… as long as they are healthy, well fed and well educated
Much of the panic about falling birth rates can be dispelled once we realise that (barring catastrophe) there will almost certainly be more people alive in 2100 than there were in 2000. But what about the distant future? Dean Spears, co-author of After the Spike has kindly provided me with projections showing that with likely declines in fertility the world population will decline by half each century after 2100, reaching one billion around 2400. Would that be too few to sustain a modern civilisation ?
We can answer this pretty easily from past experience. In the second half of 20th century, the modern economy consisted of the member countries of the Organization For Economic Co-Operation and Development (OECD). Originally including the countries of Western Europe and North America, and soon extended to include Australia and Japan, the OECD countries were responsible for the great majority of the global industrial economy, including manufacturing, modern services, and technological innovation.
Except for some purchases of raw materials from the “Global South”, produced by a relatively small part of the labour force, the OECD, taken as a whole, was self-sufficient in nearly everything required for a modern economy. So, the population of the OECD in the second half of last century provides an upper bound to the number of humans needed to sustain such an economy. That number did not reach one billion until 1980.
Things have changed since then with the modernization of much of Asia and the rise of China as the new “workshop of the world” in manufacturing. But the history is still relevant.
We can also look at the US> Even today, trade accounts for only around 20 per cent of US economic output. Given a US population of 400 million, it is reasonable to suppose that the production of goods and services elsewhere for export to the US might account for another 100 million people. Most of the needs of these people could be met from within the US economy, but let’s suppose that they employ another 100 million in their own countries. That’s still only about 600 million people who, between them, produce all the food they need, the manufactures that characterised the indsustrial economy of the 19th and 20th century, most of the information technology the world relies on, and a steady flow of technological and scientific innovation.
At the lower end of the scale, Charlis Stross has estimated a minimum requirement of 100 million people, a number that might increase in a society even more technologically complex than our own. But since current demographic trends won’t produce that number for nearly a millennium, we probably don’t need to worry (unless we want to colonise space, the context of Stross’ estimate)
In summary is no reason to think a billion people would be too few to sustain a technological economy. But would a world of a billion people look like?
It’s foolish to try to say much in detail about life hundreds of years from now. What could a contemporary of Shakespeare have to say about the London of today? But London and other cities existed long before Shakespeare and seem likely to continue far into the future (if we can get there). And many of the services cities have always provided will be needed as long as people are people. So, it might be worth imagining how a world population of one billion might be distributed across cities, towns and rural areas.
Australia, with 5 per cent of the world’s land mass and a current population of 25 million, provides a convenient illustration. A billion people would populate 40 Australias, with twice Australia’s current population density. However, around half of Australia is desert or semi-arid (estimates range from 18 to 70 per cent, depending on the classification, and not many people live there. So, the population density of a billion-person world would look pretty much like that of urban and regional Australia today.
Opinions in Australia (as elsewhere in the world) are pretty sharply divided as to whether a bigger population would be a good thing, but it’s unusual for anyone to suggest that we are spread too thinly. On the contrary, congestion, sprawl and the conflict between environmental preservation and housing are seen as the price to be paid for a larger population.
A billion person world could not support mega-cities with the current populations of Tokyo and Delhi. But it could easily include a city the size of London, New York, Rio, or Seoul (around 10 million each) on every continent, and dozens the size of Sydney, Barcelona, Montreal, Nairobi, Santiago or Singapore (around 5 million each). Such a collection of cities would meet the needs of even the most avid lovers of urban life in its various forms. Meanwhile, there would be plenty of space for those who prefer the county
With only a billion people we wouldn’t need all the space in the world. The project of rewilding half the world, now a utopian dream, could be fulfilled, while leaving more than enough room for farming and forestry, as well as whatever rural arcadias followers of the simple life could imagine and implement.
{ 28 comments }
Pittburgh Mike 07.27.25 at 1:12 pm
Silly snark deleted – please read the post before commenting
jlowe 07.27.25 at 1:28 pm
Watch that first step though – that first decade would be rough, with all of the wars and the digging and filling of mass graves. Something out of William Gibson’s novel “The Peripheral”.
