Steep population declines in most countries are expected to have negative impacts over the next several generations, but adaptation is possible

Is collapsing fertility really the end of the world?

Steep population declines in most countries are expected to have negative impacts over the next several generations, but adaptation is possible

In 1970, a woman in Mexico might have expected to have seven children, on average. By 2014, that figure had fallen to around two. As of 2023, it was just 1.6. That means that the population is no longer making enough babies to maintain itself.

Mexico is not alone: countries around the world are witnessing falling fertility rates¹. Exceptions are few. The Institute for Health Metrics and Evaluation (IHME) at the University of Washington in Seattle estimates that, by 2050, more than three-quarters of countries will be in a comparable situation.

“There has been an absolutely incredible drop in fertility — much faster than anyone had anticipated,” says Jesús Fernández-Villaverde, an economist at the University of Pennsylvania in Philadelphia. “And it is happening in a lot of countries you would have never guessed.”

The numbers are clear. What’s uncertain is how problematic this global ‘baby bust’ will be, and how nations should respond. In economies that have been built around the prospect of steady population growth, the concern is over future slumps in innovation and productivity, as well as having too few working-age citizens to support a growing number of older people. Researchers warn of ripple effects, from weakened military power and less political influence for countries with lower fertility rates, to fewer investments in green technology. It is imperative that countries address population decline and its impacts now, says Austin Schumacher, a health metrics researcher at the IHME.

Many countries have been trying to take action, and the data suggest that some strategies are helpful — if politically fraught. But to scientists familiar with the data, even the most effective efforts are unlikely to bring a full rebound in fertility rates. That’s why many researchers are recommending a shift in focus from reversal to resilience. They see room for optimism. Even if countries can only slow the decline, that should buy them time to prepare for future demographic shifts. Ultimately, scientists say, fertility rates that are low, but not too low, could have some benefits.

“We’re not not making babies,” says Barbara Katz Rothman, a sociologist at the City University of New York. “The human race is not folding in on itself.”

What the data say

In the mid-twentieth century, the world’s total fertility rate — generally defined as the average number of children a woman would have during her reproductive years — was five. (Nature recognizes that transgender men and non-binary people might become pregnant. We use ‘woman’ and ‘women’ in this story to reflect language used in the field.) Some dubbed this mid-twentieth surge the baby boom. Ecologist Paul Ehrlich and conservation biologist Anne Ehrlich saw it differently, warning in their 1968 book The Population Bomb that overpopulation would lead to famine and environmental devastation. But they failed to anticipate advances in agricultural and health technology that would enable the population to double to eight billion in a little more than five decades.

Humanity’s impact on the environment has intensified, owing to that growth and to increased consumption in many parts of the world. But concerns about overpopulation have flipped. Population growth has been slowing down over the past 50 years, and the average total fertility rate stands at 2.2. In about half of countries, it has fallen below 2.1, the threshold generally needed to maintain a steady population (see ‘Declining fertility’). Small changes in these numbers can have strong effects. A fertility rate of 1.7 could reduce a population to half its original size several generations sooner than a rate of 1.9, for example.

Source: Our World in Data (**https://go.nature.com/45RWYFJ**)

The case of South Korea is under close scrutiny. Its fertility rate fell from 4.5 in 1970 to 0.75 in 2024, and its population peaked at just under 52 million in 2020. That figure is now declining at a pace that is expected to accelerate.

Forecasts for the world vary. The United Nations and the International Institute for Applied Systems Analysis in Laxenburg, Austria, project gentler declines than the IHME does (see, for example, go.nature.com/4mtkj8b). But demographers generally expect that the global population will peak in the next 30 to 60 years and then contract. If it does, that will be the first such decline since the Black Death in the 1300s.

According to the UN, China’s population might already have peaked in around 2022, at 1.4 billion. India’s could do the same in the early 2060s, topping out at 1.7 billion people. And, assuming the most likely immigration scenario, the US Census Bureau predicts that the US population will peak in 2080 at around 370 million. Meanwhile, many of the steepest near-term crashes are anticipated in middle-income countries: Cuba is expected to lose more than 15% of its population by 2050.

