Welcome to the population paradox of the 21st century.

By Bryan Walsh

On November 15, 2022, according to the demographers at the United Nations Population Division, the 8 billionth person on the planet was born.

That 8 billion mark is an estimate — there is no real-time census of everyone alive on Earth at every given moment, which means there’s a margin of error on either side of 8 billion. But someone will be or already is Baby 8 Billion.

He or she is most likely to be born in India, which had more than 23 million births last year — 13 million more than second-place China, which India will soon pass as the world’s most populous country. And he stands a better than even chance of being a he, since boys naturally outnumber girls at birth by a rate of about 105 to 100; in India, due to a mix of cultural preference for boys and access to sex-selective abortion, that rate is closer to 108 to 100. With an average life expectancy in India of just under 70 years today and rising, our hypothetical Baby 8 Billion stands a decent chance of being alive to witness the dawn of the 22nd century.

How many other human beings will be there with him to see the calendar turn to 2100? If you think it’s tricky to count the number of people alive today, accurately projecting global population nearly 80 years into the future is near impossible, requiring countless estimates about birth rates, death rates, and movement — “sex, death, and migration,” in the words of the demographer Jennifer Sciubba. Estimated global population in 2000 stood at 6.09 billion, which would have been a surprise to the UN demographers of 1973, who projected that it would be almost 410 million larger by the turn of the millennium — an overestimate bigger than the current population of the United States.

The best guess we have — the medium scenario, according to UN demographers — is that by 2100, global population will have leveled off at around 10.4 billion. What that number means — and whether you even believe it — says a lot about what you think about the future of the planet, about the global power structure decades from now, and even about the purpose of being human.

For those who see every additional human being as one more consuming, carbon-emitting unit on a hot and crowded planet that is already well past its carrying capacity, the idea of 8 billion people — let alone 10.4 billion — is the last mile marker on the road to a climate and environmental catastrophe. It’s an old fear that dates back to the grim prophecies of the 18th-century English cleric and economist Thomas Malthus, who wrote that “the power of population is indefinitely greater than the power in the earth to produce subsistence for man.”

He has thus far been proven wrong — even with a global population more than 7 billion people larger today than in Malthus’s time, life is a whole lot better and longer on average — but his influence can still be felt in certain corners of environmentalism. It’s the animating idea behind one of the most influential modern treatises on the topic: the 1968 book The Population Bomb.

But another group sees that 10.4 billion and fears we’ll never actually get there. They pay less attention to the seeming enormity of 8 billion, and more to the slowing pace of population growth, which is still increasing, but at less than 1 percent a year — its slowest rate since at least 1950. In virtually every corner of the globe, people are having fewer babies than their parents and grandparents did.

Two-thirds of humanity lives in an area where lifetime fertility is below 2.1 children per woman, the rough level a population requires to replace itself through births alone. That includes the US, where fertility has generally been below replacement level since 1971 and where population in 2021 grew at its slowest rate since the nation’s founding. It also includes China, where the nation that enforced the coercive one-child policy out of fears of overpopulation is now in a desperate struggle to turn around its rock-bottom fertility rates. Even if global population does reach 10.4 billion by 2100 or earlier, the UN projects it could actually begin to decline after. Should global fertility fall more than expected, that decline could begin sooner and appear sharper.

That would put our species on a path we’ve never walked before, outside of temporary dips from war, disease, or famine. Population worriers see an aging world of empty cradles, sapped of innovation and youthful energy, one where “population collapse due to low birth rates is a much bigger risk to civilization than global warming,” as Elon Musk — who, with eight children and counting, seems to be doing his best to turn the problem around single-handedly — tweeted this year. They fear an “underpopulation bomb” with a very long fuse.

The truth is that human population is complicated, and there may be 8 billion ways to be wrong about it. Fevered fears about overpopulation ignore the fact that the carrying capacity of the Earth is not and never has been fixed. Technological advances, improved efficiency, and changing consumption patterns allow us to get more people out of the same amount of planet, a possibility Malthus, writing at a time when human population had taken tens of thousands of years to reach just 1 billion, simply couldn’t imagine.

