After the Spike: Population, Progress, and the Case for People

by Dean Spears, Michael Geruso

An eye-opening exploration of humanity’s unprecedented path to global depopulation and its significance from economists Dean Spears and Michael Geruso.

The world’s population has surged over the past 200 years—not due to increased fertility, but thanks to improvements in survival. Since then, our larger society has thrived like never scientific breakthroughs, a global economy, healthier lives, and social progress.

A significant shift is now on the horizon. Humanity is projected to peak at 10 billion, followed by a rapid decline. It would be easy to think that fewer people would be better—better for the planet, better for the people who remain. This book asks you to think again. Depopulation is not the solution we urgently need for environmental challenges, nor will it raise living standards by dividing what the world can offer across fewer of us.

In After the Spike, economists Dean Spears and Michael Geruso shed light on the consequences of this unprecedented shift. They carefully analyze the stakes of global depopulation, exploring its impact on living standards, climate, and even extinction. Surprisingly, they reveal that stabilizing the global population doesn’t have to mean sacrificing our dreams of a greener future or reverting to past gender inequities. Their insights challenge us to view the fight against depopulation as intertwined with social equity and the inherent value of every human life. After the Spike is a rallying call to action to ensure a thriving future for generations to come.

Genres: Economics, Nonfiction, Politics, Science, Social Science, Sociology, Society

320 pages, Hardcover

First published July 8, 2025

Reviews

[Jason Furman · Rating 5 out of 5]

“In 2012, 146 million children were born. That was more than in any prior year. It was also more than in any year since. Millions fewer will be born this year. The year 2012 may well turn out to be the year in which the most humans were ever born—ever as in ever for as long as humanity exists.”

This gripping opening sets the tone for After the Spike, a fascinating, rigorous, and unexpectedly enjoyable exploration of one of the most fundamental issues shaping our collective future: the coming global population decline. Dean Spears and Michael Geruso have written a book that is both accessible and thought-provoking, filled with novel insights that are as analytically grounded as they are socially urgent.

The central concern of the book is the “spike” of population growth that has defined the past century—and the steep, possibly irreversible decline in birth rates now unfolding around the world. Spears and Geruso explain why this shift is happening, what the consequences are likely to be, and what might be done to stabilize global population levels. They make the case not only for why the trend matters, but also why we should want more people in the future, not fewer.

One of the striking intellectual reversals over the past fifty years has been the shift from fears of overpopulation to concerns about underpopulation. Importantly, both perspectives can be valid: a fertility rate of 7 is clearly too high, but a rate of 1 may well be too low. The surprising reality is how rapid, widespread, and so far unreversed the fertility decline has been—posing significant challenges for economic growth, fiscal stability, and societal dynamism. Meanwhile, many of the dire Malthusian predictions from the 1970s have proven deeply misguided, if not outright false.

A substantial part of the book is devoted to rebutting popular arguments against population growth, some of which echo 1970s-era anxieties—such as the belief that more people inevitably mean more climate harm. Spears and Geruso challenge these ideas with empirical evidence and logical clarity. They also advance affirmative arguments for larger populations, ranging from economic benefits tied to innovation and productivity to moral claims about the value of human life and flourishing.

The book concludes with a candid discussion of the limitations of current policies and the need for more ambitious thinking. While it doesn’t offer a single “solution” to the population decline, After the Spike succeeds in what is arguably more important at this stage: raising awareness, reframing the conversation, and laying the intellectual groundwork for collective action. Problems of this scale are rarely solved quickly—but they are never solved at all unless people begin thinking and talking seriously about them. This book is a vital contribution to that process.

[Alfred · Rating 2 out of 5]

This was incredibly disappointing. It’s the fourth book I’ve read on population decline, and unfortunately, I think it’s the weakest.

There are some positives. The book highlights the global demographic crisis which is an issue that’s finally inching into the spotlight (albeit about thirty years too late). Drawing attention to this problem is important, though I personally believe it may be unsolvable without ethically questionable intervention.

Now, the problems…

It quickly becomes clear that the authors lean heavily leftward. That’s not an issue on its own, but it is when their ideological commitments lead to misleading assumptions and faulty conclusions. For example, they use the gender pay gap as a measure of egalitarianism and then compare this with fertility rates across countries to argue that gender equality is not driving the decline in birth rates. That is an astonishingly flimsy premise.

The gender pay gap, when properly analysed, is mostly accounted for by individual choices and temperament differences between men and women. This is well documented in psychological and labor economics literature. Multivariate analyses show that the adjusted gap is negligible (around 0.5%), and that men under age 40 are now often outearned by women under 40. There is also evidence suggesting potential discrimination against men in some sectors. So why use the unadjusted pay gap at all? Worse still, the authors appear to cherry-pick countries for their analysis, notably excluding sub-Saharan African nations which are the only region with consistent above-replacement fertility, and therefore crucial to any honest demographic comparison. For example, Nigeria is projected to have more native Nigerians than the entire European population by 2050.

The authors then use this shaky analysis to rule out the role of gender equality (or “equity,” as they repeatedly call it, though the two terms are not interchangeable) in population decline. This kind of overreach is both frustrating and baffling. In countries where women have the fewest opportunities, birth rates are highest. To ignore this is poor form.

Another flawed claim made in the book is that more people will necessarily mean more geniuses. This betrays a lack of understanding of intelligence research. I absolutely acknowledge that this is politically and ethically fraught territory. Intelligence is a polygenic trait and partially shaped by environment (the best available research puts current estimates at around 20-25% of the variance being environmental). Correlating intelligence with fertility is controversial and of course must be approached cautiously. Nevertheless, it’s a potentially important lens for understanding this crisis and deserves exploration.

