Why has the number of births declined everywhere, all at once?

Some blame technology, particularly smartphones and social media. Others blame a kind of 21st-century weltschmerz—a 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, titled “Why So Few Babies? We Might Have Overlooked the Biggest Reason of All,” argues that 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?

Birth rates 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 contraception use has proliferated, and as modern notions of feminism have empowered women to take more control over their bodies and their economic futures. And birth rates have continued to decline as smartphone usage has surged, as housing prices have 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 John Burn-Murdoch recently observed in the Financial Times, United Nations demographers predicted that there would be 350,000 births in South Korea in 2023; the real figure came in at 230,000. 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.

“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.” I recently spoke with Fernández-Villaverde about why the birth rate is dropping, why it matters, and just how steep the decline is likely to get.

This interview has been condensed and lightly edited for clarity.

Derek Thompson: Why is fertility important?

Jesús Fernández-Villaverde: 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.

Thompson: Tell me what replacement level means and what total fertility rate means.

Fernández-Villaverde: Imagine you have a population of 1 million people. How many children need to be born for that population to be constant at 1 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.

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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 that 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 intellectuals. 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!” I would argue the book was not very good at the time, and what a lot of the public intellectuals were saying was not really what the best demographers were saying.

Thompson: But your research also seems to disagree strongly with expert demographers today. You’ve said that you think the United Nations is overestimating the total fertility rate of many countries. Why are today’s experts wrong?

Fernández-Villaverde: The Population Division of the United Nations was created because there was a serious concern that we were having a population bomb. It’s very difficult for an institution that has spent 60 years saying we had a population bomb to wake up and say, “There is no population bomb.”

In fact, the UN has three scenarios: low fertility, middle fertility, high fertility. My scenario and their low-fertility scenario are on top of each other. It’s not that I’m very far away from the UN. We are already fighting about the second decimal. The problem is that these things, even at the second decimal, accumulate over half a century.

Thompson: I think a lot of people believe that falling fertility is mostly a rich-country phenomenon. But you point out that’s a misconception. Total fertility rate is lower than that of the U.S. in Mexico, Brazil, Colombia, and Thailand. Why is this happening at a global level?

Fernández-Villaverde: There are several hypotheses on the table, and I’m going to list them in what I think is their relative importance.

First, there’s been a huge change in social norms worldwide. This probably has a lot to do with social media and cellphones. If you’re in a country like South Korea, or in many Latin American countries, where household work allocation is very unequal, suddenly a lot of younger women are looking at the world and saying, “Why am I going to be working for my husband 24 hours a day?” Social media has really changed that perception.

Second, we have moved to an economy that is much more service-based. Service-based economies, even in India and Africa, mean people don’t work in factories that much anymore, or even in agriculture. They work in shops; they work in offices. Those are jobs much easier for women to have, because they don’t depend on physical strength. In Mexico, Brazil, or Colombia, if you are a woman 22 or 23 years old with a decent job in the service sector, and a guy comes to you and tells you, “If we get married, I’m going to be the macho in the home, ruling everything; you are going to work for me all the time, and we are going to have three kids,” you tell the guy no.

Third is what I have called the educational arms race. People are staying much longer in school. They are marrying or forming partnerships much later in life. When they are thinking about their kids, they understand they will need to maintain their kids and educate their kids for many, many years. This is particularly true in Asia—in China, Korea, and Japan, where [there is pressure for] your kid to excel in high school and college. Those are the countries with the lowest fertility rates.

The last is housing. In many countries, not in all, housing is at historical heights in relative price. That also limits the ability of families to have more children.

Thompson: Two other issues I want to put on the table. First, contraception. Second, socialization rates in the West and throughout East Asia have gone down. People socialize less, they couple up less. When you put all of this together, having kids has gone from being a necessity or a predestination to a choice.

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Fernández-Villaverde: At the very basic level, I fully agree. That’s why I already forecast back in 2001 that fertility was going to drop a lot. But if you stopped the Jesús of 2001 and told him Colombia’s fertility was 2.8 or 3 then, and asked me where I thought Colombia’s fertility would be in 2026, given all these mechanisms, I would have probably said 1.8, 1.7. What the Jesús of 2001 would have been enormously surprised by is that it’s not 1.8 or 1.7. It’s 1.1.

That’s what has surprised me, that we have not gone from seven to two. We have gone down much, much further.

You were mentioning contraception. The U.S. was around 1.9 in 2000. There was lots of contraception in the U.S. in 2000. And in 2000, the U.S. was already a service-based economy. It was already a world where women were empowered, maybe not as much as today, but not very different from today. So why have we gone from the 1.9 of 2000 to the 1.57 of today? That is the mystery.