David Mitchell 07.27.25 at 2:05 pm
A decline in world population after peaking this century to the range of 500 million to one billion over the next several centuries is almost certain to happen. The question is will it be a gradual and managed process or a series of famines, wars and widespread environmental destruction. Once the population starts to decline coupled with resource depletion the current economic system will be stressed and likely collapse. In that event a managed decline is unlikely.
Can a smaller population still innovate? Yes if you follow the “Progress is made by rubbing smart people and money together,” rule.
hh 07.27.25 at 4:35 pm
All the more reason to devote resources to preserving biodiversity, for that future rewilding!
Mark Palko 07.27.25 at 10:10 pm
One of the many fascinating things about the pronatalist conversation is that many of those most aggressively hitting the panic button are also techno-optimist accelerationists. In other words, the same people who believe the world will be completely unrecognizable in less than 20 years are also arguing that the same trends and conditions will hold for the next two to three hundred.
John Q 07.28.25 at 5:33 am
@2, @3
As stated in the opening sentence, the post is about population decline arising from falling birth rates which make famines and environmental disasters less likely. Note also that there won’t be a big “first step”. Global populations will level out and begin a gradual decline over 50 years or so.
Brett 07.28.25 at 5:49 am
“Bigger population in 2100 than 2000” might be optimistic, given that the demographic reality has consistently underperformed the UN projections. One demographer pointed out recently that since the Replacement Total Fertility Rate for poor countries is actually higher than 2.1 (due to much higher early childhood and overall mortality), we might be below the replacement level on average across the world – with population peaking in 2055 and falling after. Barring some type of major breakthrough that turns the tables (like artificial wombs, major life extension, etc), of course, which is why I do think we can’t really project usefully out to 2100.
I agree that a billion would be enough to support advanced civilization. Less than that – even Stross’ 100 million is probably higher than what it takes, given that we have far better automation and more stuff like that in the pipeline in the next couple decades. I bet with the right automation and smaller-scale advanced production, you could support a self-sufficient advanced civilization on 500,000-1,000,000 people. Some stuff might be relatively expensive compared to what we have now (and just about everything would economize on labor), but it would work.
They’d be more spread out, but unless you aggressively limit their expansion and density I think you’d see the lower population congregate into a smaller number of urban areas – while the countryside essentially rewilds or exists of almost entirely automated farms and animal husbandry set-ups.
David in Tokyo 07.28.25 at 12:07 pm
You wrote “(barring catastrophe) ”
Well, yes. That’s the 800 lb gorilla lurking in the corner. It hit 39 degrees C in Hokkaido last week (and Spain saw a seriously crazy number a while ago). Hokkaido’s supposed to be cool, and doesn’t have a lot of air conditioners. (Actually, it probably does. Most home heating units here are heat pumps and are reversible.) For you English system users, Japan defines 30 C as a “hot summer day”, and 35 C as a “really nastily hot hot summer day”. Today was 35 C here, and I had to walk a total of about 4 km in that heat (in 4 separate 1 km walks). It.Wasn’t.Nice. And it’s 35C pretty much every day, now that the rainy season is over.
As I keep saying, the articles in Science on global warming are always “it’s worse than we thought”. How much of humanity can survive with 2 degrees of warming (which we can’t avoid at this point)? How much can survive with 5 degrees of warming?
So the whole long-term population prediction business is problematic, since we’re going down, and going down fast. And starting soon. For example, what happens when the glaciers (in the Himalayas) are gone (and they are going fast), and the rivers in South and Southeast Asia dry up? It’s not going to be pretty and it’s probably happening well before 2050.
Rich 07.28.25 at 12:34 pm
John Q @6:
I think the point the earlier commentators were making is that a declining population doesn’t look like there being less people spread over all age-groups. It looks like there being many, many more elderly people, and fewer and fewer children, at least for a while. That causes immediate economic problems as there aren’t enough people making stuff compared to consuming it and needing care. Which in turn can lead to famines (and maybe other disasters) since those are essentially symptoms of economic disfunction leading to poor distribution of food.
Having said that, I’m all for a smaller earth population, if the transition is managed properly.
