Defusing the Depopulation Bomb
Book Review: "After the Spike" by Dean Spears and Michael Geruso
[Adapted from this bluesky review thread]
The world’s population is still growing. Today there are over 8 billion people on the planet. Demographers estimate the world population will grow to 10 billion in the next five or so decades. And then it will peak. And then it will decline.
The rate of population growth is falling, and is trending negative. The birthrate in the United States is 1.6 babies per couple. The birthrate in other countries is declining. If and when the global birth rate falls below 2.0 per couple, global population will eventually decline. If it stays below 2.0 in perpetuity, then the future will be far more sparsely populated than the present.
Economic demographers Dean Spears and Michael Geruso refer to this phenomenon as “the spike.” Their new book, After the Spike: Population, Progress, and the Case for People, makes the case for why we, collectively, ought to take treat this problem as a crisis-in-the-making. Spears and Geruso are, in effect, making the liberal-intellectual case for pronatalism.
Many of pronatalism’s loudest proponents are tech billionaires and eugenicists. The argument for more babies has a habit of sliding into “more of the right kind of babies” if it is allowed to go on long enough. But one can be concerned about longterm demographic trends without being a racist asshole. Spears and Geruso are economists by training. They are both tenured professors at UT-Austin. Geruso worked at the Biden White House. There is a liberal case for paying attention to this issue, and Spears and Geruso’s book sets out to make it.
It just that the case isn’t very strong.
The book is uneven at best. Its tone hops back and forth between arguing with imagined opponents and explaining basic economic concepts to an innocent, curious audience. It reads like the notes from a large lecture course where the professor is used to asking and answering his own Socratic questions. It is beset by three central problems that the the authors ultimately fail to overcome. (1) They are engaging in futurism, while dressing it up as social science. (2) They are too careful in selecting their foes, while ignoring the elephants in the room. And (3) their underlying theory of politics is ridiculously underdeveloped.
(1) Futurism Disguised as Social Science
The entire case for the Depopulation Bomb hinges on a singular empirical trend: people — especially comfortable people — tend to prefer smaller family sizes. The birth rate is below 2.0 per couple in the United States and Europe. It is declining all around the world.
If the entire world were to settle at the U.S.’s current birth rate (1.6), and if it stayed there permanently, then the world would depopulate over the course of a couple centuries. That’s just math. It’s the inverse of the hustlebro influencers on LinkedIn, talking about the secret of compound interest. If the global birthrate stays below 2.0, then we will have a shrinking global population.
On page 42, Spears and Geruso write:
The logical path from low birth rates to depopulation is short. If worldwide average birth rates go below two, and if they stay below two, then the world will depopulate exponentially. That is an if-then sentence, and we are sure its logic holds. We're not 100 percent sure that the if part is true, that global birth rates will stay below two, but declining birth rates is the clear global pattern.
How much less than 100 percent sure should we be? Not much less, according to Adrian Raftery and Hana Seveiková, two statisticians at the University of Washington. They published estimates in the International Journal of Forecasting in 2023 that there is a 90 percent chance that global birth rates will be below replacement until at least 2300, which is the latest year that they considered.
This is a load-bearing passage in the book. Spears and Geruso insist we can be nearly 100% confident that global reproduction rates will stay below zero for hundreds of years, causing exponential decline. They base this belief on an estimate in the International Journal of Forecasting.
Let me suggest that they have far too much confidence in this estimate. I am not aware of a single hundred-year prediction by any economist that has held up. For that matter, it is exceedingly rare to find a hundred-year prediction from anyone that has help up. A century is a long time. When you are predicting social phenomena that far in advance, you aren’t really doing social science anymore. You’re doing futurism. And Spears and Geruso aren’t particularly good futurists.
It’s a critical passage because the depopulation bomb is not a locked-in, path-dependent trend. The solution here really is as simple as “we’re gonna need people on average to have slightly larger families, over the course of a few generations.” The global population will continue to grow for quite some time. It will not reach its peak during my actuarially-likely lifespan. We have never experienced a massively depopulating world before.
Imagine it is the year 2175. For almost 100 years, the global population has been declining, from a peak of 10 billion down to ~4.1 billion. For the first time in history, the built environment has tremendous overcapacity. I am not sure how that would change social norms and behaviors — how politics, commerce, and culture would be transformed. But I have pretty strong hunch that it wouldn’t be a null impact. It is at least plausible that people would, on average, react to all the excess space by having slightly more kids.
We cannot have confidence one way or the other. No one is good at forecasting social behaviors and preferences 100 years into the future. No one has ever been good at such forecasts. There's a decent argument that no one ever will be good at such forecasts. This is the realm of science fiction, not empirical social science. It is a mistake to pretend otherwise.
