Population Decline Is Worse Than You Think | Prof. Dean Spears

We've already passed the point, the year when the most babies were born. If the birth rate for the world as a whole averages 1.5 kids per two adults, um, and that's not crazy. That's what it is in Europe, right? Canada is lower than that. Then we'll see the size of the world population sort of once it equilibrates falling by about 1% a year or about twothirds per century. I'd love to welcome my guest today, Dean Spears. uh Dean is a professor uh here in Austin. You're an economic demographer uh and basically one of the leading experts in the topic of population dynamics and you've actually just written this awesome book called after the spike which is talking about what you believe seems to be the this emerging very imminent problem of population decline. So to get us started, um can you just sort of lay out the picture of just how bad the problem is right now?

Yeah, thanks so much for having me here. It's great to be here. So right now we're between two important points. We've already passed the point, the year when the most babies were born. That was in 2012 when 146 million babies were born all around the world. And ever since then, it's been lower and it's declining. So the number of births per year is already declining, but we're not yet at the point where the overall size of the population has peaked. That's because it's still the case that mortality rates are going down. Um it's still the case that on average birth rates are falling. But twothirds of people worldwide live in a country where the birth rate is below two children per two adults. Um and once that once the whole once the world's average is below two children per two adults which is projected in a few decades then we're going to be close to the year of the peak in the population. So the UN projects that six decades from now in 2084. So in 2084 or thereabouts the size of the world population will peak around 10 billion people or so. And here is what I think is so striking about that. It may never go up again. As long as the world's birth rate remains below an average of two kids per two adults, you know, that's the level that's going to cause the next generation to be smaller than the one before. Um, and that could continue and continue. So that's, you know, global depopulation, the size of the world population shrinking. And it could be every bit as fast and exponential as the increase in the size of the population. So in the past 100 years, the size of the world population quadrupled from around 2 billion to around 8 billion. In the 100 years before that, the size of the world population doubled. And so it's extremely plausible that the population could shrink just as fast if the birth rate for the world as a whole averages 1.5 kids per two adults. Um and that's not crazy. That's what it is in Europe, right? Canada is lower than that. Um, if the world as a whole averages a birth rate of 1.5, then we'll see the size of the world population sort of once it equilibrates falling by about 1% a year or about 2/3 per century. And so we could fall to quite low levels in just um, you know, a few hundred years. And so, but in some sense like the number of the level is is not even the most interesting part. The most interesting part is that there's no toolkit that anybody currently has, no plan, no automatic stabilizer that would bring us back up.

So, so in our book after the spike, um what what we talk about is you know the question that we should be thinking about is is this sort of depopulation generation after generation is that the future that we should want for the world or should we instead should we let that happen by default or should we instead want the population to stabilize? The thing that sort of strikes me is how sort of counterintuitive this idea is, right? Because we've all heard about the population bomb about overpopulation. Yeah. Yeah. Exactly. There was that book by Paul Erlick in the '60s and so on which it was actually pretty bad luck. It was 1968 which turned out to be the year in which the growth rate of the population peaked. So it was pretty bad timing. What I think I I didn't appreciate is this idea of falling fertility rate. This isn't actually a new phenomenon, right? Yeah. There's evidence that it's actually been going on for hundreds of years. For as long as we have records, birth rates have been falling. So, you might think, you know, the size of the population's been growing. We've we've seen the population growing. So, it must be that birth rates have been growing. That must be what sort of brought us up this spike caused our numbers to quadruple over the past hundred years. But no, um the reason that the population has been growing is because death rates have been falling, right? And especially death rates at the start of life, infant mortality. And so, so it used to be that a baby would, you know, have a quarter of a chance of dying at the start of life or a third or even closer to a half in some places. So, it's been an amazing improvement around the world that those mortality rates have fallen. But, of course, the probability of dying in childhood can't fall below zero. So, we'll never get that advantage again. We'll never get that source of population growth again. Um, you know, it'll fall to zero and stay there. So, so you know, we've seen birth rates falling. It's nothing new, right? Even at the time of a So, this book, The Population Bomb, we talked about it's something came out in 1968 said on the cover, population control or race to oblivion. It said things like England won't exist in a few decades. And, you know, the battle to avoid famine is basically already lost. And, you know, so and so really scary, alarmist stuff, right? Um, but you know, birth rates are already falling. the the rate of world population growth was already slowing. Um and you know even in the decade after that in the 70s a lot of countries were already falling below two. So like in the 70s Europe fell below two Australia, Canada, Cuba by 1980 1/5if of people worldwide lived in a country where the birth rate was below two and it's still been falling ever since. And so it's now it's something we're seeing in a lot of places. My research is about India. India is below two now. Um and even young women in the poor state of Utra Pradesh where I work say that they want an average of 1.9 kids. And so there's nothing special or exceptional about low birth rates anymore. It's something we're seeing everywhere.

Yeah. And I mean before we I'd love to sort of dig into Do you want me to recite more numbers? I can do that. Well, one number that you know as I was researching this that just I cannot get out of my head is Okay. Yes. It's the extremist. It's It's the It's the lowest is South Korea, right? It is currently at 0.78. Yeah. Exactly. And and just to like for us to rock what that actually means, it's that in two generations time, North Korea, sorry, South South Korea, um although North Korea is also declining, by the way, which is interesting because they're so economically different. Um, but within two generations, South Korea is going to have 17th the number of babies that it's having today. 17th. So, if you just imagine what that looks like, it means that all of that infrastructure they have right now, ch, you know, schools, um, playgrounds, all these things that we associate with children, it's going to be like ghost schools, ghost playgrounds, because you're literally going to have empty classrooms. 17th. Imagine that. It's like there's like five of us, four of us. Math is wrong. um you know it's it's it's pretty wild. Um, but America isn't even you know America's actually got one of the sort of slightly higher birth rates for the west but I'd love you to talk a bit about actually the differential between um the developing world and the western world um or at least what what is the trend between the highest rates and the lowest rates.

I mean that's the thing it's it's less than you think. There's less I mean that's sort of part of what I think we learned from the India example. So, okay. So, the US has been a bit of an exception to this global trend in falling births. Not that the birth rate hasn't been falling in the US, it certainly has been. Um, but for 35 years or so, from say 1975 to 2010, it was relatively flat in the US around two. So, that was a a time when a lot of things were changing, a lot of progress in a lot of dimensions. Um, but the birth rate in the US was relatively flat and it's a bit of an anomaly. I don't think that anybody fully understands why that's the case in the US during that time. Of course, it was falling before then in the US and it's been falling ever since then in the US. And so sometimes you see research papers um that say things like why have birth rates in the US fallen since the great recession? And you know to me that research question really misses the point, right? you know, birth rates were falling everywhere before and after the great recession. Um, it just turned out to be the case. They were sort of flat in the US for a while. So, but but what I want to really do is push back against the idea that it's really different between the US and developing countries. And, you know, Latin America is at 1.8. Um, you know, we've already talked about India. Um, um, you know, other places, you know, Nepal, Bangladesh, they're falling too. They're not quite the same level. I mean, you know, China is a heterogeneous middle- inome country, but you know, it's at one. And, you know, just to talk through the math of what one is, right? That's, you know, the next generation 50%, the grandchild generation is a quarter, right? Um, and so, and so it's really a global phenomenon. Um, of course, you know, subsaharan Africa, somebody might say, what about birth rates in subsaharan Africa? on average a little bit more than four right now. Um but you know that's down from five a couple decades ago and six a couple decades before that. And you know female education is still pretty low in subsaharan Africa. Um so if you you know if you know India which is around two is maybe around 3/4s of of high school age girls going to school. Um you know Kenya is a higher birth rate around three. It's maybe around half of girls going to school. place like Mosmb beek has a higher birth rate and you know and you know maybe around a third of girls going to school and so there's every reason to think that as subsaharan Africa traces that socioeconomic development pathway that we've saw for example in India birth rates there will fall too so so I don't think it's a story of you know the rich countries and the poor countries if anything you know just like I said death rates can only go down to zero I mean birth rates can only go down to zero and so there's a sense in which the variance has to be shrink shrinking as the average goes down. Um, and that's the sort of thing that we're seeing.

So, if it is truly a global phenomenon and it doesn't seem to be that tied to income, GDP, um, what is the or at least there are big exceptions, right? Yeah. Right. Yeah. What is the cause?