Jolly Roger 07.28.25 at 4:38 pm
A sub-replacement fertility doesn’t mean that the share of old people will increase forever: at, say, 1.5 children per woman, and a life expectancy of 85-90 years, you eventually converge to some 15% of people under 20 y.o., 45% between 20 and 65, and 40% over 65.
That’s a bad dependency ratio, but not much worse than societies with a ton of children.
Getting there is painful, but once there, the real issue is how to support so many older people, i.e.: transfer income to them in an orderly way.
If the population -keeps- shrinking, that is eventually a problem, (not at a billion, but how about 1 million? How about half that?), but it is so far out that it is useless to predict future social and technological conditions.
We are currently technically able to produce children without fathers. It is only a matter of time (certainly fewer than 400 years) before mothers do not need to have a pregnancy to have children. That has its own problems, and I expect it to be fiercely opposed, but it will eventually happen and will change the situation dramatically. And yes, this is science fiction, but any scenario 400 years into the future is science fiction.
No, what the populationists are doing is basically subscribing to some version of “long-termism” and/or cornucopianism a la Julian Simon’s Ultimate Resource. They take it for granted that continuous technological advancement is possible forever, that it is limited by the number of people engaging in science, and that utilitarian considerations mean that raising the rate of technological advancement trumps basically anything else.
Tm 07.28.25 at 8:08 pm
Under current trends, the next at least 30 years will be characterized by a mismatch between large birth deficits in some societies and large birth excesses in other parts of the world. This mismatch is an unavoidable consequence of the asynchronicity of social and economic development over the last centuries. The rational response to this situation is to allow the mismatch to even out the way this has always happened – migration. Unfortunately most birth deficit countries are now governed by racists ideologically hostile to immigration. The least racist societies will be best positioned to handle the demographic transition – which, again, is unavoidable. It can only be delayed but not avoided, that’s a mathematical certainty, and the longer it’s delayed the more painful it will be.
John Q 07.28.25 at 11:32 pm
Standard measures of the dependency ratio (15-64 vs the rest) are obsolete, dating back to the days when most people left school at 15 and worked at demanding manual jobs until pension age, by which time they were too old to work any more
Under current conditions, most productive work requires post-school education or training followed by a period of work experience, with proper entry to the workforce starting between 20 and 25.
At the other end of the spectrum, people over 65 aren’t “elderly” (horrible word) in the sense of physical dependence. Our current social arrangements mean that (either through savings or public pensions) they mostly have enough to live on without working. But retirement ages are increasing as conditional life expectancy increases.
Shorter version: the numerator in dependency ratios should be people aged 25-70, and the problem disappears.
J-D 07.29.25 at 12:25 am
In addition to the point made by John Quiggin, it is important to note that however you define the age ranges, any analysis that refers to a rise in the aged dependency ratio without giving any consideration to any offsetting effect of a decline in the youth dependency ratio is valueless.
No! More elderly people (assuming an appropriate definition of ‘elderly’) does mean more people consuming and needing care, but fewer children means fewer people consuming and needing care! You’ve got a mention of children there, so how do you overlook what that means? Children consume a lot and need a lot of care!
Because in that analysis (even without taking into account the point made by John Quiggin) both ends of the age range have (appropriately) been taken into consideration.
Peter T 07.29.25 at 2:11 am
I saw one claim that soonish one quarter of the population of China will be over 80. Maybe, but only for a very short time, as average life expectancy in China is 79.
TM 07.29.25 at 6:43 am
Here’s an animated population pyramid:
https://en.wikipedia.org/wiki/Aging_of_China
Howard NYC 07.29.25 at 9:27 am
TYPO = Meanwhile, there would be plenty of space for those who prefer the county {PERIOD MISSING}
SUGGEST = Meanwhile, there would be plenty of space for those who prefer the country.
Michael Cain 07.29.25 at 3:39 pm
John Q @12:
One thing that becomes harder about work past age 65 in much of the developed world is the model that says: 8:00 to 5:00, 200 days per year, plus commuting. If the olds are going to have to work, employers are going to have to come up with arrangements to incorporate two-thirds time, half-time, quarter-time, and so on.
