What is the ideal size of the human population?

One common answer is “much smaller.” Paul Ehrlich, co-author of The Population Bomb (1968), has as recently as 2018 promoted the idea that “the world’s optimum population is less than two billion people,” a reduction of the current population by about 75%. And Ehrlich is a piker compared to Jane Goodall, who said that many of our problems would go away “if there was the size of population that there was 500 years ago”—that is, around 500 million people, a reduction of over 90%. This is a static ideal of a “sustainable” population.

Regular readers of The Roots of Progress can cite many objections to this view. Resources are not static. Historically, as we run out of a resource (whale oil, elephant tusks, seabird guano), we transition to a new technology based on a more abundant resource—and there are basically no major examples of catastrophic resource shortages in the industrial age. The carrying capacity of the planet is not fixed, but a function of technology; and side effects such as pollution or climate change are just more problems to be solved. As long as we can keep coming up with new ideas, growth can continue.

But those are only reasons why a larger population is not a problem. Is there a positive reason to want a larger population?

I’m going to argue yes—that the ideal human population is not “much smaller,” but “ever larger.”

Selfish reasons to want more humans

Let me get one thing out of the way up front.

One argument for a larger population is based on utilitarianism, specifically the version of it that says that what is good is the sum total of happiness across all humans. If each additional life adds to the cosmic scoreboard of goodness, then it’s obviously better to have more people (unless they are so miserable that their lives are literally not worth living).

I’m not going to argue from this premise, in part because I don’t need to and more importantly because I don’t buy it myself. (Among other things, it leads to paradoxes such as the idea that a population of thriving, extremely happy people is not as good as a sufficiently-larger population of people who are just barely happy.)

Instead, I’m going to argue that a larger population is better for every individual—that there are selfish reasons to want more humans.

First I’ll give some examples of how this is true, and then I’ll draw out some of the deeper reasons for it.

More geniuses

First, more people means more outliers—more super-intelligent, super-creative, or super-talented people, to produce great art, architecture, music, philosophy, science, and inventions.

If genius is defined as one-in-a-million level intelligence, then every billion people means another thousand geniuses—to work on all of the problems and opportunities of humanity, to the benefit of all.

More progress

A larger population means faster scientific, technical, and economic progress, for several reasons:

  • Total investment. More people means more total R&D: more researchers, and more surplus wealth to invest in it.
  • Specialization. In the economy generally, the division of labor increases productivity, as each worker can specialize and become expert at their craft (“Smithian growth”). In R&D, each researcher can specialize in their field.
  • Larger markets support more R&D investment, which lets companies pick off higher-hanging fruit. I’ve given the example of the threshing machine: it was difficult enough to manufacture that it didn’t pay for a local artisan to make them only for their town, but it was profitable to serve a regional market. Alex Tabarrok gives the example of the market for cancer drugs expanding as large countries such as India and China become wealthier. Very high production-value entertainment, such as movies, TV, and games, are possible only because they have mass audiences.
  • More ambitious projects need a certain critical mass of resources behind them. Ancient Egyptian civilization built a large irrigation system to make the best use of the Nile floodwaters for agriculture, a feat that would not have been possible to a small tribe or chiefdom. The Apollo Program, at its peak in the 1960s, took over 4% of the US federal budget, but 4% would not have been enough if the population and the economy were half the size. If someday humanity takes on a grand project such as a space elevator or a Dyson sphere, it will require an enormous team and an enormous wealth surplus to fund them.

In fact, these factors may represent not only opportunities but requirements for progress. There is evidence that simply to maintain a constant rate of exponential economic growth requires exponentially growing investment in R&D. This investment is partly financial capital, but also partly human capital—that is, we need an exponentially growing base of researchers.

One way to understand this is that if each researcher can push forward a constant “surface area” of the frontier, then as the frontier expands, a larger number of researchers is needed to keep pushing all of it forward. Two hundred years ago, a small number of scientists were enough to investigate electrical and magnetic phenomena; today, millions of scientists and engineers are productively employed working out all of the details and implications of those phenomena, both in the lab and in the electrical, electronics, and computer hardware and software industries.

