JOSH: Hello and welcome to Clearer Thinking with Spencer Greenberg, the podcast about ideas that matter. I'm Josh Castle, the producer of the podcast, and I'm so glad you've joined us today. In this episode, Spencer speaks with Dean Spears about depopulation and population maintenance scenarios, modeling birth rate effects, and the urgent need to align on global population strategies.

SPENCER: Dean, welcome.

DEAN: So glad to be here. Thanks for having me.

SPENCER: If the world doesn't get the rate of birth up, what's going to happen?

DEAN: The big idea at the center of our new book is global depopulation. Global depopulation is the name for what will happen when generation after generation is smaller than what came before, to see how new and different that'll be. It helps us start with where the human population has been. For a very long time, the global human population was pretty small. Ten thousand years ago, it was less than 5 million people around the world. That's about the size of Metro Atlanta. But that started to change a few hundred years ago when we got better at keeping our children alive, where 1 billion in 1800 doubled to 2 billion 100 years later, and a quadrupling since then brings us to the present with more than 8 billion people. And it's the only thing that we, you and I, have ever known, this big, growing world. But our big present is a historical anomaly. It's new. It's been brief. And the interesting question is, what comes next? Remarkably, what comes next for the world population could very well be a decline where the downslope is just as steep and exponential as the upslope. And that's going to all be about birth rates. Depopulation is the inevitable consequence of low birth rates. And when I say low birth rates, I don't necessarily mean low, like South Korea, where it's 0.7 kids per two adults. It would be enough for the world's birth rate to be low, like in the United States, where there are 1.6 kids per two adults. So depopulation is what's going to happen if, on average, for the world as a whole, the birth rate goes below and stays below an average of two kids per two adults.

SPENCER: It actually needs to be slightly higher because of death in infancy, things like that. So it needs to be 2.1.

DEAN: Right. So I like to say that if it's below two, then we can be pretty sure that depopulation is what's going to happen. Technically, not everybody lives to adulthood, and so that's why demographers say that the exact level that would balance out our comings and goings is greater than an average of two, but it's a pretty convenient shorthand that if the world as a whole is below an average of two kids per two adults, then we're going to get depopulation. Now it won't happen immediately. According to the UN demographers, we're going to hit that level of an average of two for the world as a whole in 2064, and it won't be until another couple of decades after that, until 2084, when the size of the world population peaks, because the number of deaths exceeds the number of births. But as long as the world goes to and stays at an average of two, that's going to be depopulation.

SPENCER: So what's the world average right now?

DEAN: 2.3 and it's been falling for centuries. So it was around six in 1800, it was below six, maybe five and a half in 1900, it was five in 1950. Now, these are estimates. Back then we didn't have vital registration like we have now in rich countries or surveys in poor countries. But it's been falling and falling and falling for a long time.

SPENCER: I think something people don't realize about this is that that 2.1 number is really kind of a tipping point where if you're a little bit above it, you actually grow exponentially. It could be a slow exponential if you're only slightly above it, but it's still exponential, whereas if you're even slightly below it, you're in exponential fall. So that's actually an incredibly big difference being just above it versus just below it.

DEAN: I think that's part of how the depopulation sort of slipped under the world's radar. Even back during the 20th century, when the conversation was so much about overpopulation and worries about overpopulation, the world was already moving towards it. By 1980, one in five people lived in a country where the birth rate was below two. In the 1970s, Europe crossed below two, Japan crossed below two, like Cuba, Australia, Canada. But it isn't anything that anybody knew. Some people noticed, but we didn't think about this, because 1.9, 1.8, that doesn't feel that different from a world that has two in it. The United States right now is 1.6. The difference between a world at 1.6 and a world at two or 2.1, you can see it in the statistics, but I don't think you would feel it if you went to the park or went to the grocery store or went to the swimming pool or jogged around the lake. It's something that we see in the data, but 1.6 feels normal, so we don't perceive it as, as you say, something that's going to start this process of generation after generation getting smaller.

SPENCER: I did some calculations, and I want you to check if I'm on the right track. I was thinking, is this really an issue of people deciding not to have kids, or is it an issue of people having fewer kids? I did some calculations, and based on that, I think actually, even if all the people who decided not to have kids decided to have kids, it actually wouldn't change this very much. In fact, it's much more driven by people having, instead of having six or seven kids, having two kids.

DEAN: That's such an important question because so much of the culture war type conversation distracts people from the facts and the evidence about this is talking about childlessness or people having no kids. But you're exactly right that if the average number of kids among people who are parents, who do choose to become parents, has fallen far enough, that would also cause depopulation. In the data that we can see, there are 12 countries that have a birth rate below 2.1 even among people who have children. So Portugal, Russia, Japan, Poland, Taiwan, Spain. These are all places where the average is below two even among people who have children. I myself study India in my research, and the population of India was famous in the 20th century for this overpopulation scare when Paul Ehrlich wrote his book The Population Bomb. He starts it off in India being scared of overpopulation. But one of the things that got my attention about depopulation was realizing that India is now a below-replacement birth rate country. India is below two.

SPENCER: Really? Interesting. I didn't know that.

DEAN: So not only is India as a whole below two, but back to this question of whether it is about childlessness or the average number of children people have who have children. India is split into states, which are split into districts. There are 120 million people in India who live in a district where even among people who have children, the average is less than 2.1 children. So just taking people who don't have children out of the average, 120 million people in India live in a district where the birth rate would be small enough for depopulation even when only looking at the people who are parents. That 120 million would be enough to be the 12th most populous country between Japan and the Philippines. So you're exactly right that this whole debate over childlessness or zero children is part of it. It's part of the average, but it's a distraction, I think. We see low enough birth rates in countries like Portugal and Russia and even in so many places in India.

