Episode 84 • 1 November 2025

Dean Spears on the Case for People

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Contents

About this episode

Dean Spears is an an Economic Demographer, Development Economist, and Associate Professor of Economics at the University of Texas at Austin. He is also an affiliate of IZA, an affiliate of the Population Research Center at UT-Austin, founding execute director of r.i.c.e., and director of the Population Wellbeing Intiative.

With Michael Geruso (right), Dean (left) is the co-author of After the Spike: Population, Progress, and the Case for People.

(Image) Dean Spears

Resources

Transcript

Introduction and overview

Fin: Hey, this is Fin. It’s been a while. First of all, this is just to say that the podcast is still alive — we took a bit of a hiatus since we’re both a lot busier these days, but we do intend to record new episodes, albeit maybe a little less frequently than before. In this episode, I spoke with Dean Spears. Dean is an economic demographer, a developmental economist, and associate professor at UT Austin. He has done great work on infant health and mortality and air pollution, both especially focused on India. His most recent book is about trends in world population, specifically downward trends, and the case for people. It’s co-authored with Michael Geruso and called After the Spike (Goodreads). Okay, here’s Dean Spears. Dean, thanks for joining me.

Dean: Thanks for having me. Glad to be here.

Fin: Just help me understand what’s going on with birth rates and with global population at this point in history — at the really big-picture level. What’s the main story?

Dean: Our new book, After the Spike, brings readers along on a tour of the core facts of global population science to introduce people to the idea of global depopulation — that global depopulation is now the most likely future for the human population. Global depopulation will be the name for what happens when the number of deaths in each year is greater than the number of births in each year, so the population is shrinking generation to generation or cohort to cohort. The main reason that’s going to happen is that birth rates are falling. They’ve been falling for a long time and they’re falling in countries all around the world.

The magic number is about two. If there are at least about two children in the next generation to replace two adults in the last, then we won’t have depopulation. If there are more than that, we’ll have population growth. But if on average for the world as a whole there are fewer than two children to replace the parents’ generation, then depopulation will result. Right now, birth rates are not only falling for many countries, they’ve fallen below that threshold. Two-thirds of people around the world now live in a country where the birth rate is below two. Here in the United States, it’s an average of 1.6. In Europe, it’s even lower. Texas is 1.8. Latin America is at 1.8. Many countries are below two and falling. Once the whole world reaches that threshold, shortly after that we’ll start to see shrinkage for the world’s population as a whole.

Fin: So you mentioned that globally speaking birth rates are declining. Does that mean the world population is declining? My sense is that it’s not declining yet. What’s going on there?

Dean: That’s right — not yet. We’re between two peaks. One peak, the peak in the number of births, has already happened. That was back in 2012 when there were about 146 million births, the most there has ever been in any year. We’re already past the year of peak births, but we’re not yet at the year of peak population size. That’s in part because death rates are falling and we’re living longer, which makes the population larger for a given birth rate, and in part because the population is a big, slow-turning ship, so it’s taking time for these changes to work their way through the age pyramid. Low birth rates are really nothing new — what we’re seeing is just the next step in a process that’s been unfolding for decades, even centuries, insofar as we have data.

Fin: We have some sense of the trends over time. Can we use them to make a guess about when we’ll hit peak population as well?

Dean: Demographic experts in the population science community have made guesses. You make these guesses by specifying likely trajectories for birth rates and death rates and then computing the consequences. The quantitative correctness is only as good as the assumptions about those trajectories. On the one hand, death rates — especially early-life death rates — are falling and are fairly predictable in many places, so we have a reasonable idea of how deaths will go. The main uncertainty is birth rates: how fast will they fall and how far below two will they go?

One projection is from the demographers at the UN (World Population Prospects), and their medium projection is that the size of the world population will peak in 2084 — a little less than six decades from now. Other groups put it a bit sooner, like the Institute for Health Metrics and Evaluation (IHME) at UW or IASSA in Vienna. So there’s general agreement: one group might say the 2080s, another the 2070s or 2060s, but broadly there’s consensus that if a child is born today, there’s a pretty good likelihood that child will live to see the peak in world population and the beginning of a decline.

Fin: Of course, that peak population has got to be greater than current population, just over 8 billion. But how much bigger are we talking — 9 billion or are we talking 40 billion?

Dean: People project numbers in the 10 billions as a likely place to peak. Right now we’re at 8.3 billion. Growth is going to continue but slow and round a curve where we’ll be in the neighborhood of 10 billion for a long time.

Fin: I get an impression from reading the news and reading people talk about declining birth rates that this is really a story about rich countries. Is that right?

Dean: For a long time that was the story and it still survives in the popular media. Here in the US we hear people say, oh, the fall in birth rates since the Great Recession in the US — as though nothing happened outside of the US, none of it happened longer than 15 years ago. But in fact, this has really become a global phenomenon. The earliest places to fall below two were relatively rich countries. One thing people sometimes overlook is that already by 1980 one-fifth of people worldwide lived in a country with a birth rate below two. Those were richer countries — Europe, Japan, Australia, Canada. But it’s now become something that’s happening worldwide. Of course, China has a very low birth rate, close to one. Many other East Asian countries are in the low twos. I already said Latin America is below two, around 1.8. My own research is mainly about India. India is now a below-replacement country. Its most recent demographic and health survey put it there — particularly striking because India was really at the center of the overpopulation narrative and fears of the 20th century. So the fact that India is below two, and that even within India I work in the disadvantaged states of Uttar Pradesh and Bihar in the north and young women in Uttar Pradesh say they want an average of 1.9 children, is really striking. A world where India is below two and teenage women in Uttar Pradesh want fewer than two children is a world where birth rates are below two in many places, and so depopulation comes to look like a likely future.

Fin: Got it. To try saying that back — in terms of absolute birth rates, they tend to be lower in richer countries. But below-replacement birth rates aren’t unique to the kind of rich countries you might think about, like Korea or Western European countries.

Dean: No, that’s right. The richer countries got there first, but it’s something we’re seeing almost everywhere. In fact, sub-Saharan Africa is really the only major world region left with birth rates above this average of two. But even there, it’s at an average of four, which is down and falling from maybe an average of six a few decades ago, and projected to continue falling because there’s a lot of room for improvement in human development like education in Africa. When we see that sort of improvement, it seems plausible that birth rates will continue to fall there too. So the composition of the world is going to be more weighted towards Africa as the future goes on, as birth rates in Africa catch up with the rest of the world. It has fallen from 6.4 in 1950 to an average of five in Africa in 2014 and down to 4.3 now, with every reason to think that’ll continue to fall.

Fin: You mentioned that it’s not an especially sharply recent phenomenon, falling birth rates. Can we point to some period where birth rates really began to decline?

Dean: There doesn’t seem to be any single turning-on point. Rather it seems that as long as we have records, we see birth rates falling. We see information from France a little earlier than some other places — France started falling a bit earlier — and when we look at Sweden before that, it seems to be falling too. Wherever historians have gone to try to estimate something for the world as a whole, it really fits this pattern: a worldwide average around six for 1800, five and a half for 1900, and then down to five for the world as a whole when the UN WPP statistics begin in 1950. There are fluctuations around this long-term trend — it doesn’t always fall every year in every place — but it’s a pretty consistent and convergent pattern of decline over a long period.

Causes: childlessness, economics, and culture

Fin: I think this is something I found striking from the book: of course there are differences across countries at a time and there’s lots of noise. But the main story is that for pretty much everywhere in the world, or at least for the world average, it’s been pretty much steadily declining as long as we’ve been counting. How much of that trend is being driven by more people deciding to have no children, versus people deciding to have some but fewer children?

Dean: So at least in the US popular media, we hear this claim a lot that it’s about childlessness, about more people having no children at all. But it turns out to be more complicated than that. The average number of children that a cohort of women has can be decomposed into basically two numbers: what fraction of them have any children at all (childlessness), and then, among those who do have children, how many children they have on average. Multiplying those gives you the average number of children. Low birth rates could be because many women are childless, or because people who are parents have a small number of children. The answer turns out to be that both of these things are happening.

