The Global Fertility Crisis Is Worse Than You Probably Think

Why has the number of births declined everywhere, all at once?This was the subject of last week’s Plain English episode and a new blockbuster report from the Financial Times’s John Burn-Murdoch. In fact it feels like just about everybody has been taking a crack at this question recently.Some blame it on technology. One week ago, my feed was flooded with a viral video of Connor Leahy, an AI researcher, speaking about the sterilizing effects of modern technology. Among his friends, “no one’s having kids,” said Leahy, who was 30 at the time. “Do you know how hard you need to abuse a mammal to make them not have children?” If you asked Leahy what the explanation was, “my answer is technology,” he said. “My answer is social media. My answer is AI.”A𝓸𝓯A@AndrewofAAI critic Connor Leahy Clip from the Nexus Conference 2025. #Ai #technology #techdoom4:57 AM · May 1, 2026 · 214 Views1 Repost · 1 LikeOthers blame a kind of 21st century weltschmerz—a world sadness about the state of the world and our uncertain future in it. A long essay in the New York Times by Anna Louie Sussman, entitled “Why So Few Babies? We Might Have Overlooked the Biggest Reason of All,” an excerpt from her forthcoming book Inconceivable, argued that we have “overlooked” the pervasive sense of existential uncertainty among young adults. Between climate change, rising housing costs, political instability, AI, inflation chaos, doomscrolling, and declining social trust, today’s generation is too anxious about the future to make the irreversible commitment of having a child.So who is right? Is this about phones and technology, or is it a reflection of modern anxiety about the world? Or, perhaps, both?I always like to begin my analysis of the subject here: Any complete and responsible explanation of this phenomenon cannot begin in the 21st century and should never pretend that this is some tragedy brought about by exclusively terrible things.

Birthrates have been declining in developed countries for a long time, as child mortality has declined; as women’s education has increased; as female labor force participation has soared; as modern contraception has proliferated; and as modern notions of feminism have empowered women to take more control over their bodies and their economic futures. And birthrates have continued to decline around, or even accelerated in their downturn in developed countries, as smartphone usage has surged; as housing prices of increased; as time spent at home on the Internet has grown; and as socialization and coupling have declined. The decline is accelerating faster than almost anybody predicted. As Burn-Murdoch reported, UN demographers predicted that there would be 350,000 births in South Korea in 2023; the real figure came in at 230,000—a whopping 50 percent miss. The total fertility rate has fallen below the replacement level of 2.1 births per woman in almost every country in North America, South America, Europe, and Southern and Eastern Asia. It’s falling swiftly in most African countries. And birthrates might be set to crash in China. In the 2026 paper “The Rise of Zero Fertility Desire in China,” a Brown University researcher reported that according to the China General Social Survey, the share of young women with “no desire for children” increased from approximately 5 percent in 2012 to 47 percent in 2023. The epicenters of the baby bust will surprise many people. Europe has a higher fertility rate than Thailand. Tokyo has a higher fertility than Mexico City, Bogotá, or Santiago. China may already a lower fertility rate than Japan. “Only two things are important right now in life: fertility and deep learning,” the University of Pennsylvania economist Jesús Fernández-Villaverde said at the conclusion of a recent lecture. “Everything else is noise. Once you start thinking about these, it’s hard to start thinking about anything else.” In today’s interview, Fernández-Villaverde explains:Demographics 101: Defining total fertility rate, replacement rate, and momentumWhy the world has probably already passed “peak child”Why 2023 was the first year in human history that the global fertility rate likely fell below the replacement rateWhy the question “why is the birthrate declining?”

