Perpetually Declining Population?

If the population falls the circumstances that created the low birth rate will change. This seems like the equivalent of an economist extrapolating a high inflation situation into the future and determining that only billionaires will be able to afford tomatoes.

1.66 children per woman in the US

I want to stress that this is the total fertility rate (TFR), and not the completed cohort fertility (CCF), and therefore it is not a very good proxy for what you want to measure, especially since women are having children later. I wrote a post [LW · GW] about it a while back, although it is far from perfect. You can also look it up on wikipedia or something similar.

I think one salient point is the fact that we live in a world where the number of children you have is pretty much directly equivalent to your evolutionary fitness. In the past your evolutionary fitness was bottlenecked by whether you survive childhood, whether your children survive childhood, whether you are able to feed your children, etc - all in a malthusian environment. 

This means that the selection pressure for genes that increase your fertility is extremely strong. Much stronger than any selection pressure on any single trait that has been selected for in the past, say light skin or lactase persistence in Europeans. 

I don't think the claim "if human population is only 560M a minor disaster could be enough to wipe out humanity" stands under scrutiny. There can be all kind of different arangement that these number of people live, wth different levels of fragility.

Imagine a universe with only 560M humans spreaded through the galaxy. Say there are only about a hundred people on every inhabited planet. However there are also bilions of aligned robots ensuring the wellbeing of these humans and capable to repopulate the humans if they die out.

Such arangement seems more protected from disasters than tens of billions of humans living on Earth in high density.

Any population argument that stretches centuries in the future needs to contend with whether humans will attain clinical, biological, or some other form of immortality or amortality in that time. If we increase the lifespan to 300 or 1000 or 10000 years of healthy life, that both forestalls population decline and enables those who do want children to have more of them over the course of their lives.

I take issue with the authors here:

Won't the Amish or some other high-fertility, perhaps religious, sub-population expand to be as many as we need? For several reasons, no.

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First, fertility in a high-fertility sub-group would have to be high enough (certainly above two, for example). We've already seen above that the "high fertility" of high fertility subgroups has been declining over the decades. High fertility used to mean 6 children per woman. Now it means 2.5. Before long, it may mean 1.8. Second, the children of high-fertility parents would have to be very likely to remain in their high-fertility cultural group.

I grew up in a small-town homeschooling community where large families were fairly normal, but many of the children did not go on to have many children, or homeschool their own children.

In contrast to that, I am now a member of a church where 4 children is considered a small family, and 12 children is considered a large family.

Many of the families are second-generation, and one of the topics of conversation is how to pass on a worldview that involves passing on that worldview recursively through the generations.

We're not Amish, but the Amish do seem to be doing a good job of this – per https://en.wikipedia.org/wiki/Amish#Population_and_distribution their numbers have been impressively consistent over the years. I don't know why the authors think that their next 100 years of growth would change from the last 100.

Now, it's going to take a while for their numbers to affect the global population. But it doesn't seem crazy to me that in a few centuries the world's population will be comparably large, and even more dominated by a few Islamic and Christian sects than it is now.

Ruminations on this topic are fairly pointless because so many of the underpinning drivers are clearly subject to imminent enormous change.  Within 1-2 generations technology like life extension, fertility extension, artificial uteruses, superintelligent AI, AI teachers and nannies, trans-humanism and will render meaningless today's concerns that currently seem dominating and important (if Humans survive that long).  Existential risk and impacts of AI are really the only issues that matter.  Though I am starting to think that the likely inevitable next generation of MAD - space based nukes hanging like an undetectable sword of Damocles over our heads is scary as hell too - coordinated global 1st strikes with only 2-3 seconds between detectability and detonation of stealth bombs re-entering from far distant orbits at >10km/s.

But even in their absence if there was close to a technology level freeze starting now evolution would move in to fill the gap - within a few generations individuals and cultures whose psychology or rules moved them to have more kids - eg religious fundamentalists, highly impulsive, strong maternal or paternal drives and strongly patriarchal cultures (Looking around world places that treat women like shit seems to have higher fertility) would steadily grow to dominate the gene pool - seeing a greater number of kids being born. 

Honestly this worry in general, at the current stage, seems a bundle of nonsense to me. There is obviously a real and relatively pressing issue about an inverted demographic pyramid and its sustainability - that's a different matter, as it starts being felt pretty quickly. But "people will keep reproducing below replacement rates for centuries until humanity basically goes extinct" is so absurd I can't even begin to take it seriously. The current rates of reproduction are a product of culture as well as socio-economic factors. None of those factors would survive impact with even just a halving of the current population! I can imagine a dozen ways in which the assumptions would break, from "lifestyle has worsened, thus people have a lower bar for what counts as a good situation to have kids in, rolling back roughly to the 1960s" to "a shrinking and aging population means way more opportunities for young people or working age, which raises the relative well-being of such people, which makes it easier to decide to have children". A world in which population crashes is a world in which housing and jobs are desperately seeking for people to fill them, not the other way around - incentives change wildly, and so would people's priorities. It's honestly absurd to even try to extrapolate that way. The one scenario in which I think this wouldn't happen is if somehow we all had perfect friendly AGI-powered automation, with robots taking care of all our needs and entertaining us, possibly even replacing human connections. It's up to anyone to decide whether that's a good or terrible future, or how likely it is, but it's certainly much more than just a simple extrapolation from current trends.

