“With a Whimper: Depopulation and Longtermism” (Spears and Geruso, forthcoming), a chapter in Essays on Longtermism, strives "to bring facts from population science and population economics into dialogue with the community of longtermists who are thinking about wellbeing into the far future."
The authors project just 30 billion future humans on the basis of worldwide declining fertility rates. Taking longtermism seriously as an ethical view, they examine some consequences: existential risk megaprojects look less affordable, technological growth looks slower, and so on.
I'm interested to hear what longtermists think about this.
The essay is well worth reading in full. From the abstract:
“To eventually achieve a flourishing far future, it is valuable that over the coming few centuries a complex global economy endures and the number of people does not become small enough to be highly vulnerable to extinction from a threat that a larger population could sustain. We review population projections and other social scientific facts that show that fertility rates that are normal in much of the world today would cause population decline that is faster and to lower levels than is commonly understood, threatening the long term future.”
I have some initial thoughts (but note that I don’t have any background in population science and I don’t work on longtermist causes):
- We probably shouldn’t take 30 billion seriously as the number of future humans. I agree with Spears and Geruso that their model wouldn’t “hold until the last couple only has one child”: it’s hard to imagine eschatological Adam and Eve
- But what if we did? 30 billion future humans are still more moral patients than existing humans. But there are about 30 billion existing land farm animals, and more existing aquaculture farm animals or wild animals. What this means will depend on your discount rate and interspecies moral weights
- I’m more bullish than Spears and Geruso on technological developments (in e.g. in-vitro gametogenesis) mitigating effects of falling fertility rates
- Even absent AGI or superintelligence, I expect artificial intelligence to take over a lot of innovation, so I think the rate of technological development could get uncoupled from population growth rate
- I appreciate Spears and Geruso’s warning on public policy for population control: “Governments sometimes try to coerce people to have babies; governments sometimes try to coerce people not to have babies. It is typical, with such policies, to wreck people’s lives, wreck the economy’s human capital, and wreck society’s compact between the governed and the government”. This is important.
Summary: the number of children people are having is declining, and if we project this out for several centuries we see massive worldwide depopulation. Eventually, the population is small enough that it could get wiped out by a disaster, and most people who'll ever live are in the past.
I find this unconvincing for several reasons:
They're projecting a very recent phenomenon, below-replacement fertility, to last many times longer than it has so far, instead of reverting to the historical pattern.
A lot of the constraints on family size come down to cost, especially cost of housing/land, and in a depopulating world housing and land would be much cheaper.Cheap and effective birth control is very new. Historically, explicit desire for offspring didn't matter very much: strong desire to mate was sufficient. Humanity is probably already in the process of evolving a stronger direct desire to reproduce, replacing the indirect desire. Maybe evolution is too slow (I doubt it: there's probably a lot of variety among humans here) but I'd expect to at least see the article mention this objection?
As Michael says in his comment, technological change could easily have huge effects on the parental experience, changing his many kids people want to have.
[Disclaimer: I work at the Population Wellbeing Initiative with Mike and Dean].
As quick responses to those bullets based on my own views of this issue:
Thanks!
I wrote up a draft post, focusing on heritability; any thoughts before I publish it? I'm especially curious why you think evolution is too slow -- if there's already significant variation within humanity, and we're in a new period than started recently with birth control + sex ed + lower taboos, it seems to me like it could be just a few generations before people with genetically higher desires for having their own children are having a large fraction of the kids?
I'd bet on that too -- I just think it's way less than 300y, and we only see modest drops before reversal.
I think my point on housing was wrong -- in places with declining populations a more typical pattern is probably that less desirable areas, with the least economic opportunity, depopulating faster. So there's still expensive housing in places where you can get good jobs, and prospective parents still face large costs if they choose to have kids.
But (a) your non-parent friends may not be the marginal parent and (b) some people would probably now press the button dozens of times.
My impression is this as well, but more as a cost issue and not a time issue. Childcare is very expensive (it's our family's largest expense, with three kids), and automation might be able to help with that? Not sure.
Great -- glad you wrote that post up on intergenerational dynamics (and remarkably quickly!). I haven't read through the details in a while, but I think the best paper I've seen trying to estimate heritability at the family-level is this one by Tom Vogl, which you might find interesting to dig into. I believe his headline finding is that in low fertility settings that this composition effect accounts for fertility rates being ~4% higher in this generation than it would otherwise be (but that's just a refresher from my quick skim just now).
My skepticism about evolution is skepticism about the existing variance in biological preferences for children. Obviously that's not something we can easily get at, since outcomes are the product of environment + constraints + culture + preferences, etc. But (1) this preference isn't currently common enough to push some economically developed countries above replacement rate and (2) once social/economic conditions that generate low-fertility stabilize, this sort of mental-model would always predict increasing fertility rates (since every generations composition becomes more favorable to high-fertility). I'm not sure there's even a single country with moderate to low fertility that's seen an increase over the last 10-20 years, even though the demographic transition occurred in some countries a few generations ago. (And we only have a few more, ~7-10, generations worth of time until we're at pretty low population levels).
Though I'm happy to admit that this is hard to generate convincing evidence on, so maybe in a few more generations it could start to show up in aggregate numbers. But until there's a country or two with consistent increases in fertility, through policy or evolution or whatever, I will remain very concerned that the decline will not be self-correcting.
Don't have much to add on the other points you made :)
Thanks! Published the post.
Much of this is just repeating things that others have said, but my initial position here is skepticism.
I recognise that the people working on this are better informed than me on this topic, and that seems like a relevant consideration. But I worry this is... kinda EA nerdbait. Clever big picture thinking, backed by quantitative models, revealing a hidden catastrophe that others have not foreseen sufficiently clearly. I'm not saying such things never get at the truth, but I do think it's reasonable to approach them with an initial attitude of skepticism, even in the face of the existence of enthusiastic proponents.
Many or most longtermists take artificial conscious minds seriously and as morally important, and there could be many orders of magnitude more of those in the future.
Also, even just with biological humans, we could dramatically lower the costs of having and raising children by making large parts of the process artificial, as you point out (artificial wombs, AI parents or no parents at all and more communal raising of children), allowing far more humans to exist.