But it’s not even clear that each researcher can push forward a constant surface area of the frontier. As that frontier moves further out, the “burden of knowledge” grows: each researcher now has to study and learn more in order to even get to the frontier. Doing so might force them to specialize even further. Newton could make major contributions to fields as diverse as gravitation and optics, because the very basics of those fields were still being figured out; today, a researcher might devote their whole career to a sub-sub-discipline such as nuclear astrophysics.

But in the long run, an exponentially growing base of researchers is impossible without an exponentially growing population. In fact, in some models of economic growth, the long-run growth rate in per-capita GDP is directly proportional to the growth rate of the population.

More options

Even setting aside growth and progress—looking at a static snapshot of a society—a world with more people is a world with more choices, among greater variety:

  • Better matching for aesthetics, style, and taste. A bigger society has more cuisines, more architectural styles, more types of fashion, more sub-genres of entertainment. This also improves as the world gets more connected: for instance, the wide variety of ethnic restaurants in every major city is a recent phenomenon; it was only decades ago that pizza, to Americans, was an unfamiliar foreign cuisine.
  • Better matching to careers. A bigger economy has more options for what to do with your life. In a hunter-gatherer society, you are lucky if you get to decide whether to be a hunter or a gatherer. In an agricultural economy, you’re probably going to be a farmer, or maybe some sort of artisan. Today there’s a much wider set of choices, from pilot to spreadsheet jockey to lab technician.
  • Better matching to other people. A bigger world gives you a greater chance to find the perfect partner for you: the best co-founder for your business, the best lyricist for your songs, the best partner in marriage.
  • More niche communities. Whatever your quirky interest, worldview, or aesthetic—the more people you can be in touch with, the more likely you are to find others like you. Even if you’re one in a million, in a city of ten million people, there are enough of you for a small club. In a world of eight billion, there are enough of you for a thriving subreddit.
  • More niche markets. Similarly, in a larger, more connected economy, there are more people to economically support your quirky interests. Your favorite Etsy or Patreon creator can find the “one thousand true fans” they need to make a living.

Deeper patterns

When I look at the above, here are some of the underlying reasons:

  • The existence of non-rival goods. Rival goods need to be divided up; more people just create more competition for them. But non-rival goods can be shared by all. A larger population and economy, all else being equal, will produce more non-rival goods, which benefits everyone.
  • Economies of scale. In particular, often total costs are a combination of fixed and variable costs. The more output, the more the fixed costs can be amortized, lowering average cost.
  • Network effects and Metcalfe’s law. Value in a network is generated not by nodes but by connections, and the more nodes there are total, the more connections are possible per node. Metcalfe’s law quantifies this: the number of possible connections in a network is proportional to the square of the number of nodes.

All of these create agglomeration effects: bigger societies are better for everyone.

A dynamic world

I assume that when Ehrlich and Goodall advocate for much smaller populations, they aren’t literally calling for genocide or hoping for a global catastrophe (although Ehrlich is happy with coercive fertility control programs, and other anti-humanists have expressed hope for “the right virus to come along”).

Even so, the world they advocate is a greatly impoverished and stagnant one: a world with fewer discoveries, fewer inventions, fewer works of creative genius, fewer cures for diseases, fewer choices, fewer soulmates.

A world with a large and growing population is a dynamic world that can create and sustain progress.


For a different angle on the same thesis, see “Forget About Overpopulation, Soon There Will Be Too Few Humans,” by Roots of Progress fellow Maarten Boudry.

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I'm only comfortable with more humans if we make serious efforts to increase the percent of vegans/vegetarians, or reduce the amount of meat needed by human, given how wasteful meat is to land use.

maybe, just maybe, cultured meat will come just enough time to save us. But the probability range of this is still too high for comfort.

I very strongly believe any pro-fertility incentives must be coupled with incentives to decrease meat consumption/increase vegetarianism (or increase % of power from nuclear, given that excess solar energy will also destroy habitat).

EO Wilson once advocated that 50% of the world is set aside for wilderness. Maybe that's a bit too ambitious, but I think 35% would be good enough to preserve enough biodiversity. Taiwan/Hong Kong/Japan are all densely populated and have roughly that % of wilderness/forest (they also rely a lot on seafood, which does not destroy wilderness , but is still inherently a limited resource given overfishing)

https://www.pnas.org/doi/10.1073/pnas.2204892120 is one of the most depressing findings ever.