But those who fret about underpopulation miss the fact that demographic trends for the entire planet don’t move in a single direction. Even as most rich nations face aging and eventual decline, the very young populations of sub-Saharan Africa and parts of South Asia are set for decades of booming population growth. Trends may point to the last person in Japan dying in 2500, but Nigeria is on pace to pass the US with more than 400 million people by 2055.

Just as shifting technology enables us to get more out of the planet, advances in automation and life expectancy could get more productivity out of every worker, postponing the economic drag of fewer young people. And if the world finds a way to sustainably increase migration flows from the poor but young and growing countries of the Global South to the rich but aging and eventually shrinking nations of the Global North — think of it as solving a trade deficit, but for people — we could successfully manage a global demographic imbalance that only seems likely to grow.

Population matters. If humans have become the dominant force on this planet in the age of the Anthropocene, demography will shape that force. It will shape the number of people producing carbon emissions, the number of people who need to be fed, the number of people who come up with the innovations we may need to solve both of those challenges. It will shape the age structures of entire nations, their geopolitical clout, their economic power. Over a long enough period, it will shape what kind of future we have, and whether we have a future at all. Just as climate models give us a decent forecast of what the Earth itself will be like decades past today, demography gives us a glimpse into what humanity will look like in the future. And just as climate models are a product of both the impersonal forces of our planet and the energy and environmental policies we pursue, population is a product of both the unchangeable trends of the past and the choices nations make today around family policy, migration, and technology.

The debate over global population can feel like a dead end, an unending argument over too many or too few. But that’s the wrong way to look at it. We have the capacity to add more and we have the ability to make do with fewer. What we want isn’t a single, perfect number, but a world in which people have the ability and the support to have the families they desire, one where demography isn’t a destiny, but a choice.

Overpopulation: The bomb that did not go off

To understand the core of overpopulation fears, you need to read Paul Ehrlich’s 1968 book The Population Bomb. Ehrlich wasn’t a demographer — he was an entomologist by training, who co-wrote the book with his wife Anne (although only Paul appeared as the author on the cover) at the behest of Sierra Club executive director David Brower, who was deeply worried about the environmental effects of population.

But it wasn’t numbers that caused the book to sell millions of copies. It was the language, Ehrlich’s vivid ability to capture what he called in the opening scene “the feel of overpopulation,” and the clarity of his grim prophecies of what was to come as we grew and grew. “The battle to feed all of humanity is over,” the first sentence goes. In the coming decade, the book goes on, “hundreds of millions of people are going to starve to death” — and nothing we could do would prevent that.

The Population Bomb is one of the most influential books of the 20th century. It catalyzed growing fears that we were running out of room as a species, mindlessly reproducing ourselves into oblivion like bacteria in a petri dish.

Those fears contributed to a wave of population growth measures around the globe, and with that came serious human rights abuses and atrocities. In India under Prime Minister Indira Gandhi, tens of millions underwent forced sterilization in the 1970s. In China, the one-child policy introduced in 1979 prevented an estimated 400 million births. Experts like Ehrlich did not condone the very real coercion behind those efforts, but by casting population growth as an existential threat, they helped set the stage for them.

But if The Population Bomb blew up, the population bomb itself did not. There are now more than twice as many humans alive as there were when the book was published, yet hunger, poverty, and infectious disease — the coming disasters it predicted — have all largely lessened over the past several decades.

India, the central case in Ehrlich’s book, has nearly tripled its population since 1968, while largely growing richer, longer-lived, and less hungry. Famine has hardly been eliminated from the Earth, and in Ehrlich’s partial defense, he presented possible scenarios rather than predictions in his book, even if his language sometimes tipped into apocalyptic certainty. (It’s difficult to read the line “the battle to feed all humanity is over” as anything but “the battle to feed all humanity is over.”) But what he foresaw did not come to pass.

Between 1968 and 1978, global total fertility — the average number of children a woman will have over the course of her reproductive life — dropped by one entire child, to 3.8. By 1998, it had fallen by another child, and it kept on dropping, until today it stands at 2.4 children per woman, not that much above the replacement rate of about 2.1 children.