There’s a strong correlation, if you look across countries, between the overall birth rate and the birth rate among parents. That means places where the overall cohort birth rate is low are also places where people who are parents tend to have few children, which means that there are several countries where the birth rates are lowest where the average number of children, even among people who are parents—so even setting aside the zeros, the childlessness—would be low enough for depopulation. Portugal, Russia, Poland, Taiwan, Japan, Spain: these are all countries where, even looking in recent cohorts of women who are parents, you see that the birth rate would be low enough for depopulation.

Another perspective is India, because India as a whole is at two, but India is 1.4 billion people. Not only states but districts of India have populations in the millions, so it makes sense to look at them as though they were statistical countries. India is a place where childlessness is very low. There’s a particularly strong correlation between the cohort birth rate—looking, for example, at districts—and the birth rate among people who are parents. I think it’s important to keep in mind that we see different paths. We see a path like the US, where a relatively larger fraction of the decline is due to childlessness, but we also see a path like in South India, where birth rates have fallen and there really isn’t much childlessness at all. Other places show more mixed patterns; different parts of that childlessness versus the average number of children parents have are more important at different times in England, for example. It’s this fact—that there’s no one path to low birth rates, and instead it’s a convergent outcome that different countries reach in different ways—that makes me see this as a likely future many countries can arrive at in their own way.

Fin: At least in the context of talking about birth rates in rich global north countries like the US, I often hear people talk about this in terms of income, where there’s maybe some relationship there, some inverse correlation. Is there an especially strong connection?

Dean: Sometimes what I hear people say is that the reason birth rates are falling is because children aren’t affordable—that people somehow can’t afford to have children anymore. That never made a lot of sense to me, in part because what we’re talking about is a decline in birth rates while people around the world are richer than ever before. We live in the richest time in human history, both in richer countries and, for the world as a whole, in poorer countries too. If you think affordability is the issue, we can learn a lot from some simple comparisons.

Birth rates are lower in richer countries than in poorer countries. Birth rates have fallen over time within the same country as countries have gotten richer. You can even look at microeconomic evidence—somewhat silly but causal—comparing young women who win a lottery with young women who play the lottery but don’t win; you don’t see the women who win the lottery going on to have higher birth rates. However you look at it—whether you compare places where the social safety net is more generous, where childcare is more heavily subsidized, or where university is more heavily subsidized—we don’t see those places having higher birth rates. It’s just very hard to find evidence that affordability, at least at the level of variation we see in the world, is what’s explaining this.

Fin: So if affordability is not explaining this very broad, long-running, strong trend, is there some kind of consensus answer on what it’s caused by?

Dean: No, yeah, there really isn’t a consensus answer. There’s sort of the opposite of a consensus, which is that everybody has their theory. But each theory is different and none of them really fit all the facts. And so we’ve talked about, for example, affordability and how that’s at least a pop theory that one hears a lot and that doesn’t seem to fit the facts.

Another thing that people talk about is the spread of contraception, modern contraception like hormonal methods, for example. And of course these are very important innovations and an important tool in letting people choose the sorts of lives they want and decide not to have a child or not to have a child right now. But as important as that is, it doesn’t seem to be what explains this broadly shared and long-term fall in birth rates. After all, we see the fall preceding access to modern contraception, and we see it continuing in places where contraception has long been available. So if over the last 10 years or so the birth rate in Sweden has fallen from a number like 1.7 to a number like 1.4, that’s not because contraception only now became available there.

There are other more social theories that I also think don’t hold water when you start to look at the comparisons. Somebody might tell you about religiosity and say that the decline in birth rates is because of the retreat of religion. Look at Latin America, where 90% of people tell Pew surveyors that they’re Christian; the birth rate’s 1.8. Look at India, where religion continues to play a prominent role in most people’s lives and the birth rate’s below 2. So we even see this decline in religious societies. Every US state is now below two, and that means it’s below two in Oklahoma and below two in Utah.

Another category of things people say is that maybe the problem is too much feminism or too much liberalism in the family, too many women in the workforce or something. I think there’s a lot of reasons to be skeptical of somebody saying that. They might have been opposing the gender revolution even before they were talking about birth rates. But again, let’s look at the facts and we see that the facts don’t support that. Look at India. India is a place where female labor force participation is very low in international comparison, around 40%. It’s a place where marriage remains almost universal — no retreat from marriage there. Divorce is rare. Many marriages are arranged and people start having children young, at an average age around 21, which is much lower than, for example, in Europe. And we still see low birth rates in India.

Or, if you compare countries across OECD countries, places that have a greater or lesser gender wage gap, places where the economy is more or less fair between women and men, we don’t see much of a correlation there with birth rates, except for the big outlier dot of South Korea, which has the greatest gender wage gap, the greatest inequality of all of these OECD countries and the lowest birth rate. Hardly a data point suggesting that feminism is the problem.

Opportunity costs, social effects, future technology

Fin: Here’s a question. I feel very steeped in a culture that treats having one and a half kids per couple as the normal thing. And so I’m not mystified about why people want to do that. What seems less obvious to me is why 100 years ago or 200 years ago in my country, the UK or anywhere else, people chose to have on average something more like five kids. Was that just no access to contraception? Was there some kind of self-interested motive there?

Dean: That’s a good question. And I think it’s a nice inversion of the question. I get the question all the time: why are birth rates so low today? I understand that having a kid is a hassle. You can’t have a kid and go do these other things very easily. Why would anybody have wanted more children?

So the sorts of things—well, if you’re asking about a few hundred years ago, you hear answers like the germ theory of disease wasn’t widely understood yet. Early-life mortality rates were very high, so many children died and you might have more in order to have one who survived to adulthood. That’s sort of an economics-professor way to look at it. You might hear people say things like you wanted children’s labor in family enterprises, like the family farm.

I think one thing that is at least comparatively clear is the quantity–quality story: in a society where it’s costly to invest in education and it makes sense to invest in education, that might be a reason to have fewer children. I think that’s sort of overblown as a description of what’s going on in our world today, in part because so many of the costs of building children’s skills and human capital are shared or socialized — through public education, public sanitation, public health — things that help every child grow in ways almost nobody could have earlier.

Going back to what would have happened before: even if you educated your kid, they weren’t going to go get a job that used that education. So there were fewer economic returns to investing a lot in their education, and that reduces the incentive to have fewer children. But of course there’s a lot more to it. People’s ideas of what’s important in a society are different than before. It might not be true that increases in gender equity and women’s freedom are what’s driving a fall from 1.8 to 1.4 in Sweden, but probably women’s increased decision-making power and women’s perception in society could have been a part of why birth rates fell from higher levels to more moderate levels.

All of which is to say there doesn’t have to be one single covering theory that explains the entire transition. Whatever was going on from 1.8 to 1.4 could be an intensification of what was going on between five and four, or it could have been different.

Fin: Yeah, I’m curious what you think about this very vague explanation. In some almost tautological sense, with your economist hat on, if people are choosing to have fewer children, that means the opportunity cost to having children has gone up. It’s hard to point to any one thing that increased — maybe higher education or something — but just take everything you could do with your time and money that isn’t raising children. Those things have largely become cheaper because of growth, or just more attractive and higher quality. Having kids is still really hard; it requires a huge amount of time and effort and attention, especially historically on the mother’s part. So isn’t that enough to explain a lot of it? Growth makes other things cheaper.

Dean: Yeah, we say something very similar about opportunity costs in chapter 11 of the book (see chapter 11 of After the Spike). The example we give is: let’s say it’s the middle of the night and your child throws up in their bed, wakes you up screaming, and you have to go deal with that. It’s pretty unpleasant, and probably comparably unpleasant to how it would have been a hundred years ago. Maybe it’s not exactly as bad because now you own multiple sheets and can switch them out and throw one in the washing machine — people back then wouldn’t have had a washing machine. But those are secondary considerations.

