In February 2008, a documentary film titled Demographic Winter: The Decline of the Human Family premiered at the Heritage Foundation. Featuring economists and scholars such as Nicholas Eberstadt, Alan Viard, and Kay Hymowitz, a banner declared that the film’s subject matter—the global dearth in children being born—represented “the single most powerful force directing the fate and future of society.”
At the onset of the Great Recession, the topic of low fertility rates attracted little interest from journalists, policymakers, or the public at large. A scathing review of the documentary in Harvard Divinity Bulletin lambasted an “insidious undercurrent” that ostensibly dog-whistled a nefarious agenda of the religious right.
But 17 years later, Demographic Winter proved to be remarkably ahead of its time. As two-thirds of people now live in countries with sub-replacement fertility rates and economies undergo “Japanification,” with more retirees than workers, the baby bust is no longer considered a partisan or marginal issue.
Headlines about the challenges of aging and shrinking populations now abound across the mainstream media, and a series of acclaimed books by decidedly non-conservative authors recently hit shelves, including Darrell Bricker and John Ibbitson’s Empty Planet: The Shock of Global Population Decline (2019) and Charles Goodhart and Manoj Pradhan’s The Great Demographic Reversal: Ageing Societies, Waning Inequality, and an Inflation Revival (2020).
The latest such book, After the Spike: Population, Progress, and the Case for People (2025), co-authored by economists Dean Spears and Michael Geruso, repudiates the longstanding myth that the world is overpopulated, which still lingers in popular culture and public opinion. In a straightforward and cogent manner, Spears and Geruso demonstrate that people are a net good—for innovation, for rising living standards, and yes, even for the planet.
Spears and Geruso provide a thorough rebuttal to the claim that people are having fewer children because of a lack of affordability, highlighting the role of opportunity costs in shaping fertility decisions, at least in rich countries.
But with fertility rates on the wane globally, After the Spike also presents a comprehensive analysis of the causes and consequences of depopulation and a compelling call to action. Even Princeton professor emeritus Peter Singer, who has long pushed the overpopulation argument, endorsed the book and said it challenged and changed his thinking about population.
Echoing the economic insight of Julian Simon, the co-authors note that “a good idea does not get used up.” The world is not a fixed pie, and population growth contributes to an increase in “non-rival innovation,” which benefits everyone through greater technological progress. One person’s good idea “gets copied and reapplied, endlessly.” The results of the famous wager between Julian Simon and Paul Ehrlich have demonstrated that we aren’t going to run out of resources and starve to death in a Malthusian catastrophe. As Simon correctly predicted in his 1981 book The Ultimate Resource, a rising number of “skilled, spirited, and hopeful” people results in more ingenuity, abundance, and lower prices over time.
In the years 1990–2019, global food production surged by 61 percent as the world population increased by 45 percent. In that same period, global extreme poverty fell from over one-third to less than 10 percent, and the prices of commodities became much cheaper, as Simon anticipated. Apart from wars or government mismanagement, famines have virtually disappeared.
Despite these vast improvements in material well-being, many are still gravely worried about climate change and the impact of 8.2 billion people on the earth’s ecosystems. Spears and Geruso take the threat of global warming seriously, but they also showcase how depopulation is not a path to decarbonization. Nor is there a theoretical or historical relationship between population size and particulate air pollution. Whether the population stabilizes or declines, the global temperature is still forecast to rise. “Billions of lives lived would make a small difference to this big problem,” they said.
The solution, then, requires more brains, not fewer. Our “strength is in our numbers, not just our rare luminaries.” Low fertility rates means fewer creative and scientific geniuses will be born to meet the immense challenges of the twenty-first century. As the co-authors warn, “There is no clean energy future, no answer to carbon emissions, without technological progress.”
Since the Industrial Revolution, humans have created a freer, healthier, and more prosperous world where more people can live good, happy lives. Yet these improvements have ironically led to a state of affairs in which people want to bring fewer children into an objectively better world.
Why? Most insightfully, Spears and Geruso provide a thorough rebuttal to the claim that people are having fewer children because of a lack of affordability, highlighting the role of opportunity costs in shaping fertility decisions, at least in rich countries. Fertility preference surveys, which ask respondents their “ideal fertility,” may find that people cite financial limitations as a main reason they’re having fewer children, but these surveys don’t reveal the fuller picture. They don’t ask people what they’re willing to give up to achieve their “ideal fertility.”
“Once we understand ‘too expensive’ to be about opportunity cost (rather than only money cost), we can see that there are ways that children have become more costly, if not exactly less affordable,” Spears and Geruso said. “Parenting a child, or another child, could mean scaling back educational goals, career plans, or other ambitions.” One study, cited in the book, shows no correlation in the United States between cost-of-living increases and reduced child-bearing since the Great Recession. Fertility rates dwindled in every state, yet they did not fall faster or more significantly in states where prices went up the most, as the affordability hypothesis would claim.
Government intervention via pro-natal policies or even free in-vitro fertilization (IVF) won’t meaningfully change these fertility patterns since people will only have as many children as they desire.
Spears and Geruso acknowledge that they don’t have an answer to the ultimate question that now puzzles demographers and economists: Why is fertility declining everywhere, in rich and poor countries alike?
Contrary to the Demographic Transition Model, which posits that child-bearing plummets with rising affluence and women’s empowerment, the co-authors point out that there are exceptions to every theory of declining fertility. For example, India is a sub-replacement society, yet Indian women marry young and enjoy fewer freedoms than their Western counterparts. Sub-replacement fertility is also occurring in Myanmar, Nepal, and Bangladesh, which are designated by the United Nations as least developed countries (LDCs).
Government intervention via pro-natal policies or even free in-vitro fertilization (IVF) won’t meaningfully change these fertility patterns since people will only have as many children as they desire. And the reality of the twenty-first century is that people worldwide want fewer children. A 2025 United Nations Population Fund (UNFPA)/YouGov survey found that the most common number of children people around the world want is two.
The economics profession has not yet provided a definitive explanation as to why people almost everywhere desire, and are having, fewer children. As Nicholas Eberstadt said, “The genius who finally answers that question will deserve a Nobel, but I think it’ll be a Nobel in literature and not in economics. He or she will have to channel the global zeitgeist, chart the shifting coastlines of the modern mentality, and explore the secrets hidden in billions of human hearts.”
Overpopulation anxieties are still widespread globally, with nearly half of Americans believing that the world’s population is too high, according to a 2022 YouGov poll. But if Spears and Geruso were able to change Peter Singer’s mind, perhaps they can achieve the same effect among a much wider audience.
After the Spike doesn’t have a solution to the coming global depopulation, nor does it claim to. It is a call for decision-makers and the public to begin preparing for a future with fewer humans, which is inevitably and steadfastly approaching. For up-and-coming scholars, journalists, and policymakers in Gen Z, this book outlines the dilemmas and discussions that will become increasingly pressing as they assume leadership roles in society. It is therefore an essential read for the younger demographic, which may inherit and grow old in a world “after the spike.”