SPENCER: Now you might think about local overpopulation as a different thing from global overpopulation. In other words, one could imagine there could be regions of the world where the people in that region would be better off if there were fewer people in that region. It's overcrowded; the resources can't support the people there. To what extent are there problems of local overpopulation, and how do you see that as connecting or not connecting to the kind of bigger topic of global overpopulation?

DEAN: I think that most of what we can say will really matter in the long term is global depopulation or population size because so much of what matters about other people are things that we share. We'll talk about how some of the benefits of other people are the ideas they have or the things they discover or the things that they need, and that's all stuff that's going to be shared across international boundaries. If you learn something in France, people can use that idea in Canada. Our book, our research, is really all about global population size and global depopulation. For any one given country or place or city, imbalances can be fixed by migration. People can move, but that, of course, won't work for the world as a whole. I think the things that might be challenges or need policy attention about one particular place are going to be a whole different category of questions for the world as a whole, where migration isn't an option.

SPENCER: This is speculative, but I suspect some of the fearmongering about world overpopulation actually came about from people looking at specific regions and saying this particular place seems overpopulated at this particular moment in time, which doesn't allow you to extrapolate about the world as a whole.

DEAN: And the other way around too. I think some of the people who have been talking about low birth rates as a problem mean low birth rates for their national identity, or for people like him or them, or in some of the worst cases, people who look like them, or the racial makeup of the place around them, and a lot of that's really awful stuff. So I think one of the things that's important to say is that when we're talking about global depopulation for the world as a whole, that's not what we're talking about.

SPENCER: So suppose the world survives. We don't destroy ourselves. At what point do you see this as becoming a huge problem? Because you're saying that the projection is that we'll hit about a birth rate of two in 2064, so it's still ways off. When do we really see this come into effect?

DEAN: So in 2064, the UN projects the world's birth rate will be about two. But even still, there'll be more births than deaths that year. So the size of the world population will still be growing. In 2084, 20 years later, is the projection of when the size of the world population will peak at 10.3 billion, so even more people than today. And that'll be the peak year when the number of births equals the number of deaths, and then the size of the population will begin shrinking. Now exactly how fast it'll shrink depends on exactly how far below two the world birth rate falls if the world goes to an average birth rate like the United States today. So if the world goes to an average of 1.6 kids per two adults, then maybe we'd fall back down to a number like 2 billion people over 300 years. We don't know. We don't have a crystal ball. So we don't know exactly what the future world birth rate is going to be. And we don't really have to know that to understand that depopulation is the most likely future. That's why this average of two is so important. If the world's average is anywhere below two, then we're going to get this same general pattern of global depopulation, and that's going to be something that'll have this exponential shape that could make the decline similar to the increase. One example is to think about China. China is a good example because we can do the arithmetic in our heads, because its total fertility rate now is pretty close to about one. So what China's total fertility rate of one means, if it were true for a whole cohort, a whole generation, is that for every two adults, people would be having about one child. So just to think through the math, if in today's generation there are 100 adults, a TFR of one would be 50 kids for those 100 adults. Two people make one child. And then in the next generation, those 50 kids would grow up and have kids of their own. And if they keep this fertility rate of one, then they'd have 25 children. So the grandparents' generation of 100 people would have led to a grandchild's generation of 25 people. So a quarter is small. And if that sounds absurd, remember that in the 100 years before us, the size of the world population has multiplied by four. And so, it's not impossible if the world's birth rate were like what we see in East Asian countries.

SPENCER: Yeah, it's shocking when you think about a total fertility rate of one where it's literally halving the population every generation.

DEAN: Yeah, or if you plug in South Korea's number of around three-fourths of a kid per two adults on average, then you get 12 grandkids for 100 grandparents.

SPENCER: That's wild. And it's also crazy to think about 300 years having a world that only has 2 billion people compared to what we're used to.

DEAN: But again, I don't want to say that we know, or should be confident, that future birth rates for the world as a whole, like 0.75 or 1, or even 1.2, are going to happen. Even 1.6 like in the United States, or 1.8 like in Latin America, would be enough to start this process.

SPENCER: One thing that comes to mind for me when I think about this is how reliable these projections really are. To what extent can we really say what the birth rate will be in 2050, 100 years?

DEAN: You're right. We can't say what the birth rate will be in 300 years, let alone what the birth rate will be in 10 or 20 years for the world as a whole. We can have a lot of confidence in the if-then nature of a population projection: if the world's birth rate goes below two, then depopulation will be what happens. But it's worth thinking about why we should have confidence in that. The reason I think that depopulation is our most likely future is that we see so much evidence pointing in the same direction. One is that low birth rates are a globally convergent phenomenon. Two-thirds of people today live in a country where the birth rate in that country is below two. You might be thinking of it as something familiar when you think about East Asian countries like Japan or Korea or Europe, and those are places that have either long had low birth rates or have very low birth rates. But today, it's below two, as I said, in India or in Latin America; it's the norm for the world to have low birth rates. It's also the case that birth rates have been falling for a long time, a centuries-long trend. Before most people were going to high school or college, we were seeing the world birth rate fall before modern birth control and hormonal contraception, before even the sort of vital registration systems we have now to have such detailed data. It's not a new thing that's just popped up, even though we sometimes talk about it as if it is. It would be the continuation of a long trend of falling. If you want to think that the world birth rate's not going to continue to fall, then I would need to hear what theory or reason there is for that. But there's just no coherent evidence-based reason to think that it's going to go back up. We can look at the data. There have been 26 countries where the lifetime average birth rate has ever fallen below 1.9, and in zero of those 26 has it ever gone back up to two, not in Canada, not in Japan, not in Taiwan. The fact that it's never gone back up to two in any of the 26 places where it's gone below 1.9 isn't proof that it's guaranteed never to go back up to two, but it is one of the facts that helps us see that this is the most likely future.

