They have a celebrity demographer.

Outside of Seoul, children are largely phantom presences. There are a hundred and fifty-seven elementary schools that had no new enrollees scheduled for 2023. That year, the seaside village of Iwon-myeon recorded a single newborn. The entire town was garlanded with banners that congratulated the parents by name “on the birth of their lovely baby angel.” One village in Haenam, a county that encompasses the southern extremity of the Korean peninsula, last registered a birth during the 1988 Seoul Olympics.

Haenam disappears into the sea at a windswept cape called Ttangkkeut, or “End of the World.” Not far away, there is a school that once had more than a thousand elementary-age students. When I visited, in November, it had five. A pastel rainbow brightened the façade, and out front was a statue of a singlet-clad boy with a raised torch; the plinth’s inscription read “Physical strength is national strength.” A pair of slippers had been left for me at the entryway, beside a trophy case crowded with bygone glories and a laminated poster that introduced the names and career aspirations of the three first graders (policeman, architect, idol singer) and the two sixth graders (truck driver, fighter pilot). In a memorable scene in Alfonso Cuarón’s 2006 film, “Children of Men,” a dystopian vision of a sterile world, a deer bounds through a trash-strewn school hallway. Here, dereliction was kept at bay: the corridors were bright, broom-swept, and freshly painted. The former chambers of a departed principal, dusted as if in anticipation of parent conferences, were spectral; the empty room next door had a hulking public-address console, with five microphones set at varying heights. It was as if everyone had evaporated overnight.

The school administrator, Lee Youngmi, efficiently if warily welcomed me into a main office lined with spotless devices—a spiral-binding machine, a laminator—and offered me ginger tea and cookies. When she’d first arrived, ten years ago, there were sixty students. But the surrounding town had since drained away. The large cattle market, which used to be candlelit until well after dark, is gone, as are the brewery, the lumber mill, the police station, and the post office. Parents fought to preserve the school as a center of civic life, but their children now complained that there was no one left to play with. Teachers called the current group of students, in a reference to an old Korean superhero cartoon, the Eagle Five Brothers. Lee was accustomed to solitude. When she left me in the room, she reflexively flicked off the heating.

The sixth-grade teacher, Kang Wooyoung, a man in his twenties, had a similar air of resignation. His two students had been together since they reached school age. When I asked if they got along, he seemed baffled by the question: they fought sometimes, sure, but they didn’t know any other children their age. “The advantage is that I can be super intimate with the students,” he said. “The disadvantage is that they cannot learn to socialize in a group setting.” One of his sixth graders was disabled; a special-education teacher was retained on his behalf, but the line item was hard to justify. The patterns of the children’s lives were unlikely to be upended by the arrival of a strange new kid or the torment of an unapproachable crush. The school may be closing next year. Kang had loved his first teaching job, his own childhood dream. But he didn’t have any friends in town, either.