Thompson: More education for women is good. More freedom for women is good. I’m very pro–access to contraception. So the reasons for the decline of fertility are a mix of, I think, quite clearly good things and arguably bad things. Similarly, the implications of the decline of fertility combine both upsides and downsides. Let’s talk about the upsides first.

Fernández-Villaverde: In a world where population doesn’t grow or where population starts going down, we will consume less energy, or the growth of energy consumption will be smaller. That’s good for the environment.

Second, it will help us redesign a lot of cities across the world. I’m originally from Madrid, in Spain. A lot of the residential neighborhoods in Madrid are ugly. People don’t see those when they come to visit Madrid, but they are really ugly, because in the 1960s and 1970s when population was growing very fast, you had to build these horrible high-rises just to put people under a roof. We are not going to need those ugly high-rises. We can demolish them.

Thompson: What are the downsides?

Fernández-Villaverde: The obvious thing that comes to mind is Social Security. Everything related to retirement benefits, Social Security payments, the equivalent of Medicare and similar health programs for the elderly across the world, that’s going to impose a tremendous amount of cost on the planet. But also you are going to start being forced to close primary schools. The school district here in Philadelphia, where I live, was just forced to announce a couple of weeks ago that they are closing a lot of primary schools because there are no kids. That’s a serious disruption for a lot of local communities. You will be forced to close hospitals. You will be forced to close a lot of other public services.

Finally, if fertility really stays at 1 or 1.1 for a long time, I don’t think we appreciate how big a change this is. Now I’m going to make a crazy forecast, and I want everyone to understand this is a crazy forecast. Let’s suppose Thailand keeps its current fertility rate of 0.8 for 200 years. Thailand right now has 63 million people. At the end of 200 years, it will be around 2 million people.

Thompson: Sorry, 2 million?

Fernández-Villaverde: Two million. How do you wind down a society of 63 million people into 2 million? When population starts falling a lot, countries may do crazy subsidies for having kids—things can change. Maybe the people who are still having kids tend to have more kids, and they grow as a share of the population. All of those things can happen. I’m just highlighting that these things compound over time. You are going from a society that has 63 million people to a society that has 2 million. It means you need to close 98 percent of the hospitals of the country. It means you need to close 98 percent of the schools of the country.

Thompson: It also seems to me that the politics of immigration become a significant and unavoidable part of sustaining the welfare state, because what do you need to sustain a welfare state? You need taxable income. Where does the income come from? It comes from people. And if you’re running out of people, you need to import people, and that’s called immigration. But in my experience as someone who lives thousands of miles away from Europe, it seems to me like practically every country that allows immigrants to become a certain share of their population almost always has a populist backlash.

Slashing Social Security creates another backlash. So you find yourself in an environment where there is no long-term popular solution to your political problems. That’s what I see as an outsider.

Fernández-Villaverde: Exactly. Japan right now is around 98 percent ethnically Japanese. If we wanted to keep the population of Japan constant in 200 years through immigration, in 200 years Japan will be 5 percent Japanese and 95 percent non-Japanese. This is not about bringing in a few immigrants. This is about changing your country. That country will not be Japan. You may say, “I’m perfectly fine. I’m not attached to the idea of Japan in the abstract.” But I can see a lot of Japanese say, “This is not about being a xenophobe. This is not about being anti-immigrant. This is about not having a country anymore.”

In Spain, in addition to Spanish, we have regional languages like Catalan. The problem is Catalonia is getting a lot of immigrants. The immigrants are not Catalan speakers. Their kids may learn Catalan in school, but they don’t speak Catalan. Given the current level of immigration, Catalan, I have forecast, is doomed as a language. It will not exist. Some people will always speak it in a small village in the mountains, but as a working language of day-to-day life, Catalan is doomed. If you’re a native Catalan speaker, this is existential. So this is not about being anti-immigrant because I’m a nasty guy. This is not about being racist. This is just about saying, “Don’t I have a right to my language to still exist?” I’m an immigrant myself, so it’s not that I’m against immigration. But like everything, it needs to be within a reasonable degree.

Thompson: You said only two things matter in the world. One is fertility. The other one is deep learning—AI. How do these trends intersect?

Fernández-Villaverde: They intersect to some degree, but not as much as sometimes people think. If, thanks to artificial intelligence and robotics, a lot of jobs can be done by computers and robots, and that generates a lot of economic growth and that helps us to pay for Social Security, that will make the transition much easier. I’m a bit of a techno-optimist in that sense, and I’m glad this is happening. I think it’s going to give us more degrees of freedom to adapt our society.

But coming back to my point before, this is just not about GDP. My wife and I love to go to a small village in England to spend some time on vacation. It’s a lovely English village. They recently closed the local pub because of population decline. The problem is the local pub in an English village is not just the place you go for a beer. It’s the place where you meet your neighbors. It’s the social gathering place of the village. How are you going to substitute that with artificial intelligence?