And the thing is, unlike an issue like climate change, there is not destructive feedback loop here. We needed to take action earlier on climate, because every gigaton of carbon makes adaptation harder. Our inaction yesterday narrows and worsens the range of our potential futures. By contrast, our collective-babymaking-inaction today does not foreclose the possibility that future generations could choose larger families.
The authors acknowledge in the final chapters of the book that they do not systematically know why people en masse display this demographic preference. But they dismiss the possibility that future generations might develop different preferences on their own out of hand.
This isn’t social science. It’s sloppy futurism, wrapped in a thin veneer of social science.
(2) The Elephant in the Room
Spears and Geruso are quite selective in who they choose to argue with and how they frame the problem.
They insist that we have a choice, as a global society, between population stabilization and population decline. Section 2 of the book (chapters 3, 4, and 5) debunks arguments for why a smaller world population might be preferable. Section 3 (chapters 6, 7, and 8) makes the “Case for People.”
These are pronatalist arguments, but the authors never utter the word “pronatalism.” Chapter 8 is an argument for longtermism, but does not use the term or make mention William MacAskill. They do, however, thank MacAskill and Toby Ord in the acknowledgements section. Malcolm and Simone Collins (pronatalism’s Thiel-adjacent, media-thirsty celebrity couple) also go completely unmentioned. Elon Musk — pronatalism’s loudest, wealthiest, and most problematic advocate — never receives a mention in the text.
They do mention the Musk Foundation in the acknowledgements section, though. In 2021, Musk donated $10 million to support their research.
This matters because all of the arguments Spears and Geruso offer in favor of population stabilization serve equally well as arguments for massive population increase. Musk and the Collinses and a whole lot of longtermism-adjacent thinkers believe we ought to produce infinite humans. Particularly smart ones. With the “right” genes. And the “right” culture. Spears and Geruso address none of these problems or contradictions. They want to make this a choice between population decline and a stable, flourishing population. They don’t want to defend the terrain that their (much more powerful) fellow-travelers have staked for themselves. It is baggage that they check through to their destination, inviting readers to relax and enjoy the flight.
(And the crisis they envision “After the Spike” evaporates if we consider the possibility of a future where global birth rates rise above replacement rate. If, in 2125, after forty or so years of population decline, people start preferring marginally larger families again, then the global negative population trend would reverse itself. It really is that simple.)
By contrast, the authors devote one and a half chapters to debunking Paul Ehrlich’s 1968 book, The Population Bomb. Spears and Geruso are very interested in convincing readers that Paul Ehrlich was wrong. He was. But that was fifty-seven years ago. At some point, the focus on Ehrlich is just a means of dodging present-day controversies.
Nowhere do they engage with what strikes me as the strongest argument against pronatalism:
The opposite of pronatalism isn’t antinatalism. Or at least it shouldn’t be. The opposite of pronatalism is leaving people the fuck alone.
(But what about all the future humans that could hypothetically be born one day?!? Shut up. That’s what. Leave people’s reproduction choices the fuck alone.)
(3) Pollyanna Politics
There is a passage in chapter 9 (“Depopulation won’t fix itself”) that I found jarring in a revealing way. Spears and Geruso write “Don’t expect depopulation to fix itself. We cannot count on automatic stabilizers to avoid depopulation, if humanity does not choose to change its course.”
You cannot write serious nonfiction about humanity choosing a course of action without also developing a theory of politics. Politics is how “humanity” chooses a course of action. If you stay doe-eyed about the politics, then you’re just doing bad futurism for an audience that already agrees with you.
The implicit theory of politics in After the Spike is Pollyannaish to a fault. They assert with undue confidence in chapter 3 that population growth won’t have negative climate impacts, because of the U.N.’s Intergovernmental Panel on Climate Change (IPCC) established climate targets. A child born in 2025 will be living in a carbon neutral world by 2050. They do not even consider the possibility that we might not meet those IPCC targets.
In the final chapter, they admit that they have no proposed policy solutions. (They spend chapter 10 dismissing government control as ineffective and chapter 11 dismissing market incentives as basically pointless.) So they instead declare the answer is to “aspire bigger:”
Confronting depopulation needs both seriousness and optimism, too. We believe that the facts and the arguments, the statistics and the ethics, will someday make stabilization a widely shared goal. (…) Change often starts with just a vision and commitment.
The year is 2025. One of these guys worked in the Biden White House. He still clings to the bedrock belief that facts, arguments, statistics and ethics are how we set the direction of society. This is Tinkerbell reasoning. It’s as if they tuned out the past quarter century of political developments and just watched reruns of The West Wing instead.
And I find this troubling because of all the pronatalist baggage that they conveniently shipped through.
Dean Spears and Michael Geruso seem like well-meaning liberal intellectuals who are genuinely concerned about long-term demographic trends.