The uncomfortable reality is that, on average, the most intelligent individuals tend to have fewer children, while those with lower cognitive ability tend to have more. This is a trend that is observable across and within many countries (and has also been historically true since records began). To be clear, this is not a call to reverse feminist gains. Just as advances in cancer treatment allow children with hereditary risks to survive and pass on those genes (a negative we accept as part of a net positive) the strides made toward gender equality have also produced unintended consequences, including fertility decline.

More intelligent women are more likely to delay childbirth due to extended education and career development. They're more likely to use contraception effectively, avoid unplanned pregnancies, and prioritise long-term goals. These are all behaviors correlated with higher intelligence. As a result, many don’t consider starting families until their late thirties or beyond, by which point fertility declines and complications increase. Meanwhile, earlier and higher fertility rates are more common among those with lower cognitive ability. And yet, astonishingly, not one of the four books I’ve read on this topic meaningfully engages with this dynamic.

The authors also dismiss the “Great Man” theory of scientific progress outright without evidence. While it’s true that scientific breakthroughs often depend on enabling systems (funding, institutions, collaboration, and so forth), those systems still require great individuals to emerge within them. The biggest breakthroughs are the result of singular minds whose contributions shaped entire fields: Darwin, Newton, Faraday, Lavoisier, Gutenberg, Pasteur, and Cai Lun as examples. Ignoring the role of individual genius oversimplifies the story of human advancement.

In the end, this book felt poorly grounded. The authors’ ideological leanings compromised its reliability and obscured a complex issue behind misleading data and unconvincing arguments.

What a shame.

2 out of 5

[Stetson · Rating 3 out of 5]

This is a technocratic (read economic policy analysis) analysis of the global decline in fertility rate over the last few decades and what this will mean for humanity moving forward. The ethical and political perspectives of the authors figure prominently in the interpretation of the data and their conclusions. They're left-liberal utilitarians who want to balance the importance of economic growth and general prosperity against concerns about equality, fairness, and environmental worries.

I didn't come to the reading experience with many concerns about overpopulation. I've long believed that popular Malthusian predictions have been thoroughly debunked by the pace of productivity growth and that productivity growth is related to population size. Any of our future challenges will likely depend on having enough smart and ambitious people to throw at a problem. In this way, I read the book to learn more about what can be done to boost or stabilize fertility, especially in already advanced nations.

The authors have no real answers on this front and largely dismiss the avenues that do seem to show promise: religiosity and increasing the status of men (relative to woman).

will return to this to add more insights. I was hoping for a more data rich work too.

[Santi Ruiz · Rating 3 out of 5]

Workmanlike review of the basic narrative: we’re going to hit peak humans on the planet shortly, and what comes next could be bad. But lots of pieces missing: several sections rely on the UN population data without challenging it, for instance.

More importantly, the argument for seeing population decline and low fertility as problems are pretty neutered, inert, largely because of the authors’ political commitments. I understand this is meant to be an econ-first book, but it tries to bring home the emotional seriousness of the problem, and it’s therefore odd that nowhere does the joy of children appear, or any remotely normative idea about family life. In 4 pages of acknowledgments, the children of the authors are not mentioned. It’s hard to advocate for having more children if you don’t feel free to say, “more people should have more children.”

[booklady · Rating 2 out of 5]

Some excellent information in this book, primarily the insistence that nothing we do to lower birth rates now is going to have a significant positive impact on our environmental crisis for YEARS. We need to see and address that issue separately. In fact, babies born today have (and will continue to do so) much less negative impact on the environment than their grandparents and parents did because we have already found ways to deal with carbon emissions and other toxic effects which we humans have on the environment. The lesson being, we need to continue to pursue other means to reduce our harmful impact on our planet. Those of us in the First World contributing the most harm must take the leadership in this area, but killing our children or refusing to have them is not going to help in the short term where we need to do the most work, and could have significant adverse impact in the long term.

That said, the authors view abortion as "women's health care". Included is a story about one author and his wife who he says was refused medical assistance after a miscarriage by doctors in the state of Texas after the passage of Section 170A.002 of Chapter 170A of the Texas Health & Safety Code. This law did prohibit abortions in nearly all circumstances in Texas. However, since when does assisting a mother either deliver or remove an already dead fetus as a result of a miscarriage fall under the heading of an 'abortion'? I don't find this situation anywhere in the text of the law and don't know where to go to check on the author's assertion of this information. However, given the emotionally charged time period we live in, I can see poor women being told this to sway them to become pro-abortion. I did not see the need to include this story if the authors wanted to make a 'Case for People', but they also included 'progress' in their title and society today considers it progress to kill living babies in the womb. I do not. That was done in ancient societies which are extinct today. I hope our country survives this barbaric trend and returns to its respect for, LIFE, Liberty and Justice for ALL, including unborn Living Babies in the womb.


p. 38. 'The unspoken assumption that population growth could never turn negative is an assumption that birth rates could never fall below replacement, below two. But two has never been the end point where birth rates stop. We have data that speak to this because below replacement birth rates aren't new. Already by 1980, more than one in five people worldwide lived in a country with a birth rate below two. ... History has had plenty of opportunities to show us a case of two births per woman being special, to show us a country where falling birth rates got to two and stopped there for keeps. But that has never happened. ... It's easier to be right about the past than about the future. So we're not saying that everyone should have known exactly what today's birth rates would be. But many people overlooked even the possibility that birthrates could go below two and stay there, implying negative populations growth.'

[Ericka Clou · Rating 4 out of 5]

A lot of interesting facts, but I'm not persuaded by the conclusion. There is a lot of untapped human potential in our current world, and that might account for solutions to many of the problems cited by Spears and Geruso.

[Matt · Rating 5 out of 5]

This is a terrific book. Short, extremely readable, humane, and important.

It makes a compelling case for the fact that a) population decline is likely, and that b) would be very bad if it happened. Lots of people already know that fertility rates have fallen below replacement level. Most people assume this means that population will "level out." But this book shows persuasively that this is not the most likely outcome. The most likely outcome is continuing decline, with a resulting global population much, much lower than our present levels.