I can imagine humanity going voluntary extinct in the future. Making children is just one possible activity among many, and the number of possible activities and their attractiveness is probably going to grow, so at some moment most people may go "meh, too much effort". Or there can can be some weird economical effect where most people won't be able to afford children -- not because of meaningful resources such as food, but because of some bullshit reason (something that becomes infinitely expensive for some stupid reason, such as university education, will be considered a basic human right and you are not allowed to have kids if you can't afford to buy it for them). Or there could be a passively-aggressively unfriendly AI which can't hurt or defy humans openly, but may subtly discourage them from reproducing, because it is allowed to destroy humanity as long as it happens voluntarily and nonviolently. All of this seems possible to me, and yet the article seems needlessly alarmist.

The combination of technological progress and population decline could make children much cheaper. Just ask people how many children they would have, if they had universal basic income, affordable housing, affordable robotic nanny, and affordable robotic tutors. (As opposed to today, when often both parents need a job, stuff is expensive, and yet most people choose to have kids.)

I am curious about the specific details of "minor disasters" that can wipe out a population of 500M, but cannot wipe out a population of 8000M. Fewer people would probably still be distributed across the planet. For example, lower population density and more time spent online would reduce the risk of pandemics.

Well what about (wealthy) governments evolving a solution to fertility? So far governments have found it easier to import foreigners, where all the costs to raise them to educated adults have been paid for and they already have a professional job offer. This "brain drain" strategy only works until there is nowhere to drain from. (because the most populous countries that provide educated individuals are both becoming relatively richer and experiencing their own population declines)

As far as I understand it wealthy governments have barely tried seriously at all, perhaps from various Overton windows about how parents are supposed to be responsible to care for their own children. (Yet the education and career system withholds the funds to do so until parents are near the upper end of their prime breeding years. In addition housing shortages created almost entirely by the government, as well as medicine and education costs ever rising, mainly as a consequence of government action, cause the obvious consequences)

The government could afford to pay a lot more to young adults for the burden of having children. Each child is millions in lifetime income to the government if they succeed.

The government could do a lot of things to maximize the return on its investment.

One of the big problems with creche parents is statistically strangers care for others children less than their own and commit abuse. But with ubiquitous surveillance - lots of cheap cameras streaming to the cloud with basic AI to transcribe and look over the footage - abuse would be nearly impossible, and professional adults who's salaries are mainly paid by the government could take care of the young children, freeing up the parents to finish school/early career/socialize and have additional children.

Combine things like this together and you could settle on 4+ children per mother - where some have 10 or more as it is profitable to do so - and essentially eliminate your problems.

IMO I think the most important takeaways from this work are the following:

1. Assuming you both have a view where certain humans are positive EV in your book and you think the long term matters, extinction risk reduction may look far less valuable, and in particular we can no longer assume that mere global catastrophes are survivable for the human race, like nuclear war or bioweapons, since we can no longer assume that humans will breed back from a mere catastrophe. Thus, extinction risk no longer looks that special in the grand scheme of things, and global catastrophic risks look more valuable for prevention.

2. It imposes a deadline on long-termism, and in particular means that we can no longer appeal to very long-term projects. This type of reasoning was implicit in some arguments against making advanced AI like Geoffrey Miller's arguments, and while I think it could be salvaged somewhat, I do think that most reasoning related to hundreds to thousands of years long feedback loops or more needs to address the paper seriously, or it has 0 expected value in my book.

3. For those who believe that certain humans have positive EV in your book, then becoming grabby soon (as in the next few centuries) is very important, and that it's plausible that the actions taken in the next few centuries determine pretty much the whole expected value of the future, and depending on whether infinities are supported, may be the difference between a future where the expected value is 0, and a future where the expected value is +infinity or -infinity.

4. While I don't believe that this model will always be robust in all situations, I do think it's central conclusions are probably going to hold up assuming a non-grabby humanity in the next few centuries, and a humanity that doesn't get rocked by any global catastrophes, because of the essential uniformity of fertility and the inability of cultures to get out of the low fertility state once they get into it, combined with poor at best transmission of high fertility genetics.

Yes, this will definitely be a problem starting in a few decades. Developing technology that can help people have kids (in vitro gametogenesis, and especially artificial wombs) is going to be important. Artificial wombs are harder, but probably more impactful for overall fertility rates in vitro gametogenesis.

Will Chertman wrote a very nice whitepaper on fertility last year, but I can't seem to find it now. (edit: here it is: https://docs.google.com/document/d/e/2PACX-1vT1hgf95phUa4e1nqf2VTfjFmUeSBwb7mihE86cU6bE1EI-EZteWm6UmeC18PJSs3Laog4rP7qKtT1j/pub)

I don't see any reason how the population can stabilize at the arbitrary level of 560 million. Either it will start to increase again at some point (due to cultural shift, natural selection or some other reason), or it will decline until the collapse of the industrial civilization. But in that case, with no universal education anymore, the demographic transition will reverse, and the population starts growing again to limits imposed by pre-industrial agriculture (which is somewhere around 2 to 3 billion, not half a billion).