Sub-Saharan Africa is the notable exception. By 2100, more than half of the world’s babies are likely to be born there¹, despite it having some of the world’s lowest incomes, weakest health-care systems and most fragile food and water supplies. Nigeria’s fertility rate remains above four, and its population is projected to grow by another 76% by 2050, which will make it the world’s third-most-populous country.

Still, fertility-rate trends are hard to predict. Data gaps persist, and many models rely on the expectation that rates will rebound as they’ve done before. And as the Ehrlichs’ failed forecasts show, the past isn’t always indicative of the future. “We are groping in the dark,” says demographer Anne Goujon, programme director for population and just societies at the International Institute for Applied Systems Analysis.

What’s driving the decline?

The factors behind fertility collapse are numerous. They range from expanded access to contraception and education, to shifting norms around relationships and parenting. Debate continues over which factors matter most, and how they vary across regions.

Some drivers reflect positive societal changes. In the United States, data from the US Centers for Disease Control and Prevention show that fertility has declined in part because of fewer unplanned pregnancies and teenage births. A long-term drop in domestic violence might also have contributed. Research in 2018 by Jennifer Barber, a sociologist now at Indiana University in Bloomington, and her colleagues showed that women in violent relationships have children at around twice the rate as do those in non-violent ones².

Globally, access to contraception has helped to decouple sex from reproduction. In Iran, a national family-planning campaign that started in the 1980s contributed to the largest and fastest fall in fertility rates ever recorded: from nearly seven to under two in less than two decades³. The country reversed course around 2006, and is once again promoting policies to increase fertility rates.

Young people in wealthy countries are also forming fewer partnerships and having less sex. Alice Evans, a sociologist at King’s College London, has suggested that online entertainment is outcompeting real-world interactions and eroding social confidence. As women worldwide have gained education and career opportunities, many have grown more selective. Women want independence, while many men expect a “servant at home”, says Fernández-Villaverde. “Women are asking, ‘Why would I marry this person?’ A lot of men are undateable. Truly undateable.”

This disconnect fuels trends such as South Korea’s Four Nos feminist movement — in which many young women are rejecting dating, marriage, sex and childbirth — and a similar ‘boy sober’ movement among US women.

Mexico is one of several countries that has a fertility rate below replacement level.Credit: Bernd Vogel/Getty

Many young people are also pursuing more education so as to gain jobs that might come with high stress and little stability early on. As a result, even people who pair up might postpone having children or have trouble conceiving because they are older. Those who do have kids face pressure to prepare them for the same high-stakes race for university and career, says Matthias Doepke, an economist at the London School of Economics and Political Science. “It’s not like we have withdrawn from parenting. It’s just that we concentrate all this investment, all these hours, on fewer children.”

Rising costs create further pressures. A UN survey of more than 14,000 people in 14 countries found that 39% cited financial limitations as a reason not to have children (see www.unfpa.org/swp2025). In US cities, births have fallen most sharply where housing prices have risen most rapidly (see go.nature.com/4tqqzsg).

Ultra-low fertility rates tend to emerge where these pressures converge, says Doepke. In South Korea, he says, housing is expensive, the parenting culture is intense and the working culture rewards long hours.

Other contributors include declining sperm counts, potentially linked to environmental toxins. Many prospective parents also have growing anxiety about political and environmental instability, as highlighted in the UN survey. It’s not clear which of these many factors are most important in individual countries. But ultimately, low fertility rates “reflect broken systems and broken institutions that prevent people from having the number of children they want”, says Stuart Gietel-Basten, a sociologist at the Hong Kong University of Science and Technology. “That is the real crisis.”

Countering the crash

The fallout will play out differently around the world. Middle-income countries, such as Cuba, Colombia and Turkey, could be the hardest hit, with falling fertility compounded by rising emigration to wealthier nations.

Urban–rural divides will also deepen. As young people leave small towns, infrastructure such as schools, supermarkets and hospitals shuts down — prompting more to move away. Often, it’s older people who remain.

Globally, ageing is the core issue with population decline. In countries that have shrinking fertility rates, the proportion of people aged 65 or older is projected to nearly double, from 17% to 31% in the next 25 years (see go.nature.com/4fspvh5). As life expectancy rises, the demand for physical and fiscal support grows, yet there is a lag in supply. For the majority of countries hoping to break the fertility fall, tools exist. These include financial incentives, such as US President Donald Trump’s proposal to give each newborn baby US$1,000 in an investment fund.