So what, you ask? To this question, the authors present two answers. The first is moral. People are good. That's easy to overlook when you're just talking about numbers. But imagine a stadium full of people who actually exist, some of whom you know, and many of whom you don't. Now imagine that roughly half of them simply never existed at all. If you think that would be loss, then you have at least some reason to worry about future population decline.

The second reason is economic. People are not just good, they're productive. They create new ideas. And they serve as trading partners that make a lot of what we care about possible. If you like going out for Thai food, the reason you're able to actually do it is that there are a lot of other people around who like Thai food too. Those people aren't your competitors in some zero-sum contest. They're the preconditions of a lot of economic activity on which your own well-being depends.

Why are people having fewer kids? The short answer is opportunity costs. There are just a lot of other things people can do with our time and resources now, including both better work and better leisure opportunities. The better life gets, the more we sacrifice by having kids.

What can we do about it? Here the book is - self-consciously - at its weakest. The authors admit that they don't have any solid answers. We know a lot about what *doesn't* seem to work. Giving parents baby bonuses ("Trump Savings Accounts"), subsidizing day care, giving out free IVF, banning abortion. All of these have been tried, and all of them have failed to bring fertility rates back up above replacement levels. There may be other, independent good reasons for doing some of these things. But if your goal is to prevent population decline, you're going to have to look elsewhere.

And where do the authors suggest we look? Well, they kind of don't. What they say is that we should try to make life better for parents, so that more people choose parenthood willingly. But there's not much at all here about what that would look like in practice, how to weigh the various costs and benefits, and so on.

The authors recognize this shortcoming. Their story is that the first step toward any change is getting people to be aware of the problem, and to care about it. Once that's done, solutions can come later, in much the same way that we started to address climate change by making people aware of the problem decades ago. That's a fair point, I guess, though I suspect many readers will, like me, come away a little disappointed not to have heard more in the way of policy suggestions, even if those suggestions weren't conclusive.

[Sam A · Rating 5 out of 5]

"the spike" is a (rather profound, imo) description of the explosion in the world population seen in (just) the last two or three centuries that is now beginning to lose steam and could soon fall just as rapidly as it rose (pictured on the cover). i first read about this topic from spears' nyt piece, which you should read if you're on the fence here. if you read that piece and this book, i suspect you will spend a lot of time thinking about a world where, for every, say, 10 or 20 people, there is instead 1. without the book, i would not have known how realistic the latter could be. but even if i did know, without the book, i might've thought fewer was fine or better. spears and geruso argue--quite compellingly--that fewer is worse. the clearest argument for me was that scientific discovery and technological innovation--which make us all better off--come from people. i actually now consider the premise lots-of-people-is-bad-for-the-world to be completely absurd, and i pretend that i never thought otherwise. it's a pretty powerful perspective to have, one that generates compassion for other people--most of whom we will never meet--in a strange but sincere way. as it turns out, that is exactly the purpose of the book. spears and geruso do not propose a solution for "depopulation." it doesn't require one. we've all rationally chosen to have fewer kids over time. but it's possible that we (like me) haven't thought through the implications of what's transpiring as our preferences are changing. the book describes so many of these implications. not only do spears not propose a solution, they show empirically how even the most coercive and heinous measures are ineffective. rather than propose a solution, they story-by-story, fact-by-fact get readers to care about our dwindling numbers, knowing, perhaps more clearly than anyone else on earth, that people are capable of charting a new course--if they decide to. it strikes me as entirely possible that we could all look back at this book one day, as the point we decided to and, if the authors are correct (as they seem to me to be), the point we changed the future as fundamentally as we have at any point before.

[C · Rating 2 out of 5]

Before getting to the whole of the book, I feel compelled to question the author's overly frequent mention of the drug, Diclegis. If the authors had walked over to the pharmacy school on their campus, they could have learned a little about this supposed wonder drug exemplar of medical progress and discovered it's actually just a repackaged combo of two medications - vitamin B6 and doxylamine - that are available over-the-counter and have been for decades. It should also be noted that both are very, very cheap AND that Diclegis is VERY expensive (for what it is). Basically, a company saw an opportunity to get an FDA indication for morning sickness using two very cheap medications. If anything, this is a failure of the US legal/medical system generally since a combination drug used to be available until it was withdrawn because of the cost of defending frivolous lawsuits and is now available again but at a huge markup to the components. Progress?!?!

I thought these guys were economists?

Back to the book generally: it feels like the author's wanted to write a slightly different text but their political leanings wouldn't allow them to and as a result, it's unconvincing and muddled. In a weird way, it feels like a therapy outlet for the authors own disappointments with their families being smaller than they would have liked.

Most of their thesis rests on the belief that "more good is better" and their central claim is more people equate to "more good." BUT - they state that a total fertility rate of 3, 4, 5 or maybe even more probably is too much. But why? No satisfactory answer. And they are clearly squeamish about their thesis' implication on abortion and handwave it away as personal choice. Again, their statements that any person - even one living what we in the US would consider a miserable life - would still consider their life worth living leads to a logical and ethical conundrum for them which is never quite resolved beyond "we don't want to force anyone into anything."

Spears & Geruso try to explain away the environmental objections by detailing how it's really too late for a population drop to affect global warming and only policy changes can save us now. And they manage a fairly convincing argument. They then note a few specific examples such as China's reduction in particulate pollution while adding 50 million people, the harm to ozone being addressed via slashing use of CFCs and the elimination of leaded fuel. These are well and good but are narrow problems with arguably single-button policy fixes. They avoid any discussion of things like ecosystem collapse due to things like overfishing, biodiversity falling and so on that are more diffuse and challenging to measure and are almost entirely the direct result of human behavior to address needs/wants.

Ultimately, it seems that S&G envision a future where most of humanity lives almost entirely in high-rise apartment flats in dense, resource-efficient megacities, eating a sustainable primarily vegetarian diet and recycling most of their consumption. And all that by "policy choice." I guess? Because that's really the only way nature recovers its degraded ecosystems while our population stabilizes at or increases from its current level.