KD 07.29.25 at 3:39 pm
Another snark deleted. Please don’t comment further unless you are willing to read and think about it
Not sure why people are responding to this post by making points that are right there in the OP, and sneering about them, but please stop.
Alex SL 07.29.25 at 10:47 pm
Jolly Roger,
Bit tangential to the main point, but I would be shocked if an artificial uterus will ever be feasible. The interplay between mother and child during pregnancy is extremely complex; not just a nutrient funnel, but also developmental and emotional. To cover merely one subaspect of the developmental aspect, I remember reading years ago about a rich guy who funded pet cloning technology to “resurrect” his dog and was then very disappointed to lean that a cloned cat has very different fur patterns than the individual it was cloned from – because that pattern isn’t determined entirely by the genes of an individual but by interactions between that individual and the mother during pregnancy. Some things in biology are really very, very complicated, and pregnancy and brains are top of the list. It is well possible that both pregnancy and human cognition can only be reproduced by building an artificial biological system that is so close to being human itself that even tech bros would recoil in horror at the reality of it.
And, of course, “this will be possible 400 years into the future” assumes an unbroken trajectory of scientific progress that seems unlikely to remain unbroken under climate change and resource overuse. We can already see signs of growing societal decline around us, starting with a growing number of failed states and an increasing immigration panic in the nations that, for now, remain prosperous, which leads to increasingly dysfunctional governance there, making their own eventual collapse more likely in the long run. The level of societal and technological sophistication that our descendants 400 years from now are most likely to experience is some equivalent of the nascent Frankish kingdom whose people had forgotten how the Romans were able to maintain aqueducts and sewage systems, only this time the warlords will have semi-automatic guns instead of swords. They will be lucky to remember what vaccines were, and artificial uterus won’t be in reach even if I am wrong and it is theoretically possible.
KT2 07.30.25 at 2:51 am
Alex SL @19 “Bit tangential to the main point, but I would be shocked if an artificial uterus will ever be feasible.”
Never say never Alex. Your doom scenario and civilization amnesia I do unfortunately have sympathy for… especially global warming and “warlords will have semi-automatic guns instead of swords.”
As does JQ saying “(if we can get there).”
Yet science advances and Capital Controls & Capitalises continue…
David Mitchell @3 “Can a smaller population still innovate? Yes if you follow the “Progress is made by rubbing smart people and money together,” rule.”
[1] “COLOSSAL SECURES $200M, ADVANCING DE-EXTINCTION SCIENCE THAT SOON COULD RESURRECT THE WOOLLY MAMMOTH”
JANUARY 15, 2025
…
“On Wednesday, the company announced it had secured $200 million in Series C funding led by TWG Global, bringing its valuation to $10.2 billion.”
…
“We have a 17-person artificial womb team, and so what’s great about the thylacine project is while they do have a placenta that shows up at the end of gestation, it’s not truly needed, like it is like in a mouse, a pig, a human, or an elephant,” Lamm said. “You can get them through gestation without having to go through the full placental interface of attaching to a synthetic uterine wall like the inside of the uterus.” …
https://thedebrief.org/colossal-secures-200m-advancing-de-extinction-science-that-soon-could-resurrect-the-wooly-mammoth/
And Mitochondrial replacement therapy via three parent babies.
One baby via MRT in 2016.
Eight born up to 2025. [3]
Yet it looks like Colossal Biosciences + money + brains ( [1] above) may out engineer MRT…
[2] “World’s first three-parent baby raises questions aboutlong-term health risks”
Published: September 28, 2016
Joanna Poulton, University of Oxford
…
“In Mitochondrial replacement therapy (MRT), embryos of the couple at risk of having an affected child are generated in a test tube. In this case, the nucleus that contains all of the genetic material apart from the mitochondria was removed from the mother’s egg and placed into an egg with healthy mitochondria, from which the nucleus had been removed. The egg was then fertilised with the father’s sperm and the resulting embryo was placed in the mother’s womb where it developed into the baby.
“This means the baby has three genetic parents: the father who supplied the sperm, the mother who supplied both womb and the egg nucleus, and an anonymous donor who supplied healthy mitochondria. Of these, the mitochondrial DNA is by far the smallest contribution. This type of three-parent baby is new, although other types have existed for many years.