That's a great question. And, and you know, I'm I'm a professor for my day job and professors are paid to have theories and everybody has their theories. But the trouble with this one is that no every all the theories disagree and none of them quite fit the facts of the bigness of declining birth rates. The bigness both over time something that's been going on for not just decades but centuries you know essentially everywhere we have data back to you know Sweden you know hundreds of years ago. Um you know France was at three at the beginning of the 1900s. So bigness over time but also bigness over space and something we see in a lot of different places. And I think the bigness over space is something that really lets us rule out a lot of silver bullets. Um and so you know some people for example would say you know the problem is you know this is something that I might hear from like a one of my colleagues in sociology or something. The problem is sort of neoliberalism or capitalism or something like that. But then you can look at countries where the state has a much bigger part of the economy um you know like northern Europe you know like Sweden or Denmark or something like that and you see lower birth rates than the US. Somebody might say the problem is the decline in religion or the retreat for marriage. Um but you know you look at Latin America where 90% of people tell surveyors that they're Christian and you see 1.8. You look at India where religion is still a very big part of people's lives and you're below two. That's also a place where um you know almost everybody gets married and starts having kids at young ages um like in their early 20s and so so you know there are exceptions there too. India is a place where female labor force participation is still pretty low. So in the US there's a or in Europe there's an important story around career family conflicts and that is important for a lot of people but that's not the monoc cause either and we know that from places where you know India has low birth rates despite low female labor force participation. So whatever it is we we sort of see exceptions or or we see I guess the way that I think of it is that low and falling birth rates seem to be a convergent phenomenon. That's something where there's a lot of a lot of headwinds against having a lot of babies. And so so that's theoretically important. It's also important for telling us that if we do think it would be better for the population to stabilize, we shouldn't think that any sort of, you know, quick fix is going to be what changes this.

I mean to to try and answer the question of what's going on, you know, I can sort of give an economics professor answer um which is to talk about opportunity costs. So, you know, the opportunity cost is what you give up to have something. The opportunity cost of a kid is what you give up to have a kid. And so, we live in a world where a lot of things are getting better. If what you like is work, work is getting better, especially if you're a woman relative to a few decades ago. If what you like is play, play is getting better. If what you like is just sitting doing nothing, then now you have playing video games. Yeah. You have a washing machine and a dishwasher to do your laundry and wash your dishes. And you know, doing nothing is better, right? Um and so and so I think like whatever it is other than having a kid is probably pretty different from, you know, now contrast that with somebody waking you up at 3 in the morning to tell you that they just puked in the bed. uh you know that is probably pretty similar. Now it's not exactly similar. You do have a washing machine. You can afford extra sheets. You can afford the little plastic thing that you put under the sheet, right? Like it's not exactly the same. But I'm going to I I venture that it's fundamentally similar to being woken up at 3:00 in the morning to being told that you puked the bed. And also getting a kiddo hug is probably fundamentally similar like the good side is too. And so I think at some you know, what's true of young women in Utra Pradesh and people in Canada and people in Austin and people in South Korea I think you know, that so much of the things are getting better and so it's sort of not despite that but maybe because of that that people aren't choosing to have as many kids and if that's right then you know, it's almost tautological right to say that people aren't choosing something because the opportunity cost is going out because the alternative is getting better. Um but um but you know maybe something like that is part of the story that unifies it. But you know my silver bullet explanation probably isn't right either.

So what about the just role of fashion? Mhm. Because I think about it now you know growing up in the UK in the '9s. Yeah. It was kind of looked down upon on people who had large families. It was just like a sort of viewed as a kind of low class thing and upper class or middle class or whatever tended to you know it's like oh no you have two children or something civilized maybe three but I think more of that is like viewed sort of almost like through a snobbish lens um perhaps because culturally it's associated with like still sort of developing economies as opposed to a developed one. So yeah, I I wonder like how much of it is actually just like momemetics essentially and it was viewed as a high status thing to have few children few children but maybe through your work right now saying actually it's not a good thing. You're not doing your part. You're defecting from the the group that what's good for humanity. It might become fashionable to have many kids again.

Well, I mean, setting aside what what I might or might not change about the world. I mean, to consider sort of Don't underestimate women. I mean, I um I I mean, I think we're sort of not yet in a position where everybody thinks that stabilization would be better than depopulation. So, maybe we can start with that side of the conversation. But, uh yeah, I mean, no doubt people's idea of what would be a good life for them is influenced by what they see. um um you know that's just part of being human and and and you know I think if there's any hope for birth rates going back up I think it's a version of that where we create a future where you know we make parenting better and people see that parenting is better for people but you know I think we also have to grapple with some facts like even in subpopuls where birth rates have tended to be high and there, you know, would be pressure or social pressure for birth rates to be high. We're still seeing birth rates falling. So, so maybe the social forces towards high birth rates, but like what counts as a high birth rate is going down over time.

How much does actual like infertility play a role? Have there been any notice able trends in terms of just like Yeah. infertility rates? Yeah, obviously people are having choosing to have children later, you know, we all know like the younger you are generally the more fertile you are. So that would naturally create a form of infertility but could it be that there are like chemical factors or other lifestyle factors that are globally contributing to this?

Yeah. Okay. So there are various facts and various directions there. I mean on the topic of like you know chemicals or microplastics that you sometimes hear like I don't think that can explain why it's been falling for such a long time. like remember we talked about like the earliest records we have of like France being at three in 1900. Um but you know but you are right that that's all post-industrialization though it's would is everything we know post-industrial like Sweden in the 18th century or but you definitely right almost everything we know is post-industrialization in you know in the sense of steam and water wheels and yeah um but okay so okay what about disinccondability right we know that As people get older, um it's harder to get pregnant and have a kid and not have a miscarriage. And that's really important for a lot of people's lives. And in my family, we had several miscarriages and we ended up having much bigger spacing between our our first kid and our second kid than we wanted because of it. Um and so it's a huge deal in people's lives. Now, the question is, is that what's going on at the population level? I mean at in at some sense we know that no country or US state or Canadian province has ever had a birth rate as high as two and had an average age at first birth as as high as 30. Um but that doesn't mean that it's necessarily because of biological infundability. It could just be that that's the life that people are choosing. The real question we want to know is if people were more fundable, would we see higher birth rates? Um uh and so you know one thought experiment that we talk about in the book is to imagine a baby button. So you push the button and you get a baby. Um you push it again and you get another baby. Push the baby as many time push the button as many times as you want. You get that many babies. They're yours to love and care for and take care of and do so many things for years and decades to come, right? Um, and I think, you know, when you think about the thought experiment of a baby button, you know, you know, my family would have pushed the baby button um to skip those miscarriages um and it would have been glorious. We probably would have, you know, thrown a big party like a wedding or something and invited everyone we love and the picture of it would have been, you know, the biggest picture on our house or something like that and we would have had two kids. Um, you know, we would have we would have skipped the the sadness and pain of the the miscarriages and IVF and all of that. Um, but we wouldn't have had more kids, right? because an awful lot of the costbenefit decision of whether or not to have a kid happens, you know, after the baby comes out and is on the outside. Which is not to say that pregnancy and child birth and um are not, you know, painful, harmful, risky, and bad in many ways. Um and it's not to say this wouldn't make people's lives a lot better, but when you look at survey data of of, you know, people, you know, in their 40s, right, not that many people say that they want that many more kids. And so I mean I I think that that this sort of technology could be wonderful, could make many people's lives better. Let's invest in it. Let's make it happen. Um but if if the idea is that that's what's going to bring birth rates back up to two. I mean okay okay everything I say I'm going to say let's pivot to India. But I mean let's pivot to India right? That's a place where the average birth rate is below two. people tend to start having kids in their early 20s, have one or two or maybe three and then have permanent contraception surgery, you know, tubal liation um within their 20s um electively and then not have kids. So like that's not a low birth rate because of of people being too old to get pregnant. That's because people are having a small number of kids and choosing to stop. And so that's speaks to the fashion thing or whatever they whatever is determining their decisions.

Yeah. Cultural choice. Yeah. Yeah. Okay. So we we've touched on a bit and then we will obviously when we open it up get more into sort of the the mechanisms behind it because I imagine I saw like a lot of ideas coming up already. Um but before we go any further I would love to sort of tackle the problem of the common intuition that many people hold myself included sometimes. I feel myself wrestling with this. You know I come from a kind of environmentalist background. Um and that is this idea that actually we do have many very pressing environmental issues, not just climate change, one you know many different types. Um and generally speaking those are driven by humans and so more humans is bad and therefore fewer humans might be good. Can you talk through the reasons why that's well steel man it first but also the reasons why it's wrong.