One thing you didn’t mention is the benefit of parenting: that nice snuggle you get from your limp child at the end when you’ve finally gotten them back to sleep. My point being, that’s probably about as good as it would have been 100 or 150 years ago. So if the benefits aren’t much better, but everything else — whether it’s getting to work a career you care about, pursuing education, listening to your favorite podcast, playing a video game — might be better in comparison. I think there’s a sense in which that’s definitely right. As you say, it’s tautological and not all that helpful as an explanation because what we really need to know is what things are competing with having children. But yes, that’s part of the story.

Fin: Because you also mentioned culture as well as just the narrow economic story. Do we know much about the peer effects of having kids? If my friend starts having kids earlier than I do, am I more likely to have more kids?

Dean: It’s a great question. It turns out to be one that’s really hard to get a statistical handle on because you need to find some sort of reason that your neighbor or your friend, someone related to you, had more kids that wouldn’t have had a direct effect on you having more kids. So it’s hard to really study in a way that you can learn about. Some of my collaborators and I call ourselves the Tornado Club because we spent a long time trying to brainstorm some way that you could estimate this. One of us said, well, what if a tornado goes through someplace? But of course, that’s going to have a direct effect on the people too. So it’s a hard question to answer, but it really stands to reason because as you say, once birth rates get low and people expect birth rates to be low and people organize society around birth rates being low, the cost of deviation or being different gets bigger.

I think something that we overlook is that falling birth rates can only go so low — they’re bounded below by zero. That means not only are birth rates getting lower, birth rates are getting more similar. There’s less diversity; differences between groups are smaller than they used to be. So in India, where Hindu politicians have long complained about the higher birth rates of Muslim families, Muslim families now have a lower birth rate on average than Hindus in India did back when this complaint first surfaced. The difference on average between Hindus and Muslims in India and their birth rates is lower than it’s ever been. The difference between Black and white birth rates in the US is lower than it’s ever been. The difference between Oklahoma and Connecticut’s birth rate is lower than it’s ever been. In all these ways, as birth rates fall, they become more compressed — there are more similarities and fewer examples of high birth rates to look to.

Fin: When we’re thinking about how this plays out, we’re trying to forecast across the decades. One thing that feels tempting to me is to usually treat countries that tend to be richer and also have lower birth rates as being in some way ahead in time of developing countries, and you can use that as a way to maybe anticipate the path that a developing country will go through. That helps us know what the world in 2060 looks like. Does that seem right?

Dean: I don’t have a crystal ball. I don’t know exactly what’s going to happen, but I do think we can learn something from these comparisons. One thing I sometimes do is compare sub-Saharan African countries to, for example, how Uttar Pradesh looked 20 or 30 years ago. Uttar Pradesh is this populous, disadvantaged state in North India that happens to be the place I study. We have data on it from 20 or 30 years ago because there were Demographic and Health Surveys in 1992, 1998, 2005. Sub-Saharan Africa as a whole has a birth rate around four. If you look at the bigger countries that have had DHS surveys there recently, you can see that in most of these African countries there’s a lot of room for improvement left in female education and female literacy. If you look at the similar surveys from Uttar Pradesh 20 or 30 years ago, when its birth rate was closer to four, you also see that female secondary education and literacy were a lot lower back then.

That suggests to me that as long as it’s plausible Africa will follow a comparable trajectory to how Uttar Pradesh improved human development, it’s also pretty plausible it’ll follow a comparable trajectory of falling birth rates — not step by step, not perfectly, but broadly comparable. Africa would have to be on a very different path for the improvement in human development that still lies ahead of it not to result in lowering birth rates, which is why the UN projects it to fall below two.

Fin: This makes me think one misapprehension you might have is that because birth rates are lower currently in certain countries — especially richer countries — we should expect the population share of those countries to go down until regions or countries with higher birth rates make up a larger share and then birth rates stabilize or even increase again. Most of the world now is made up of countries that previously had high birth rates. You were saying that doesn’t look exactly right because even in the countries with the highest birth rates, those rates are declining over time.

Dean: That’s right. The places where it’s still above two are falling, and many places you might think of as having higher birth rates are also below two or close to it.

Fin: And then maybe a follow-up thought is: maybe that’s true nationally, but there are smaller groups with unusually high birth rates and cultural attitudes or traditions connected to that. So we might expect they’ll make up a higher and higher fraction of whatever countries they’re part of. But maybe there’s something about these groups in particular where the birth rates are especially robust against this declining trend. Eventually the Amish will inherit the world or whatever group it is. Is that plausible?

Dean: Well, I mean, birth rates are falling amongst the Amish. Birth rates are falling amongst Mormons. Birth rates are falling amongst Catholics. And people decide not to be Amish or Mormon or Catholic anymore. And so if it really truly were the case that there were some subpopulation that had an average birth rate of three and were able to maintain that amongst all of its descendants, forever, then yes, that would be sufficient for positive long-term population growth. But notice I said all of its descendants, not merely the descendants who continue to call themselves group members. Part of the problem is that people leave the fold. People stop being in the group. I think all sorts of people do things that their parents didn’t, and they think and do things that their parents didn’t. Humans don’t just hang together like that generation after generation. And even if some small group continues to have high birth rates, what counts as high birth rates can go down over time. We give the example in the book of the Catholics of Quebec in Canada, which in the mid-20th century had very high birth rates, but they didn’t take over the world. We’re not all speaking French with a Quebec accent these days. That’s because birth rates there fell amongst people who still call themselves Catholics, and many people there no longer call themselves Catholics. So even the fact that there is a culturally significant group with high birth rates is no guarantee it’ll continue, especially as they get larger and larger and time goes on. Human culture just doesn’t stay that stable.

Policy implications: ageing, voters, and climate

Fin: Maybe to say some of that back, there’s a certain trickiness to the fact that you could ask any adult-age member of an Amish community and say, how many kids do you plan on having? And they could truthfully give a large number and that could turn out to be true. But still, that Amish population doesn’t have to grow indefinitely because you can just leave the community before you reach adulthood.

Dean: Right. And when they’re telling you about their ancestors, they might not be telling you about the ones who left. I don’t want to appear to be claiming to be an expert on the Amish in particular, but just in general, for this to happen it would have to be sustained over many people, over an exponentially growing number of people over very long time. That just doesn’t seem to be the track record humanity has shown us.

Fin: Since we’re thinking about the future.

Dean: People.

Fin: Like talking about artificial wombs or some other technologies that make pregnancy less costly or just bringing a child to term. Wouldn’t that really just increase birth rates?

Dean: Let’s specify what we mean. You’re saying some sort of technology where you could have a baby without having to undergo pregnancy, miscarriage, childbirth, the trauma of childbirth, the health risks—no more stillbirths, let’s say, none of the nausea. This all sounds pretty wonderful, and I think for a lot of people it would be wonderful. My own family had three miscarriages, and they were real tragedies and made us scared about continuing to try to have kids. But I’m skeptical that it would really raise birth rates by that much for the population as a whole. Let’s think through why. If there were some way to sort of just magically order up a baby, we would avoid a lot of sadness, sure. But we would have ended up with two kids, which is the number we ended up with—we’d just have gotten there more easily and less painfully. The basic reason is that as challenging as pregnancy and childbearing can be for some people, and as important as that is, it’s not the only cost or input in making the next generation. There are long nights and long years and a lot to do ahead of you, and you’re a parent for the rest of your life. All of that factors into the decision. So yes, it could be really beneficial, but I don’t think it’s going to, for enough people, radically change decision-making relative to all the other things that go into deciding whether to have a child. It’s not like we haven’t had other things that made being a parent easier. I mentioned washing machines earlier—that’s my favorite example. It used to be really hard work to wash clothes. Now we have washing machines and microwaves and dishwashers and TVs and iPads. Some people have the Snoo. Many people have infant formula. If breastfeeding isn’t working for your family or isn’t what you choose, you have an alternative. And despite all these things that have made parenting easier, we still see falling birth rates. I hope there will be considerable advances that make it easier for people who want to choose to have a child and even give people the option to skip pregnancy altogether. But I think that’ll still be only one part of the cost–benefit decision about having children.

