“Why don’t you mention the problem of overpopulation?” Whenever I give a talk about climate change and what to do about it, or about human progress during the past two centuries (or about any other topic, really), this is the one question that never fails to be asked during the Q&A. It is almost always meant to be a rhetorical one. The root cause of all our worries about climate and environment, or so the questioner believes, can be summarised in three words: too many people. Without addressing that root problem there can’t be any hope of a bright future. People beget more people, and before long you get an exponential growth curve that ends in disaster. A ticking time bomb. An explosion.
For the past few years, I have been the holder of a Chair at Ghent University dedicated in honour of Etienne Vermeersch, a Belgian philosopher renowned for many things but perhaps most notably for his early warnings about overpopulation and his advocacy for birth control. A few years before his untimely death in 2019, he expressed his “despair” at his failure to convince our political leaders to take overpopulation seriously.
Etienne was an intellectual hero of mine for whom I have huge respect, but this is the only thing about which he was dead wrong. Because there is no problem of overpopulation. In fact, before long, we will have to start worrying about underpopulation, caused by rapidly falling birth rates. It turns out that this is bad news not only for humanity but also for the planet, because more humans means more available resources and less destructive impact on nature.
Come again? More humans means more available resources? No, that’s not a typo.
First of all, some empirical facts. Global population growth peaked in the late 1960s, when the average woman had 4.5 children, and it has been declining ever since. In country after country, we have seen fertility rates take a nosedive after the death rate did the same thing. Global fertility today has fallen to about 2.3 births per woman, barely more than the replacement rate of 2.1 (the number you need to maintain a population). No country appears to be immune to this ‘demographic transition’, not even—despite popular misconceptions—traditional and religious societies.
Declining birth rates are driven by the same factors pretty much everywhere, regardless of cultural differences: higher incomes, better education for women, and access to contraception. As the Swedish physician Hans Rosling wrote: “Once parents see children survive, once the children are no longer needed for child labor, and once the women are educated […], across cultures and religions both the men and the women instead start dreaming of having fewer, well-educated children.”
In demography today something like the following rule applies: birth rates are always falling faster than you think, even if you take into account that birth rates are falling faster than you think. Every time we take a closer look at a particular country or region, fertility figures turn out to be lower than expected. A few years ago, the U.N. still forecasted that the global population would peak around 11 billion at the end of this century, which was already a slower growth rate than represented by earlier predictions. But according to a 2020 study in The Lancet, we will never reach even 10 billion, and the global population will start shrinking as early as the 2060s. In Nigeria, the most populous country in Africa, the U.N. now forecasts a population of 350 million by 2100, which is 200 million less(!) than its estimate of ten years ago. In countries with the lowest fertility, the U.N. had assumed stabilisation around 1.75 children per woman, but that turns out to be too optimistic, as well (or too pessimistic, depending on your viewpoint). In countries such as Thailand, Greece, Italy, China, Japan, and many others, fertility rates have dipped below 1.5, and in South Korea they stand at a whopping 0.78.
Those who have long predicted a catastrophic population explosion, like Paul Ehrlich of The Population Bomb fame (who is now 91 years old), can now heave a sigh of relief. Except many of them will hardly be satisfied that we have averted the worst. Eight billion people, they’ll say, is already way too many. The celebrated primatologist Jane Goodall recently suggested that if she had a magic wand, the one thing she would do would be to (painlessly and mercifully) reduce the number of people on the planet. By how much, exactly? By about 95 percent, she suggested elsewhere—back to where we were 500 years ago. (If I had a magic wand, I’d just eliminate poverty and hunger rather than eliminate people, but let’s move on.)
Now, Goodall’s is a pretty extreme proposal, but I think many people (even smart and caring people) share the intuition that many global problems would be solved if only there were fewer of us: resource depletion, food security, pollution, climate change, freshwater supply, war. Name any problem, and someone will blame it on overpopulation. These people will cheer on the falling fertility rates everywhere, and would like to speed up the decline if they could.