Yeah. Okay. I mean, first of all, talking about coming from that background, you can Google like Dean Spears proceedings of the National Academy of Sciences and you can find a paper from about 10 years ago of, you know, me saying, you know, maybe something about population saving us from climate change, something. Um, so I I mean I think like it is a it is a a very reasonable thing to think. Humans have done harmful things to the environment. um uh humans pollute um with their economic activity and otherwise. So, you know, fewer people, fewer problems, maybe that's the solution and and it makes some it makes a lot of sense. Um but it turns out not to be that easy. Um so, so let me start with a story. Um so, in 2013, particulate air pollution in China was just awful. like little particles measured with a measure called PM 2.5 about their dynam diameter in the atmosphere over China. We hear about it from Beijing, but it was really all over. Um was just terrible. And the newspapers called it the air apocalypse. Um the US embassy said it was 755 on a scale of 0 to 500. Um and it was and to get to put that in perspective, like the average in the US that's acceptable is like 35 or something or 50. And even that would be pretty high. I mean that would be a bad day. Yeah. Um um um so really really bad, right? Um and so that was 2013. That was when like the air apocalypse hit the news. Um and then what happened next? So over the decade after that, the size of the Chinese population grew by 50 million people. 50 million people. That's more than like Canada or Spain, one and a half Texases, I guess we could say. Um and so a large increase in the size of the population. And so if more people are more environmental problems, then what happened to the particle air pollution in China? Well, you know that I'm telling the story. And so it fell. Um it fell by about half. Um and it's not just China. Um you know, over that same decade, the size of the world population grew by 750 million people and particle air pollution fell worldwide, too. Um and so it's because those people, all the millions of them, did something else. And I mean in the case of China, it was really about policy and enforcement and regulation. Yes, technology, but like using technologies that otherwise existed in other places um where people were, you know, burning coal or doing industry, enforcing rules, a little bit of enforcing it for for vehicles, but the bigger deal was industry. In other words, the the the powers that be made the decision not to do that anymore and enforce not doing it. And that turns out to be how we have made progress against environmental challenges. Every time we've made progress against environmental challenges, not by having fewer humans, but by having the humans do something else. So in the 80s when I was a kid, people weren't talking about climate change yet. What you heard about was the hole in the ozone layer. Um but and chlorofluorocarbons from your spray cans, right? And so we didn't solve the hole in the ozone layer by reducing the size of the population. We got rid of the CFC's in in the 70s. We didn't solve um um lead in gasoline like lead pollution by having there be fewer drivers. We got rid of the lead in the gasoline in the '9s with acid rain. It was it was the sulfur dioxide regulation. Right? That's how we invol solve environmental problems. And so yes, billions of us are going to have to live differently in as response to the climate challenges, but that's different from saying that billions of us need to not live.

Yeah. I mean, climate seems like a fairly to me at least a fairly cut and dried one because we are starting to see the decoupling between um energy and carbon emissions. So even if the population grows and energy usage grows over time the the carbon curve should at least sort of start to level off and and then an even decline. Um, similarly atmospheric pollution, similarly the ozone layer. That's an like that's like the glowing example of the time we had like a really big coordination problem effectively that's global and through various events including, you know, smart incentives, people getting together, but also we got damn lucky because it happened to be that it was like this big very visualizable like hole. You could draw a picture and put it on the news and go look there's a hole over the over the Antarctic. This is bad. We got to do something. Oh, and there's one simple mechanism and it's basically just this company, DuPont. Um, pretty much them. Uh, you guys are bad. Stop it. And they were like, "Okay, We better put some money into R&D." Some and found they found an alternative to CFC's. And and so, you know, it it's a beautiful example of us coming together to fix a coordination problem on that scale. But it's also one of the easier ones. And where I guess I'm a little skeptical is there are a number of other sort of they called planetary boundaries, right? these ideas of um the different processes on Earth um whereby you know if we go beyond a certain limit, it's not guaranteed that it's going to be bad and create some kind of bad chain reaction, but we're going outside of um our realm of certainty. And out of if there's nine different key processes right now, we've sort of gone beyond the realm of certainty on six of which climate change is one. And some of those other ones, it doesn't seem so clear to me that we are decoupling. for example, um the nitrogen fixing, uh you know, the fact that like there's all this utrofication and leeching of um important nutrients out of the soil and going into our waterways. Um we're way beyond the realm of like normality there. Uh similarly, water usage, fresh water. Um and then like all of the novel particles that we're just spreading all over the world like PAS and antibiotics that are going into the soil. And so there's this like I guess there's many of these different other ones and it's not clear to me that population levels are sufficiently decoupling fast enough. So I'm curious what your thoughts are.

Absolutely. We we need to do more. Like I'm I'm not here saying that what happened in China to reduce particle pollution was in any sense like automatic or historically determined. I'm saying that actors made decisions and and and and things changed, right? Um so I mean I think you know on on climate change as you say that's sort of an easy one because it's just a a matter of timing. Um you know we need to decarbonize relatively quickly. Some people say years like 2030, some people say years like 2050. Either way, um um you know, if you have a baby today, by the time that baby grows up and is deciding whether or not to have babies, you know, enough decades will have passed that we'll be at that point. So, I think, you know, climate change is just too urgent. We can put that in a bucket. What about other things, right? Th this isn't me saying that the solutions will be automatic. This is me saying that we need to solve the environmental problem the way that we have solved other me environmental problems which is taking them on headon and not saying reducing the number of people is the way to do it. And you know, remember when we talk about, you know, limits, right? I mean, that's that's the sort of way that Erlick would have talked in 1968 that we we can just only have and only feed so many people, right? And and and to him and to a lot of people at that time, that just seemed, you know, more than self-evident. But in fact, on every continent and every decade, food availability has gone up. And it's, you know, not just food. You see the improved nutrition in people's bodies. I mean I mean since in in the couple decades that I've been working in India, you see that the average kid in India is taller than they used to be. um you know they're eating better food and they're having less disease and so and so people would have thought something very similar about a hard limit on the number of population about nutrition and you know through the intentional action of you know of researchers and and policy makers and and innovators um um we got better at growing food and so I think I think that's that's the that's the response to the environmental concern. What we need to do is take the problems head on and not some sort of bankshot through population size.

Yeah. And I mean it does seem like a lot of again this keep mentioning Paul Erlic but he's such an archetype of this. Uh it his whole thesis maybe someday people will sit around and say gosh that spear is he was sure wrong about everything. That's what that's what I can hope for. Yeah. It's a nice guess it's a good outcome if that's that's the case. But um yeah, it's it's it's a form of false zero sum thinking um which can be incredibly damaging because it's it's if you make policies based on the fact that oh this is a completely fixed pie and there's nothing we can do and we can only divide it up and you're just neglecting all the sort of well frankly known unknowns but even unknown unknowns that can come through human innovation and that's where you end up in these really dark places I think um quite regularly. Um, and actually you made a a point when I was reading through your book that I had not considered before, which was really cool that made me like grock this idea of actually more humans are better. For example, with something like climate change, yes, okay, we're currently producing more carbon, but at some point we're going to reach this peak and then it's completely decoupled and we're going to have so then it doesn't matter if we have more humans because the energy they're they're using is not contributing to climate change. But if we have fewer humans, we still have this like surplus of carbon in the atmosphere, right? We got to do something about that. And if now our population especially like the sort of okay like scientific research population which is arguably one of the biggest dem you know demographics that is reducing the people who are likely going to be inventing carbon sequestation technologies and all of these other ways to try and draw down this excess carbon they're not having babies there's fewer people to actually try and find the solutions to get rid of this um this surplus. So that that was like a really good point that I feel like or just to manufacture the machines or plant the trees or or split up the rocks for the weatherization process, you know, you know, I I think, you know, I don't think this is like the first paragraph of what to say about population, the climate, but I think it it is important that, you know, one day we're going to have a big negative emissions problem that that will have reached, you know, zero per person net emissions and Then we have the negative emissions problem of needing to suck the carbon back out of the atmosphere. And so what do you think is who's what's going to what's going to do a better job of that, right? A bigger or smaller world economy. It's sort of funny. This is one of these things that we discovered by accident. we were um doing we had taken um the you know Nord house climate economy model that he got the Nobel Prize for and we're sort of you know he sort of takes population as just an input to his model right and um so we were saying in that model what if we vary the path of the population you know then how much of a difference does it make to climate change and that like peak temperatures and the answer is not very much um but we sort of discovered by accident and I sort of like I I first thought that like the the posttock research scientists on our team have made a mistake. were like, you know, Kevin, go back and look at this again. But like, in fact, the larger population ultimately leads to lower temperatures in the long run. And it's because the model did allow for these negative emissions where, you know, a larger economy that's doing more can plant more trees, split up more rocks, whatever it is. And so Exactly. So, it can it can just exactly go the other way. Right. And and another point you made was uh that certain big risks that we might face or problems are very much a fixed cost. So, okay, I don't think asteroids are likely to be happening anytime soon, but let's say an asteroid was coming to Earth. Which population size is more likely to actually deal with it? 10 billion people or 1 billion? Like given it's going to cost, let's say, 10 trillion or some huge proportion of GDP? Um, and again, like that sort of made me go, huh, okay, we we do we do actually need more people there.