SPENCER: Have there been countries that have significantly increased their birth rate, even if it wasn't going from such a low starting point?

DEAN: I don't know. I'm not 100% sure off the top of my head, for example, what happened across the US baby boom. We know that the year-to-year birth rate went up. It's actually a harder question, and the more important question is what happened to the birth rates of cohorts or generations. Part of what's hard about the demography of birth is that different times or different generations might change the age at which they have babies, and so it looks like the birth rate's going up, but it's not because people are having more babies over the course of their whole lifetime. They're just having them at different ages. But I do know that for the countries where we have data, we haven't ever seen the sort of reverse that would bring the birth rate back up to two to stabilize the population.

SPENCER: Let me give you an argument about why birth rates might go up, and you tell me why it's flawed, okay? So imagine that you have lots of types of people in the world. Most of them have low birth rates, but there are some types of people. Let's suppose the Amish. Let's just take an example. They have high birth rates, and let's suppose that for whatever reason, that type of person is able to maintain them, for whatever factors we don't know what they are. For a while, you'll see populations fall and fall and fall, because most of the people in the world have these low birth rates. But the groups that are able to maintain a high birth rate will become a larger and larger share of the population until eventually they are the population, because they're going to grow exponentially while everyone else is shrinking exponentially.

DEAN: I'm so glad you asked about this because we get this question so much that we wrote a research paper about it and published it in the journal Demography. The question of whether there is a small subgroup that has higher birth rates, such as the Amish, is everybody's favorite example. Then aren't they going to take over the world? And wouldn't that be enough to cause long-term population growth to be positive? The Amish aren't the only group in history that we can learn from that has had higher than average birth rates. My book, After the Spike, is co-authored with Michael Geruso. Mike's family comes from the French Catholics of Canada, from Quebec, and in the 20th century, they had as high birth rates as anybody. His grandmother's generation had, I don't know, maybe nine siblings in it or something, but Mike has one brother, and he has one kid. We've seen examples of populations that have had high birth rates, large families, and then it has gone down over time. It's important not to cherry-pick the examples and just think of one group that has high birth rates. Even groups with high birth rates can get smaller. The thing that matters is that it is a mathematical theoretical possibility that a cohesive group of people could have high birth rates, and generation after generation could ensure that they have positive population growth and eventually would be close to 100% of society. In models of mathematical biology, that's the sort of thing that falls out if you have a high birth rate, but you can immediately see why that wouldn't apply to people because people aren't just mathematical biology. People make decisions. People have cultures. People have societies that change. For this sort of thing to happen, two things have to be true generation after generation. One is that the children stay in the subgroup; they don't leave the subgroup and join the broader society. All of these nine siblings of Mike's grandparents from the Canadian Catholics are not all Catholic anymore in any relevant sense. The first thing that happens is the group has to stay together over time. The second thing that has to happen is that the younger generation has to continue to have high fertility just like the older generation does, and they don't have to have their birth rates fall. It might be that the younger generation still has higher birth rates than average, but higher birth rates than average could still be below two, or just put more simply, things could change. The culture could change. It's a mathematical possibility, but it's a mere mathematical possibility, and it isn't the sort of thing that we see happening around the world.

SPENCER: It seems like you need a very strong culture, something like a religion that tells you you have to have as many kids as possible, or you're a bad person, and then, if they're able to keep a tight end?

DEAN: Well, I just gave you the example of Catholicism. Although, that's not what I want to necessarily say Catholicism is, but this is an example. I study India, and in India, there's a lot of finger-pointing and conversation about birth rates being higher among Muslims and Hindus. That's been the sort of thing that politicians in India, especially Hindu politicians, have pointed at over the decades as they consider it a problem. If you look in India and split up the population not only by religion, Hindu and Muslim, but you split it up however you want, by education, by rural, urban, north, south, and make teeny tiny groups, what you see is that birth rates for all of these subgroups are falling over time. Yes, they're falling for Hindus; they're also falling for Muslims. Yes, they're falling for people in urban India; they're also falling for people in rural India. If all of the subgroups' birth rates are going down, then it's just not going to be the case, empirically, that there's a laggard group where the population is going to take over because their birth rates are enduringly high. It's a theoretical possibility, but it's not what we see in the world, and it just feels implausible to me that generation after generation would hang together like that. I'm a dad; I've got kids. They don't like everything that I like, and that's just part of being human.

SPENCER: Yeah, it's just, I think the sort of potential there is that you only need one group that can achieve this right now. Maybe it's not that likely, but if one group around the world is able to have such a strong culture.

DEAN: Centuries after centuries, no matter what else changes.

SPENCER: Yeah. It's a bit of a long shot, but I don't know that we can fully rule it out.