Their ethical/moral case rings hollow: the Universe certainly has no *need* for humans. The Earth and its flora & fauna got along just fine before we arrived - probably better. Does Humanity need more humans? For perpetuation of the species, sure. Does it need 1 or 4 or 8 or 12 billion? That is harder to answer and perhaps does not have a *true* answer.

As a conversation starter, the book is... fine? As anything more, it falls flat.

[Tamara]

Very weird book. Unpersuasive and kind of pointless - and I think the global drop in fertility is strange, dramatic, needs explaining and is probably symptomatic of nothing good. But the moral and technical shallowness and profound lack of curiosity about what people are actually thinking and choosing here, left me creeped out nevertheless.

[Sangita · Rating 5 out of 5]

This book makes the progressive case for why we should worry about depopulation. The authors carefully and compellingly argue for why a smaller population on its own will not solve problems like climate change, environmental degradation, and gender inequality. They also make compelling arguments for why more people are better. Highly recommend!

[Zack Subin · Rating 4 out of 5]

Highly persuasive, thoughtful, and timely; slow & repetitive in places.

[Sarah Jensen · Rating 5 out of 5]

After the Spike: Population, Progress, and the Case for People – A Bold Reimagining of Humanity’s Demographic Future
Rating: 4.7/5

Dean Spears and Michael Geruso’s After the Spike is a masterful synthesis of economics, demography, and ethics that confronts one of the most underdiscussed crises of our time: the coming era of global depopulation. As someone who has oscillated between Malthusian anxieties and techno-optimism, this book left me intellectually invigorated and emotionally unsettled—in the best possible way.

Why This Book Matters
The authors dismantle the seductive but flawed narrative that fewer people automatically mean a healthier planet or greater prosperity. Their analysis—rooted in rigorous data yet accessible to non-experts—reveals how depopulation could exacerbate inequality, strain social systems, and even worsen environmental outcomes by shrinking the labor pools needed for green transitions. The chapter linking fertility decline to gendered labor inequities is particularly revelatory, reframing demographic stabilization as a feminist issue. Spears and Geruso’s proposal for pro-natalist environmentalism (a term I now can’t stop thinking about) challenges readers to see population policy as inseparable from climate justice.

Emotional Resonance & Intellectual Thrills
Reading After the Spike felt like watching a high-stakes chess match between doom and hope. The sections on demographic headwinds (e.g., aging societies struggling to fund pensions) sparked visceral anxiety, while their case studies of communities thriving through intergenerational cooperation restored my faith in collective ingenuity. I found myself scribbling notes in the margins about how their insights apply to local housing policies—proof of the book’s practical urgency.

Constructive Criticism
While the macro-level analysis is stellar, the book occasionally glosses over cultural nuances (e.g., how pronatalism might clash with reproductive autonomy in different regions). A deeper dive into technological mitigations (e.g., AI’s role in offsetting labor shortages) would have strengthened their solutions. The prose, though clear, could benefit from more narrative flair to match the gravity of its subject.

Final Verdict
After the Spike is essential reading for policymakers, environmentalists, and anyone who cares about the future of human flourishing. It’s not a dystopian warning but a clarion call to reimagine progress—one that left me convinced that demography is destiny, and destiny is ours to shape.

Thank you to Edelweiss and Simon & Schuster for the gifted copy. This book transformed my understanding of population dynamics from abstract statistics to a deeply human story.

Pair with: Empty Planet by Darrell Bricker and The Wizard and the Prophet by Charles Mann for a fuller picture of demographic debates.

For fans of: Factfulness by Hans Rosling, The Great Demographic Reversal by Charles Goodhart, and The Dawn of Everything by David Graeber.

[Rob Sedgwick · Rating 4 out of 5]

This book's message is that a declining world population is a bad thing. The birth rate is below replacement levels in most of the world now, and has been for some time, although the population will continue to rise as the delay in people dying leads to a lag of many decades. The central argument of this book is that fewer people will mean fewer opportunities, and people who might have been born will never be born.

My problem with it is that it fails to mention other species. Yes, I care about future humans to an extent, but I also care about other mammals and life forms in general.

It looks at ideas and policies for addressing the number of babies women have, and reasons why the birth rate is falling (spoiler: nobody really knows).

Many people use reasons for population changes as their pet explanation, usually aligned with their politics. It's also linked with racism, as Africa is the one continent where the population is still growing. My guess is people just have more ways to spend their time, and probably don't even copulate as frequently as in earlier times when lighting was hard to come by and we didn't have all our gadgets. Certainly, giving people a financial incentive to have children only goes so far and has not proved to be the silver bullet.

Predicting many decades ahead is a dangerous game to play, and anyone reading back will almost certainly find this book's arguments to be quaint and probably wrong. Technology changes so fast that women might be able to have children for many more years in the future, and may not even be needed to bring the baby to term.

[Julia Turner]

After the Spike tackles one of the most complex and divisive topics in contemporary history with thoughtfulness and nuance. Spears and Geruso have crafted a book that manages to be both intellectually rigorous and deeply human, a rare combination that elevates this work above typical academic or policy discussions.

What sets this book apart is the authors' ability to navigate the sensitive topic of population dynamics without falling into ideological traps. The authors' unique combination of empirical evidence and personal experience creates a narrative that is at once intellectually satisfying and emotionally resonant.

After the Spike is a book that trusts its readers to engage with complexity while never losing sight of the profound human dimensions of demographic change. In an era of oversimplified takes on complex issues, this thoughtful, evidence-based approach is both refreshing and necessary. Most importantly, it is a book that you could (and should) read with and share with anyone in your life.