One objection I often hear though to this idea of uh okay well sure the population is going to decline um but aren't we moving into the age of AIs even AGIS and automation robots can't they just fill the shortfall yeah

I mean, so you know, there are people here who know more about that than I do um but you know I think nobody knows everything about what's going what AI is going to bring I mean there are some economists like Eric Bolson who think that maybe we're going to see like a 7% improvement to GDP or something like that. There are some like Deron Asimoglu who would say like you know a 1% or something like that. I mean you know nobody really knows but I guess the question is like what is AI going to do to the marginal product of humans, right? like if if we're so I mean we sort of haven't gotten into it but like like just to sort of we're sort of you know part of what we're saying in this book is that other people are as you say win-win um that you know their lives are good for them and their lives are good for you. We're we're made better off by being in a world with other people in it. Um and you know there are a number of reasons for that. One is that when other people want and need the same things that you want and need, they make it more likely that you'll get it. um you know where are you going to find you know uh u an event like this in a space like this? Are you going to find it in a city with other people in it or in a depopulated rural place? Well, of course you're going to find it in a city with other people in it, right? Other people make it possible for the things that you want to happen. Um but another part of the case for people um is as you say that people create things, people invent things, people discover things and realize things. you know, why do we have better lives, longer lives, glasses and antibiotic pills and vaccines and and microphones um that people a few hundred years ago didn't. It's because of the knowledge that the people over those couple hundred years have developed. And you know, one person learns an idea and other people can learn it and build on it. you you have a kid, a sick kid with an infection, you give them an antibiotic pill, that antibiotic pill is gone and used up forever, but the formula of it is still there for somebody else to use again. Um, and even more than that, the knowledge of the germ theory of disease and the basic understanding of what it's all about is still there for other people to use and innovate and build on. And so, um, that's called the theory of endogenous growth. Um and um and it's an important part of how macroeconomists understand why our living standards are are higher than in the past. And what's the core thing there is that we're better off because of what other people have learned. Okay, great. So that's part of the case for people. And then and then Liv comes along and says, "But what if we're not going to need people anymore, right? um you know what if um you know what if AI does all of that thinking and learning for us? Um and so and so it's true like you know um I mean the first thing to respond is there's at least some important probability that we're going to be in a world where we you know need people to be doing important things for a long time. And so you can scale everything I'm saying by that probability. Um and you know that's that's the cheapest answer. Um but you know there's there's a more sophisticated answer which is that um you know for this sort of discovering things work that people do you know AI might turn out to be a substitute for humans or AI might turn out to be a compliment for humans and increase the productivity of other people. Lots of other technologies have been have been compliments for humans. Right? So when um when spinning yarn when was mechanized right that was a substitute for what humans did nobody did that work anymore right but when um but when um you know factories themselves with powered by water came online that was a compliment for human productivity and made humans more productive. So you know one possibility is that new technologies will be a complement for what humans learn and discover in which case the case for people will be all the stronger. Now I'm a demographer. I don't know which of those is what's is what's going to happen but I just want us to to raise the possibility quite possibly AI not only leaves space for humans to continue to contribute to progress but actually makes humans more productive. Plus also it would be very sad if again like we are missing current projections in I think is it 50 years time there'll be about a third of us or twothirds of us um a third of us won't be here or imagine your family like all those missing people and it's nice I would rather be friends with humans than robots. Um I'm sure the robots are going to be great but or both but I mean I mean but um yeah I mean um I guess the question is how many how many robots make up for one human? Now we're getting into the utilitarian Well, right. So part of the case for also, you know, I said part of the case for people is that they want and need things and sort of they economically demand things, right? Like you want there to be other kids who like if you're like a parent, you need there to be other parents so that your kid can have a a school, right? And and like you need other people to to need the things you need. you know, when my mom was sick with a rare form of cancer where where we lived in Oklahoma, there wasn't, you know, well, first of all, only 640 people had ever had that cancer um since the 1970s. So, nobody knew anything about it. But even in order to learn that, we had to drive to a big city where there was a hospital where there would be a doctor who would even sort of know that fact, right? If what you need is specialized treatment, you need other people who need that. If what you need is a kindergarten, you need other people who need that, right? and the AI isn't going to do that same wanting and needing for us. And so that's another thing that we might need other people for. And finally, as you say, part of the case for people is that they make us better off, but you know, we're here to talk about win-win. And part of the case for people is that, you know, we might think that there's value in people getting to live good lives.

Definitely. So what are in your views the best strategies to try and get people um all over the world but especially in the countries where the rates are at their most lowest and the problem is most drastic to actually get them to start having more babies?

I in case you've been waiting I'll I'll I'll disappoint you right now. I don't have the solution with a capital S. Um I I don't think anybody does yet. Um, you know, I think what we're it it would sort of be preliminary, I think, to be saying, here's my legislative proposal or something because we're not yet in a world where there's even

Much of a anything like a consensus that stabilizing the population would be better than than depopulation. Where, you know, we're raising the question. And and frankly, what we're trying to do is say you can be a person who cares about environmental stewardship, who cares about reproductive freedom, who cares about gender equity, who cares about all sorts of priorities, and also care about birth rates and the size of the future population. That we're trying to bring more people and more voices into this conversation so that maybe someday more of us will think that, you know, we shouldn't just accept depopulation as default, and that stabilization might be a a better future.

But you know, when I, but I'm not like hopeless about thinking that we don't have the answer. Um, because I sort of think about that we're, you know, the UN projects the size of the population to peak in 2084, six, six decades from now, right? Maybe it'll be that, maybe it won't. But, you know, six decades ago, um, was the 1960s, when there was, you know, first starting to be some policy attention to climate change as a problem. So, you know, Johnson gave a speech to Congress about burning fossil fuels and and, you know, that wasn't the beginning of people collecting data on it, like Arrhenius had done, like atmospheric chemistry calculations that were pretty close to true even before then. But I think there was something notable about what people were thinking and talking about six decades ago. Um, and, you know, six decades ago, if at the beginning of the climate policy conversation, somebody had just stood up and sort of spouted off whatever policy prescription happened to come to their mind, it probably would have been ridiculous. It wouldn't have been fact-based and it would have driven people away, right? Saying like, "We're going to get rid of the internal combustion engine in 1965," um, would have made you political enemies. Um, um, but it's good that people were talking about the challenges of climate change back then, even though we didn't yet have the journal Nature Climate Change or college majors in it, or all of the technology and knowledge and social movements and political movements that we have now. It's good that people were talking about climate change back then, six decades ago, because it's because they were talking about it back then that we know so much more now.

And so, and so the hope that I see is that we're starting a conversation now, um, you know, several decades before the size of the world population is projected to peak. And, you know, more people are going to learn and talk about this between now and then, learn the facts, start thinking about what might be different. And then it does, I think, go back to what you were saying about, um, social influence can be win-win or it can be lose-lose. Um, you know, none of us is born in a with like a an ideal fertility rate imprinted into our DNA somewhere, right? That's something that that, you know, develops over the course of a life and changes over the course of a lifetime, for that matter. It depends on what we see other people, uh, succeeding with, what we see other people rejecting. It depends on the world around us. It depends on what we make easy for people.

So, you know, if if we were to as a society come to decide that stabilizing the population would be better than depopulation and that we were going to find a path to that that perfectly preserved people's freedom to choose to parent or not to parent. Two on average doesn't mean two for everybody, but if we were to sort of make the investments that supported people who did want to choose to parent in a really big way, right? I'm not talking about like a $5,000 child tax credit. I mean, how many of you would marry somebody different for $5,000, right? I mean, like that's not the amount of money that's going to move people's family formation decisions. But if we were in, well, I see a hand raised over there. If we were, if we were in a really big way going to invest in taking better care of our caregivers, doing more to share the work and making the next generations dads, doing more to share the work and making the next generation, then maybe we would see more people feeling like they could fit that in to the life and goals and education and work that they want. And probably not immediately, but maybe the next generation after that would learn from that example, and the next generation after that would learn from that example. And then maybe people would start wanting something different. But it, but, but it's not going to be, it's not going to be turnkey in any way. And I, and I think it starts from a broader recognition that maybe stabilization would be better than depopulation.

Well, in the sort of spirit of getting more voices in, and I know that there's a lot of burning questions, uh, let's open this up. Um, feel free. I mean, from my end, I would love this to be as much an exploration on like what we can do on to try and solve this, but if any of you have objections or further questions that I haven't touched on, then, then use that. Adrian was first. So, I may have missed something, but if I gather correctly, since population has been declining for, um, as long as we've been keeping records, or birth rates have been, right? The population? Yeah, birth rates. Does that mean that modern birth control hasn't really had an effect on birth rates?

That's a great question about about contraception, right? So, no doubt contraception is very important in people's lives. Not having contraception I is, you know, bad for people's lives, especially about, you know, everyone should have the opportunity to choose whether to be pregnant, not to be pregnant, not to be pregnant right now, to wait for another time. And, you know, having access to contraception and abortion, you know, to let people make the decisions in their lives and decide when to be pregnant, that's very important. And it's a further social scientific question whether the decline in birth rates can be accounted for by the spread of modern contraception. And just as you say, we see birth rates falling and and people controlling their fertility in other ways, you know, spacing and timing, um, before the existence of modern contraception. And we also see birth rates continue to fall, um, in places that have had access to modern contraception. So, you know, um, uh, Sweden happens to be at the top of my mind. Um, about a decade ago, it had an average birth rate of 1.8. I think now it's maybe like 1.5. That's, you know, not because, um, hormonal contraception, other modern methods only came to Sweden, you know, 10 years ago or something like that, you know, so it doesn't explain the continued fall that we're seeing from a number like 1.8 to a number like 1.4. So, so yes, people should have the healthcare that they need of whatever form, including that, but I don't think that that's really the statistical, that that really fits the facts.