DEAN: You're right. It's a mathematical possibility that we can't rule out that we'd have positive long-term population growth this way, even if it seems unlikely. And perhaps even more importantly, I'm not here to say that we're guaranteed to have long-term depopulation. What I think the evidence tells us is that it's the most likely future and a future that's really likely enough to be worth considering and planning for. Because I just want to get back to this number two, an average birth rate of two. Reasonable people can all disagree about what a good long-term size for the world population would be. Would it be better if we leveled off at 9 billion people or 4 billion people, or 3 or 2 or 1 billion people? Fine, that's fine. But here's the thing: for stabilization to ever happen at any level, even to maintain a tiny global population of less than 1 billion people, the same math applies. For every two adults, there must be about two children, generation after generation. It's true for a big population. It's true for a small population. And so if we agree — and not everybody does agree yet, and that's something we should talk about — but if we agree that a stabilized future would be better than a depopulating future, then one day we'll have to bring birth rates back up to two. And that's something that I don't think anybody has a good evidence-based plan to do.

SPENCER: Because even if you think it's better to have a smaller population, do you think it's good to have a population that exponentially declines where every generation just falls indefinitely?

DEAN: I think even amongst people who think that it would be better if the world population stabilized at 2 billion people instead of today's 8 billion people, anyone who thinks that they want to stabilize at any level agrees that we'll have to have birth rates come back up to two and stay there. That means it's worth thinking about what the path to that might look like.

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SPENCER: Why does this matter? Who cares? Does it matter what the world population is?

DEAN: Our case for people starts with recognizing that it's not a coincidence that humanity has grown richer and healthier over the past few decades and centuries. In the same decades and centuries that we've grown more populous, living standards have been increasing, poverty has been decreasing, and life spans have been growing longer as the population grows. That's not a coincidence because progress comes from people, meaning that we're each better off if we share the world with more people, more people living at the same time as us or living before us. So let's think about this question: why do you and I lead richer lives today than anyone could have dreamed of a couple hundred years ago? We have glasses to correct our vision, Tylenol for our pain, more books than we could ever read, safe office jobs, economic and social safety nets, kindergarten, phonics classes, podcasts, and we're almost certainly likely to survive childhood, at least in developed countries. Why do we have all of this good stuff that people didn't have a couple hundred years ago? It's the same rocks and dirt beneath our feet that they had, the same sun shining overhead, the same wind blowing. We're richer today because we now know better things to do with this knowledge. That's the difference. We now know how to take the silicon, gold, and copper that were always in those rocks and make the computer chips that power our headphones, microwaves, MRIs, and washing machines. We know how to harvest the power of the sun and the wind into electricity that makes these things go. We know how to farm more efficiently so that it takes the work of fewer people to feed more of us. We know how to make soap and sewer systems and a germ theory of disease to prevent us from getting infections. There's so much I could say here, but it's this knowledge that is the difference from what's come before. We get to that knowledge because of one another, because of the people who have come before us or live with us and learn things and try things. Some of that is active research and development, like in my job as a professor, where I'm a researcher, but much of that is just the things people learn by doing. That learning builds up this wealth of knowledge, and knowledge like that is a very special type of economic resource. Ideas are a special type of resource that gets used but doesn't get used up. Ideas can be reapplied endlessly. They're a renewable resource, and so more people means more ideas, more progress, and better lives. This is a familiar story in macroeconomics. It's a concept that won Paul Romer a Nobel Prize in 2018, and it's a big part of why a stabilized future population would be better than a depopulating future, because a depopulating future would have fewer people accumulating these discoveries and making life better for the other people who live with them. Other people living with us are part of what makes our lives good.

SPENCER: Is there another reason that we really want a larger population rather than generating more ideas?

DEAN: Yeah, there are other ways that people make us better off. When we think about population economics, a lot of people would think that other people would have more mouths to feed or competition for the things that they want. I just told a story about people on the supply side of the economy coming up with ideas and discoveries. But you might raise your hand and say, "What about people on the demand side of the economy taking the things that we want?" It turns out that even on the demand side of the economy, other people are still part of producing or part of making it so that our needs and wants are met, and that's because other people need and want the same things that we do. That sounds paradoxical, but it makes sense if you think of the economics of fixed costs. Fixed costs are the costs of any activity happening at all, whether it's a business being open, a charity running, or a government program happening. Fixed costs are just the cost of being in business, of doing something. If there are more people who need and want the things that you need and want, then the fact that they are needing and wanting it helps meet those fixed costs and make the thing happen. If that sounds abstract, let me give an example, thinking of cities. Depopulation is coming for the world as a whole. Our book, After The Spike is about the depopulation of the world as a whole. But it helps to think about cities as a metaphor. When my mom had a rare form of cancer that few people have, we weren't able to find the care that she needed in the smaller place where we lived; we had to drive to a bigger city where it made sense to have the sort of hospital that would have a specialist to know about this type of cancer. And it's not just medical treatment. Where are you more likely to try the newest restaurant or see the new concert or get on an airplane with enough other people who want to go to the same destination you do to make a flight worthwhile? All of these things are more likely to happen in a city with more other people than in a less populated or rural place, and that's because other people needing and wanting the same things that you need and want makes it economically feasible, makes it possible to happen.

SPENCER: It reminds me of how in Manhattan there's a rice pudding-only restaurant. The only thing they serve is rice pudding. I kind of think about that as, "Where else could that be? There aren't that many places in the world that could support that, maybe Tokyo, right? Maybe London, but you really need some crazy amount of population density to have enough demand for a rice pudding restaurant."

DEAN: Right, where else could that be? And when else could that have happened in Manhattan back when the population was smaller? For something like that to happen, you need enough other people who also want it. To use the corny, old metaphor about the economy being a pie that's getting sliced up, the worry is that other people are going to eat your slice of pie, or you'll get a smaller slice of pie. But what that overlooks is that somebody has to bake the pie in the first place. Somebody has to start the rice pudding restaurant in the first place. And that's only going to happen if enough other people want it. So part of the case for people, part of the reason that it's good for you that there are other people living with you is that they make stuff like that available for you.