The rate of population growth fell as well, to the roughly 1 percent it sits at today. Our total numbers kept rising, of course, and someone from 1968 would likely find our world today unimaginably crowded; Delhi, the city where Ehrlich begins his book, has grown tenfold from 3.2 million to some 32 million. But that growth has slowed to a pace that the population bomb crowd likely wouldn’t have expected, even as the world proved far better at absorbing that growth than they would have predicted.

It’s easy to look back in hindsight and see everything that Ehrlich and others raising the population alarm got wrong. But it’s also easy to imagine that if the trends of 1968 had simply continued, the battle to feed humanity really was over. In 1968, global total fertility was nearly five children per woman. Annual population growth was 2.1 percent, by some estimates the highest it had ever been in human history, and — though now I’m at risk of making my own prediction — will likely be the highest humanity will ever see. And it came at the end of nearly a decade of growth above 2 percent, after nearly 70 years in which global population had more than doubled.

To look at a global population growth chart from the vantage of 1968 is to see a hockey stick that seems to have only one direction it could possibly go: up and up and up.

What’s wrong about The Population Bomb isn’t what’s interesting about it today, as we tip over to 8 billion people. The study of population, especially when it’s done with an eye to policy, has something in common with the study of subatomic particles: The act of observation changes what we observe. “People who dismiss [Ehrlich] for his inaccurate forecasts miss the point,” Jennifer Sciubba writes in 8 Billion and Counting: How Sex, Death, and Migration Shape Our World. “Forecasts don’t predict the future — they drive investments in the present.”

The mistake Ehrlich and his fellow travelers made was their assumption that the trends of the present would continue unabated into the future.

They failed to foresee the transformative effects of the Green Revolution: the transfer of higher-yielding seeds, chemical fertilizers, and irrigation methods to the Global South, a movement that would save an estimated 1 billion people from starvation and earn its chief figure, the agricultural scientist Norman Borlaug, a Nobel Peace Prize just two years after The Population Bomb was published.

They failed to foresee that in then-poor countries like South Korea, the total fertility rate had already been plummeting during the 1960s, creating a demographic dividend — that is, a surge in economic growth that comes from declining birth and death rates that lead to a bulge of young workers with fewer dependents.

They failed to foresee that as people across the world grew richer in the decades that followed, and as their children became increasingly likely to live to adulthood, they responded almost universally by having fewer babies, whether it was Pakistan, where birth rates dropped by almost half to 3.4 children per woman from 1968 to 2020, or the US, which went from 2.5 to 1.6.

Most of all, they failed to understand that there is no such objective thing as “overpopulation” — that the Earth has no fixed carrying capacity for human life. In prehistoric times with prehistoric technology, the limit might have been 100 million people. At the dawn of the 20th century, when the world’s population was around 1.6 billion, we may have been close to our limit, until scientists Fritz Haber and Carl Bosch created a means to artificially synthesize nitrogen fertilizer for crops at industrial scale in 1909-10, vastly improving agricultural productivity and creating what energy and environmental researcher Vaclav Smil called “the detonator of the population explosion.”

This is the story of humanity ever since our population began its upward swing in the 19th century: growth, whether of people or of material demands, brings us up against what appear to be limits, until we find a way to burst through and keep growing, only to repeat the process again.

To say there are side effects is putting it lightly. The explosive growth of human population has come at the direct expense of the wild animals that share our planet, not to mention the tens of billions of farmed animals that suffer to make our dinner. And climate change presents the greatest challenge of all — more people, after all, mean more carbon emissions and more warming. The fact that we’ve managed to innovate our way around what appeared to be unbreakable environmental limits in the past shouldn’t lead us to assume that we’ll always be able to do the same in the future. But while total carbon emissions have largely kept rising, albeit more slowly, global per-capita carbon emissions appear to have peaked around 2013 and have largely declined since, even as per-capita GDP has continued to increase.

This shift wasn’t inevitable — just as a mix of tools like contraception, shifting preferences, and some government policies contributed to a drastic drop in fertility and population growth, success against climate change will depend on the technologies we invent and the policy choices we make. But there’s reason to believe that just as we have largely decoupled food from population, we can do the same with carbon — especially if, as it turned out we were with population growth in 1968, we’re only at the beginning of a much more drastic decline.

