Tim Dyson, a demographer at the London School of Economics who studies world population shifts, told TMD that the forces behind today’s falling birth rates stretch back centuries. Broadly speaking, birth rates began exceeding death rates in Europe around the late 18th century, a pattern that spread across the globe. After that, Dyson said, births gradually coming into alignment with deaths after a long period of population growth.
Demographers call this shift the “demographic transition.” Until recently, most assumed that while births would fall, they would eventually stabilize at around 2 per woman, producing a global population that would converge at a rough equilibrium.
That hasn’t happened. Dyson points to compounding factors: Longer life expectancies have reduced the need for “insurance” children, and women have developed social roles less oriented around childbearing. Then there are broader social changes—women entering the workforce, becoming more educated, gaining more control over their life paths—that have made two or more children far less of a default.
Other demographers flip the causation. Wolfgang Lutz, director of the Wittgenstein Centre for Demography and Global Human Capital, told TMD that “the education of women is the key factor in bringing down fertility.” He points to Thailand, where compulsory education laws in the 1970s preceded a TFR collapse from above 6 to just over 1 today. “The timing is different,” Lutz said, “but the essential process is universal.”
The sub-Saharan outliers share the inverse conditions: high infant mortality, limited access to education (particularly for women), and economic structures where children contribute to household labor and elderly care. As those factors change—as they have across Asia and Latin America—fertility tends to follow.
Whatever the precise mechanism, it has translated into concrete lifestyle preferences, noted Nick Eberstadt, a demographer and political economist at the American Enterprise Institute. “The most powerful predictor of fertility differences across countries and within countries over time that I have ever come across is the number of children that women say they want to have,” he told TMD.
The decline also hasn’t tracked neatly with national wealth—which might seem counterintuitive, given that the main exceptions to birthrate trends are among the world’s poorest nations. But middle-income countries now match or undercut wealthy ones: Colombia (with a GDP per capita of $7,919) has a fertility rate of 1.6, on par with Britain (with a GDP per capita of $53,246). Once the conditions that drive high fertility—infant mortality, lack of women’s education, agrarian economics—begin to shift, wealth alone doesn’t determine how far rates fall.
And those conditions have now shifted almost everywhere. The U.N.’s widely cited estimate of a population peak around 2080 rests on the assumption that global fertility rates will soon begin to level off—a prediction rooted in the belief that once women reach a certain level of education and workforce participation, birth rates stabilize near replacement level. But in country after country, rates have continued falling past that point, with no floor yet in sight. Just one-third of the world’s population now lives in a country where TFR is above the replacement rate.
Lutz argued that assuming TFR will continue to fall indefinitely to a near-zero level would be a mistake, citing flaws in some historical population projections. In 1968, Paul Ehrlich predicted that overpopulation would lead to mass famine and social instability in his book, The Population Bomb. But Ehrlich’s research ultimately proved incorrect because it rested on the assumption of constant fertility rates and failed to account for the possible effects of more efficient resource management or changing social structures. “It’s equally wrong to keep the declining rates of today constant,” Lutz said.
Even so, in some places, the decline is already drastic. South Korea, with a TFR of 0.75 in 2024, now has a population in which more than 20 percent of people are over 65, and, according to some projections, could shrink from 52 million today to roughly 12 million by 2125. Politicians have characterized the country’s low birth rate as a “national emergency” and have pledged to implement a range of policy measures, including paid parental leave, flexible work schedules, and housing assistance.
Societies will soon confront a rising “dependency ratio”: the number of non-working people relative to working-age adults. In 1945, the U.S. had 12 retirees for every 100 workers. By 2030, that figure is projected to exceed 35 per 100—threatening the long-term solvency of Social Security and Medicare.
“The fiscal picture is going to get really tough,” James Feyrer, a Dartmouth economist who studies how population issues relate to the economy, told TMD. “You have to take care of all those elderly people, and they’re a lot more expensive than kids”
But focusing narrowly on economics misses something deeper, argues Anna Rotkirch, a demographer and director of the Population Research Institute in Helsinki, Finland. “Fertility is about much more than who will pay up pensions,” she told TMD—it’s about the kind of societies people want to live in.
Rotkirch argued that much of the decline in birth rates stems from fairly recent developments that have made it harder for people to meet romantic partners and form families, especially in the West, citing research showing that the expansion of internet access consistently correlates with lowered fertility rates. She also noted that the rise of social media has likely played a role in reducing the time younger people spend dating, and can also amplify negative narratives about dating and parenthood.
Reversing the trend has proved stubbornly difficult. Few countries have consistently achieved higher fertility rates through technocratic solutions, Lutz said. “Politicians think that they can steer fertility, but directly, it’s very hard,” he said, pointing to Hungary, which has large tax benefits for parents, including a lifetime income-tax exemption for mothers who have two or more children, and politicians who consistently talk up their government’s pro-family orientation.
In 2019, its TFR was 1.55. Now, it’s 1.38.
Rotkirch said that governments have generally failed to take the problem of declining populations seriously enough, arguing that the challenge will require measures like reshaping career paths to be more conducive to having families, countering negative views spreading on social media of romantic relationships and families, and rethinking the structure of the social contract among generations.
Dyson put it more bluntly: “Very clearly, men are going to have to become more like women” by taking on a larger role in running the household and raising children. And there’s evidence that this shift is already underway in some countries—in the U.S., millennial fathers report spending much more time on child care and household chores than even five years ago.
But even as countries begin to explore policy and cultural solutions, few have found a way to bring fertility back up. “This is a continuing march to ever lower levels of fertility,” Eberstadt said. “Nobody has a good theory to explain how low it can go, or why.”