SPENCER: Sometimes, when depopulation is discussed, people worry that in a depopulating world, there will be all kinds of economic calamities, like the stock market will collapse because there will be fewer consumers to buy products. People will become increasingly poor as companies do worse and worse and so on. Do you think that's a realistic concern?

DEAN: One concern that we often hear along these lines is about the age structure of the population, that there will be too many older people, not enough middle-aged people, too many people taking money out of pensions and social services, not enough people paying into it. I think that's true, but that's not something that in our book we talk a lot about, in part because we think the reasons to care about depopulation and the case for people are sort of bigger than those familiar concerns. Yes, I do think that there is an important case for people, an important economic case, that stabilization would be better than depopulation. But when I think about it, I think of it less in terms of these macroeconomic crisis reasons than just about the progress that we could achieve. Our case for people is part of a vision of continued progress towards an abundant future where things today that there isn't a solution for, rare forms of mucosal melanoma, like my mom's cancer, the example I gave, or other problems that don't have solutions, the next pandemic that comes up when we need a vaccine for. Things that we don't know how to do now, things that aren't solved problems now, could be solved problems in the future if we have the people, if we have one another to help get us there. And that's what I think really stands to be lost in a depopulating future, rather than a stabilized future, the benefits and the progress that we get from one another.

SPENCER: Some people insinuate that our society is a kind of Ponzi scheme, where, because we had a growing population for a long time, we are able to shunt more and more onto the younger generations to support the older generations. If that ever were to stop, it would be like a Ponzi scheme running out of money, and everything goes down. Some people say that Social Security is like this, that the only reason we're able to support it is because we have a growing population base. So you don't see that as essentially very important to the argument. Or do you disagree that that's true? Or do you just not think it's the central point?

DEAN: I think I would have a different framing. One person might look at people taking care of one another, using the tax and transfer system to help the poor and share risk and make society a safer place for everybody, and say that's a Ponzi scheme.

SPENCER: But I think they're not saying it's a Ponzi scheme because it's transferring money. I think they're saying it's a Ponzi scheme because it depends on there being a growing number of young people relative to old people. Does that make sense?

DEAN: Yeah. No doubt we'll have to have economic adjustments to handle an aging population. We've done it before. In the last 75 years, the average age in the US has gone up by nine years. In the next 75 years, the average age in the US is projected to go up by another seven years. So it's something we've been handling and we'll have to handle again. I think what I would say is that it's great that we depend on one another and help one another and have these transfers across generations. That's nothing to regret, the way that talking about a Ponzi scheme might make it sound. But let's keep it up and make sure that we continue to be able to get the benefits of living in a world with other people.

SPENCER: One thing I wonder about in this whole topic is how well we really understand why birth rates have declined so much. And I've heard a lot of different theories. How well do you think we understand it, and what do you think is the most credible theory?

DEAN: So there are a lot of people who say they know why birth rates are declining. The problem is that if you ask 10 people who confidently claim to know the answer to this, you'll probably just get 10 different answers. I don't think it's true that anyone really knows. To walk through the various sorts of things people say before we dive into any of them, I've heard people blame the free market economy or capitalism. I've heard people blame the decline of marriage. I've heard people blame individualism. I've heard people say it's contraception or feminism or women's labor force participation. You hear all of these things.

SPENCER: Even wealth. Some people say, "Oh, it's just a natural result of being more educated or having fewer farmers."

DEAN: To everybody, this is the single most important case to somebody. But I think none of these explanations take into account the bigness of the long-term decline in birth rates. By bigness, I mean it's something that's been going on for decades or centuries, going on from before the invention of modern contraception. It's happening in countries around the world, so any sort of explanation seems to have a hard time meeting these facts. The most common thing I hear is that children just aren't affordable, especially in the United States. But when you look at the evidence and the data, it's really hard to believe this story that it's about affordability. For starters, the world is richer than it used to be, just as you were saying, and birth rates have gone down. People in poorer countries tend to have more babies, not fewer. Sub-Saharan Africa is the poorest region on Earth and also has the highest birth rates, and we see this pattern within countries too. It's also the case that if you look at more direct inputs to affordability, countries that have free daycare or heavily subsidized or free college or social safety systems don't have higher birth rates than the United States. In the US, it's 1.6, but in Denmark, it's 1.5, in Sweden and Norway, it's 1.4, and in Finland and Canada, it's 1.3. So policies that make children more affordable don't seem to make the difference. Finally, if you're into this sort of research, we have a natural experiment where researchers looked at what happened when some women won the lottery and how that compares to women who played the lottery and almost won or won smaller amounts. What could be more of a randomized experiment than winning the lottery? What we see is that women who win the lottery don't go on to choose larger families than women who lost.

SPENCER: And they don't choose smaller families either. Just kind of the same.