Fin: Yeah, I think that’s a really great point. And that thought experiment—it’s in the book I think—where you suppose you have a button where you can—yeah, a baby button. Cost savings.

Dean: How many times would you push it?

Fin: Yeah. To me — and I don’t think this is a great example because there are lots of confounding differences — it’s possible for prospective parents to adopt a young child. If the only relevant factor were the cost of pregnancy, and otherwise there were benefits to having a child, you’d expect far more adoptive parents than we do see. I have a vague understanding that in some places there is actually a shortage of adoptable children.

Maybe another question: you’re describing a future where, because birth rates are declining, the demographics of living people are skewing toward older average ages. I’m interested in the political upshots. If among the voting-age population more people are old or even past retirement, you can imagine a dynamic where, as a bloc, they’re voting for transfers from the young to the old. Maybe that’s self-reinforcing — it becomes less attractive to have kids because life looks more difficult. Is that galaxy-brained or a real thing?

Dean: Or that society is missing opportunities to invest in making parenting easier when more people are older — and maybe as time goes on we’ll see even more of that. I don’t think anyone has a policy that, in the short term, is really going to move the needle on people choosing to become parents. So I don’t think that’s exactly what’s going on here.

Also, relative to what I might have believed 10 years ago, anyone who’s been watching U.S. politics has learned a lesson about the economics-professor models of people voting for their economic interest: people don’t always vote strictly for their economic interests. So I’m less confident about predicting how older and younger cohorts will vote than I might have been a decade ago.

What we do know is that there have been more than 20 countries where the lifetime birth rate for a cohort of women has fallen below 1.9 — meaningfully below two. In a lot of those places, governments have announced or claimed policies to make it easier to be a parent. I think there are 26 such cases, and in none of those 26 have we seen the lifetime birth rate later rise back above two. That tells us something: when many people start having few children, it can become a self-reinforcing equilibrium. It also tells us something about the efficacy of these policies — whether the issue is an aging population or the limits of what governments can do, we don’t see policy turning things around so far.

Again, I don’t have a crystal ball. It’s not proof that birth rates won’t go back up, but we’re not seeing them increase in the places where they’ve been low.

Dean: I’m glad you put it that way. I’m glad you asked a balanced, even-handed question. Is global depopulation something to welcome? Is it something that we should work to avoid? I think a lot of people don’t yet know that depopulation is the most likely future, and so they’re not really even considering the question. But when people learn it, for many people the first reaction is: yes, this is something to welcome. This is something to celebrate. For many people that’s about the environment. Maybe other people think that lowering birth rates is the only path to continued gender equity. These are all very important considerations.

But one place to start that I think people miss is that the alternative to depopulation doesn’t necessarily have to be population growth forever, generation after generation, century after century. Conceptually, there’s a third option, which is that instead of long-term global depopulation, we work toward long-term global population stabilization. We work toward a future where roughly our comings and goings are balanced — not literally every year, but where the long-term birth rate averages out to around two children per two adults. Roughly our numbers stay the same size.

And part of what we’re trying to do in After the Spike is at least put that on the table as an alternative to consider, so that people who are skeptical about long-term positive population growth forever will at least realize that there’s an alternative to depopulation. Once we’re thinking about stabilization, you might ask, well, stabilization at what size? Stabilization starting when? I think what’s important to recognize is that nobody should really claim to have very quantitatively precise answers to those questions. In After the Spike we argue that stabilization would be better than depopulation, but we don’t specify whether that’s stabilization at 8 billion people or stabilization at 4 billion people. If you think the better future would be one where the world population goes over its peaks, begins to decline and then levels out and stabilizes at around 4 billion people, that’s a type of stabilization and would be consistent with the story we’re telling — that it’s better than global depopulation. But it’s important to notice that any stabilization at any size would require an average birth rate of two, meaning an increase in the birth rate someday. All I want to do is get clear that, for starters, that’s an alternative we should be willing to consider.

Fin: And so maybe we should be comparing — just to make things simple — a stabilization pathway where over the next few decades population levels out at some, let’s not put an exact number on it, but some familiar level, versus indefinite population decline after we pass the peak. And presumably when we’re talking about population decline, in some literal sense something’s going to break eventually, but I guess there’s bracketing that.

Dean: Right, I think that’s right. We don’t know exactly what will happen if the population gets really small — as you say, probably not good — but I also don’t think we have to get into that to see why depopulation could be worse than stabilization, why depopulation might not be a future to welcome and stabilization could be better. For us, it really has to do with this idea that other people, when their lives are good for them and they’re good for you, that there’s goodness in good lives and that a world with more good lives in it counts for something. Depopulation is a loss of those experiences that won’t happen in a depopulating future.

We also think that what an economist would call the externalities — the effects on other people — net out to be positive. It’s not that everything about other people is good, but overall other people living is good for you. Other people make you better off. They’re not simply competing for the goods in the economic world that you want. Other people, on net, are part of how you get the good things that you want.

Fin: The thought is, if you bring a new person into the world, it’s good for them. I’m glad that I’m alive.

Dean: Exactly. I’m glad that I’m alive.

Fin: And it also has benefits for the rest of the world. Maybe we can talk about that second part first. I imagine that when people — let’s say in the US or the UK — are considering whether to have kids, maybe around my age or a bit older, something that weighs on their minds is the climate-related harms that the kid would cause, because they’re going to be consuming a lot of material goods, using a lot of water and producing a lot of emissions. They are contributing to that polluting engine that is the US economy or whatever country you’re talking about. So it feels like intuitively the ledger tilts in the negative direction. Maybe it’s a favor to my kids to bring them into the world, but there’s something kind of antisocial about it because other people are bearing the burden of an extra person consuming stuff. Is that a good way to think about it?

Dean: Well, let’s jump in on the environment, because I think it’s important to be very clear about something: yes, humans are and have been very polluting. Climate change in particular is a big, important, and urgent crisis. And it stands to reason that if, all along for decades and centuries, there had been fewer of us, then we probably wouldn’t be facing the same sort or magnitude of climate crisis that we’re facing now. Humans have polluted a lot. Now, as important as that is, I think it’s a separate question whether depopulation projected to start six decades from now in the 2080s is the solution we’re looking for to our climate crisis. If you have a child today, that child will be deciding whether to have a child in, I don’t know, 25, 30, or 35 years—around 2055. And 2055 is just too late to be part of the timing we should be talking about for decarbonization and our climate challenges. We need to be much quicker on finishing the decarbonization project. Experts can debate the exact timeline, but we can all agree it needs to be done much faster than the peak of the global population six decades from now. So the first and biggest reason why depopulation just won’t have the climate benefits people tend to attribute to it is simply tied to timing: depopulation is just going to come too late.

Benefits of people: scale economies, ideas

Fin: So that’s a good point. I could still think that it’s true that it’s eventually an antisocial thing to have a kid. But the harms only start mattering many decades from now. So it’s not only bad, but it’s also too late. It’s not a positive case.

Dean: Let’s hang on climate a little bit longer. Because even if depopulation is going to come too late, it’s a separate question whether putting humanity on a path toward stabilizing the population instead would cause too much harm for the environment. How much would it increase long-term temperature change for humanity to go on a stabilization path rather than follow the likely path toward depopulation? How much worse would it be for the climate?

We asked this question in the book and in our research. To answer it, we need to be precise about what we mean by “stabilization.” In the book, we stack the deck against ourselves. We ask: what about a stabilization path so ambitious that it would have had to have already started—where birth rates increase in places where they’re low—so we’re on a path to a future population that peaks and then hangs out there forever at a population larger than today’s? That is essentially impossible as a practical matter. But we can still consider, what if we stabilize at a number like 11 billion people stabilizing in the 22nd century? How much worse would that be for the climate than if we follow the most likely path of going over the peak and then population falling forever?

