Today there’s a new trend of population birth rate collapse doomers that are making the same error of extrapolating trends in complex living systems using math built to understand non-living systems, then freaking out about the results. Different graph slope, same error. They will be wrong too.
Not really. They are basing it on extrapolation of our understanding of humans, not some abstract "non-living systems"; specifically, our present understanding is that as people age (past say forty or so) their chance of dying steadily rises and their chance of producing offspring falls. While this may be overcome with new technology (the same thing that borked the Club of Rome's forecasts), absent any change in the basic facts of human biology the population collapse is inevitable.
(For similar reasons, countries that have favored having sons over daughters are in an even worse bind; excess males simply don't increase your rate of child production).
But we know that humans actually have some kind of non obvious feedback mechanism we don’t know how to model whereby too many males in a society cause women to be more likely to be born and vice versa. Stands to reason that the same is true for childbirth (I believe this has been observed in other species quite a lot although not directly in humans yet) - when resources are tight, reproduction slows down until there’s available resources at which point reproduction increases again. These feedback mechanisms would seem to make sense from an evolutionary perspective in terms of making sure the species has a higher chance of survival through various societal and environmental changes. It’s possible we’ve disrupted it of course through technology via birth control but hard to say given that birth control isn’t that new (“new” for women and more effective than ever, but not new).
I don’t think a population collapse would mean the end of humanity. Just a prolonged adjustment period to society but we have more people than ever in the world. If the concern is the stability (economic or social) of a given country / power structure then sure - no guarantee any of that survives that but that’s also something we’ve weathered many times in the past (often more violently than what we’ve seen in recent history in the West).
There is a short window of human fertility. Let's assume you are "smart" and wait until you are out of college. You might start at 22 and have a little over 13 years until it's its considered a geriatric pregnancy.
If the economic or social constraints are such that individuals are unwilling to bear children then that is it, you do not get to try again.
Today we straddle those in the fertile window with student debt, high rent or an impossible housing market, thus less chose to have children.
This is not to say that it's a cataclysm, but it's certainly unsustainable from a societal standpoint.
But those aren’t intractable issues and society will adapt. I think that’s key critique - extrapolation is a problem when you have feedback systems to adjust to changing environmental conditions. Like even if no one has kids for 10 years, we still have new ones being born. If it’s super critical to society you’ll see all sorts of programs and support spring up to encourage people to have larger than today normal families (eg offering free childcare etc). Also, you seem to have dismissed geriatric pregnancies out of hand (not to mention limiting counting pregnancies to specific subgroups for some reason because you view other types of kids as undesirable?) but I don’t see why that’s the case - children born during this time are still children. Fertility levels may be reduced but they still happen.
The point is that the claim that we’ll have a species-wide population collapse seems unreal when we have more people on earth than ever and we have lots of children at every age group giving us lots of shots to adjusts to problems. Not to mention tech that extends the fertility age well beyond the limited window you’ve said.
There’s a lot of baked in stereotyping it seems like on your end of what “acceptable” children look like that may be worth unpacking more than there being any serious concern about a population collapse.
Economic and social constraints? By world metrics we cant even see the horizon of economic limits at the commodity level, production is seemingly hyperbolic. The economic constraints that you feel have next to nothing to do with what it actually costs to furnish a modern first world life for you. Maybe you are actually feeling your currency being steadily debased for decades, maybe you are actually feeling a top marginal tax rate ~37%, maybe you feel the loss of gainful employment due to trade agreements, but thats all political.
It's not a cataclysm, but it means that for the next few generations, the fertility window of women must increase and the attractiveness of men has to increase. That is going to be a very slow process. There is no way this mechanism is fast enough to prevent any declines predicted until the year 2100.
So on the one hand you're objecting to "extrapolation" and on the other you're claiming that hypothesizing feedback mechanisms we don't know how to model, that have not been observed in humans, and so far as I know don't even exist should be fair game?
Look at Japan[1] -- roughly two thirds of their population is over than child bearing age, so even if the remaining third starting having babies at the replacement rate, their population will continue to diminish for decades. But of course their fertility rate in nowhere near replacement[2] and even the UN doesn't expect it to be that high in the foreseeable future.
Will the Japanese population disappear? A declining population isn’t the absolute end of the world. Human population has ebbed and flowed throughout time. What I’m saying is that we’re at 0 risk of a world wide population collapse.
Also the feedback mechanism for sex selection isn’t some hypothetical thing I invented. Look up Trivers-Willard hypothesis. Whether there’s a similar social pressure mechanism that determines how many offspring someone has I don’t know, but it’s silly to rule it completely out of hand when we know that social pressure between people do impact number of children.