First of all, thank you for this post.
This, at least, it was useful to sit and think a bit about the matter.
As I wear the clothes of the Devil's Advocate, I'd like to do a concurrent post to state why the arguments you put in front were not acceptable (when not actually impossible):

More geniuses

We can state without any doubt that the Earth population incredibly increased in the last decades. All I can experience, especially in the last decades, is the poor quality of the humans (at least, judging from their posts in the social networks). This means:
- more recurring grammatical/orthographic errors (people who don't know even their home country's language);
- people speaking about topics where they've got not minimal experience (hence, spreading out ignorance rather than knowledge);
- people speaking not to add something to the debate but just on a "clickbait" basis.

And I mentioned only the too evident issues. There are many other issues, some related to the above.
To cut a long story short: if you can't provide people a proper education anywhere (use of the technologies included), you are not increasing the chance of getting geniuses but the chance to widen the ignorance pool where the humanity is going to feed on. 

More progress

  • Total investment. I wish it was so. This is (at least) a naive conception of humanity. I'm going to give you good news and bad news: good news are that the money for such investments already exist; the bad news are that the owners of their money don't want to spend a single penny for them.  So, if you want to get more investment, you have to create politically and economically the reasons for they would find profitable (or more profitable) to do so;
  • Specialization. Here we go to a previous issue: if you can't provide people a proper education, you are not creating many more specialized workers but only more people who always have a worse knowledge of the basics of their job (and of the other jobs too, which means always more people wanting to have their say to "actually teach papa to screw");
  • Larger markets I'm going to give you the same bad news and good news I gave you before. These markets would actually exist already now, but we're using them in the wrong manner. Gandhi used to say: "Earth has enough resources to satisfy anybody's need but not to satisfy anybody's GREED. If only we could understand (and make it understandable to the right people) the difference between need and greed your hopes would be somehow possible;
  • More ambitious projects 
    Stop. 
    If you studied Ancient History properly you must know that the way Ancient Egypt took large masses of people to work to these more ambitious projects was force them to do that in SLAVERY. We should have put behind us that word from the Enlightenment Age (which - it is useful to remember - also made a significant contribution to the creation of the United States of America). 
    Are you REALLY sure that you want to turn back the clock of Time to THAT? (not to mention that, in spite of that, still today in the 21st Century we have large portions of Earth where we keep on accepting, socially or politically, slavery).

"In fact, these factors may represent not only opportunities but requirements for progress. There is evidence that simply to maintain a constant rate of exponential economic growth requires exponentially growing investment in R&D. This investment is partly financial capital, but also partly human capital—that is, we need an exponentially growing base of researchers."
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You keep on considering the issue in terms of QUANTITY, forgetting totally the QUALITY, which is what, in your perspective, really makes the difference.

"But in the long run, an exponentially growing base of researchers is impossible without an exponentially growing population. In fact, in some models of economic growth, the long-run growth rate in per-capita GDP is directly proportional to the growth rate of the population."
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What kind of models of economic growth are we talking about?
With numbers at hand, in the current models of economic growth that are applied globally from those self-named "civilized countries", the only growing thing is poverty. In favor of the concentration of wealth in fewer and fewer hands. Is this your conception of "growth" and "civilization"?
All the above is also weakening Earth security. 
Because the poorer are people, the lesser are valuable their lives. 
And the lesser are valuable their lives, the easier would be they are going to devote them to criminal projects in exchange of some quid, whatever they may be. 
Just because they've got actually nothing to lose (neither their own life itself).

To cut a long story short, in the current models of economic growth the only thing growing is - with poverty - the manpower of criminal organizations (terroristic ones included, that you state you wanna fight in words but in the end you are feeding in practice).


More options

  • Better matching for aesthetics, style, and taste.
  • Better matching to careers. 

