Limits to Growth is possibly the least accurate book ever widely read. They got absolutely nothing right, and it should be read as an example of how “experts” can get things so entirely incorrect despite their credentials and models.
One might justifiably argue that the quantitative predictions made by the book hinder, or even compromise, the deeper, more important point of it. But the latter was unfortunately correct, and plenty of quantitative data are there to back it up: https://www.nature.com/articles/s41586-023-06083-8.
> In 2015, a calibration of the updated World3-03 model using historical data from 1995 to 2012 to better understand the dynamics of today's economic and resource system was undertaken. The results showed that human society has invested more to abate persistent pollution, increase food productivity and have a more productive service sector however the broad trends within Limits to Growth still held true.
Give it 20 more years, they can "recalibrate" again and find another imminent collapse: any model with enough free parameters can match any input you like.
(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).
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).
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.
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.
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.
[1] https://www.populationpyramid.net/japan/2023/ [2] https://www.macrotrends.net/countries/JPN/japan/fertility-ra...
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.