DEAN: Yeah, there's no statistical evidence of a difference, is my recollection. So whatever is happening here is more complicated than just dollars or affordability. That's one example. Another example, sort of a classic narrative, is female labor force participation, or more broadly, the conflict between career and family. In a place like the United States, there really is a big conflict for a lot of people between career and family. That's the title of the economist Claudia Goldin's book, Career and Family, in which she talks about how, especially for educated elite careers and professions, there are really high returns for working hard all the time. If you want to get the most out of your elite career, you're going to have to work all the time. She calls these "greedy jobs," and you can see how, if you're thinking of a family with two adults, it's going to be really hard to have children if both adults are going to do this sort of greedy job. It's going to force some really hard trade-offs, not only between earning money and having children, but also equity between the two spouses. It seems you can't both have "greedy jobs" and have children. That's really hard, and it's hard for a lot of people, so it makes sense to think and talk about that when we're discussing why birth rates are low. But I keep bringing this back to India because I think we learn so much about the fact that India also has a below-replacement birth rate. In India, female labor force participation is pretty low in international comparison; it's 40% in recent data. Female labor force participation is low, and still birth rates are low. There are many places and families in India where we see low birth rates without any sort of conflict with women being in the paid labor force. So that's not an explanation that works either. I think we could go through the whole list and find important counterexamples like that. That's important because it underscores how much we have to learn about low birth rates as an emerging property of people around the world. It also tells us something about how robust this future is likely to be, how plausible it is that low birth rates are going to be the continued future. Even in these different environments with different economies, different policies, and different cultures, we're still seeing convergence towards low birth rates. That's the sort of thing that gives me confidence that this is likely to be a future that continues.

SPENCER: Would your bet be that this is a highly multifactorial issue, where it turns out to be just 20 different factors, each contributing a small amount? Or do you think that there's going to eventually be some smoking gun that explains this, and we just haven't figured it out yet?

DEAN: I think whether it's multifactorial or there's a smoking gun, perhaps, depends on your level of abstraction. One of the things that Mike and I talk about in our book is the idea of opportunity costs of children going up. To economists like us, the opportunity cost of something is what you give up in order to have it. One way of thinking about falling birth rates all around the world is that for a lot of reasons different in different societies, the opportunity cost of having a kid has gone up, and so people are less likely to choose it. Whether that opportunity cost for you means having a job to earn money, or having a career or a vocation that you care about, or equity within a family, or investing in your children's education, or for some people, just doing whatever you want to do with your life that sounds good to you, that's better now than it used to be in the past. In all of those ways, the opportunity cost of having your kids has gone up. I say that, but then I immediately want to push back on myself and say that there's something tautological about saying that people aren't choosing something because the opportunity cost of it is going up.

SPENCER: That's only if you're an economist.

DEAN: That's right. And it's a framework that helps see how big the forces are, the headwinds against parenting, the forces pushing people to choose lower birth rates. But I think that's the closest we come.

SPENCER: Do you think if we could make some kind of opportunity cost indicator that measures in each country the opportunity cost, we would see that this is really tightly coupled with the birth rates over time?

DEAN: I think, again, maybe this is just my tautological economist hat. I think we do have that indicator, and it's the fact that birth rates are falling. But yes, I think if we had some way of measuring what people are giving up, and in particular, what they would be giving up that matters to them in having a kid, I think we'd see that going up in lots of different places.

SPENCER: And to unpack why that's tautological when you look at it from an economist point of view, but not necessarily from other points of view, people just don't always behave rationally. You might say, "Of course, if opportunity cost goes up, they're going to have kids off. But maybe people are not acting rationally." Or maybe there are other factors, constraints or things like that, that could cause this, that have nothing to do with opportunity costs.

DEAN: That's right.

SPENCER: But I think that's an interesting theory. I hope someone tests that. I hope someone comes up with some opportunity cost indicator and demonstrates that it really does strongly predict birth rates across time and within and across countries as well. What about these experiments where different governments have tried to pay people to have kids or give tax breaks? My understanding is that they have not worked. Is that correct?

DEAN: I think you're right. I think the evidence shows that these sorts of policies of money or subsidies or cash don't really have a big effect on the total number of children people have over the course of a lifetime. It might push around at what age people have children. If I say that I'll give you X number of dollars for having a kid next year, and you were already planning on having a kid at some point in the next two years, you might decide to do it sooner than you otherwise would, and then not have the kid later as a result, but the total number of children you have overall would stay the same.

SPENCER: Doesn't this suggest that either the opportunity cost framing is wrong or that the dollar amounts given are just not large enough to move the needle?

DEAN: Yes, that's right. I don't want to claim that there's no enormous amount of money that could move the needle. But we learned something by looking at the sorts of social policies we talked about that separate places like Denmark and Finland from places like the United States. That's a lot of social spending. We know that the Biden-Harris administration had, I think, a $3,000 child tax credit expansion a few years ago, and that didn't kick off a massive revolution in birth rates. At some level, I don't think we should be surprised by this, because when people are deciding how many children to have and at what stage in their lives and with whom and where, these are some of the biggest decisions in people's lives. These are how people write their own autobiographies, and it matters a lot to people. We know it shouldn't surprise us that even thousands of dollars doesn't move the needle. One question I sometimes ask people is, "For $3,000, would you agree to marry somebody other than the person you married or plan on marrying?" I've never heard anyone say, "Yes, I would marry a different person for $3,000." Given that, we probably shouldn't think that very many people would form their households and families in other ways for that much money about having a kid either.

[promo]

SPENCER: What do you make of the correlation, which I think is true, between having kids and religiosity?

DEAN: I don't know. It's not something I've studied. Where my mind goes is India, where essentially everybody, at least in a statistical survey sense, would tell a surveyor that they're part of a religion, that religion is a part of their lives. In the United States, a lot of people would be others or nuns or atheists; that's not what you would see in the survey data in India. And yet we still see birth rates falling there too, and India below two. I don't know if India is the only example, but India would be a good example of a country where it's a highly religious society, not just on paper, but in it really mattering for people's lives. And we still see birth rates low and falling. Latin America, also, as a whole, is 1.8, and Latin America is a society that is pretty religious, at least according to these statistics. A 2014 Pew study of Latin America estimated that 90% of people are Christian and 70% of people are Catholic in particular.

