Another consideration is the ongoing research on extending/prolonging lifespans. If successful, I would expect birthrate to plummet, and child-centred cultures to diminish. (And to our detriment, in my opinion.)

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The trouble with most scenarios is: The Hegel. Thesis-Antithesis. Development A will lead to change B which will affect A. But extrapolation is fun, as is nitpicking; thus my 11 nits:

1. Extinction: see Hegel: less kids - less people – more space – more kids. If I had 3 bedrooms more, we had 2 kids more. Also more gas, land, power per person – makes people richer (see Europe's boom after the plague); richer and more space= more kids (see 2).

2. Poverty: Nationally in the west, TFR is a U-curve, the poorest AND richest have more kids. The richest have most. - That said, one wonders what will happen in Pakistan and Nigeria this century.  

2. Big War: More poverty, sure; more kids: maybe, but much lower survival rates if Civ. + health care crashes + high radiation, possibly. HC may often be a „wasteful signal“, but for mom+kid surviving birth, it actually has some use - https://ourworldindata.org/maternal-mortality#where-are-women-most-at-risk-of-dying-in-childbirth .  

3. Old Moms: Sounds like more will have a kid, but mostly ONE kid. More mature mothers are more „responsible“.

4. Frozen Eggs: See 3. Mostly an excuse to delay kids „till the 12th of never“!

5. Robot Nannies: Yep, nice. But robot-wifes/hubbies might be much easier to do – total fertility crash in a generation. ;)  

6. DNA Selection: Given time and evolutionary pressure (TFR is BIG pressure!), this is my No1 scenario. Bryan Caplan is „dark triad“? As me (5 kids)? Conformity is no issue when all those child-less died out.

7. Insular Subculture: Amish, Mormons, orthodox Jews are doing fine – and a billion muslims. Not so insular, maybe. 

8. Parenting Factories: lol. AI-kids are even cheaper – and they shall call in as often as you like! Though I like the efficiency gains at this family of 181: https://en.wikipedia.org/wiki/Ziona#:~:text=Zion%2Da%20(76)%2C,state%20because%20of%20the%20family video (when they were only 175): https://www.youtube.com/watch?v=CX4H0mn0qKA

9. Gap Decade: Too expensive. And the non-kids-crazy will just travel the globe + tik-tok.

10. Gender Roles: that seems the most far-fetched, but see 6 and 7.

11. Nation Subsidy: Sounds more efficient than 9. Say 500k for 1 kid, 50k for each more should cover the opportunity costs for most. Might be well be worth it, if those kids are „high-quality“. Big IF.

12. Kid Debt/Equity: Actually a lot like 11. Private investors might be much better in finding the „right rate“ for each kid: „This will return just 1 million over a lifetime, we pay 20k now for the right of 10% of his income - incl. dole.“ „This one is high-value, as parents are obviously doing fine, we will invest half a million by providing a ‚free‘ nanny and a place in a 'Chinese kindergarten'.“

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> If world fertility averaged 1.4 for 1660 years of 25-year generations after a peak of 10B, humanity would go extinct. If fertility averaged 1.0, that would take only 830 years.

830 years??

I definitely don't expect current projections to be valid 830 years from now. We're gonna be robots, or vat-grown genetically engineered organisms the size of mice, or expanding through the galaxy with warp drives, or all dead. The most likely outcome apart from "all dead" is that AI will take over, and projections from that point will be determined by what the AI wants to do.

If regular biological evolution plays a role, this comic comes to mind: https://www.smbc-comics.com/?id=3130 The idea is that to have a ton of children you have to be able to make a lot of money to be able to raise them, and want to do that. So we may see some "hyper-fecund mega-nerds," with lots of money and lots and lots of children, and this phenotype could become dominant in the long term. We do already see a few billionaires with many children, such as Elon Musk.

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Everyone ignores the obvious fact: by 2050 half of the population will be African (living in Africa, Europe and USA). And by 2100, most of the population will be African and African hybrid. And when Africans take over all countries and societies will collapse back into primitive conditions at best, but probably more chaotic like today's Somalia.

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Evolution will just replace one set of genes (those that don't value having children) with another (those that do) as you have pointed out before Robin. The timeframe that this will happen over depends on the exact heritability of the preference for more children, but any heritability at all is enough to make this happen on a fairly short time horizon. See for example this paper (https://www.sciencedirect.com/science/article/abs/pii/S1090513817302799). The outcome in the short term will be a much more religious and conservative world as Hutterites, Mormons, Orthodox Jewish people, and religious Catholics and Christians become a larger portion of the population (see for example Shall the Religious Inherit the Earth https://www.amazon.com/Shall-Religious-Inherit-Earth-Twenty-First/dp/1846681448). In the longer term it is likely that offspring of extremely productive people that also value children like Elon Mush will come to dominate as they will be able to outcompete others. But this is less certain because the people being outcompeted may have enough power to band together to stop it. I guess the biggest irony is that people like Elon are worried about a declining population when its genes like his that will prevent this from happening to any appreciable degree.

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what sense does any of this make in a future with 2.7 C warmer global temperature?

we have 1000 times too many people anyway. "declining fertility" should be renamed "lessening desperation of the overpopulation crisis".

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Averages don't work well in demography. If some small subpopulations have higher birth rates they'll be obscured by the averages but dominant in the long run -- the largest eigenvalue determines the long run behavior. Expect the US to become Hutterites and Orthodox Jews. I don't know who the corresponding groups are in the rest of the world.