Eventually those two futures will be very different, billions of people different per year. But that “eventually” takes centuries to work itself out. Remember, population is a slow-turning ship that turns over at the level of generations. So during the coming decades or even the coming century, even if we assume it takes another 100 years for decarbonization—that we’re on a completely bad-news climate path and don’t stop carbon emissions for another 100 years—there just aren’t that big differences in population size over that time. And all along that decarbonizing path, emissions per person are falling as they are now. By the time there’s a difference to speak of in the size of these two population paths, emissions are much lower than today. So even on such a pessimistic climate path—100 more years until decarbonization—even such a big difference between population levels makes only a tiny fractional difference to temperature change in the end. It’s too late in history relative to the climate challenge for any plausible change in the population trajectory to make a meaningful difference to the climate future.

That definitely does not mean ignore climate change. It doesn’t mean climate change doesn’t matter. It means we shouldn’t expect humanity’s choices about population to have much to do with the climate outcome. What we should do for the climate is work very hard on decarbonizing and lowering carbon emissions and get that done soon, as all the climate scientists tell us we need to. Whether or not six decades from now we depopulate is a separate question because we’ll have gotten decarbonization done.

Fin: So I found that very interesting. I take it the point there is mostly that decisions around having children are just less relevant, less timely than you might think for climate change, and there are other decisions we can make which matter hugely more. So let’s focus on them. Isn’t there also some positive case—some benefit to having more people around?

Dean: Yeah. And I want to be clear, and in After the Spike we’re not trying to give anybody advice on whether or not they should have children. There are plenty of books out there that will tell you what to do with your own life, and I encourage you to read them if you want to. That’s up to you. What we’re doing in After the Spike is really asking about the bigger picture for society as a whole and saying: it might not be that you’re making a mistake if you don’t have children, but society might be making a mistake if we don’t do more to make it easier for people who want to choose to have children someday. What we need to do right now is have conversations like this one about a future that’s still unfolding so that maybe someday we can choose to make policy choices around it.

Dean: So what have we said? We’ve said that one reason stabilization might be better than depopulation is because of the goodness in people’s lives — that’s something to value. We’ve said that one reason depopulation might be better than stabilization is if that’s better for the climate, although that turns out to be unlikely given the timing of climate change. If what you care about is the climate and decarbonization — and it should be something to care about — you can focus on that, too. But we can care about more than one thing at the same time.

Dean: One of the things I’ve said is that other people’s lives are good for you. Other people’s lives have positive externalities: we are made better off by living in a world with other people, and whatever it is that we want or need is more likely to exist if other people want and need it too. Why is that the case? A big part of it comes down to scale effects generated by fixed costs.

Dean: A fixed cost of some activity is just the cost of the activity or program happening at all. It’s easiest to think about businesses. The fixed cost of a restaurant is the cost of the restaurant being open — the space, the rent, the utilities, separate from the labor and the ingredients. If a restaurant doesn’t get enough customers to cover its fixed costs, it’s just the restaurant being open at all that becomes unsustainable and it’s going to close. A business has to have enough demand to cover its fixed costs in order to stay in business.

Dean: But it’s not just businesses. Many things have the property that a big fraction of the costs, or maybe all of the costs, are in there being something rather than nothing, and there’s almost no cost in additional people using it. Take this podcast. We’re here recording a conversation; you’ll edit it and put it on the internet. That all happens whether 10 people listen or 10 million people listen. An extra person downloading the podcast doesn’t consume it more quickly — there’s almost no marginal cost. All of it is the fixed cost of existing at all. In a future with more people, they won’t use up our podcasts faster, but they’ll be an audience base that can justify or make feasible more projects with large fixed costs.

Dean: It’s true of government programs and services, too. You’ll have more and better elementary schools with better-staffed kindergartens doing a better job teaching phonics in a world where there are more children for them to serve. You’re more likely to have a functional hospital that offers the specialty care you need if there are other people who need the same care; otherwise a doctor can’t keep a practice open and will move or change specialties. A public bus route, public transit, a sewer system — all of these things are more feasible where more people need them so they can cover fixed costs.

Dean: Cities are a great way to see that. Why do people move to cities where rent is higher? Part of the reason is to be near other people who want the same things you do — to try the new restaurant, to see the new performance, to take an airplane flight from point A to point B. In a future that’s depopulating compared to a future that’s stabilized, there will be less of that variety, less creation, and fewer public services for everybody.

Fin: Yeah — if the world economy were made up of a million people, then there’s really just no space in that economy for, let’s say, a specialist in a rare disease that affects one in five million people.

Dean: Right, exactly. And so if you’re unlucky enough to get it, there’s going to be no treatment. And maybe you won’t get that particular rare disease, but you’ll get some rare disease and somebody else will get some other rare disease.

Fin: And just because of these returns to scale and economies of scale that are kind of everywhere, any given person in that small world is, all else equal, less wealthy than in a larger world.

Dean: That’s right. I mean, less wealthy in the meaningful sense: what capabilities do they have access to? What can they get if they want it?

Fin: Right?

Dean: We tend to think of the economy as a fixed pie — that other people are eating the pie and leaving a smaller and smaller slice for us. But this way of thinking about fixed costs tells us something different: if there aren’t other people, pies don’t exist as slices — pies come as whole pies. To abuse the metaphor, you’ll never think of slices of pie the same way again. If there aren’t other people who want a slice, no baker is going to bake a whole pie just for you. You need other people who are interested in pie for you to get any slices at all.

Fin: So this applies to technology in general, right? Once you devise a new technology it’s cheap to teach other people to adopt it. For example, early efforts to develop solar panels made them cheaper; those efforts would have been harder to justify if you knew you were eventually selling into a much smaller market. The fact that the world is so big helped get, I guess, Japan and Germany early on and China later and so on to care about developing this kind of technology. And that applies across the board. Simar, right?

Dean: No, I think that’s right. I think humanity has seen that there’s a lot of learning by doing in the production process of renewables, like solar panels. By making them, we learned how to get better at it. And there’s a related idea here that this sort of accumulation of ideas or learning by doing is another big part, another big reason why other people’s lives are good for you.

So let’s take a step backwards. Why are our lives today so much better than lives 200 years ago? We have antibiotics to treat our infections and glasses to improve our vision. We have good nutrition. We can choose from a variety of food. We have Zoom calls like this one from people far away. Why do all of these things exist in our world today and not 200 years ago? It’s not that the rocks beneath our feet are different or that the wind or the sun is blowing and shining in a different way. It’s all the same planet, right? But we know more what to do with it. We know how to take silicon out of those rocks and turn it into computer chips, which we then can use to make podcasts and Mario Kart. We know how to harness the wind and the sun to power it. We know things that people didn’t before. And that is fundamentally the driver of long-term improvements in living standards: these ideas and this knowledge.

I don’t want to create the misimpression that it’s only high tech that I’m talking about. This sort of knowledge takes many forms. We know better how to organize a kindergarten, how to teach phonics. We know how to organize a parliamentary democracy. We know medical tech that now seems very old fashioned to us, but is completely life saving. And the thing about these sorts of knowledge is that it has this same fixed-cost, marginal-cost property: all of the costs of an idea are the creation of the idea. Once an idea exists, it simply doesn’t get consumed or used up.

Let me tell you what I mean by that because it sounds sort of weird. The economist’s word for it is non-rival. An idea or a recipe or a blueprint or a theorem is non-rival, meaning that if it gets used, it doesn’t get used up. So take a sick kid with an infection and you’re going to treat that kid with antibiotics. If you give that kid an antibiotic pill, the particular antibiotic pill is completely used up. Nobody will ever take that pill again. It’s gone. But the idea, the recipe, the formula to make it, and even more importantly, the science and the germ theory of disease behind it, will continue completely undiminished for the next doctor or the next scientist to use again to stamp out the next pill and treat the next kid. The scarcity is only in the physical production and distribution of the pill itself, but there’s no scarcity in the most important resource, which is the knowledge, the recipe.

And so here’s why that matters for a depopulating future. If we have our ideas that we know about science, if we have some formula from a chemistry textbook, that’s not going to get consumed or used up by a larger future. If there are 10 billion of us instead of 5 billion of us, or 6 billion instead of 3 billion, we’re not going to use up the formulas in our chemistry textbooks faster. They’re going to continue completely undiminished. But if we have fewer of us making those discoveries, then we’re going to find those things more slowly and we’ll be on a slower path to inventing what’s next. So in a depopulating future relative to a stabilized future, we’re going to do less of the discovery, the learning by doing, the tinkering around and the finding of process improvements that we’ve done all along to make one another better off. And so, will we be making slower progress towards a better, safer, and healthier future?