“MRT is being developed by groups in the UK and US to help the families of patients who have mitochondrial disease with a high recurrence risk in future children.
…
[! Astounding ! ]
“Being born to a woman who is not your genetic parent may be acceptable to some people, given that perhaps up to one in 10 people in the UK do not identify their genetic fathers correctly– but it may have been unacceptable to this family.”
…
https://theconversation.com/worlds-first-three-parent-baby-raises-questions-about-long-term-health-risks-66189
[3]
“Mitochondrial replacement therapy
…
“The therapy is approved for use in the United Kingdom[1][2] and Australia.[3] Eight babies have been born using MRT in the UK as of July 2025.[4][5][6] ”
https://en.wikipedia.org/wiki/Mitochondrial_replacement_therapy
###
I am presently (for a friend! tell your doc to do more simple blood tests!) asking specialists about confounding genetics for 2x treatments of a reproductive system cancer. 2 x genes indicate a specific treatment and 1 x gene counteracts and induces a tolerance for treatment negating/ lessening treatment effects. The specialists are all aware, yet only those patients with money, time and brainspace will get the benefit until properly incorporated into policy and payment system.
JQ “It’s foolish to try to say much in detail about life hundreds of years from now.” . Oh well…
I’d say in 2425 there will be ? million / billion humans, either abundance, or dystopia + enclaves. The enclave dwellers will be able to afford an artificial womb & MRT. The urge for offspring will see capital provide the service…
“Capitalism is the astounding belief that the most wickedest of men will do the most wickedest of things for the greatest good of everyone.”
~ John Maynard Keynes
Ala Elysium… “In 2154, Earth is overpopulated, diseased, and heavily polluted from ecocide. The planet’s citizens live in extreme poverty. In contrast, the rich and powerful live on Elysium, an orbiting space station just outside Earth’s atmosphere, with luxuries including Med-Bays, medical devices that can heal any disease or condition.
“Spider, a hacker living in Los Angeles, runs a space shuttle operation to smuggle people into Elysium.”
Elysium (film) – Wikipedia
Yet I don’t see, even with artificial wombs, an effect on debate re natalism, nor population effects to any great extent, even in 2425. And if humans still have agency, we won’t want artificial wombs to be batteries.
Unless the civil amnesia is strong, or WW3 wipes data.
Let’s hope not.
“We have flown the air like birds and swum the sea like fishes, but have yet to learn the simple act of walking the earth like brothers.”
Martin Luther King, Jr.
David in Tokyo 07.30.25 at 2:27 pm
The idea that the world will still be a habitable planet in 2050 is becoming less likely by the day.
https://www.msn.com/en-us/news/world/japan-records-highest-temperature-on-record/ar-AA1JzcU4
Also, FWIW, the “de-extinction” stuff is largely seen as painfully ridiculous lying sleazy garbage by actual scientists. Makes fun headlines, though.
Also hilarious is that there are something like 24 companies*** (all vulture-capital funded) that claim they’ll have commercial fusion reactors up in 10 or 12 years, although none of them is using a technology that’s been demonstrated to work in the lab, let alone at scale. (The headlines announcing the LLL fusion tests that released more energy than put it have been scientifically accurate (and not lying sleazy garbage), but every article (in the lamestream press) actually was lying sleazy garbage, in that none mentioned that the amount of energy requried to (a) make the target* and (b) to generate the laser pulse that set off the reaction** were both many many orders of magnitude larger than the amount of energy that came out of said pellet when it was imploded.
*: This bit wasn’t mentioned even in the good scientific journal articles. Sheesh.
**: This bit was covered in the “good” articles.
***: There were at least 12 using a variety of methods at one point, and a recent article mentioned 12 using one particular method (stellerator), so there may be some overlap there. The stellerator idea isn’t complete lying sleazy garbage, but it’s not yet been made to work.
John Q 07.31.25 at 8:24 pm
Michael C @17 Yes, work patterns will have to change and are doing so already.
Much of the sloppy thinking about population arises from taking a 1950 model of the life course, and assuming that nothing changes except for fewer babies and more old people. For example, even though 70yos today can expect to live for 20-25 years more, their health status is assumed to be the same as those in the past when conditional life expectancy was 10 years.