And yet, there are good reasons for thinking that precisely the opposite is true: the more people there are, the more solutions to problems will be found. Many predictions of population doom never materialised because they started from the misguided assumption that the impact of the average individual on the planet (in terms of food, resource use, pollution, and so on) has remained constant throughout history. But history belies that assumption at every turn. If we still lived like our hunter-gatherer ancestors, as Matt Ridley said in an interview published in 2009, we would have needed about 85 Earths to feed the planet’s population at that time (6 billion people). “If we’d gone on as early slash-and-burn farmers, we’d have needed a whole Earth, including all the oceans. If we’d gone on as 1950[s] organic farmers, we’d have needed 82 percent of the world’s land area for cultivation, as opposed to the 38 percent that we farm at the moment.” Ridley said this almost 15 years ago, but, amazingly, the figure is still 38 percent, despite a billion extra mouths to feed and enormous gains in welfare and calories consumed per person.
The Simon Abundance Index, named after economist and cornucopian Julian Simon, shows that resources are becoming more abundant and cheaper as the world population grows. It sounds crazy and counterintuitive, but that’s often the case with science. Take agriculture. Especially since the Industrial Revolution, humans have been drastically shrinking their cropland use per capita, and there is no reason to believe this progress can’t continue. With novel technologies like precision fermentation and vertical farming, we could further shrink our “foodprint” by at least three quarters, thus freeing up more space for nature to flourish. With clean energy technologies, we can completely decouple material well-being from CO2 emissions, for the first time in history. With further progress in materials science, we will be able to find abundant substitutes for every kind of raw material we currently use, thus permanently rendering moot any worries about “resource depletion”. With nuclear fusion or ultra-cheap solar and storage, we could have virtually unlimited energy for millennia. Et cetera.
The problem is that none of this progress happens of its own accord. We need massive investments in fundamental scientific research, and collaborations between academia and industry, to bring all these technologies to maturity. We need a society that believes in technological progress to improve the lot of humanity (and, eventually, of other animals). And here comes the crux: none of that is likely to happen in societies with dwindling and aging populations.
Older societies are less dynamic, more resistant to change, and less creative. Most scientists and inventors achieve their breakthroughs in their twenties and thirties, so fewer young people means fewer good ideas (and more older and infirm people to be supported by those fewer ideas). Until we design AI systems that can completely take over our scientific labours, the only genuine engine of progress on this planet is the kilogram of grey matter inside our skull. And with fewer and fewer fresh brains to produce and exchange ideas, the engine of human progress could soon be grinding to a halt (although the world still has huge reserves of underutilised brainpower in poor countries today). As Josh Smith and Jennifer Morales from the Center for Growth and Opportunity put it: “People are not just bellies to fill or a carbon footprint to minimize. People create solutions.” A 2022 paper by the National Bureau of Economic Research compares U.S. states and shows that ageing is already a persistent drag on economic growth and productivity; when the proportion of the population over 60 years old increases by 10 percent, economic growth (GDP per capita) decreases by 5.5 percent and productivity by almost 4 percent.
A demographic trailblazer such as Japan gives us a foretaste of what lies in store; not so long ago, the country was an economic powerhouse and global innovator, but now it is mostly stagnant (though still rich) and dependent on innovation and growth elsewhere in the world.
Moreover, future progress in science and technology promises to be ever more challenging, because the lowest-hanging fruit has already been harvested by earlier generations and only the hard-to-reach ones remain for us to grasp. Innovations are becoming increasingly harder to find, and we have to keep employing more and more scientists and resources to expand the horizons of knowledge. If controlling nuclear fusion were so easy, I’m sure Robert Oppenheimer or Werner Heisenberg or Lise Meitner would have cracked it a long time ago, along with nuclear fission.
That does not mean that human population should increase indefinitely. Strictly speaking, as anti-growth prophets like to point out, nothing can grow forever on a finite planet (or in a finite universe). But the upper limits to human population across the universe are entirely theoretical and completely irrelevant for our purposes, given the unpredictability of future technologies. Right here and now, we should forget about overpopulation and start worrying about underpopulation. My friend Etienne and the other population catastrophists had it exactly backwards. The greater the number of humans on Earth, the more we can reduce our impact on the planet. To dream of a planet with fewer people is to dream of stagnation, regression, and decline.
As a die-hard atheist, I’d never have thought I would agree with the Old Testament, but here goes: “Be fruitful and multiply, and fill the earth…” (Genesis 1:28).
(Published first in Quillette. Many thanks to all my Roots of Progress fellows for their inspiration and feedback, in particular Jennifer Morales, Jason Crawford, Heike Larson and Robert Tracinski , as well as to Simon Friederich and Nick Brown).