Air pollution harms and policy lessons

Fin: In a sense, I get to sit on top of all of the ideas and tinkering and learning by doing that the roughly 80 billion or so people who have lived and died before me came up with. And now that we have this kind of embarrassment of ideas, I don’t need to feel bad at all about benefiting from them because it doesn’t make it any more expensive for the next person to come along and benefit from those ideas.

Dean: That’s right. When you factor a difference in squares in an algebra class, the next person is completely free to factor a difference in squares in an algebra class.

Fin: And this, again, extends forwards, right? So it’s not a reason to think that, on the level of a society, there’s some badness to stabilizing population. Because at least when we’re talking about ideas, you’re not using ideas up, but you are producing more of them if you have more people around.

Dean: Right. And so we won’t be making as fast progress. We won’t be saving lives, improving safety, helping people learn as quickly if there aren’t as many of us who create these things. And again, it’s not just high tech. Part of my work is in India in international development. I work with a nonprofit that has teams of nurses that do low-cost neonatal healthcare and lactation consulting to prevent neonatal deaths — early-life deaths that are really likely to happen among premature or underweight babies. They aren’t using fancy machines. They don’t have incubators like you might find in a richer country, but they do have something from somewhere else. They have techniques that were developed in Colombia called kangaroo mother care that they use to teach moms to keep babies warm and to promote breastfeeding. Some doctors and nurses in Colombia decided that they weren’t going to give up despite not having incubators, and they refined and developed these techniques, which of course were further refinements and developments of things that mothers and midwives have been doing since time immemorial. Now nurses in Uttar Pradesh, India can learn from this and use it to save lives in India because other people came before them and learned about these techniques. In all of these ways we can continue to accelerate progress toward a better future by building upon the ideas that one another build.

Sometimes somebody will ask me, “But don’t we already have it so great? Why do we need more innovation?” They’re probably thinking of some sort of new addicting app or game for their smartphone. Yeah, my iPhone’s good enough. Maybe it is. But there are a lot of people out there who don’t have it, whose babies are still dying from being born too small or too prematurely and not having treatment. There’s still improvement to be made in our world. It’s a blinding mistake of privilege not to think that there’s lots of progress still to be made. Even for the distribution as a whole, we want the future to be better for everybody, right? There’s no such thing as good enough. There’s nothing about our lives in 2025 that are good enough. We should want better, faster progress toward a fairer, safer, healthier, richer, more flourishing, more joyful future. Part of how we get that is from the contributions of all of us.

Fin: And one thing that makes me think of — again, I’m thinking of environmental worries, thinking about climate — you can look at decade-by-decade deaths from natural disasters in the world or in a given country and they tend to be declining quite impressively. This is not because we’ve managed to eliminate natural disasters; it’s because we’ve been able to handle them better. Part of that is we have great new ideas for how to mitigate the harms. When you become wealthier as a society, you can afford to put these protections in place. You can afford to filter drinking water and build flood protections.

Dean: Not just wealthier, but numerous, right? It doesn’t make sense to have a water treatment plant or a sewage system for just one family. When I’m in India, we have these RO filters — RO plants — for our water inside our one house and it uses electricity and is quite an expense. What you really want is for that to be shared by a whole community. That’s what makes it more affordable. So that’s just another example of these fixed costs.

Fin: Yeah, maybe we could talk about air quality, since we’re talking about environmental effects. Tell me a bit about the harms of air pollution. This is independently of temperatures, I take it, and of changes to climate. I guess most of your work on this is in India. Why care in particular about air quality?

Dean: And when we talk about air quality, one of the most important things to discuss is particulate air pollution — little specks in the air. Sometimes you hear this called PM2.5 because it refers to the diameter of the particulate matter. We know particulate air pollution is really quite deadly: it kills more people than temperature- or climate-related deaths, and it stunts the growth of children exposed to it. The little particles, when you breathe them in, get into the tiny sacs at the end of your lungs. It causes older adult mortality, raises blood pressure, and prevents children and workers from concentrating. It’s just really bad for humans.

People often ask, after we discuss the quantitative irrelevance of population change to future climate change, what about other environmental challenges? That’s an important question because many of us overlook particulate air pollution as one of the most serious environmental challenges humanity faces.

I spend a lot of time in India — North India, Uttar Pradesh, Lucknow, and places north of that like Sitapur — and those places are every bit as bad as Delhi, which you hear about a lot in international news. But it’s not just India. In 2013, China experienced what was called the Airpocalypse, when particle pollution rated around 700 on a scale that normally runs 0–500; it was widely covered in the New York Times and elsewhere. The U.S. Embassy even advised families to leave. That event is worth discussing in a conversation about population and the environment for two reasons. First, air pollution is not a straw man — it’s very important. Second, air pollution works on a shorter timescale than climate, so we can learn from what happened afterward.

In the decade-plus since 2013, the Chinese population grew by about 50 million people — more than many European countries, roughly one and a half Texases. And yet particulate air pollution in China fell by more than half over that decade. It’s not just China: globally, the population grew by around 750 million people while particle air pollution fell considerably.

That said, not everywhere improved. India still faces very high particulate pollution, in part because policymakers there haven’t made the same choices China did. China closed down coal plants and enforced regulations that required producers to adopt technologies closer to the international frontier. India, by contrast, hasn’t made the same political decisions; people complain about pollution, but there isn’t a widely shared sense that it could be much better, and in a democracy it hasn’t been a major voting issue. When I wrote about particulate air pollution in India in 2019, I asked people whether they’d vote differently based on any party’s stance on the issue — no one said yes. In China, they did.

What we learn is that a growing population can coincide with improving environmental outcomes when societies make different policy choices. Air quality in China isn’t the only example of progress against environmental challenges. In the 1980s there was widespread concern about the ozone layer hole, and the Montreal Protocol in 1987 banned many ozone-depleting chemicals. In the 1970s and later, leaded gasoline became a major concern and was regulated out in many places through legislation like the Clean Air Act in the U.S. Acid rain was a big issue in the 1990s, and amendments to the Clean Air Act addressed sulfur dioxide emissions.

We haven’t solved all environmental problems — many still lie ahead — but when we’ve addressed destructive and polluting activities, we’ve done it by confronting those activities, not by reducing the number of people. The way to lower human environmental damage is to lower per-person environmental harm, not to lower humans. That’s the lesson from the record: China improved its air quality while its population grew, and so did Mexico, by reducing per-person harms and changing what people did. For climate change or any other environmental concern, the approach is the same: reduce per-person harms.

Dean: If, like me, you care about the consequences of humans for non-human animals, we’re so far from the frontier of what we could be doing to make things better for non-human animals and reduce our per-person consequences for other animals. What we need to be doing is getting closer to that frontier too. There’s no practical alternative to reducing our per-person environmental harms and it’s what we’ve always done before. So I think it’s important not to get distracted by population change or depopulation that is projected to come six decades from now and instead concentrate on reducing our per-person harms.

Fin: And if I remember right from the book After the Spike, there is some kind of plot pointing out there’s not even any discernible relationship between the population of a city and the severity of air pollution.

Dean: That’s right. Or of a country, right? We have a graph plotting the population density of a country against average particulate air pollution in that place, and you just don’t see a relationship there. That’s because it doesn’t directly depend on how many people there are. It depends on what those people do, what sort of policy choices they make, and the technologies they use.

Fin: Can I zoom in on one thing you mentioned? You said you spoke to people in India, in North India, and asked them whether they would change their vote if there were different policies around air pollution. Why are people not more engaged?