Gar Lipow 07.31.25 at 11:57 pm
One thing that has been left out in dependency arguments – Productivity increases. If we look at ILO figures, labor productivity between 2014 and 2024 worldwide increased just a hair short of 18%. That happened with wars, genocides, pandemics, environmental catastrophes. If we have complete doom, dependency ratio won’t matter. Otherwise, productivity increases should make up for any increases in dependency ratio, even without people having to work until they are 80. I will add that it is easy for people with desk jobs to think increasing the retirement age is no big deal. But most jobs in the world still involve physical labor. If less these days is working in a factory, more is standing at a cash register, or stocking shelves in retail stores or warehouses or doing deliveries, or a million other types of gig work, or various kinds of care giving. None of those are things you necessarily want to be doing at 68.
MisterMr 08.01.25 at 6:20 am
My two cents: a problem that will arise some hundred of years in the future and that can be solved by any generation in the middle simply by having more sex without contraceptives is not a real problem.
The question Is more about family values and gender roles, but then let’s speak of these instead of weird projections on natality in the distant future.
Philip Cohen 08.01.25 at 1:39 pm
Don’t forget people can start having more babies any time they want. Demographic projection is mechanical and easy – predicting human behavior that far out is foolishness.
Seekonk 08.01.25 at 8:15 pm
I realize the focus here is the minimum number of people necessary to sustain civilization, but my concern is that our current population is overwhelming the planet’s resources and ecosystem.
There is a 1999 Cornell University study that says: “Democratically determined population-control practices and sound resource-management policies could have the planet’s 2 billion people thriving in harmony with the environment. Lacking these approaches … 12 billon miserable humans will suffer a difficult life on Earth by the year 2100.” http://news.cornell.edu/stories/1999/09/miserable-life-overcrowded-earth-2100
dk 08.02.25 at 12:10 am
@21 Speaking as a former research physicist in high-power lasers, yes, the LLL fusion data are surely real. However, LLL press releases regularly characterise them as “providing more energy than they put in”, which is in fact lying sleazy garbage. There is an agreed figure of merit for a workable power source, namely, that wallplug efficiency must exceed 100%. LLL is nowhere near that and IMO never will be, owing to basic physical limits on laser efficiency.
David in Tokyo 08.02.25 at 1:48 am
Speaking about not even making it to 2050:
Today’s Japanese newspaper reports that 2023 featured the hottest July in recorded history. As did 2024. As did 2025. This July was 2.86 degrees C hotter than the historical average. We’re a whole degree ahead of the “If we hold warming to 1.5 degrees by the end of the century we’ll be okay” thing.
Really. We’re not making it to 2050.
(Yes, three data points is still weather, but the numbers are enough different from historical levels to be concerningly indicative of climate trend.) Also, two of Japan’s major rice-producing regions saw 8% and 15% of normal July rainfall. Oops.
Also, what Philip Cohen said.
As a joke, I asked my SO (who is seriously lefty and reasonably well informed about things) “What is the difference in population in Japan now versus that in 1935/1936 when Japan was heading to a catastrophic war based on a policy of exporting excess population (and thus needing colonies such as Manchuria) and exporting* labor to Brazil, Hawaii, and other places).” The correct answer is Japan’s current population (which is already declining, causing great freakout here) is about TWICE what it was in 35/36. Said SO’s initial reaction was “Of course Japan’s current population is lower.” But, knowing that her SO is a twat, she stopped herself, and at least reasoned her way to the current population being larger.
My point here is that we’ve already got plenty of people, way more than we’ve ever had before, and we need to focus on making life better for the people we’ve got now, making sure there’s still a habitable planet for them and their kids.
We really need to stop talking about stupid science fiction scenarious that concern about is only advantagious to rich folks and tech bros.
*: Japan had a big family policy, encouraged folks to have lots of kids. But when the smoke cleared, folks found out that Japanese inheritance laws/policies meant that everyone except the eldest son was sh!t out of luck, creating an enormous class of poor folks from not all that badly off families. So the rising population starting in the mid-Meiji period was a disaster.
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