Empty cradles: The underpopulation bomb

In 2015, the Chinese government did something it almost never does: It admitted it made a mistake, at least implicitly.

The ruling Communist Party announced that it was ending its historic and coercive one-child policy, allowing all married couples to have up to two children. That was how dire China’s demographic future had become.

The one-child policy had helped lead to the mother of all demographic dividends, as China’s working-age population grew from 594 million in 1980 to a little over 1 billion in 2015. China’s dependency ratio — the total young and elderly population relative to the working-age population — fell from over 68 percent in 1980 to less than 38 percent in 2015, which meant more workers for every non-working person.

More young workers who had fewer young or old dependents to care for was the fuel in China’s economic rocket engine. But no fuel burns forever, and over the past decade, hundreds of millions of Chinese have hit retirement age, with a plummeting number of young people to replace them. So the slogans went from “Having only one child is good” to “One is too few, while two are just right.”

How did the Chinese people react? Not by having more children. By 2020 China’s total fertility rate (that is, the number of expected births per woman over the course of their reproductive lifetime) had fallen to just 1.3. For the people of China, if not the government, it seems two was not just right.

So in 2021, the Chinese government tried again, turning the two-child policy into a three-child policy. That same year, fertility fell again, to 1.15, putting it among the world’s least fertile countries. The UN now projects that China’s population has peaked, while other demographers, noting the unreliability of government statistics in China, believe it has been shrinking for years. (Maybe a four-child policy will do the trick.)

If population decline can come for the first country to reach 1 billion people, it can come for anyone. And while China’s demography was skewed by the one-child policy, dozens of countries without a similarly coercive program have seen near equally drastic dropoffs in fertility, much older demographics, and population decline, either now or soon. The most recent numbers for Japan: 1.3 births per woman, and a population shrinking by 0.5 percent. For Italy: 1.2 births, and population shrinking by 0.6 percent. For Portugal: 1.4 and 0 percent growth. For Russia: 1.5 and shrinking by 0.4 percent.

The US, while long an outlier among rich nations in its relative fertility, is far from immune. Fertility has continued to decrease, especially after the 2007 global recession.

You can see the effects in the declining number of children in America. In 2022, some 24.8 million are under the age of 6. That’s about the same number as in 1962, during the height of the baby boom — but that year children under 6 made up more than 13 percent of the total population, compared to a bit over 7 percent today.

At the same time, the nation is growing older, as many of those who were children in 1962 enter what we still — though perhaps for not much longer — call “retirement age.” There are more than twice as many Americans 65 and older as there are under 6 years old, making up 16 percent of the population. The total number of elderly is projected to reach 80 million by 2040 and nearly 95 million by 2060. That means more people beyond the traditional working age, and fewer younger workers to support them — the opposite of a demographic dividend. And the projections are even starker in much of Europe and East Asia, where fertility is lower and population aging is unfolding faster.

Put that all together — the emptying cradles, the aging citizenry, the dwindling growth — and you have what some call an underpopulation bomb for the 21st century. Hence the efforts of countries from Hungary to Russia to South Korea to France to Japan to, yes, China, to offer benefits, including cash, aimed at inducing their citizens to procreate more. “The lack of children, which causes an aging population, implicitly affirms that everything ends with us,” Pope Francis said last year. “Without births there is no future.”

By this point, you should know to be wary of anyone who makes future projections based primarily on present trends. But I feel confident in saying that the chance that countries with sub-replacement rates and falling fertility will suddenly reverse themselves and begin a new, lasting baby boom is about as likely as the Pope playing striker for his beloved San Lorenzo football club. There has been little sustained success from recent government efforts to encourage fertility. At most, as in Hungary — whose ultra-conservative Prime Minister Viktor Orban is dedicating 5 percent of GDP to pro-fertility policies — baby bonuses might encourage women to have babies earlier than they would otherwise, but not necessarily to have more.