Dean: I think people there don’t really have a sense of it being changeable or fixable. They just sort of think of the particulate air pollution as a property of the weather. They even use the word mausam (Hindi for weather). You can sort of see how the word monsoon sounds similar. They use the word mausam to describe it. It’s not seen as a policy variable, but even more importantly, it’s not seen as something that could be better. If you’re an early-adult voter, you don’t have a lot of memory or experience of blue skies and not being exposed to this sort of particulate pollution. So it’s harder to imagine that it really could be different. In some sense, we humans are bounded by what we feel we can aspire to. The particle air pollution in North India has been so bad for so long and so consistently for so many people that there’s just not a sense that it’s even plausible that it could be better.

AI impacts, politics, and research directions

Fin: I want to ask a set of questions you’ve probably heard a lot and probably find annoying by this point. So—AI, right? Most people anticipate transformative effects from AI, maybe quite soon. You could imagine that this changes the most reasonable projections for what happens with birth rates and world population. And you might also imagine it undermines some of the reasons for concern about depopulation or some of the benefits of people. We could start with just this descriptive question: could you imagine a future where the overall cost of raising kids does fall significantly? Education could become much cheaper and more automated; childcare—we’re getting pretty speculative here—but you can imagine robotic assistance with raising children. Without speculating about when this happens, if ever, is that not a future where you should just imagine that birth rates increase again because suddenly it’s much less costly?

Dean: Maybe—if by hypothesis it’s not a hassle in any way to have a kid, then yes, I would expect birth rates to go up. There’s still a lot of relentlessness to it. Each night you’ve got to put the kid to bed. Each morning you’ve got to get the kid up, get them dressed, feed them, make their lunch. Maybe you’re describing a world where all of that is made seamless and easy by robotics and AI that we trust entirely integrated into our lives, and it does everything from wiping our kids’ bottoms to giving them a smile and hug on the way to school, even as they give us a grumpy cold shoulder, and it prepares their meals and everything else. If we get to that world, would more people have kids? That’s sufficiently far from a world I have experience with to make it tough to speculate, because probably a lot of other things would be really different too. Maybe we’d have artificial opportunities to make ourselves happy in ways that still outcompete having children. So I don’t know.

If you want to say, “Dean, you’re an economics professor, and surely you’ll agree we could conceivably change the private costs and benefits by enough to have birth rates go up,” then I’ll say, sure—conceivably. It’s hard for me to see that happening on a foreseeable timeline that soon. But I’m not here to say we should all believe global depopulation will certainly happen with probability one. What I’m saying is that this is a likely-enough future to be worth our attention now. I hope there are people working with complexity and sophistication and emotional nuance on ideas and technologies that can make parenting easier, better, and fairer, and I’ll be excited to see that.

Fin: Yeah, it’s an annoyingly reasonable answer. So the other side of that question is the more normative part, which is: let’s speculate that the kind of idea-production benefit of human researchers can get significantly replaced and automated. And so now there’s no longer this ideas-based case for people. So you really don’t need a human doctor who is a specialist in the rare disease anymore. In that speculative future, what is the remaining case for still caring about how many people there are? And maybe it’s just this intrinsic point, which I guess you’ve mentioned but haven’t elaborated on.

Dean: Yeah, exactly. I’ve said that there were three — in After the Spike we have three chapters in the part of the book that’s about the case for people. One of them is, as an economist would say, people in the social welfare function: people’s lives and their experiences, the concept of what’s good, and the fact that in a depopulating world there’s going to be fewer good experiences — fewer hugs, fewer nice cups of coffee, fewer pleasant podcasts, whatever it is you like. There’s going to be less enjoyment because there are fewer people doing the enjoying. So if you want to stipulate that AI is going to be good at enjoying in a morally relevant way, then great. But otherwise, I think that’s at least one reason we’ll still need people: there aren’t good experiences without somebody experiencing them.

Another part of the case for people that we talked about was this whole thing about fixed costs and other people on the demand side. You need other people to want and need what you want for it to become feasible or practical for somebody to provide it to you. We need other people, in short, to want things so that we can get them. I don’t think we should be confident that AI is going to want the same things that we want or that AI is going to provide the demand side of the economy in the way that other people do. If you want sandwiches and I want sandwiches, there’s more likely to be sandwiches if somebody thinks we’ll be there to want them. So even if AI lowers costs on the supply side, we still need to think about the demand side.

Coming back to what you really asked about: the innovation case is really a case about other people on the supply side — other people having ideas. Maybe AI will have ideas, which means we don’t need people to have ideas. But if both people and AI are part of the production of ideas, one possibility is that AI is a substitute for human contributions, and another possibility is that AI is a complement. New technologies have often been complements to human production: the factory, the waterwheel, the pencil, the spreadsheet. Computers have made humans more productive and humans have made computers more productive. What we want are human-computer teams.

If AI turns out to be complementary to humans, it’s all the more valuable to have other humans around so they can make complementary teams with the AI and promote progress. Is that the path we’re on? I don’t know. But at least it’s one way we shouldn’t be so sure that even if AI is really good at research, it’s necessarily going to be a substitute for humans.

I also wouldn’t have written this book if I didn’t think that the goodness of people getting to live good lives is a core reason why depopulation would be worse than a stabilization future. It’s a huge missing out from all of the experiences that people could have. So whatever we might think about these economic reasons that other people are good for you, they matter because stabilizing the population might in many ways pay for itself over the long term. But I think the most important argument is the goodness in good lives.

Fin: Well put. And I wonder if a point that gets lost here is—even if we’re imagining futures where there is more substitution rather than just complementing human work—in either case, unless something goes wrong, it’s totally plausible that life gets even better.

Dean: If we could either have another couple of kids get to live with the average life in the UK or the US today, or with the average life in what’s now the UK or the US 400 years ago, right? We would choose for them to get to live today when lives would be so much better. I don’t think anyone will really consider that a hard question. And if we think that lives are going to be even better a few hundred years from now, then we should be all the more excited about people getting to experience that. Less disease, more safety, more fun to be had. I talked earlier about the washing machine—less drudgery, probably ways that will be hard for us to imagine because we’re so used to that drudgery. So let’s work towards that happening and hope that there are lots of people around who get to enjoy it.

Fin: Yeah, a set of questions I was interested to ask is Paul Ehrlich; if there is a villain of your book, it’s this guy. Maybe people have heard about him, heard that he was kind of wrong in some pretty important predictions. I feel like I know less about the effect he had on the world. Did he ever really influence policy or was he just kind of an intellectual talking to the public without any kind of consequences?

Dean: It’s an important question and I don’t really know the answer. There is a wonderful book called Fatal Misconceptions by Matthew Connelly, who’s a historian. It’s a history that traces the population-control movement in the 20th century. And of course we see some truly terrible things coming out of it, like the emergency in India, where Prime Minister Indira Gandhi and her son did a lot of harm with forced sterilizations. The Emergency and other episodes show how governments took away people’s opportunity to choose the families they would choose. And, of course, there are places around the world where different versions of that still happen today. In Texas, where I’m talking to you from, we see successive legislation to take away people’s reproductive freedom in healthcare. So this idea of population coercion is not only something from the past; it deserves our attention and the time to reject it.

Now, how individually important Paul Ehrlich or other spokespeople were, I don’t know. One thing you see in the history is that there were networks of people who shared this idea. You know, it’s easy to get confused between two levels: if an individual family has fewer children, that might allow them to invest more in the health and education of each child; versus if humanity as a whole has fewer children, that might be good. Things happen differently at different scales. So you can see how many people thought that policy to reduce birth rates—which was, unfortunately, a short step to coercive policy—was something to be promoted in the 20th century, especially during the era of high-modernist approaches to international development, where people imagined that you could sit around in economics professors’ offices like this one and figure out what’s good for everybody. I don’t know how much of that was because of Paul Ehrlich and how much would have been supplied by somebody else if he weren’t around. After all, in our chapter on innovation, we say it’s not about rare luminaries; it’s about the cumulative processes that so many people contribute to. But I do know that these unquantified and uninterrogated ideas—that there are just flat too many of us—have real power over a lot of people.