[Michael Schwenger · Rating 3 out of 5]

This book has some pretty interesting info and anecdotes. They describe the problem of population decline pretty well, but the proposed solutions are super disjointed and contradictory. In Chapter 11, they describe how investing in support for parents (free or subsidized daycare/healthcare/parental leave) has shown zero success at preventing declining birth rates in Sweden and other countries. 30 pages later, they seem to present the same idea as the solution to the problem.

[Francis Tapon · Rating 5 out of 5]

The University of Texas authors, Dean Spears and Michael Geruso, have written a mind-blowing book! It's my second favorite book of 2025!

The Population Whimper

When I was born, Paul R. Ehrlich's book, The Population Bomb, was a mega-bestseller. Although I never read the book, my generation believed the book's message that humanity is dangerously overpopulated. The book gave me one major reason not to have children. The book made intuitive sense, built on Thomas Malthus's observations, that if our population continues to expand, we will eventually hit a brick wall.

However, Ehrlich, a Stanford biologist, made these stunningly wrong predictions in The Population Bomb:

- Mass Starvation in the 1970s and 1980s: The book opened with the statement, "The battle to feed all of humanity is over. In the 1970s hundreds of millions of people will starve to death in spite of any crash programs embarked upon now." 
- England's Demise by 2000: He suggested that England would not exist by the year 2000 due to environmental collapse related to overpopulation.
- Devastation of Fish Populations by 1990: He predicted that all significant animal life in the sea would be extinct by 1990, and large areas of coastline would need to be evacuated due to the stench of dead fish.
- India's Famine: He predicted catastrophic food shortages in India in the 1990s that did not materialize.
- United States Food Rationing by 1984: He envisioned the U.S. rationing food by 1984.

Instead of all this doom and gloom, here's what happened: we went from 3.5 billion (when Ehrich wrote his doomsday book) to 8 billion people today, most of whom are fat. Today, our biggest problem isn't famine but obesity.

Dean Spears and Michael Geruso's new book should have been called The Population Whimper because it says the opposite of what The Population Bomb said. Forget a catastrophic demographic explosion. We're going to suffer a catastrophic demographic implosion.

The graph on the cover of After the Spike sums up the problem: during a 200-year time period, the human population will have spiked to 10 billion and then experienced an equally dramatic fall.


Three criticisms of After the Spike

For a book packed with counterintuitive arguments, it's remarkable that I can only spot three flaws. Admittedly, these are minor critiques, as they will disappear if we stabilize below 10 billion.


1. Wildlife lost

The authors correctly argue that the environment has been improving even as the human population has been growing rapidly. For example:

- Air and water are now cleaner than they were 50 years ago, when the population was half its current size.
- Our per capita CO2 consumption is falling.
- Clean energy production is at an all-time high.

There's one metric that authors overlooked: wildlife.

As the human population doubled, we've needed more space for growing food. This has led to a decrease in habitat, which is why biologists refer to the Anthropocene Extinction.

- While fish farms are efficient, overfishing continues.
- The Amazon gets denuded to make space for soy and cattle plantations.
- The loss of African wildlife habitats is acute, as the African population is projected to quadruple in this century.

I imagine that the authors of After the Spike would counter:

- National parks didn't exist 200 years ago.
- Green revolutions and GMO foods have made the most productive farmers ever.
- De-extinction may restore extinct species.

And they're correct. There are bright spots. 

However, as we approach 10 billion, wildlife will continue to suffer and be marginalized. The book should have mentioned that.

Dean Spears and Michael Geruso would likely agree that if humans continue to grow nonstop, wildlife will continue to suffer.

However, they aren't arguing for nonstop human expansion. They want stabilization.

When you combine stabilization with technology (e.g., vertical farming and lab-grown animal products), we would reverse the downward trend in wildlife habitat.


2. Increased energy consumption

Dean Spears and Michael Geruso celebrate humanity's progress in energy efficiency and productivity. However, they overlook these facts:

1. The Rebound Effect (Jevons Paradox):

As energy efficiency improves, the cost of using energy services effectively decreases. This can lead to:

Increased usage of existing services: For example, more efficient air conditioners might lead people to cool their homes to lower temperatures or for longer periods. More fuel-efficient cars might encourage more driving.

Adoption of new energy-intensive activities: The increased affordability of energy services can enable entirely new consumption patterns that were previously too expensive to adopt. Think about the proliferation of data centers for AI and digital services, or the growth of electric vehicles. While individual electric vehicles (EVs) are more efficient than gasoline cars, the rapid increase in their adoption contributes to overall electricity demand.

2. Economic Growth and Rising Living Standards:

Increased demand for energy services: As economies grow and incomes rise, people generally desire greater comfort, convenience, and a wider range of goods and services. This translates to greater demand for heating and cooling, larger homes, more personal transportation, more manufactured goods, and more leisure activities, all of which require energy.

Industrialization and urbanization: Developing economies, in particular, are undergoing rapid industrialization and urbanization. This involves massive construction, increased manufacturing, and the expansion of infrastructure, all of which are highly energy-intensive. Even with efficiency gains, the sheer scale of this growth drives up overall energy consumption.

Emerging technologies: The growth of data centers, AI, and other digital technologies is leading to a significant increase in electricity demand.

3. Population Growth:

While efficiency might improve per unit of output, the overall global population continues to grow. More people, even if individually more efficient, will inherently consume more energy in total.

4. Shifting Economic Structures:

Some economies are shifting from less energy-intensive sectors (like agriculture) to more energy-intensive ones (like manufacturing or specific services).
Even within industries, while individual processes might become more efficient, the overall scale of production can increase dramatically.

5. Energy Price and Policy Factors:

Low energy prices: If energy remains relatively inexpensive (due to subsidies or abundant supply), the incentive for significant behavioral changes to reduce consumption might be diminished, even with efficient technologies available.
Policy limitations: Although many countries have energy efficiency policies, their impact may be offset by other factors that drive demand.