    It's the same old story: humanity will have more of these if they will be trained to. 
    Otherwise, the only things growing - together with poverty and the manpower of criminal organizations - are Fascisms
    There is an increasing list of countries where,  foreign people are not only felt as an advantage, but rather a danger ("they come here to feed criminal activities", "they come here to steal our jobs", "they come here to steal our women", etc.). 
    The reason is, from my point of view, quite simple. Let's say we have a house with three rooms: this house would be comfortable to - let's say - no more than 3-4 people (one room per person). If you wanna host some more people, you will have to increase the quality of services provided by the house, to compensate that there will be a bit lesser. 
    Because one of the fault of your scheme is that you completely ignore that the Earth resources are limited. You want more people but you didn't tell us how to feed them, how to water them, how to educate them, in a world that's already at stake to do that with the current number. 
    So, going on with my metaphor, we've got currently the three room house (that - it has to be clear - won't have any more room, at least in the short term) with about 6 people in it, where 1 person has his/her own room and the other 5 are fighting among them to compete for the remaining 2 rooms. Let's say that 2 of the 5 people fighting will find an agreement to get another room together in the end (hopefully, in an optimistic perspective). There are still 3 people remaining and fighting to compete for the only room left. And let’s also say that, if in a house there are three people fighting among themselves, cohabitation is not the maximum of happiness even for the other three who are trying to live in peace.
    And would you want to get in some more people in such a toxic environment? 
    What exciting perspectives of life could you provide them?
     
  • Better matching to other people. Even on this side, it's the same old story. 
    You won't solve the problem if you increase the number of chances without increasing the quality of chances.
    I can offer my personal single heterosexual man, if someone can find it useful.
    What I experienced on my own skin is that our consumerist vision of society has led us to also consider interpersonal relationships as "products". This means that we no longer want to build and spend on improving a relationship with anyone when, given the huge availability of choices, we can fuck off our partner and take another one with the same nonchalance we have in changing the brand of our washing machine soap.
    And when you've got another partner the game starts again. 
    Women (I talk about them because I'm interested in women, but I guess I can tell the same thing about men) spend their lives collecting dozens of toxic relationships where they always pour on the new partners all the toxicity they have had from the previous ones, charging the righteous for the sinner. And in the end, the only thing left to do is escaping from that hell. 
    The result is that, in the end,  neither of them both will believe in a healthy relationship anymore, but they will always think the other as an automatic dispenser of money, favors and sex (if you manage to get to sex). And when they can't accept the other one has gone away and has the right to have a less toxic relationship, the story often ends with a murder or a suicide, when not with them both.
    I think this is not the right way to achieve an increasing Earth population.
    I think the time has come to provide our children with a "sentimental education" before a sexual one. Something that will teach them to respect other people and to treat people as people and things as things, and not people as things and things as people. But it's very hard to teach to someone something you haven't learnt for yourself yet. So, before teaching to them, we should start to learn this for us in advance!
    To cut a long story short again, we have to invest more in the quality of what we've got instead of more quantity!
  • More niche communities.
  • More niche markets. 
    You will have to build up in advance a world with a social, cultural and economic system that would encourage this. Until then, your project is simply not possible, when not naive or incoherent.
    Because in the current one, you are doing exactly the opposite.

Deeper patterns

  • The existence of non-rival goods.
  • Economies of scale. 
  • Network effects and Metcalfe’s law. Value in a network is generated not by nodes but by connections, and the more nodes there are total, the more connections are possible per node. Metcalfe’s law quantifies this: the number of possible connections in a network is proportional to the square of the number of nodes.

    Metcalfe's law talks about the number of nodes. You can get all the nodes you want, but if the quality is poor, they're going to last the twinkling of an eye. 
    And, in the end, the number won't be exactly what you expected!

A dynamic world

I assume that when Ehrlich and Goodall advocate for much smaller populations, they aren’t literally calling for genocide or hoping for a global catastrophe (although Ehrlich is happy with coercive fertility control programs, and other anti-humanists have expressed hope for “the right virus to come along”).
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Nice one to talk about these good ideas. 
So, if maybe they still have not taken them into consideration (I can't believe that, but you'll see...), now they'll surely do!
 

A world with a large and growing population is a dynamic world that can create and sustain progress.
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I remain with my opinion that, before thinking of a larger population on Earth,  we should work on improving the quality of life of those who are still living here, in advance.
And there are still loads of things to do just to make it become acceptable.
I'd love to change my mind if you've got more consistent argumentations than those you already provided in that sense.

Thanks anyway for raising the topic, which is everything but not relevant.
Best regards,
A.F.