SPENCER: So religiosity hasn't been declining in these countries.

DEAN: It might be declining, but it's still pretty high. Fair enough if you want to say that there's some deeper variable that's not measuring the right thing. Maybe they go to mass less frequently, or something, I don't know. But anyone who wants to say that it's fundamentally about religion, I think, needs to grapple with Latin America, 90% of people telling surveyors they're Christian, still below replacement. In India, almost everybody says religion is a part of their lives, still below replacement. It seems like that's not the explanation that's going to get us there either.

SPENCER: Just to give a data point here, we did an analysis and found that in the US, there's about a 0.2 correlation between how many children you have and whether you agree that religion is important in your life. So it's kind of an interesting data point. Shifting topics a little bit, this idea of global depopulation has been wrapped up in the culture wars. How do you see this as connecting to the culture wars, and what do you think the right way to view this is?

DEAN: Yeah, you're right. There's a real culture war around birth rates in the US. The right wing in the United States is very interested in low birth rates, and it's often tied up for them with national identity or their views on immigration. For some prominent people, it's tied up with their goal to revert to traditional gender roles, or they want women in the home. In its worst forms, the right-coded concern is a concern about who's having the babies and the racial makeup of the country. It's really awful stuff sometimes. In reaction to that, as an understandable immune response, there's been a rejection among the political center and especially on the left, a rejection of ever even talking about low birth rates and what they mean and whether we should welcome low birth rates or worry about them, whether we should welcome depopulation and worry about it. People who care about reproductive freedom and autonomy have put up a firewall politically. There's an idea out there that to be concerned about birth rates must imply you are against women's progress or reproductive autonomy, you must want to ban abortions, and we wrote this book in part to tear down that wall, because we are people who believe in reproductive freedom and autonomy. We are people who believe in progress, and we are also people who think that low birth rates matter, and we want to bring more people into this conversation who feel they haven't had a place in this conversation before, because the reality is that low birth rates are here, and that isn't automatically changing just because Democrats, liberals, and progressives don't engage or don't talk about it. I want my team, by which I mean everyone concerned about broad-based progress in a liberal society, to be part of this conversation. If we don't, then the only people who are going to be part of how society responds to this are the illiberal forces, the people who are using this as a tool to get whatever they were already after.

SPENCER: Sometimes, when people talk about the idea that there might be benefits from increasing birth rates, it can come across as though they're saying that women's rights should be eroded. That those two things are in tension. What do you think about that?

DEAN: A stabilized world population would mean more children, more childbirth, and more child-rearing than in a depopulating future, one with lower birth rates. You're right for this reason and more. It's important to ask what stabilization instead of depopulation would mean for women. Would achieving stabilization mean rolling back the hard-won gains towards a more equal society, or regressing to how things were before? I think that is an important question. It's not wrong to be asking that question, but part of what I want to say is that when asked like that, the question isn't ready to be answered, because we could be thinking about more than one possible path to a stabilized future. What it means for equity would depend on how the population stabilizes. I want to be very clear that when I'm talking about a path to a stabilized future, I don't have in mind any sort of path through coercion, through fewer freedoms or opportunities or protections for women. I think that a future, a path where people are forced or pressured to have a larger family than they want, would be a disaster. What we talk about in our book, the only future we advocate is a future in which people in free and fair societies weigh their options and on average decide that the best life for them would be parenting two kids. The path to that is only possible if parenting changes for the better, more support, more flexibility, more funding. I think that is the only possible path to a stabilized future, and that we can make a fair and stabilized future that is good and free and fair for women and men, and has an average birth rate of two. There is no inescapable dilemma here, but we're only going to get there if those of us who believe in that sort of future are part of the population of how to respond to low birth rates. Part of what I have to say here too is, to my fellow dads or possible dads. I'm a dad, if we're going to have a future with a lot of kids in it where people are choosing to be parents, we all need to do a better job of sharing the work of parenting. That means everybody, and it very specifically means dads. Dads can't get pregnant, but we can do so much else. We can clean breast pump parts. We can get up at three in the morning to soothe a crying baby. We can cook dinner, do laundry, pack snacks, and handle the text messages from the babysitter. We can remember all the things to drive to and to do. Sometimes people act like a child is made just over the course of the nine months of a pregnancy. But that's wrong. It takes more than nine months to make a new person. It takes many years. I've got a five-year-old and an infant, and I can tell you confidently that the work of making my big kid is far from over, and the fact that it takes so many years more than just a pregnancy means that there's plenty of time for men to share the burdens. Part of my answer is that we can do more to share and spread around the pains of making new people. It's not just about dads. It's about people who are currently of the ages where they have little kids, and maybe people who are of another age in adulthood who don't have little kids. There are so many ways that we could, if we all shared the idea that a stabilized future would be better than a depopulating future. I think it's important that we don't have that consensus yet, and that's part of what our book is for. If we did, and let's assume for now that we did have a consensus that a stabilized future would be better than depopulation, the place to start isn't by asking more of women. A good place to start would be dads doing more and everybody doing more to share and lift the burdens of making the next generation.

SPENCER: Are there technologies on the horizon that could increase birth rates but also make it easier to have kids? For example, you can imagine artificial wombs where women might not actually have to go through pregnancy, and that could maybe reduce the cost of having kids to your body, the physical toll, etc.