THEREFORE: While technological advancements and efficiency measures reduce the energy intensity of specific activities, these gains are often outpaced by the aggregate increase in demand for energy services driven by economic growth, rising living standards, population increases, and the adoption of new, energy-intensive technologies and behaviors. The challenge lies in achieving a proper decoupling of economic growth from energy consumption, and ultimately, from carbon emissions.

Humanity's per capita energy consumption has been steadily increasing with each passing century, a trend that is unlikely to change soon. Therefore, humans of the 26th century will consume far more energy than those of the 21st century. 

The authors of After the Spike would probably argue that in 2525, we'll be using a clean energy source (e.g., nuclear fusion), so it'll be irrelevant that our per capita energy consumption increases ten times. 

Again, short term, we're going in the wrong direction. However, in a stabilized world, we won't have a problem.

3. Designer babies

The authors of After the Spike never addressed the potential impact that designer babies may have. I coined the term "Homo-enhanced" to address our desire to overcome our biological limitations. 

Couples are already using IVF to select the gender and eye color of their babies. Soon, we'll be able to edit and select for more complex traits such as height or even intelligence. It's easy to imagine a world like Gattaca, where parents collaborate with CRISPR-powered gene tools to create custom-made babies.

One reason some people don't want to reproduce is that it's a crap shoot. Any parent who has more than one child will tell you that each of their children is quite different from the others. Given that they grow up in the same environment, it suggests that genetics is a decisive factor.

Until now, we couldn't mold our children's DNA. Soon, we will. 

If we were to remove the lottery aspect of having a child and allow parents to design their children, perhaps there would be a baby boom.

Dean Spears and Michael Geruso would probably argue that this is unlikely or centuries away from happening. We'll be descending the steep population slope long before we are homo-enhanced.


One trillion humans in this millennium?

In the Bulgaria chapter of my book "The Hidden Europe," I observed that Bulgaria is depopulating faster than any other European country. Having peaked at 9 million in the late 1980s, a century later, it will be half that size.

Despite that, in that chapter, I predicted that in 500 years, we'll have one trillion humans in the solar system, with at least 100 billion on Earth.

This video explains how and why that may happen: 
https://www.youtube.com/watch?v=8lJJ_...


Conclusion

In 2075, will After the Spike: Population, Progress, and the Case for People look as stupid as The Population Bomb looks 50 years after publication? Does After the Spike make the same errors as The Population Bomb?

Paul Ehrlich's underestimated technology and the continued collapse in fertility rates. As Dean Spears and Michael Geruso point out, fertility rates have been declining since they were first measured. Had Ehrlich extrapolated the trendline, he would have realized that our demographic collapse was imminent, not an explosion. Furthermore, technology solved many of the problems Ehrlich imagined.

Is After the Spike making the same error?

Fertility rates won't fall forever. They must stop. Otherwise, we'll become extinct.

However, will fertility rates soar due to technology or some other reason? What could make our fertility rates return to three or more? Here are a few ideas:

- We master fusion energy, providing us with ultra-cheap energy and dramatically decreasing the cost of having children.
- Robots perform most jobs, leaving humans with ample time to raise large families. 
- As the negative effects of depopulation start rippling across the world, a global cultural panic erupts, prompting people to prioritize reproduction.
- Homo-enhanced humans, merged with artificial general intelligence, decide to proliferate to dominate the planet.
- Vertical farms and lab-grown cultured meat improve the environment so dramatically that humans feel less guilty about having three or more children, and generous subsidies offset the costs.

Admittedly, these scenarios are unlikely to occur within the next 50 years, so "After the Spike" won't become the joke that "The Population Bomb" became in 50 years.

Still, I predict that Ehrlich's great-great-granddaughter will write The Population Bomb II: Thomas Malthus Will Be Right Someday.

If you're still undecided, consider that the book features numerous graphs and illustrations that will rewire your brain. Buy After the Spike: Population, Progress, and the Case for People.

Verdict

10 out of 10 stars!

[Susannah Petitt · Rating 4 out of 5]

Great read as an introduction to demographic economics and why birth rate declines need to be reversed
A left wing and modernized Julian Simon’s Ultimate Resource

[Katherine · Rating 5 out of 5]

An extremely timely book on the falling global fertility rate, accessible and enjoyable to read even if you're not an expert. This book challenges the widely accepted idea that shrinking populations are a net positive for the global community. Like many, I grew up hearing that smaller families were essential to fighting climate change, but the authors make a persuasive case for disentangling these two important issues, and present a rational argument for why more future lives are important. They also explore the path ahead, including the possiblity of public policies which could try to change birth rates, and reveal that most of them fall flat. It’s both a puzzle and a powerful call to action- how can we build a future that welcomes more children into the world?

[Redmer Nijboer · Rating 3 out of 5]

Concept is great, but book could have been more creative in offering solutions and providing some more perspective on what could resolve the problem the authors laid out.

[Marcus W · Rating 2 out of 5]

I find a lot of the criticisms of other reviewers here silly. The political debates Americans are obsessed with seem to leave them unable to read this book for what it is. The progressive advocating is not the issue with this boom. The issue is rather that it's written by two authors who seem to have lived lives with broad and varied experiences, yet write as if they have spent their entire lives stuck in the offices of a university.

There are no compelling or relatable arguments or philosophical discussions in this book. I've often discarded the ivory tower description of academics, yet this book makes me fully understand it.

Perhaps the most remarkable aspect of this book is that it turned me from being in favor of a higher birth rate to not wanting to be associated with people on the left or right holding that position.

If fewer people means less academic work like this it might be a good idea after all.

[Peter · Rating 3 out of 5]

If you've been following pro-natalist views, and especially the demographic aspects of it, this book is a pretty big disappointment. I hope it doesn't become the popular book on this view. The book has odd digressions (I guess they had to make their word count), too many anecdotes about the author's lives, and lots of sequiturs. Read it if you don't know much about the issue; then move on to better developments of the view.