Had overpopulation worriers noticed that countries like Japan and South Korea had already started their demographic transition toward lower fertility during the baby-booming 1960s, they may have been slower to predict a population bomb. But among nearly all rich and middle-income countries, there’s simply no evidence that dwindling fertility is likely to reverse in a sustainable way. The transition is largely complete.

The population bomb’s last tick

Demography is not a single story. While much of the Global North ages and eventually shrinks, in much of the Global South, population is still growing like it’s the mid-20th century.

The UN projects that sub-Saharan Africa — where total fertility rate has fallen by more than two children per woman from its 1970s-era peak, but still stands at 4.6 — could almost double its population from 1.2 billion in 2022 to nearly 2.1 billion by mid-century. In fact, more than half the increase in global population by 2050 is projected to come from eight countries: Tanzania, the Philippines, Pakistan, the Democratic Republic of the Congo, Ethiopia, Egypt, India, and Nigeria.

Asia will remain the planet’s most populous continent, North America and Europe most likely home to its richest (and, increasingly, oldest) citizens, but the story of human growth in the 21st century is largely the story of Africa.

How that story will go depends on an array of questions: Can fast-growing countries in sub-Saharan Africa follow the example of East Asia and make the most of their enormous demographic dividend — or do they risk squandering it, as much of Latin America did, by failing to provide education and economic opportunities? Can they do so in the face of climate change, which will hit these countries disproportionately? Can the geopolitical balance of power — which for so long has been tilted against Africa — be reset to more fairly represent a human future that will be defined in many ways by whether African countries succeed or fail with their youth? And will aging countries in the Global North in need of workers be open to allowing more migration to flow from young countries of the Global South?

That last point may be the most important of all. If aging countries on a path to shrinking can’t convince their citizens to significantly expand their families — and evidence suggests they can’t — immigration from the remaining young parts of the globe may be the best way to stave off economic and demographic decline, while also giving millions of potential migrants a fairer chance at a better life.

But that would also require international migration on a level the world has never seen before. Even in the midst of unprecedented movement, voluntary and otherwise, as of 2015 less than 4 percent of the world’s population was living outside the country where they were born. And yet that has already been enough to inspire an anti-immigration backlash in the West that shows little sign of abating anytime soon.

Aging countries of East Asia like China and Japan have little history of immigration and little interest in encouraging it, while Europe has become deeply fractured and increasingly hostile over the question of migration.

The US though, where nearly 14 percent of the country is foreign-born, has a chance to be different and, in doing so, exert more control over its demographic destiny than any other nation in the world. Unlike a baby boom — which is unlikely and would take two decades or more to yield productive workers anyway — opening up the flow of immigrants would begin to pay off quickly. People want to come — by one estimate, 42 million people in Latin America and the Caribbean say they’d migrate to the US if they could. It’s up to us to decide to let them in.

And while it’s highly unlikely that the US or other rich, aging countries will return to the days of more robust fertility, that doesn’t mean we shouldn’t look to policies that can support people who do want to have more children.

The average number of children US adults report is “ideal” sits at 2.7, according to a 2018 Gallup poll. That’s a slight increase over recent years, and roughly one child over actual fertility. How reliable those survey answers are is up for debate — people may be reporting what they think is the right number, rather than their actual desires — but it does indicate the existence of some gap between the family size Americans want and the ones they feel able to have.

From enhanced child tax credits to better support for child care to regulatory changes that encourage marriage rates — which have been declining in the US even as it’s still connected to higher fertility — far more could be done to help Americans have the number of kids they want, whatever that number is. That includes flexible work options — 2021 saw an unexpected mini-baby boom in the US that researchers partially connected to the rise of remote work.

Just as there is no such objective thing as “overpopulation,” so it goes for “underpopulation.” Population is what we make of it. The demographic trends that will set the boundaries of the future — sex, death, and migration — can seem unimaginably massive, but they are the product of billions of individual decisions: who to marry, whether to have children, where to move, and who to vote for.

Not even the Chinese Communist Party could ultimately control the population of their country, but each of us has some small voice in the human map to come. We can vote for policies that support families or immigration. We can have more children — or not. Demography doesn’t make us. We make demography.