Fin: I feel like there’s an almost elephant in the room: when talking about birth rates and fertility, it has political connotations. At least in my head, it feels uncomfortably associated with the political right. Often, there’s some reaction like “this is a little meddling” or even creepy—why are you interested in this? Certainly there are a lot of extreme people who are very interested in it. I’m interested in how you think that association formed.

Dean: You’re right, especially in the United States. I saw a poll recently where if you ask people in the US or the UK whether low birth rates will eventually be some sort of problem, most people in both countries say no, low birth rates are probably fine. But in the US, there was a big partisan split between Democrats and Republicans. In the UK, it really didn’t have the same partisan split between Labour and Conservatives — similar levels of “no” in both places. So the polarization on this question that’s found in the US isn’t found everywhere, but it’s especially polarized in the US.

And I think that makes a lot of sense because the idea of taking away people’s reproductive health care is much more salient and present and real in the United States than it is in other countries where this is more settled politics. People in the US have seen this fight really happen. So it makes sense that some of my friends and allies on the US political left would want a strong firewall between those of us who believe in progress and fairness and making good lives for everybody, and any suggestion that low birth rates might be a policy issue. I see where they’re coming from on that firewall, but even so, I think we need to tear that firewall down and that’s part of the project of the book, because otherwise we’re going to hand the whole conversation and stage to people on the right.

Those on the right are already linking low birth rates to programs to restore their idea of tradition, or dreams about rolling back the gender revolution and creating a less fair society where women participate less. But it’s important to remember they were already advocating a less fair society and rolling back gender equity long before low birth rates became a prominent diagnosis.

For a long time, we’ve treated some work as the only “important” work and pushed care work — taking care of one another and raising the next generation — onto others, usually women. If that’s how we organize things and talk about care work, it’s no surprise many people will say, “No, thank you, I’m not going to do it.” We see that repeatedly and in specific places, like women in South Korea — a particularly gender-unequal society — having very low birth rates.

So one of many reasons to reject misogynistic views that low birth rates justify rolling back gender equity is that it’s clearly not going to work. Making lives worse for women and making parenting harder for them will not cause more women to choose parenting; it will cause them to refuse. Taking away people’s reproductive health care and freedom is not going to cause higher birth rates. We know that from the data: in Texas, after repeated laws trying to reduce access to reproductive health care, the most recent full-year birth rate we have, for 2023, was 1.8 — below replacement and lower than any year in Texas before COVID. Restricting access hasn’t raised birth rates in Texas. We’ve seen similar stories elsewhere.

This sort of coercion or nostalgia for inequality is, among all its other problems, simply not a solution for low birth rates. We need people who believe in progress and fairness to speak up so those who would take us backward don’t dominate the conversation.

Fin: And to try is to say some of that back. So there is this association, especially in the US, between discussing population and birth rates and why these things might matter socially and a certain kind of political misogyny. You could say, why is this? Well, you might reasonably think if you live in the US or in a state which in particular is restricting reproductive rights, that this is just a cover — and not to generalize — but it is often, at least if you spend enough time on Twitter, it does seem to be men worrying out loud about mostly what women are allowed to do. I guess I’m interested to press on: if not that set of beliefs — which obviously isn’t the only set of beliefs — what are some of the more positive upshots? You’ve written a book about this because you think it matters. What can people take away in terms of changing attitudes or how to think about how and why this stuff matters?

Dean: A big reason to think it matters is the one we’ve talked about: the value in getting to live a good life. If you’re grateful for your life and you think there’s been joy and goodness in it, then future people will probably feel the same way. And that’s not a reason to force anyone to be a parent who doesn’t want to be, in part because forcing people to be parents over the long run just isn’t going to work. But it might be a reason to start a conversation about how we can support more people to aspire to choose parenting and also choose good things for their lives.

There are lots of ways that that sort of freedom and support would make the world a better place. One of the ways is that it would let more people enjoy goodness and good lives. Now, that’s a long-term, generations-level project: to make parenting fairer and better, and something more people feel like they can choose. I think any policy change we implement in the next few decades wouldn’t really have that big an effect on its own. But if we did all we could and the next generation did all they could, then eventually we might start to see another generation growing up in a world where parenting is easier, fairer, better supported, and they feel like they can aspire to more and choose higher birth rates. That could start building a future that captures more of the benefits people create for one another.

So that does not mean go out tomorrow and pass any particular piece of legislation. I think anybody who’s looking at this and saying that this is a reason to support their particular bill is really either confused or trying to confuse you. What we need to do right now is, one, bring more people up to speed on what’s going on — the basic facts — and help more people see that depopulation is a likely future and it may not be something to welcome. Then we can start to build towards a consensus, which we don’t have yet, and that matters in a democracy: a consensus that stabilization would be a better future than depopulation.

And we can also get to work on the long project of social science, research, and social mobilization to start to think through, build out, and test other ideas. Remember, the UN projects that the size of the world population is going to peak in the 2080s (UN World Population Prospects). That’s six decades from now. Six decades ago was only the very beginning of people beginning to talk in policy-making public spaces about climate change. Yes, scientists knew before then — a few scientists did — but we were only just starting to learn about or talk about the policy implications of climate change six decades ago. Lyndon Johnson gave a speech to Congress, for example.

If somebody back then had said, “let’s go right now and forcibly take away everybody’s internal combustion engines in the 1960s,” that would have been a bad idea. It wouldn’t have worked. It wouldn’t have been politically feasible. And it would have set back having a good conversation and learning what we needed to learn. But we’ve spent those six decades, among other things, learning. Now we have journals like Nature Climate Change. We have climate models on our computers. We have academic departments about sustainability and majors. We know things we didn’t know. And we also have social movements and political progress that we didn’t have.

So I think over the six decades between now and when depopulation is projected to start, what gives me hope about this very difficult challenge is that people could confront it in ways that we can’t now anticipate and know all the details of — just like we’ve seen happen with climate change. People a few decades from now might know a lot more than we do about what to do.

Fin: Okay, maybe part of what I’m hearing there is on an individual decision level: if you’re choosing not to have kids based on some unfortunately mistaken belief that it could really be the thing that matters for turning around the ship on climate change, then that’s a real shame. You’re missing out on something that would otherwise be just a very meaningful experience and a good thing for the person you’re bringing into the world. And to that extent, it’s useful to correct those misapprehensions and get things clear. Beyond just helping people think more clearly around these decisions, there’s this bigger societal-level question. And the idea is not, here’s the policy. It’s earlier than that. It’s a bit of a flippant word, but you need conversation, you need buy-in.

Dean: Hey, let’s talk. Hey, let’s do research. Hey, let’s devote some PhD theses to this and academic careers to this, and let’s learn more.

Fin: And yeah, speaking of research, are there any PhD theses you’d be especially excited to read? What are the burning questions?

Closing remarks and podcast outro

Dean: Yeah, I think here’s what I would like to see happen. There’s this field called population ethics that’s in philosophy and theoretical economics, like micro theory, that’s really tried to tackle this question of: is it better if more people get to live good lives? How should we evaluate policies when the number of people who live will differ, which, incidentally, isn’t a special case — the number of people who will live will always differ with any important policies. So that’s the question of population ethics. And then on the other hand, we have all this applied social science and demography and applied economics and sociology. And never the two shall meet, right? The applied people don’t talk to the population ethicists; the population ethicists don’t talk to the applied people. I think a lot of the founding population ethics research—if you read some of the things Parfit was writing in the 1970s and 1980s—was really motivated by thinking about the environmental challenges of the day, the ideas people had then about overpopulation, but then it really went on its own little theoretical path. I think depopulation calls us to bring those two paths back together again and start more dialogue between the ethicists and the empiricists, between the theorists and the applied people, about how population ethics and applied population science can inform one another today.

Fin: Dean Spears, thank you very much.

Dean: Thanks for having me.

Fin: That was Dean Spears on his book After the Spike, which I will link to in the show notes if you want to get your hands on it. I’ll also mention that I’m now helping run a new podcast for the research organization Forethought, where I currently work. It’s called ForeCast, and it’s more narrowly focused on questions around transformative AI. If that sounds interesting, I’ve also linked it in the show notes. Okay, thanks for listening.