is so hard to answer quicklyWhy most people underrate the long-term effects of low birthrates on world affairsThe compounding effects of sub-replacement level fertility: “If Thailand keeps its current fertility rate of 0.8 for the next 200 years without immigration, its population will decline from 63 million to 2 million.”Derek Thompson: Why is fertility important?Fernández-Villaverde: Because demographics is destiny. The number of children born today will determine how our society will look in 30 to 40 years. The year 2023 was a unique year in the history of humanity, because it’s the first time our total fertility rate as a planet fell below replacement rate. That has never happened before in 200,000 years. That means the world population will peak in another 30 years or so if the trend continues. Some things will be good, some will not be so good. Thompson: Tell me what replacement level means and what total fertility rate means.Fernández-Villaverde: Let’s start with replacement, which is the easiest. Imagine you have a population of one million people. How many children need to be born for that population to be constant at one million in the long run? It turns out that for every woman in that population, you need 2.1 kids. Why 2.1 and not 2.0? Two reasons. First, there are a little more boys born than girls, around 105 boys for every 100 girls, if you don’t do anything like selective abortions. Second, not all girls who are born will move on to become mothers themselves. They will die of accidents or other reasons before they enter their fertile ages. So you need every woman to have 2.1 kids on average to keep population constant. That’s the replacement rate.The total fertility rate is an estimate of how many children women will have in a given population. When we look at the U.S. right now, the fertility rate is around 1.57. That means the average American woman is having 1.57 kids. Because the replacement rate is 2.1, a way to think about it is that we have a shortfall of slightly over 0.5 kids. There is a subtlety I want the audience to understand.

The total fertility rate is an estimate. It’s slightly different from what we call completed fertility. Completed fertility is when I go back to women who are already 50 years old and see how many kids they actually had. The problem with completed fertility, which is what we really care about in the very long run, is that by definition it takes decades before we can compute it. So if we are going to make any forecast about the future, we cannot rely on completed fertility.Thompson: In your Miami speech, you said “peak child” might already be behind us. I want you to explain what that means and why, if peak child is already behind us, the global population isn’t already falling.Fernández-Villaverde: Let me start with the second and come back to the first. In demography there is something called momentum. Momentum means the population will keep growing for 15 to 30 years after you fall below the replacement rate. Let me give a simple example. Imagine you have a spouse and only one kid. You are below replacement rate, but you are two. You have two parents, your spouse has two parents. You are not replacing yourselves, but your parents have not died yet. The fact that you have one kid still increases the population. The problem is when your parents die, we have not replaced them.During the 1980s and 1990s, a lot of women were born on the planet. They had their kids in the 2010s, and that’s why the population is still growing. The grandparents of these girls have not died yet. What will happen is that when these grandparents, the generation born in the 1950s and 1960s, start dying, that’s when the population goes down. The analogy I love to use: think about a gigantic oil tanker. When you start changing the direction of the oil tanker, it has so much momentum that it takes time before it turns, but it is already cooked in. The number of children on the planet has been going down since around 2012. It’s just that their grandparents have not died yet.And then the first point: yes, as a planet we are below replacement rate. We are not producing enough kids to keep the population constant.

There are countries like the U.S. and Western Europe for which we have very good data. There are countries in Sub-Saharan Africa where the data is not so good. So all of this is done with some degree of uncertainty. I’m pretty sure it was 2023, but it may be the case that in 10 years, where we have slightly better data, it may have been 2022 or 2024. The big picture doesn’t change if it is one year up or another. Everything we observe is that fertility on the planet is continuing to go down very fast. In 2024, fertility was below 2023, and in 2025 it was below 2024. My educated forecast is that we are going to continue seeing this drop in fertility for the next 20 to 30 years, nearly for sure.Thompson: Given your educated estimate, what is the decade when the global population will start its structural decline?Fernández-Villaverde: At this moment, I would say 2055. In 2055, the world population will start going down. Thompson: If you go back to the 1960s and 1970s, it was common for public intellectuals to predict the global population would rise and rise until the environment buckled and we suffered ecological disaster and widespread famine that wiped out billions of human souls. That has not happened. Global fertility has declined significantly. It’s falling faster than practically anybody predicted, certainly folks like Paul Ehrlich, author of the infamous book The Population Bomb. Why do you think these so-called experts were both so confident and so wrong?Fernández-Villaverde: The wording of your question already tells you a lot about the answer, because you used the word “public intellectual.” You didn’t use the word “demographers.” I’m a professor at Penn, and we have—sorry to brag—what I think is one of the best demographics groups in the world. Had you gone to our population study center in 1968 or 1969 and asked professional demographers what they thought about Ehrlich’s book, they would have probably said, “Eh!”