See a spike when modern, uh, birth control was introduced. I don't exactly know. I mean, I can give an example of like in Romania in the 1970s with Ceaușescu's decree 770, um, contraception and and abortion access were suddenly banned and removed overnight. Um, and so like you're talking about a spike made me think of that, cuz you do see a big spike in birth rates, right, when that happens. Um, but then what you see is over the next decade or so, birth rates continuing to fall. Um, you know, more or less at the same rate that they would have, that they were falling in other sort of middle-income countries. Um, and so showing that, you know, people were making decisions and, you know, making, um, family formation decisions of other forms, you know, using, you know, other methods. Um, and so, and so yes, so, so what does that tell us? I think it tells us that like if you surprise people by taking away a method that they thought they're going to have access to, that could be suddenly really destructive. Um, and then in the long term, um, you know, populations are on average able to pursue what people want. Now, that doesn't mean that everybody gets the parenting life that they want. Far from it. On average, you know, nobody gets the exact parenting life that they want. Um, um, but, like you do see that on average there's a pretty clear correlation between the average number of kids that people want in a society and the average number of kids that people have in a society. It's not perfect. It, the lines cross one another, right? It's not like exactly tracking the 45-degree line, and, and, you know, the deviations are really interesting and fill interesting journal articles. Um, but like the, the R-squared, the correlation is pretty high, like, you know, at the population level, uh, what societies get tends to be pretty close to at the population level, what societies want.

Cool. Um, yeah, I've read the studies around disaggregation of all the causal factors around urbanization, contraception, education, all those things contributing in different ways. My my question is, are there subpopulations in India or in other urbanized economies that are modern that are going the other direction where they've not only where they've been able to sustain, you know, at least, uh, you know, population stability, if not population increases, and what have those subpopulations or sub-policies or anything else done differently than those around them?

That's a great question, and we, we get this question enough that a couple years ago, we put a paper in the journal Demography, um, you know, about, you know, can, can high birth rate subpopulations cause positive long-term population growth? And like the answer is like, it's mathematically possible, but it, you know, empirically depends on a couple things being true, right? So, the, the high birth rate subpopulation has to stay high in the sense of above two, generation after generation after generation, right? Um, and so, you know, the answer to your question for India is, you know, you can split India into 16 different groups, you know, Hindu, Muslim, rural, urban, educated, not educated, whatever, you get all 16 lines, you know, some are higher and some are lower, but all 16 lines are going down, right? So they're not all below two yet. Um, but, you know, people in India, like Hindu politicians in India used to say, "Oh, Muslims have more babies than Hindus do," right? Um, and Muslims do have more babies than Hindus do, but it's gone down for Muslims, and it's gone down for Hindus. And so, if even high birth rate places are above two, you know, like Utah, for example, is like every other state below replacement. Um, is it okay? I say, like, Hasidic Jews in Brooklyn and Mormons were the two that came to mind in the US. Yeah. So, I mean, the Mormon birth rate's around five right now, and it used to be higher than five. Um, and, you know, so we get the question of Mormons a lot, right? And so, you know, you know, at the simplest answer, the birth rate amongst Mormons, not Mormons, Amish. I, I'm sorry. I apologize to anyone listening to this. Um, so hard to be in the academy where you have to just pretend like you have to hold both sides of your opinion all the time. That must drive you crazy. Um, I actually don't know the, I don't know if there is an estimate of the birth rate amongst Mormons.

Does anybody know that? Like I read somewhere it was around fourish recently. I heard it's increased heavily to 2-something again, but I'm not sure. I thought Amish are the only US that is still managing to stay above. So Amish is, you know, higher than average, but also falling. Right. Right. Yeah. Used to be over six, now it's like four level or something. So, I mean, the example that I like to talk about is the Catholics of Quebec, um, in Canada, because, uh, this is exactly what I was looking for. Um, because really, um, because this is like super niche. I would never have known this. Yeah. Because, um, my my co-author Mike, uh, his mom grew up speaking French and, you know, descended from the, the, you know, Quebecois Catholics. Um, and, you know, where birth rates were numbers like 10 or 12, right, in the mid-20th century, um, and, um, so not that long ago, right? Um, but, you know, we're not having this conversation in French with a Quebec accent, right? The Quebec Catholics have not taken over the world, um, and that's because birth rates there fell. Um, you know, Mike, um, has one other, um, and, you know, so on. So, so I think it's easy to have like survivor bias or hindsight bias, um, and talk about the subpopulations that we know about, but there are other subpopulations like this that anybody would have picked out, um, as as a candidate, um, for, you know, "this is going to take over the world," that have then not done so because birth rates have fallen. So, it's not enough for your birth rate to stay high. If what high turns out to mean is 1.9 instead of 1.5, um, that wouldn't cause positive long-term population growth. So, so, no, there really aren't.

Um, yeah, suppose we should let some women talk as well. Yeah, actually, that's I was going to say my hot take as a as a woman, but not just a woman, but a career woman. Um, I actually do feel like it's the Industrial Revolution, um, as a as one of the causes, but not for the reasons cited. Um, from my perspective, I actually feel like there's this perceived dichotomy for many women that I've spoken to where either you get to have a fulfilling career or you get to have children, have a vocation or have children. But I just feel like our ancestors simply did not have this perceived dichotomy. Pre-industrial life, everyone contributed. And the concept we, uh, that we now have, the 9-to-5 career only really existed after the invention of the assembly line. Um, and so pre-industrial revolution, you know, we didn't live that way. Um, everyone, all hands on deck on the farm, whatever. If you had a store, your kids came in, they helped greet customers, right? So, um, our education systems and workforces, they still model this assembly line model, this 9-to-5 model, especially with AI. Do we need that anymore? And so, um, I feel like that's largely not conducive to family systems. And it's funny that you brought up South Korea, cuz I spoke to a diplomatic delegation from Japan and South Korea of women in STEM, and they couldn't even fathom the concept of having children in the workforce. And then one person in the room, I forget like which country she was from, but she was talking about during the pandemic, they did, and it kind of changed everything for her. So I actually, you know, I wonder if we could just change the model for how we integrate children into our lives post-AI, post-industrial revolution. And like just thinking about it in a way where, um, to like cite win-win, it's like, why, why give up career? Why? Why? Uh, because you hear a lot there. There really is just on the media as a woman this perceived concept that either you're a stay-at-home mom or you're this career woman. Well, why not both?

Yeah. I mean, I'll say, you know, on the question of being a stay-at-home mom or working. I mean, let's also point out that, uh, dads can do more, and maybe that'll be part of the answer, too. Um, but I, yeah.

Hi. Um, the question I had was kind of focused on some of the, uh, two core costs of population decline that I see that, um, you didn't touch on. I'm, I'm, I'm curious. I, I imagine they've occurred to you, but maybe there's a reason not to bring them to attention, but I, I agree with your key point around like there's not yet a general cultural consensus that population decline is a problem and like maybe stabilization is a better idea. Um, some frames that I found particularly powerful is that the Social Security Administration was introduced in order to try to take care of elderly people who are in desperate poverty. We don't want elderly people to be starving to death and horribly neglected medically or financially. Um, and we've been able to support elderly people in our civilization when we have a handful of working people who are able to support each elderly person. I don't know what the number is right now. Maybe it's three or four working-age people for every elderly person who's retired. Um, I think it was about nine months ago that I asked ChatGPT to help me do the math. If we extrapolated forward the birth rate of the United States today for a number of decades, I think it's 1.7, 1.8, something like that, um, what would need to change in terms of the tax burden on working people, uh, in order to keep stable the, um, support that retired people received, or on the flip side, if the tax burden as a percentage of income did not change, how much would their support, um, reduce over time? The numbers were pretty brutal after 50 years, which I'm sure you're familiar with. Um, so that's like number one: Do we want elderly people not to be in desperate poverty? Um, and I think there's also a significant challenge around like, do we get to keep having democracy if there's four elderly retired people for every working-age person? Because it's not clear to me that that's true. If the, if the elderly population that votes at higher rates keeps voting for more and more money to be extracted from the working-age population in order to make sure that they maintain a decent lifestyle, I don't know that we get to keep having democracy. So, I, I think those for me are some of the harder-hitting points around like, whatever your perspective around climate change is, whatever your aesthetics around whether humans are good or bad for the planet, if you want elderly people not to be in desperate poverty and you want to keep democracy, we probably need to stabilize the population. Um, so those are, those are hard-hitting points for me. I imagine you've come across them. I'm kind of curious what your perspective on is, is that a good meme to spread, or is that maybe a bit too confronting, perhaps?