But JD Vance is our pronatalist Vice President. And Elon Musk is the world’s wealthiest pronatalist dirtbag (and one of the authors’ main funders). And Malcolm and Simone Collins get invites to the White House. These are people who read about Gilead in the Handmaid’s Tale and thought "sounds great let’s give it a try!”
The liberal-intellectual case for pronatalism population stabilization, at a time when the extreme-right pronatalists control all the levers of government, is neither a neutral or innocent exercise. The political use of this book is to advance forces already in play that the authors would personally find abhorrent.
There is nothing in this book that suggests we need to treat global depopulation as a crisis right now. There are good political reasons not to.
If current demographic trends continue for decades, then my kids should maybe worry about this stuff someday. We face bigger problems here and now.
(4) The Missed Opportunity
The most frustrating part of the book is that, if the authors would simply jettison the unnecessary crisis-framing, there are several progressive, pro-family policy ideas that the authors could do a better job of advancing.
There is an offshoot of pronatalism that focuses much more on the near term than the long term. (I’ve discussed it once before) It notes that a large, aging population of retirees paired with a small working-age population is far from ideal for a country’s tax base and social stability. (Gideon Lewis-Krauss covered this subject for The NewYorker earlier this year. Always read Gideon Lewis-Krauss.)
It stands to reason that, in precisely the same way that governments provide tax breaks to incentivize home ownership (because governments think home ownership is good, and would like to encourage a bit more of it), governments could do a lot of small-bore policy to making parenting small kids a bit easier.
This has always struck me as the strongest argument of the bunch. I was a bit surprised to find that Spears and Geruso never take it up. They do write about how the culture of parenting ought to change and become more coequal. They do note that there are a lot of things governments could try, even if early attempts haven’t produced major effects thus far.
If you believe — as Spears and Geruso (and I!) do — that more people are generally better than fewer, then there are a lot of policy levers that governments could try to pull. None of these policy levers are silver bullets. But we also do not need a silver bullet. We need marginal effects, spread out over a very long period of time. There are good, prosocial policy choices (universal pre-K! Generous parental leave! Affordable and plentiful housing!) that we ought to pursue anyway.
We don’t need to pursue these policies because we dread “The Spike” 50-100 years from now. We ought to pursue them because they would make people’s lives better today.
But that would be a far different book than these authors set out to write. They ultimately do their cause a disservice. Someone else, in a different time and place, will have to write it.
I almost feel I'm going to have to read this in order to join in this critique, because this is just SO characteristic of how a certain kind of social science-inflected advocacy works, and it doesn't seem to matter how long the trail of havoc and failure is behind that sort of intervention, they just keep coming.
The basic lesson that everybody should have learned from population studies and demography in the second half of the 20th Century is that extrapolating from present trends as if they are themselves purely natural and will continue unabated unless managed through policy--and not through politics--is the worst mode of futurism and at the roots of most failures of forecasting and prediction. That kind of analysis often historically shallow--the connection between doom-casting demographers who were calling for strong interventions into population growth and deeper histories of global and local population increases after 1500 were very weak.
That's problem #1, because a better consideration of the full body of social history that was attentive to changes in population that included but was not limited to family size, age of marriage, ease or difficulty of migration, urbanization, nutrition and diet, epidemiology, administrative systems, legal systems, etc. would have or should have told late 20th C. demographers to cool it with the dimestore Malthusianisms.
Problem #2 is a direct result of that, which is the crude instrumentalism of how they fit policy to desired outcomes. Since they saw population growth as 'natural', they thought of government interventions in unbelievably crude terms--sterilization, legal constraints on family size, mandatory use of birth control, punitive taxation, blanket campaigns of secularization, etc. In reality, it turns out that slowing population growth in a sense took care of itself, or arose from causal roots that most demographers and environmentalists were ill-positioned to notice or evaluate: women's rights, urbanization, consumerism and middle-class cosmopolitanism, easily available but not legally compulsory birth control, etc.
Which all should weigh on anybody worrying about present trends. I wouldn't say so much "hey, relax, it'll all take care of itself", but if we're talking one to three centuries in the future, pretty close to that. As you say, the only thing worth doing are "marginal effects, spread out over a very long period of time". Populations are not something you manage like the hot and cold water faucets on a sink.
I think you have to contend with an even bigger question that always springs to my mind when prenatalism arises: so what if the population shrinks? Our current economic model depends on growth. But that’s a pretty anemic and incurious way to think about this question.
Humans need food, water, and shelter to survive, and they need healthy social structures, art and leisure activities to enjoy, and work that gives their lives meaning. How exactly is the mere fact of depopulation a threat to these goals? Sure, we might have a lot of empty infrastructure, but I don’t see how that meaningfully threatens our future.
Am I missing something? If we leave market economics aside, is there anything that says humans can’t flourish with a global population of five billion or three billion or even one billion?