[Fin Moorhouse · Rating 4 out of 5]

You stand now at the top of the Spike with 8 billion others. The story of the future starts with understanding the fact that most of those 8 billion others don't (or didn't, or won't, once they grow up) aspire to parent very many children.

It's obviously a world-important topic, whatever your particular views on it. And this is about a good as a popular treatment of world population and trends in fertility than you could hope for: clear-headed, humane, careful. Similar vibe to Hannah Ritchie, who is quoted extensively.

Things I learned: globally speaking TFR has effectively always been declining since the first good records. Declining fertility is not a break in a trend; but passing from meaningfully above 2.0 to meaningfully below 2.0 nationally and soon internationally is and will be new, and marks the break from ~exponential population growth to ~exponential decline. Yes TFR is notably low in rich countries, but it not distinctive to rich countries. India is below replacement, China is well below at 1.00. I doubt I was alone in vaguely thinking population decline would reverse once high-fertility groups come to dominate the general population, i.e. the Amish will inherit the Earth. But, no, this is not at all given and looks empirically untrue. And finally we know very little about how to turn things around through public policy.

It is very, very salient how cautious Spears and Geruso are trying to be about the politics of population decline. As a topic it is so strongly associated with the political right, and (in the views of many) a particular kind of creepy, prying obsession with controlling women's reproductive choices, continuous with trying to restrict access to reproductive healthcare and even contraception. The authors obviously don't share these politics and (rightly) want to rescue the topic from its current political connotations. I am mostly very glad they are taking on that task, though given that I trust Spears and Geruso are not in fact prying misogynists, I might have preferred more focus on content and information and less of the defensive caveats and niceties.

It's also notable how much population decline has in common with climate change as a social issue, given the very different cultural valences of the two topics to date. Both are problems of global and intergenerational public goods and bads; both problems of underincentivised externalities; both problems where poorer countries are largely exempt from blame; both problems where are choices today only really return to us decades hence.

[Eric · Rating 5 out of 5]

Such a provocative and powerful call to think creatively about humanity’s future!

In After the Spike, Dean Spears and Mike Geruso offer a penetrating disruption to many commonly-held misconceptions about the consequences of the rise (and fall) of human population. Supported by thoughtful research and analysis, using data from across the global historical record, Dean and Mike debunk misconception after misconception. And they do so in the most inviting way. They share about their own lives and families as they endeavor to bring the reader beside them as they share their thinking, based on research, about the state and future of human life. They also ask hard questions about that future and challenge us to consider our role in charting a course forward.

In reading After the Spike, I saw clearly how I had oversimplified many demographic issues and jumped to incorrect conclusions. I had accepted assumptions about causal connections between population and environmental, social, and economic problems. Those assumptions have been passed around like superstitions, and they lived in my mind as truths. It turns out that having more people does not have to equate to having more problems. Not only were the causal connections debunked, but in many cases Mike and Dean revealed there wasn’t even a correlation.

The environmental, social, and economic problems we face arise from (or are resolved by) the choices we make. And, the good news is that, “most progress in science, technology, and society is the lift of many hands and many minds.” Dean and Mike offer an optimistic view of our ability to think and work together. They don’t pretend to know all of the solutions. Rather, they ask great questions that call for us to join them in creating solutions.

We face a coming change from population growth to population decline. Dean and Mike invite us to consider carefully what we will lose if we allow depopulation to proceed, and they make a strong case for stabilizing human population. This stabilization would require a significant shift in the current trend in falling birth rates. That is a delicate and complex conversation, and the authors do an excellent job laying out the intellectual, social, and emotional terrain we would need to traverse if we choose to encourage people to produce more people. As parents themselves, Dean and Mike recognize the challenges inherent in having and raising kids. From the start, they make it clear that, “This book is not about whether or how you should parent. It’s about whether we all should make parenting easier.”

[Leslie]

A mixed bag, honestly. My biggest frustrations were the weird end-of-history vibes, the sometimes handwavy demography, and the painfully naive belief that "depopulation" is something we can talk about (and even "solve") without courting a massive antifeminist backlash. They argue that women's progress happened while fertility rates were around 2 (in the 60s-90s); therefore, a society in which maintaining a fertility rate of around 2 *is positioned as a dire need* wouldn't have to be bad for women. I don't think the latter follows from the former at ALL. And I don't think saying "look, if you want to raise the birth rate, oppressing women doesn't even help" (which they do, in detail) is a winning counterargument to the kind of people who are generally interested in population collapse narratives, as recent developments in American culture and politics make clear. The oppression is kind of the point. (Overall I'm a bit sad for them that the book came out under Trump - it takes a bit of the shine off the Ezra Klein-style "gee whiz, everything's simply getting better, forever" tone.)

That said, there were parts I liked. The population and environment chapter was very good, as was the "coercive population control doesn't work" chapter (despite caveats above re: rhetorical effectiveness). I even liked the energy and general thrust of the conclusion's focus on how a society that values children might look different - even though I strongly disagree that we need to get to work on "stabilizing the population" right now.

I don't know if someone with different political commitments than mine might find the arguments more appealing; I think any reader might find them a bit wishy washy. We want more babies--but only if people want! We think more humans are better--but we'll only go as far as arguing for "stabilization" at some unspecified number, not growth! I think this is because it's actually very hard to be in favor of population targets and also be humane. They're trying their darnedest (and I do think they're humane!) but it just falls flat without a much more thorough excavation of the political and philosophical commitments that motivate their relative restraint.

[Elizabeth]

As heard on The Indicator from Planet Money (We're nearing 'peak population.' These economists are worried)

Over the past century, the world's human population has exploded from around 2 billion to 8 billion. Meanwhile, the average fertility rate has gradually declined. And if that trend continues as it has, we may soon see a crash in the population rate, which some argue could have disastrous effects.

Today on the show, we talk to co-authors Michael Geruso and Dean Spears about their forthcoming book After the Spike: Population, Progress, and the Case for People . Together, they explain why you should care about declining fertility rates.