No, no. Um, in fact, I'll say you sort of, um, anticipated my semi-interesting thing. You, you took my bit, um, about age and voting. No, no, I'm just kidding. Um, but, uh, yeah, so I, you're right. If you, if somebody told you an economics professor was going to be sitting around talking about low birth rates, then you would probably assume the conversation is going to be about the age pyramid of society and government budgets and things like that, because that's what you hear about the most. And I think like the main reason that, uh, Mike and I don't talk about that much in after the spike is that it is something that you're sort of hearing from other other places. Um, um, um, you know, we think that this, that these other really big parts of the case for people, um, you know, about, um, about progress, about, um, you know, other people making things possible when they want it, and yes, about the, the value in getting to live a good life. You know, we think those are sort of underemphasized by comparison. Um, so that's a big part of why we talk about it. Yes, I think you're right that one of the, um, okay, you know, so the median age in the US population, um, in 1950, I think was 29, um, and in the last 75 years since then, has increased by nine, uh, age years, um, to 38, and is projected, um, over the next 75 years, over an equal span, to increase by seven age years to. So, so the increase in the, the median age in the US that's coming is actually smaller than the increase in the median age in the US that, you know, for better or worse, one way or another, by hook or by crook, has gotten us here. Um, but one of the things that, so make of that as you will, but as you say, I think it will shift voting patterns. And so back on the question of environmentalism, I mean, we know that younger voters tend to be more environmentalists than older voters. Um, and so, you know, that's one thing that might shift as, as the age structure of the population changes. We, you know, we should expect, you know, voting patterns to shift with it. Now, is that the, is that the meme that's going to get people interested in learning these facts and talking about this question? Your guess is as good as mine on that.

Are there structural or economic incentives that have proven effective in increasing birth rates?

Yeah, I mean, I think not really, right? Um, there can be a short answer. Um, um, not, not in terms of long-term lifetime birth rates, right? If you offer somebody an incentive, you know, it's a, you know, let's just say that I were to go and give you $5,000 if you become a parent in the next three years, right? You might do it, um, but then not have a kid that you were otherwise planning to have six years from now. And so, so I've accelerated when you have a kid, um, but I haven't changed your lifetime average number of births. And so, so that, so, so we call that like the tempo versus the quantum of fertility. And that's something that makes it really hard to study and learn, like from the effects. You know, you, you can do your, your fancy, your fancy statistical study of an effective policy on birth rates, but are you just studying the tempo or the timing of when people have their births? Are you studying the lifetime differences in birth rates? And I think when you study the lifetime differences in birth rates, it's really hard to find, um, lasting effects. Like, remember the thing I said earlier, would you marry someone different for $5,000? So I think that like what really matters, what really influences me is bigger picture evidence, like, you know, university is free in Canada, and the birth rate is lower, right? You know, things like that, in terms of nothing. You know, even countries that think they have policies haven't brought us up to two. And, and here's this one, um, in, so this thing that matters, the completed cohort fertility, how many kids you have on average over your whole, your whole adulthood, right? So you have to be a relatively rich country with good statistics to even be able to compute that as opposed to like a cross-sectional survey, but for the places where we can compute that, there have been, uh, 26 countries where since the mid-20th century, um, we've seen completed cohort fertility fall below 1.9. Um, right. And in lots of those are places where countries think they have policies to increase birth rates, or, and lots of them are places that have social safety nets and all these policies they were talking about. And some of these are places that don't. But of those 26 that have ever had completed cohort fertility fall below 1.9, zero of them has it ever gone back up to two. Um, and so, you know, that doesn't mean that it's impossible, but it means that there's not a precedent that we can draw on.

I asked so many questions. No, the, um, first question I have is kind of like a, uh, the academic. Has anybody ever studied, we always talk about infant mortality, but what about the probability of getting a kid to 18? So, in Lincoln's time, death was rampant, right? People, a lot of people, maybe they, they survived childbirth, but they didn't make it to 18. And perhaps, um, has there been any study or has it been embedded kind of in the hive mind that I need to have five kids to get two kids to 18? You know, go further back. I need 12 kids to get, uh, two kids to 18 or or to get three kids to 18 and out on their own. Has that any, has there been any data or study on that as opposed to just the infant mortality part?

Yeah, absolutely. So like, sort of pre-adult mortality. And so like there's a paper by, um, Stuart Guttentag and co-authors that sort of goes through for states of India and computes just this number you're saying of like, what, because, you know, in a, in a state where the, the pre-adult mortality rate is higher, the replacement birth rate would be higher. And so the replacement birth rate might be a number closer to two for a state in the south like Kerala, but closer to three for a state in the north like Uttar Pradesh where pre-adult mortality is is greater. So, so yeah, absolutely. That's, that's a great question. Um, and then I'm not yet on the camp of stabilizing population is a good thing. And I, I want to stay on one vertical to not like dominate. Was I want to push back on the AI and embodied intelligence because we talked about it being more productive. The ability to enhance humans in order to create and do things. Doesn't that mean we we can get by with less humans? Maybe a population of 1950 or 1980. Like we're talking about trying to change. People have run the experiment and people have said my quality of life is better with two kids or less. And you know, I tell people, one kid's an accessory, two is a circus, right? And so, and I'm a parent, right? Like you have one kid, it's an accessory, you can get by. You can do anything. You have two, it's a circus. And then three, it starts to get crazy, right? And I think hidden in the data is people's choice is that I have a better life, a more fulfilling life with less kids. And here we are trying to, you know, talk about, hey, for the good of my neighbor or some, you know, other out there, you want me to have a less fulfilling life by having more kids. I mean, it's just like kind of smacking us right in the face.

Well, that's not what I'm saying, so I need to jump in. I don't, I don't think that anybody is making necessarily a mistake if they look around the world that we have and decide that not being a parent or not having a kid isn't the right decision. What I am suggesting is that we might all be making a mistake as a society if we're not choosing to build the structures and make the investments that would allow and support more people who want to be parents to choose to do so. Um, that's, it's a, it's a very different question. I think that we can agree that parenting should always be a free choice. Um, and that doesn't specify everything about a society. So, you know, the law says that parenting is a free choice, abortion is legal, and contraception is legal in France. And the law says that parenting is a free choice, and abortion is legal, and contraception is legal in South Korea. Um, but the birth rate in France is more than twice what it is is in South Korea because there are other things that matter for the decisions that people make for their lives, what they aspire to, and what they feel like they can achieve. And so this exactly isn't, um, me or, or I mean, I don't know what I mean, or saying that, um, that, you know, that individuals are making the wrong decision. It's me saying we should be starting a conversation about what sort of of equilibrium we might want to build towards, you know, over the years or decades. And that maybe that's one where we want to do more to share the burdens of costs of creating the next generation. Do more to to make it easier for people. Do more to to pitch in and help. Um, um, so that it's not all, you know, landing on the, you know, few years in working-age adulthood where you're parenting and having your young kids at the same time. Um, you know, I, that's the question that I, that that, that I think we should be talking about. That that presupposes the new tools and AI don't augment and fill the gap of less humans. Right. How do we know that? How do how do we know that a million robots are only equivalent to four billion humans?

Okay, so this brings us back to that part of the case for people is the the case from, you know, the, you know, endogenous growth macroeconomics, that growth and improvements in living standards come from improvements in technology, which have generally come from from discoveries from other people. Now, one question you're raising is maybe we don't need people to do that anymore. Um, I mean, you know, maybe yes, maybe no. Maybe AI will be a substitute for human innovation. Maybe AI will be a complement for human innovation. Maybe AI will free people up from doing that work so that people end up doing something else productive for one another, and we still need people, but to do something else. I think all of those things are possible. And even if I knew for sure that we didn't need, um, people to be doing the innovation, I would still think that there would be an important case for people. Um, part of it is what I said is other people wanting and needing things that that people are good for you, even when they're on the demand side of the economy. But I think another part of it is that, you know, this invites the question of, does it matter how many people get to live a good life? Um, you know, if, you know, what, what a lot of people don't talk about when we're talking about this is that, you know, one path is a path where many billions of additional lives could get to be lived that could be really good and wonderful and valuable and full of happy experiences for the people who live them. And so, one question we should ask is, is would the absence of those lives be, you know, would it be a nothing? Would it be something to celebrate, or would it be a loss to mourn because of those experiences in it? And, you know, I, I don't expect that I'm going to change anybody's mind on this question or settle it right now. But, um, you know, to give my answer, I would say that I think that, you know, more good is better, and that that includes the good of getting to live a good life and have good and happy experiences. Um, and that it, that it does matter that, um, you know, if people don't get to live those lives now. To say yet again, the fact that something matters doesn't mean that it's the only thing that matters, and it doesn't mean that we should, you know, take away people's choice or impose it on anybody. But when we're thinking about which path should we build towards over the long run, perhaps one of the things that we should be asking is, is it better if more people get to live and experience good lives rather than fewer? Now, I suppose you could come back and say, maybe AI is going to have good experiences and do all of the enjoying for us. Um, I would say that I would just say that the, the, the net sum total of fulfilling lives would be higher with AI and less people than with more people. But you can't go there forever, right? Because like, what if you have one person and infinite AI? No, I, I, so there is some, something where it's still better. You know, I'm nobody, but I would say stabilizing at 10 billion is not the optimal point. You have to, this is important. Let's talk about this, right? Because I'm also not saying that we should stabilize at 10 billion. Nor am I saying we should stabilize at 8 billion or 6 billion or any other number. Right? I don't think that anybody knows or could know the number that we should stabilize at. I think, you know, that would be sort of beyond what we could hope to know. But here's what I think is fascinating. If you think that we should stabilize the size of the population at some level someday, then you're on the team of needing to find a good path to an average birth rate of two, needing to raise the birth rate at that someday up to two. Is stabilizing the population at any level, even a level much smaller than today, will someday require an average birth rate of two. And that's something we don't know how to do.

