The Depopulation Bomb
What if the challenge for humanity’s future is not too many people on a crowded planet, but too few people to sustain the progress that the world needs?
After the Spike: Population, Progress, and the Case for People, by Dean Spears and Michael Geruso, Simon & Schuster, 320 pages, $29.99
Natalist panic is rife nowadays. The White House is weighing initiatives to boost the number of births, ranging from a $5,000-per-baby bonus to awarding "National Medals of Motherhood" to mothers with six or more children. In March, the NatalCon gathering in Austin, Texas, declared that we're "living through the greatest population bust in human history." In April, the tech billionaire (and father of 14 children) Elon Musk posted on X: "Low birth rates will end civilization."
And yet the world's population continues to grow: 132 million people were born in 2024, boosting the global population by 71 million. Over the course of my lifetime, the U.S. population has risen from 160 million to 342 million and the world population has grown from 2.6 billion to 8.1 billion.
Still, given current trends, demographers calculate that world population will likely peak at just over 10 billion later in this century and then start to fall. Why? Because people are choosing to have fewer children. The total fertility rate—that is, the number of children the average woman has over the course of her lifetime—has been falling for decades. On a global scale, it has dropped from 5 kids in the 1960s to 2.2 children now. In the U.S., the rate has fallen from around 3.6 in 1960 to 1.6 today. That is well below the population replacement rate of 2.1 children per woman.
Even if Musk's end-of-civilization worries are a bit hyperbolic, should we be concerned about impending depopulation? In After the Spike, the economic demographers Dean Spears and Michael Geruso argue, somewhat persuasively, that we should.
The book's first section shows that current fertility trends will yield a spike in population followed by accelerating population decline. Since many people still believe that a world with fewer people is worth pursuing, the authors next turn to dismantling the case against more people.
The most infamous modern prophet of population doom is the Stanford biologist Paul Ehrlich. In his 1968 bestseller, The Population Bomb, Ehrlich proclaimed that the "battle to feed all of humanity is over. In the 1970's the world will undergo famines—hundreds of millions of people are going to starve to death in spite of any crash programs embarked upon now." Instead of that doomsday scenario, farmers deploying modern tech have boosted the number of daily calories per person by more than a third since the 1960s. Instead of rising death rates, global life expectancy rose from 57 years in 1968 to 73 years now.
Spears and Geruso comprehensively demolish Ehrlich's doomsaying. They fully acknowledge that human activities have harmed the natural world, but they make a strong case that human ingenuity is addressing such environmental concerns as man-made climate change and declining biodiversity. "The data tell us that lives are better now than lives were in the past—even though there are many more lives around. Fears of a depleted, overpopulated future are out-of-date," they rightly conclude.
So why are birth rates falling all over the world? The authors knock down the conventional hypothesis that rising monetary costs are to blame. The real costs of children, they argue, are the opportunity costs: "what a potential parent would be ready to give up to have an extra child." The seductions of the modern world include higher paying work, longer vacations, restaurant meals, sports, video games, innumerable on-demand entertainment options, and so forth. "Once we see that costs include opportunity costs, as life becomes richer and more rewarding, children cost more," they say. "Even if we eliminated every dimension of social inequality and unfairness between women and men, the opportunity cost of having a child would still be greater in the richer, freer, better-entertained future than it was in the past." And as demographic history shows, fewer and fewer people are willing to pay those costs.
The authors fear a depopulating world will bring permanent economic and social stagnation. More people mean more ideas, and more ideas mean increasing abundance and better solutions to problems. "Without people to do the discovering, innovating, and testing, less creation will happen. Less advancement. Less progress," they argue. "A larger future is a future with more total innovators."
To have that more innovative future, Spears and Geruso want to move from depopulation to population stabilization. "The economics of scale and shared innovations mean that we can do more good together than alone," they observe.
Spears and Geruso admit that they and other demographers have identified no policies that have ever lifted a country's total fertility rate once it has fallen below the replacement level. They point out that "population control has never controlled the population." To illustrate their point, they compare China's fertility trend under its one-child policy to the trends of peer nations. There is no discernable difference—fertility was falling at basically the same rate in each country.
Neither outlawing abortion nor limiting contraception has had any discernable effects on these trends either. For decades, procuring or providing an abortion was a crime in South Korea, a policy that didn't end until 2019. Yet that country has the world's lowest fertility rate of 0.75 children per woman.
What about cash payments, subsidized child care, longer maternity and paternity leave, or free in vitro fertilization treatments? None of them, wherever tried, have sustainably boosted birth rates.
Spears and Geruso also take on the argument that the heritability of high-fertility cultures will prevent depopulation. This is the idea that the children of groups that give birth to large families will themselves choose to have big families. Consequently, these high-fertility groups will eventually outbreed and replace the low-fertility people and thus boost future population growth. One problem: Contemporary high-fertility groups today have lower fertility than in their own pasts. They too are tracing the downward slope toward below replacement fertility.
Despite these policy failures, Spears and Geruso worry that demagogues will use concerns over low birth rates to pursue unsavory agendas "of inequality, nationalism, exclusion, or control." While they strongly believe that "it would be better if the world did not depopulate," they also defend reproductive freedom. "Nobody should be forced or required to have a baby (or not to have a baby)," they maintain.
The book's biggest flaw is that the authors mostly elide the inception and spread of the crucial economic and political institutions of liberty—strong property rights, free speech, the rule of law, self-government, etc.— that enabled the simultaneous increase in prosperity and population over the past two centuries.
So what to do about depopulation? Spears and Geruso say they do "not pretend to offer the Solution. There is no Solution with a capital S. Not yet." Instead they invite readers to work toward societies where "parenting can be combined with other paths to well-being and value; where parenting is fun, rewarding, and great more of the time." Avoiding depopulation is a worthy endeavor, but that means figuring out how to lower the opportunity costs of parenthood.
This article first appeared online and has been updated for print.