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Uh, the way that natural selection works is that the strain of humans who want no children will go extinct and the strain of humans who want children will continue. Whether the wanting is genetic or cultural I don't pretend to know, but a culture can go extinct just as can a genome.

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GPT-4 generated:

Certainly, Mike. Continuing to channel Peter Zeihan's perspective, here's a unique scenario that might align with his thinking:

Helix: 2023-08-24: [Peter Zeihan's Perspective]

Scenario: Geopolitical Realignment and Demographic Partnerships

In a world where fertility rates continue to decline, particularly in developed nations, a new form of geopolitical realignment emerges. Countries facing severe demographic challenges begin to form strategic partnerships with nations that have younger, growing populations.

Demographic Partnerships: Developed nations with aging populations and low fertility rates enter into agreements with developing countries that have youthful demographics. These partnerships involve facilitated migration, education, and employment opportunities, creating a symbiotic relationship where both nations benefit.

Economic Integration: The agreements extend beyond mere labor exchange and encompass economic integration, technology transfer, and investment in infrastructure. The developed nations gain access to a young and vibrant workforce, while the developing countries receive investment, technology, and expertise to boost their economies.

Cultural Fusion: This scenario leads to a unique cultural fusion, where traditional barriers break down, and new hybrid cultures emerge. The blending of different traditions, values, and lifestyles creates a dynamic and innovative environment that fosters creativity and progress.

Strategic Alliances: These demographic partnerships evolve into strategic alliances that reshape the global geopolitical landscape. New blocs form based on demographic compatibility rather than traditional political or economic alignments. These alliances lead to a reconfiguration of global power dynamics, with new leaders and influencers emerging on the world stage.

Ethical Considerations: The scenario also raises ethical questions about sovereignty, identity, and the potential commodification of human capital. The agreements must be crafted with care to ensure that they are mutually beneficial and respectful of individual rights and cultural integrity.

In conclusion, this scenario of geopolitical realignment and demographic partnerships offers a novel approach to addressing the challenges of declining fertility rates. It recognizes the interconnectedness of demographics, economy, culture, and geopolitics and presents a vision of a future where nations collaborate in innovative ways to overcome shared challenges. It reflects a world that adapts to demographic realities by forging new paths of cooperation and integration, reshaping the global order in the process.

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Your nine scenarios all seem to assume that culture determines reproductive behavior. I doubt that.

As I learned it and believe it, families get smaller when they get comfortably rich. People who can't keep themselves out of poverty breed like mad in the hope that the kids can support them in old age (a function substituted by social security in rich countries).

Therefore I predict that the coming Great Reset, which is intended to and will impoverish most of us, will result in a massive population explosion. In trying to prevent Malthus from being right, the green movement will have made him exactly right.

From there, we can expect Armageddon within a century from now.

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Sep 8·edited Sep 8

If high desire for more children apart from a culture that pushes in that direction and apart from the desire for sex, is in anyway transmitable from parent to child it should turn around at some point but I agree with the insular groups idea. Like a genetic desire for children gets stronger. Fertility was once controlled by the desire for sex rather than the desire to have children but it could be that some people have a stronger genetically controlled desire to have children.

Groups like the Amish, Laestadian Lutherans and orthodox Jews will become larger parts of the population.

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I’m a bit shocked that the equivalent of the elephant in the room is not even whispered of herein. Are folks seriously concerned that human fertility rates will be what dooms us?? Maybe ya’all need to spend some time in the real world??

“The implications of energy inequality for climate change policy

The study projects energy use through mid-century and finds that, without energy efficiency improvements, “energy footprints would double by 2030, and more than triple by 2050, with half of the increase occurring in India and China.” With rising incomes, more spending will shift from basic goods to luxury goods, especially transport, which at least at the moment is primarily powered by fossil fuels. And that could be a disaster for the climate.”


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I've put some related prediction markets on manifold into a group, here: https://manifold.markets/group/human-population-crisis

Some of them partially overlap with the list above. There is still some work to be done to create markets for some of the remaining ideas.

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How about state-hired surrogates that perform gestation services for gene-screened zygotes? Right now there are many people in this world willing to pay lots to adopt healthy white kids, so this program could be cash-positive as it meets that demand. It also need not be based in the same country as the adoptive parents. I'm not advocating this, just suggesting that such a program would have motive, means and opportunity.

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I would put Last Career as more likely, which is good news considering it is #2 in the "wanted" scale. Biologically, there are only so many levers we can push to live a meaningful life, and parenting is high up there. Pairs with the Wealth scenario. Once the world is sufficiently automated we will find having children a valuable use of time

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In my own life: I would have more kids (a 3rd and possibly 4th?) if housing were cheaper and if daycare wasn’t so expensive (and daycare is expensive because local labor is expensive because housing is expensive).

I would guess the answer here is more tied up in housing than you would think. A declining population may put less pressure on housing stock and allow for parents to much more easily afford kids.

(Some assumptions here are that existing housing is permanent/trivial to renovate compared to creating more density or using additional land, and also that people won’t demand more square footage over time)

I would also vote for older moms. See this article on Rapamycin and ovarian health here: https://gethealthspan.com/blog/articles/rapamycin-ovarian-health-and-fertility/. I’m currently taking it through this startup. I know many moms at daycare with their first child between 35 and 38 who would likely want another child if possible; rapamycin and IVF could help with this.

Additionally, the cultural bit is important. Right now there’s a sense that having more kids is bad for the environment. I think as we feel the terrible effects of depopulation the culture will change.

All this to say; I think some automatic stabilizers *will* kick in and tech will help as well. Though is there a point to worrying about the human population with AI about to transform everything?

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