If we had fewer people, what would that actually mean? Like, if you look at a family photo and you have currently five people in that family photo, that family photo would have had only three or four people. Is that something you actually feel as happy about having had as a family photo as the one where you had five people in? And I think that the answer for most of us is not. If this room in South Korea, where if we were in South Korea with this room in two generations, we'd be 17th of our age, like people. It's like, sure, we might arrange ourselves differently. Where there we are still finding like ways to be 30 of us. There are fewer groups coming together talking about fewer various things. That seems pretty bad. So like, in, I, I, that's just on the other side of the equation. I'm not sure where it ends up, but like, that's something to consider. Usually we like the people around us, and the more people we have, the kind of like more fits and better friends we can also find and better partners. You know, the whole, like, is there someone for everybody? Well, not if there's only like, uh, very few people, then there are like some very good ones, some very bad ones.

What if the hive mind of the world has already solved for the optimal number and that's why birth rates keep going down?

No. So, so maybe. But I think, and so, and that's what I wanted to get to is when you said this point about the thought experiment, I actually wasn't initially into the thought experiment about pressing the button to make the baby because I thought, uh, the obvious answer is like, well, I often wake up with a hangover and a baby very, very frequently, in fact. Or if Liv tells me, "Oh man, should we, should we?" Is not just a button, right? Maybe. Exactly. No, but, but, but that's exactly. I think what would happen because that is what we also see with policy in countries when they enact something, right? It initially has an effect and then it falls back down to what it was. So I think the button after hangovers would end up with, "Now I protect the button very heavily when I go out drinking." And it's like, two keys in the nuclear submarine or something, which, which, exactly, don't, don't touch my button. It's, it's, it's the red button. It's a very important button.

One consistent thing across populations, across demographics, well, across subpopulations, also, that overall, there is definitely a trend to more energy per capita use, more like wealth per capita. And the thing that comes along with it is more opportunity per person. So the thing that seems to be most consistent around this, if I was to point at like a single thing that is the most consistent, it's not female education or something, it would actually be just the broad scope of opportunity costs of having a child. And Bill's point of, yeah, but maybe we're like discovering kind of like our own personal net fulfillment. But I think that comes, if I was to take the economics lens, from we've been increasing the benefit from other ways of spending time, but we've kind of nearly had a fixed cost of having a child throughout generations. So like, if I take the economics lens and like the other way to reduce the opportunity cost, like if I was a supervillain and I wanted more babies, I'd reduce female education. I'd make us poorer, and we'd have more babies. And I'd increase infant mortality, and we'd have more babies. Terrible answer. Let's not do that. I think maybe the silver bullet is the opportunity cost lens. It's just that it consists of so many things. And maybe the reason we don't see, whenever a country tries to do subsidies, cash incentives, all of that, they only ever give like 10 to 20% of the lifetime cost of a child. Anyway. So the thing I wonder is like, are, do you see the reduction of all of the things, maybe being sufficient in total, like where we make it easier? We increase the cultural appreciation of mothers. We increase the, uh, fertility range of age. We, um, just like really many, many things stacked together rather than these 10% things.

Mothers and fathers, I want to say, and caregivers of all types. So I think we're going to have to share these costs, um, as part of it. But yes, I mean, we wrote this book because we think that something different might be possible. Like, if we didn't think it was possible to shift away from depopulation to stabilization, then we, then why would, why would we write this? Why do we do this? Just because it, and I think that's what we learn from thinking of, you know, cases like the long-term response to climate change, um, that you can, you can make progress towards something even if you don't know at the beginning how you're going to make progress towards it. So, so I don't have the solution, but I, but exactly for the reasons that you were getting at, Liv, about, um, about, um, you know, social influence and that nobody's born knowing what they want. I think if we were to radically change our support for for caregiving and parenting, um, then, you know, over the generations, we could create a situation where, by expanding people's opportunities, right, by letting people fit more into their lives, we could have people growing up and seeing a model where you can be a parent and, and have kids and do other great things too. And yeah, I think over, I think over time that could shift what people come to expect, what people's vision of a good life is. It's not just going to be a few thousand dollars. It's, you know, it starts with the incentive, but it doesn't end with the incentive. I mean, you know, right now it's summer, which means that my big kid isn't in school, and I have to do something else, and that's a huge pain, right? I mean, it also means that he's not learning, um, or at least not learning in the same way, which also matters. And so, I mean, there's just so many things that we could do, you know, so, so, you know, what my spouse says is like, what we need to do is get rid of the nuclear family, and we have to all like live together and take care of the kids like that, and as long as we insist on the nuclear family, we're hosed. And I don't know if she's right or she's wrong. Uh, I'm just trying to say maybe it's just a problem with me. She has like, what we need to get rid of is being married to you. But, um, what's y'all's thinking about adaptation? And my, I'm coming from the assumption that, yeah, more humans typically is good, but it seems like if it's so bad at a certain point, obviously everyone will realize that and we'll start having more kids. So are, is there a fear that it just will be too catastrophic too fast? Or the fail, like the proposal is birth rates get low, people look around and say, "Hey, birth rates are really low, maybe exactly for that reason, in sort of a pro-social way, we should choose to have more kids." Yeah. Or alternatively, because if we, again, we look at history, it tends to be that when the world gets kind of shitty and poor, and everyone's doing badly, what happens? No one has anything else to do but have sex and have kids, right? No, but it, it seems like there the opportunity, because if the world has gotten shitty, everyone's poorer, the opportunity cost has gone down. I can't help other number of reasons like for adapting or change. Sure. Yeah. I mean, it could be a pro, you know, a conscious decision, or it could be an unconscious decision, essentially. But it feels like it doesn't seem clear to me that it will just trend downwards exponentially to zero. There might be some moment where it's like, well, now a culture has taken over because everything's so bad. People have forgotten what it used to be like, and it's like, well, let's just pop out 10 kids because we got nothing else to do. Okay, great. Yeah.

So, I mean, we have our graph, like you might have like seen the picture that we drew in the New York Times article where we basically say, okay, total fertility rate of 1.6, go. And it, you know, goes on forever and ever. And, you know, people write in to say, well, of course, you shouldn't think that's empirically what will actually happen. And, you know, indeed not, right? It's, um, it's sort of an, it's the answer to an if-then question. If the birth rate, you know, goes to a number like 1.6, then this is what you'd see. No, I don't think that the population would follow that path forever. I think, you know, eventually, as you say, something important would break, um, and, and we, you know, would no longer be able to follow that if-then anymore.

Is it something important that's going to break? Something that's going to, you know, wipe us all out, like maybe a a pandemic where there's not enough, you know, so think of, um, you know, COVID came along, and there were 8 billion of us, and we were able to come up with vaccines, um, that, you know, the vaccine has this property of like a once and for all thing where, of course, you have to manufacture it and put it in people's arms and get people to come get it, but you only need one recipe, right? Um, and so like in a, in a smaller population, would we be able to come up with that? Um, and I don't know. Um, but, you know, the other possibility is the one that you raised, where the, whatever knocks us off the path and causes, you know, basically makes us poorer and causes birth rates to go up. That could be what happens. That would be very bad. That's not what we're hoping for. Um, I think, you know, that would be a reason not to, to do this if we thought that were what's going to happen. I don't see a lot of evidence of in a future where people are accustomed to, you know, choosing whether to be a parent or not and have access to contraception, have these tools, a lot of people decide to have more kids for the greater good or something. That's just, that's just sort of an unreasonable. I mean, that's, you know, how many people, that's not how we're, that's not how we're fixing climate change, exactly. Um, you know, it's not what we see happening in South Korea. We see the birth rate continuing to fall. It's not what we see happening in China. We see the birth rate continuing to fall. Um, and so I guess I'll stop there with some statistical evidence and not to keep speculating.

Yeah. I just had a quick, I had this weird, uh, I had a strange thought. I come from the oil and gas world. Along 15, 20 years ago, we are 100% sure about peak oil in America. We're like, there's no way we're going to peak out. And then all of a sudden, technology-wise, we figured out, oh, we can use this technology called fracking and go after shales, and all of a sudden, boom. Is there, I was thinking, can you like, is it possible? I'm reading all these crazy articles about like a ton of young people my age have like embryos saved, right? We're like smarter, we're like thinking ahead. If tomorrow Elon Musk invents some crazy technology where you can take those embryos and like grow them without having to do them yourself, and it's healthy and whatever, could something like that where you're wrong, the Dean's wrong, and it's not 10 billion, it's 2030 or something, like AI unlock some sort of technological innovation where that we're not thinking about?

I mean, in in your embryo scenario, does somebody still have to parent them and do the work of taking care of them and feed them and drive them to school and all of that? And yeah, um, the Tesla bot, the Tesla bot is going to do that. Yeah. I mean, I, I think I have a lot of confidence in the if-then. If birth rates fall below two for the world as a whole, then global depopulation is what's going to happen. And I also think there's a lot of empirical evidence that should make us think that global average birth rates falling below two is the most likely future and would be that way for a long time. Could something else happen? Sure. I don't have a crystal ball, but I think it's the most likely future. Uh, I was just curious on what the data showed for 2020 during the pandemic globally on the population.

rates. Did we get busy? From my understanding, just a lot of people had a lot of children. I was just wondering what that data showed.

