It's a self-correcting problem. The people who don't have children select themselves out of the gene pool and are replaced by those who do have children.
Genetics can only have a minor influence on number of offspring, because the genetic makeup of basically every industrialized nation did not change completely within 20 years.
If there was no other factor apart from genetics, it is decidedly unclear if that could stabilize population numbers on its own.
But it won't have to, almost for certain, because non-genetic mechanisms will balance this in all likelyhood ("organized" incentives from states and also emerging ressource over-supply), and those mechanisms will work MUCH faster than genetics ever could.
Also collapsing populations will lead to resource scarcity. One of the many negatives of low fertility is that you end up with far more elderly than working age people. Any given market will also naturally decrease in size, all other things being equal. These factors, amongst others, will completely wreck economies which may well end up creating a vicious cycle against fertility.
Another reason I think 'organized incentives' will be unlikely to achieve much is that Scandinavia had been at the forefront of fertility collapse in Europe and they have both an exremely strong social safety net as well as great minimum maternity benefits. Clearly there are other factors than economic inability driving people to go childless or to only have 1.
[1] https://english.kyodonews.net/news/2024/06/3918e2481936-japa...
[2] https://www.service-public.fr/particuliers/vosdroits/F13213?...
https://www.pewresearch.org/religion/2017/11/29/europes-grow...
Do the people who don't have children send resources to relatives who do? Making the family more succesful?
Not to mention it isn't a binary really. There is a middle ground of simply having less children. A family that has a single child is still below replacement and quite different from a family with 5. Regardless, genes are still being passed on.
However i disagree with the mechanism you propose. Having less children can be evolutionarily advantous in some circumtances. People will have less children when it makes sense, and have more children when conditions change and that make sense.
Having kids early precludes education and career focus -> Education and career focus gets you money and prestige -> Folks want money -> Folks want to avoid having kids early -> Fewer kids.
It's all based on a couple misconceptions that a) you can't have what you want now if you have kids and b) you'll want what you want now when you have kids.
Try this thought experiment on for size:
Initially, you don't have kids b/c you don't want to avoid this vacation ($5k?) and that opportunity (A few years at a good job?)
But consider the reverse: If you had kids, and they were going to die if you didn't turn over $X, what value of X is "too high"? There is no value of X that is too high, you'd happily give everything you have to bring your kids home safe. Why don't we give a meager few years of our lives to have kids and get them through the infant stage until our lives return somewhat to normal?
Why do we all pretend that $5k before kids is somehow not the same as $5k after kids? It's not a trap - parents do want their children, do love them, and are willing to drop money to have them, but we only recognize this after they have them. Substitute money for a job change, a spouse choice, etc.
It's a weird cognitive dissonance that we don't recognize this for ourselves when we're young, and I'd argue it's mostly this cognitive dissonance that stands in our way. So, some tangible improvements and a slight increase in number of successful people having kids would probably dispel that misconception.
I have, and it’s miserable for the parents and often traumatic for the kids. At least if the jobs are at all challenging.
https://en.m.wikipedia.org/wiki/Kin_selection
(Used to be a biologist)
If you're talking about environmental pollution and declining fertility because of it then that's something else but even then, those who manage to survive and persist in a polluted environment will be the ones who pass on copies of their genes.
That's.... not how humans work. If people choose to have less children, which has very little to do with their genetics, there are fewer children to replicate, not "replacement" with children who are genetically determined to be fecund.
They are taking issue with the ludicrous assertion that falling birth rates are "self correcting" because the offspring of people who do replicate are somehow genetically predisposed to have more children to "replace" them.
If someone has a different perspective on this then they are welcome to make their version of the problem explicit and concrete and explain what exactly they propose as a valid intervention for fixing it. I suspect and am almost certain they have not thought about the issue as rigorously as they think and are simply parroting popular talking points they've seen and heard on social media platforms about the impending collapse of civilization caused by declining birth rates.
The implications of this may have been exaggerated of course. But it's quite clear that it is not being "self corrected" by the offspring of people who do choose to have more children than the replacement rate being genetically [or culturally] predisposed to breed like rabbits...
Biology and evolution by definition is determined by those who reproduce offspring, those who do not will be replaced by those who do. Put another way: Generation B and onwards are the offspring of Generation A who reproduced.
Or more specifically, that humans in many parts of the world are reproducing at below replacement rate.
Reproduction below replacement rate means that those who do not reproduce offspring are not replaced by the offspring of those who do.
Nobody is arguing that Generation B aren't the offspring of those who reproduced, they're arguing that this detail is essentially irrelevant to how many children Generation B will have and therefore birth rate decline need not be "self correcting" and empirically isn't in much of the world.
Given a long enough time span, everyone alive will be the children of those who reproduced. Generation B will be composed of Generation A reproducers. The world of tomorrow will be owned by those who reproduce today.
Not true. If my brother reproduces, then about half of my genes are still getting passed on. If my cousin reproduces, 12.5% of my genes are still getting passed on. If the argument is that pure gene selection will determine the outcome, then you can’t treat genetics as some simplistic binary.
Religious people belonging to certain religions/sects do have a lot more children even in the contemporary world. Maybe the world of 2100 is going to be a lot more religious than today.
The development is certainly visible in, say, Israel, or even migrant communities in Europe. Europeans must now be a bit careful not to insult Islam; that wouldn't be the case fifty years ago.
> The countries that are above breakeven (2.1 children per woman) are all in Africa or are dominated by religions which oppress women. And poor.[4] "Peak baby" was in 2013 worldwide.
>There are two futures, both bad. "Keep 'em barefoot and pregnant", or "Will the last one to leave please turn out the lights."
It sounds wild, but we already professionalized a lot of other activities that were "naturally" done by households, such as fuel gathering, cooking, home construction and small agriculture.
We are now very, very far from our hunter-gatherer roots.
The idea of mechanizing/automating/centralizing that stuff is irking me in general. One could argue that the biologisms which evolved us, and we with and through them, are just another, rather imperfect way of doing this, by slow, biologic means.
IMO this only leads to transhumanism, which I consider BS, because it will produce shadows/weak simulations of the real thing and philosophical zombies.
For example, https://en.wikipedia.org/wiki/Birth_rate#/media/File%3A1910-... shows it going from 8 around 1940 to 12 around 1957 and back down to 7 around 1972 in the USA.
Personally I just think it's just a lot of hassle and I don't think it adds much value to my life. Others will of course differ in opinion hugely.
One thing is sure to me though, humanity isn't going to die out. Our planet is overpopulated as it is.