Related episodes:
Babies v climate change; AI v IP; bonds v world

For sponsor-free episodes of The Indicator from Planet Money, subscribe to Planet Money+ via Apple Podcasts or at plus.npr.org .

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[Andrew Kondraske · Rating 4 out of 5]

"After the Spike" is what a good, contemporary non-fiction book directed at an educated but lay audience should be: well-researched and thorough, but without getting lost in too many technical details or academic jargon; possessing a clear, well-articulated point of view about its subject matter; informed by a willingness from the authors to share details from their personal backgrounds that shape said point of view; offering humility towards the limits of what current knowledge can tell us about the subject matter; written in an accessible, relatable prose that makes the reading breezy.

There were some minor points where I wasn't quite on board with the book's conclusions, most notably the assertion that more people inherently equates to more progress and innovation. Their case is well-argued and it strikes me as generally true, but perhaps less relevant for our current situation. A world with 5 billion people is certainly going to create more than a world with 10 million, but will a world with 10 billion create more than a world with 5 billion? Does the sheer number matter less than whether the population is increasing or delcining? OR does ther number of people matter, but much less so in the post-industrial knowledge environment we are in now, and perhaps even less so in whatever sort of scientific and economic conditions we are heading into? These are empirical questions, but ones that are almost impossible to answer. I'm glad the authors have raised them, but not totally convinced they represent the most persuasive case for directing our efforts at bending the population curve back up.

In any case, I do think our impending population decline is a real issue that will hav e dramatic effects across the globe, and one that perhaps isn't getting enough attention outside of niche online communities. I'm glad this book exists and hope that more folks give it attention.

[Ahmed · Rating 3 out of 5]

This is one of those books that feels like a long, careful blog post accidentally left in the oven until it turned into an academic monograph.

Dean Spears has a deceptively modest goal: to understand why population growth rates are declining, what that means for human welfare, and whether we should be worried that the world might soon run out of people who want to have people. It’s the kind of question that sounds like a setup for a dystopian Netflix series but ends up being about fertility rates, GDP, and something called “the spike” (basically, the once-in-a-species demographic surge we’ve just lived through).

Spears argues that more people, up to a point, might actually be good, because ideas come from brains, and more brains mean more ideas. The book’s best parts connect population dynamics to innovation rates and moral progress, like if The Case Against Education and Superforecasting had a nerdy demography baby. He even wanders into the “longtermist” territory without saying the word: asking what happens when the lights of civilization slowly dim because nobody’s left to keep them on.

But the prose often feels like it’s being held hostage by regression tables. Spears is obviously a brilliant economist, but at times it’s like reading a very polite argument between Excel sheets. He’s careful to never make a moral claim stronger than “we should think about this more.” I respect the restraint, but it left me wishing for more of the fiery weirdness that makes a book like this stick.

Still, the central thesis: that a shrinking population is not just an economic problem but a moral one, lands. It’s the kind of book that doesn’t change your mind immediately but quietly rearranges the furniture inside it.

Verdict: An earnest, data-driven case for worrying about low fertility that stops just short of saying “Elon Musk was right.” Worth reading if you like your existential risk with p-values.

[Will Clark · Rating 4 out of 5]

Important, thoughtful and measured.

I picked up this book because a couple years ago I made a tit of myself opining about our “unsustainable and selfish” population size in an environmental class. I approached the issue from a nature orientated perspective that led me to conclude: there are too many people on the planet.

I now believe I was wrong. The authors are respectful and evidenced in the way that they both deconstruct the assumption of increased carbon emissions with a larger population and the now obvious and imperative benefits that a larger population bring for the of our quality of lives.

However, I think the authors left whole in their argument by failing to acknowledge that we share this planet. That the size of our population and the way we live our lives affects the lives and systems of the natural world. I don’t think it’s a fundamental flaw and I can see how changes in food production and efficiency increases in land use could mane positive progress from where we are today.

Despite this gap, the book succeeds in confronting an awkward yet looming issue that so far has been the territory of the religiously minded far right. It does this with honestly about the scale of the problem, respect for women and effectively counters the narrative surrounding women’s role in a more fertile society that dominates much of those of the rights thinking surrounding population.

Critics argue that the book fails to provide solutions and a way forward. However, I think this is one of the authors best decisions. It respects the readers ability to be left without the satisfying feeling of “there’s a plan it’s all going to be ok”, and respects the complexity of the issue by acknowledging that so much more work needs to be done and this book is only the start of the beginning of that work.

It won’t satisfy those desperate for an excuse to return to the 1950s, and it doesn’t have all the answers. And that’s why it’s a fine book.

[E · Rating 3 out of 5]

I appreciate the authors' interest in the reality that the global fertility rate is dropping below 2.0 (replacement level). Infant mortality is almost to zero and obviously can't go any lower, while life expectancy is growing but obviously could never offset a fertility rate lower than replacement level. So total global population will plateau and then begin to decline.

Once it begins to decline, it will do so (relatively) quickly, and could be below 2 billion in 300-400 years, especially if fertility continues to drop.

That's all facts thus far. As for why to care and what to do about it, the authors are as strong on the former as they are on the latter. We need a critical mass of humans in order to ensure that standards of living will continue to increase. The authors also warmly welcome the value of a decent life, even if not one with Western income levels. They do this from a secular perspective.

The authors are strongly opposed to forcing women to have babies. I totally agree. But somehow they think this means be opposed to abortion. Being pro-life is not "forcing women to have babies." That is looking at it exactly backward.

Anyhow, as I said, they are very weak about how actually to increase fertility levels. They do point out that no one else has figured it out either, anywhere on the planet. They do not think religion is the answer--they note how even groups like the Amish or hardcore Muslims are decreasing in rate (yet still above replacement). I'd argue that Bible believing Christians have been above 2 for thousands of years, and still seem to be so. But that would require some serious statistical work to prove.