Yeah, I don't know. Um, yeah, from what I've seen, it was actually kind of the opposite. Uh, fertility rates went down even further during CO. It was actually quite a re I mean, there might have been a slight peak, but overall 2020 to 21, they I think a lot of nations reached their lowest fertility rates historically, which is interesting.

It's not a great time to be in a hospital. No, exactly. Like I think electively I'm sure there are a lot of accidental pregnancies cuz people are just like locked down and we're like well what else are we going to do? But um I think people isolated too. Yeah. Expect less.

I have a question for the room real quick. Uh for those who don't have children in the room after this conversation, how badly do you want to go make babies? That's a very it's a really bad seriously. I'm part like are you guys going to do your part? What's up? Eigor, are you updating I'll do one of the necessary things to have babies. You've done enough practice. Be the change or be the change.

Okay. I as a childless person, this actually was kind of my question. um sort of to isolate the solution, but just out of curiosity, is there some any significant global data that this change in birth rate is coming from the people that are having no children at all versus meaning fewer people are not having children at all or the people who are having children are having fewer because of maybe resources or all these other possible reasons? And then do you think that changes the solution? because it's such a different question. Going from 0 to 1 is very different than 1 to 2 to 3. So, does it change the way you look at the solutions?

I'm so glad you asked that because I just happened to be working on a research paper about that. Um, and um the the answer is that it's more about people having kids having fewer kids than it is about more people having no kids. So, we hear a lot of this narrative about childlessness. Um but you can sort of you know as you say the statistic the average number of children amongst people who have children right that's been going down too. Um and in particular there are lots of countries like the low the places where birth rates are pretty low like your your Portugals and your Russas there the average birth rate amongst people who do have kids would still be low enough for depopulation. Um and so like it's a pretty strong correlation between the overall average birth rate in a country and the average birth rate amongst uh amongst people who do have kids. And so we see them going down together. And so so it's not just like the people who have kids are staying the same. That number so so what are the facts? That number is going down too in a lot of places. It's low enough that even if everybody were the people who have kids, it would still be below two. Um and if you sort of break it down to the into the accounting more of the difference is globally is about people um u having fewer kids who have them. This is a case where the US is a little bit of an exception and the increase in childlessness is a bigger part of the picture for the US overall. But if you like plot all the dots from all the countries um you know it's it's more about average number of kids amongst people who have kids.

Is there any fulfillment data on between people who have kids? So on average are the people who have two kids happier than the people have four kids. Is there any kind of data in that?

Yeah, exactly. That's that's right. That's sort of the right question to ask because like it's not sort of a randomized experiment whether you have a kid or not. Um and so like the um so uh Angus Deon has a paper with Arthur Stone looking at this. It's not about how many kids you have. I think it's just on the margin of are you a parent or not. Um and you know what they find is like amongst people who have they look at the Gallup world poll data. So that's these happiness questions and what they find is you know um you know people who have kids like the highs are higher and the lows are lower would be a simple way of summary like more good days more bad days. Um um um but it's hard to sort of say cause and effect because people choose to have kids.

Story checks out. Yeah. Yeah. Um well actually this uh one of the things I wanted to say was partly to that point um or that question. Um I've heard in interview with therapists and also people in the family law space that there is I don't know if this is going to enroll people and having more children from hearing this but um that having one child or two versus three or four there's a pretty big gap in the amount of inshment that occurs. When people have fewer children, they are more imshed with them and they're positing that this is less psychologically healthy for everybody involved. And it leads to more embittered challenging custody cases where the the parents like I want the one kid. No, I want but if it's for like please God, take them take them for a week. Okay, you have them back now, please. So So there's some benefit to this.

Um and then just a couple other points. The thing about aging populations earlier, this seems like I'm half Singaporean. This is like maybe a very Singapore specific solution because it's one of the most densely populated countries on earth and also the value system I think culturally there is it's more so socially oriented of what do I do to help the the greater good and the group and they have subsidies for example for housing for elder aging parents to move into the same complex of flats that their children live in so that they can all live near each other and support one another and so it puts less strain on on government resources.

Um and then last point, oh yes, um so I don't know how much this would make a difference, but the um my understanding is the American OBG Association recommends that physicians not offer women a blood draw for AMH antimmalarian hormone that would indicate ovarian reserves because it can cause them undue stress. So if a woman is they will ask about contraceptives um like you know how do you want to prevent pregnancy but they don't say do you want a family in the future do you want to get a sense of your ovarian reserves now um and some women go into parameopause in their 20s we just don't know and so there is a very simple way to test for this that they are specifically not telling women about as a policy um which might help somewhat at least in the US all right has there been any research done on are people having less sex are they may be less sexual with the advancement of technology and people connecting through the phone rather than personally meeting being one and the other factor is cost of living since it's exponentially higher and more expensive to live the age of the average person who's even buying their first home is much higher now how does that relate to just it all being possible yeah

so I don't know exactly the answer to the question of whether people are having less sex and whether you know how much that was it does sort of bring me back as everything does to the case that I do know which is India where you know marriage remains almost universal and at young ages and people tend to be having you know a small number of kids and then having permanent contraception surgery. At least that would be one case where people are you know having a small number of children um and exactly implementing the plan they want to in sort of in a in a marriage where you know they are having say do is that is that government encouraged like is there is there social programs to have fewer kids? I know India's got a very large population.

Well, I mean, there was definitely hugely coercive policies in the 20th century to try to, you know, force people to not have kids in the sense of like in some cases involuntarily sterilizing them. Um, you know, that um was awful and hurt a lot of people. Um um you know, these days, you know, in some cases the official messaging is reversed. Um but you know it's still the case that like the place where I work like the district capital town where I work in Utra Pradesh like in the walk from like the office to the hospital you see like a sign painted on the wall that's like has you know that says like don't have too many kids. Um so I don't know how much that does to anything but um but the other question uh you had another question it was interesting and important. Yeah. And affordability. Um I mean I think that is important. Um I think you know we talk a lot in the book about how the affordability of kids can't be the whole story because you know we do see lower birth rates in richer countries. We see that as the world's gotten richer as a whole birth rates have gone down. We see that places where things are more subsidized. You don't see people having more kids. Here's a sort of little cute um economics thing is there's a research paper looking at what happens when young women win the lottery. Um you know comparing them as a control group to young women who played the lottery and maybe like won a small prize but didn't win the big prize. And so it's pretty much a randomized experiment. Um and uh what that paper found, you know, for whatever this is worth, um is that the women who win the lottery did not go on to have more kids over the course of their lifetime than the woman who did. And so that the woman who won did not go on to have more kids than the woman who did not win. Um and so I think that like at least bounds um how much money is the is the constraint.

Steph, I know you had a burning question. Did you want to ask it or Okay, so first I'll say that I'm prohuman. I have lots of humans. I have four of them. So, I'll put that out there. Um, winning. I did it accidentally. Um, it happens to the best of us. I I do want to ask so when thinking about this space, I feel like a first I don't trust humans to predict the future. It feels like we never get it right. Even if you looked at what people were saying last year, no one can predict where we're at now. And so I'm wondering in all of your research, is there anyone that you've run into where they just don't have the data yet? Like you ran into them and you're like, "Oh shit." Like intuitively this feels like they're on to something, but they just don't have the data that's proving it yet. And someone that we should be watching.

H Let's see. At the person level, I don't have the answer. I don't know. One thing that that makes me think about though is that this could be a case where like the longer term could be easier to predict than the shorter term. Like you talked about like next year or something like that. I think like next year, who knows, right? You know, one group wins the election, the other group wins the election, you know, who knows? I think I I wouldn't want to stand here and say that I think I know what the birth rate in any place or the population size in any place is going to be, you know, 5 years from now, 10 years from now. you know, migration, for example, would have a lot to do with that and migration has a lot to do with what's legally permitted. I think this is a case where it's easier to say, you know, just like with climate change, it's sort of easy to say like the big picture, if you burn a lot of carbon dioxide, then you'll increase the or you put burn a lot of fossil fuels and put carbon dioxide in the atmosphere, then you'll increase the the temperature. I think here we can say like you know if the world's birth rate goes below two and stay there then we'll see this exponential depopulation and I guess I just want to stop there and not try to be more precise than that.

Thank you so much everybody. Um, thank you all. This has been fun. Thank you. Uh, unsurprisingly there was a lot of comments and I'm sorry for any of you who didn't get to speak that wanted to. Um, Dean, thank you so much. Uh, this is excellent. I hope this is, if anyone was undecided, it's moved you in the direction of babies. I know. Uh, Eagle, are we going to talk? Back to practice. Back to practice again. Thank you so much for having me. Thank you, Dean. This is amazing. Yeah. And and and everybody get his book when it comes out. I really recommend it. Now you can applaud.

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