DEAN: I think that it's sort of imaginary, but an artificial womb could do a lot to make a lot of people's lives better, and if it made people not have to suffer, not just the pains but the real medical and biological risks of being pregnant, that would be wonderful. In my own family, my spouse had a lot of miscarriages, and that was just awful. If people could skip that, that would be another great thing; if people didn't have to have nausea in pregnancy, that would be great. It's another question whether artificial wombs, as good as they might be, would raise birth rates. I think that just goes back to the same point I was just making: as big a deal as pregnancy is, it takes a lot more than that to make a person, to make the next generation. Making a person takes years, and an imaginary question I like to ask is, "Let's say that we had something even better than an artificial womb. We just had a baby button, and you could push the baby button and you would get a baby. How many times do you think you would push the button? How many times do you think people overall would push the button?" Because part of the rules are, once the baby comes out, you still have to parent it. I suspect that a lot of people would be delighted to push the button and skip the pains and risks of pregnancy, childbirth, infertility. I doubt that enough people would push the button to raise birth rates back up to two, and that's because there are still all of the many costs that continue after a kid is born. I'm skeptical that that sort of technology could make lives a lot better. It could be part of the steps towards a bigger future, but I don't think that we should think that that would be the silver bullet.

SPENCER: Before we wrap up, some people argue it'd actually be better if the population declined considerably. Not necessarily that they wanted it to be in free fall and fall exponentially forever, but at least for a while they might want it to shrink. Do you think that there are any good arguments, any advantages of having a smaller population in the world? If so, what do you think those advantages are?

DEAN: In our book, and I guess it's also what I actually think, we're not taking any position on what the stabilized size of the human population should be. Would it be better if the world population stabilized at 3 billion people rather than 6 billion people? I don't know, and I think that question is just beyond what we could know given the state of social science, environmental science, all of that. I think that's just too precise. So I officially have no position on that question, and I think it would be really hard to know. What I will say is that if you think that it would be good for the human population to stabilize at 3 billion people instead of depopulating generation after generation, then great. We should be interested in a lot of the same questions, because even so, we're going to have to figure out how to get the birth rate to hover around two once we get to that 3 billion size. One thing that people sometimes say in particular is that it would be an advantage for the population to shrink in order to solve our environmental problems, that we should welcome depopulation as a response to climate change. That particular argument, I think, doesn't work out, at least not for where we are now in 2025. Depopulation is going to be too little, too late for our environmental challenges. The size of the world population isn't even projected to peak until 2084. We're going to be growing for six more decades into the future, and I don't think that any sort of change in the population or birth rates that happens on that decades-long time scale could possibly be fast enough. You have a kid today or you don't, and they'll be deciding whether to have a kid in the future or not. In 20 or 30 or more years from now, some of us become parents in our 40s, and 30 years from now is 2055, by which time we need to be all the way decarbonized, or very much on the way to it. Environmental challenges, like climate change, are just too urgent relative to depopulation. Depopulation is coming fast at the level of generations, but not at the level of years. To the particular argument that we should welcome depopulation as a solution to climate change, I say no; depopulation is too slow for that. What we need to do for climate change is decarbonize and not get distracted by the population.

SPENCER: Final question for you: suppose a listener is convinced by what you're saying, and they think, "Oh, yeah, this seems to be a problem. It would be great if we could get the population to a stable level long term." What do you want them to do?

DEAN: Yeah, if you're convinced, or even if you're just curious or think that there might be something here, what I want people to do is invite more people into the conversation, because most people aren't convinced yet. The old, outdated tropes of overpopulation are still out there, and they need to be retired one factual, compassionate, forward-looking conversation like this, one at a time. So we need to make that case, the case for people. That's why, in our book, After the Spike, we go chapter by chapter, taking on these outdated ideas. We take on the idea that population is what's going to determine our climate outcomes, and that depopulation will save the planet. We take on the idea that there's an inescapable dilemma between a world with freedom and opportunity for women and a world where enough people choose to be parents and choose enough children to stabilize the population. We take on the idea that life is bad and getting worse, and that something we didn't talk about today, but one of the things I hear is that, how could you want there to be children in such a deteriorating world? I don't think that's the right way to look at the world. I think that there are challenges, but things are getting better, and we have to take on that idea, too. And so all of these things are worth pushing back on, and it's worth making the case for people and talking to people. We don't have that consensus yet that stabilization will be better than depopulation, but we could. And so if you're convinced, or even if you want to learn more, I think, bring this conversation forward. Talk about it with somebody else.

SPENCER: Dean, thanks so much for coming on.

DEAN: Thanks so much for having me.

[outro]

JOSH: A listener asks, "What's a fallacy or bias that you've noticed yourself being frequently prone to, and why has it been challenging to overcome that?"

SPENCER: I can sometimes fall into the planning fallacy, where projects take longer than I expect, even though I'm aware of the planning fallacy, and even though I sometimes increase my estimates on purpose to try to adapt for it, they can still take longer than I expect. So that's something I think I've gotten better at over the years, but it's still a challenge. I think I sometimes fall for the sunk cost fallacy, where I get stuck on a project because I've invested a lot of resources in it, even though I'm aware of the sunk cost fallacy, and I try to avoid that. I could be subject to doing things for social fear reasons where I don't want to hurt someone's feelings, especially, or don't want to let someone down. And obviously, hurting people's feelings is something we should try to avoid. Letting people down is something we should try to avoid. But I think sometimes those things weigh too heavily on me, and there should be a limit to that. Sometimes you can make a bad decision because you're so worried about letting someone down or hurting someone's feelings, and so that's something I'm working on, trying to be appropriately sensitive to them, but not oversensitive to that.