I'd take a different answer to this question: philosophy. In times before Abrahamic religion developing or adopting a life philosophy was seen as a practical obligation for a man. This is where you saw the rise of everything from the Pythagorean to the Stoics. It seems that the rise of Abrahamic religions is what largely brought an end to this and mandated a sort of one-size-fits-all philosophy for everybody.
Now in modern times many people have moved away from religion, yet most aren't replacing that philosophical void with anything comparable. And I think this naturally leads to things like hedonism which is completely unsatisfying over time, or even nihilism which is even less satisfying. One could even argue this issue is directly related to the collapse of fertility in developed nations.
I think that a personal life philosophy is absolutely critical for having a contended life. And I use contended instead of 'happy' as part of my own philosophy of life. I don't think happiness is or should be a goal. Happiness is a naturally liminal emotion. And seeking to extend it is only likely to leave one 'unhappy', so to speak. So instead I think we should pursue contentedness. Being satisfied or pleased with one's life does not mean one is necessarily happy, but it certainly means you're content with it.
Or maybe we've made life so expensive (in time or money, but "time is money") for people even before having kids that they don't want to or feel they can't take on the extra load of being parents.
Edit: this isn't a very different take from yours, TBH.
I think that is a significant factor as well - we can debate how related or not it is. I think in this case, there was a gradual ratcheting effect of how much work is extracted from people who would otherwise be contributing to childcare i.e. "the village" of elder people and women. No doubt this has a separate negative impact on the fertility rate. All IMO though, these are speculations without rigorous quantitative backing.
IMO, the birth rate drops to replacement level when women are freed. It's additional pressures that collapse it from replacement (or a slow decline 1.9) to South Korean levels.
People overwhelmingly view the ideal number of children to have as way more than we're having. [1] So people are likely choosing to not having children for other reasons.
Here [1] is a poll on desire to have children. The percent of Americans that do not want children is negligible, about 6%. So asking about the ideal number of children to have and comparing that against the number of children that people end up having is a very valuable datum. Because it may be that somebody sees the ideal number as e.g. 3, but only expect for themselves to be able to have 1.
I'm not sure if you cited that because it's the first to come up in a web search but the fact that "undecided" was not an option is a red flag in my mind.
"When asked about having children, 51% of young adults who are not parents say they would like to have children one day. Three-in-ten say they’re not sure, and 18% say they don’t want to have children."
The survey questions [1] have more details than the article. They offered a 'no opinion' choice which was rarely taken. As for what you linked to, you have to be aware of studies of small samples. The number I gave (about 6% not wanting kids) and what you referenced are probably not incompatible. It's just that when you filter down to people aged up to 34 with no children, you're obviously going to artificially inflate that percent because you're excluding everybody having children.
In other words, imagine if 70% of people that want to have children have had at least one child by the age of 34. So we start with e.g. 100 people where 6 don't want to have children (appealing to the 94/6 ratio from the older study). Then we remove 70% of the 94 that do and we're left with 28 that do and 6 that don't, so now the 'don't want' group make up 18% of the total sample. And I think 70% of people that want to have children, having had at least one child by 34, is a very reasonable ballpark.
Check out the questions [2] they asked, in the study you linked, and you can see that you end up with a highly unrepresentative sample of society: 33% live with their parents, 19% are unemployed, 44% receive financial assistance from their parents, and they're democrat:republican at a near 2:1 ratio.
I will day that I'm struggling to align these survey questions with human nature as I understand it.
I have a friend who "wants kids" and two different women, when they reached a certain age in their 30s, signaled they wanted to marry him and have kids.
But they both exhibited red flags that caused him to decline. One woman didn't act like she liked him, even though she was also saying she wanted to settle down together.
The other woman was unwilling to discuss how they'd raise the children given the fact they were from different religious backgrounds.
Given he's now in his 40s he'll likely never have kids.
I suppose if he was super passionate about kids he'd enter an unhappy marriage and make sure he got some kids out of it, before possibly ending up divorced.
So wanting children was more a conditional thing than a binary thing, and I don't know if these surveys can capture that.
I can't say too much about that exact scenario, but I think a practical issue for people is waiting for the perfect conditions. And in general, those perfect conditions never come, yet the years fly by so incredibly fast.
And for women this is particularly true. Because in practical terms you're going to have at least a couple of years between kids. At the minimum this is because their cycle is suppressed while breast feeding, and then it generally takes a number of months to get pregnant, even moreso if somebody is in their 30s, let alone 40s. And so if you want to have 3 kids, it's a practical necessity to start very early - that's pushing towards a decade of time.
So modern society is really rather a lie in this regard, and I think that's been quite harmful. Because this lie is encouraging all of us (male and female alike), to push parenthood out later and later. And that dramatically increases the odds that 'later' eventually becomes never.
The miniscule amount of written work that survives to the present really makes it difficult to do any more than speculate about the philosophies broadly held in the times before Abrahamic religion.
Abrahamic religion didn't really became a major factor in the world until Constantine. So for instance for the entirety of Ancient Greece and the majority of Ancient Rome, Abrahamic religions had no meaningful influence, and there are extensive writings from this time. But while I think it's useful to consider their views, I again think the real goal is to develop one's own philosophy.
We all have different perspectives on life. For instance many things that people all value like freedom and security, are mutually exclusive at extremes. In ancient times one could also see a wide array of philosophies that all sought a similar end of 'happiness' or contentedness, yet they took radically different perspectives on the way to achieve such - e.g. stoicism vs epicureanism.
But these are issues that many people simply never stop to even consider what they think about, and so they drift somewhat aimlessly which I think is going to make it very difficult to find contentedness and direction in life.
I think it's fair to say that "Abrahamic Religion" here means specifically "Christianity and Islam". Judaism arguably encourages exactly the sort of philosophy you're talking about, and other Abrahamic offshoots like Druze are not influential.
That said I'm not actually fully convinced that Christianity and Islam discourage personal philosophy in the way that you say. The Greek philosophies you mention were largely the playground of the Greek elite, and plenty of parallels exist in the Middle Ages and beyond. I don't know that personal philosophical enlightenment from a random subsistence farmer is any different between the two eras.
Fair point, though I'm not entirely sure the shape that Judaism took in its relatively early days. But one thing I'd say is that the same remains true to this day. The people suffering for lack of meaning and direction, and casting aside religion, are not the people working the fields. Such work provides a sort of meaning and comfort all its own, as the work is inherently virtuous. It's people with relatively leisurely and highly compensated but completely meaningless and unnecessary (and even socially detrimental) work, that are left to search for meaning in it all.
I think happiness is an inevitable byproduct of honestly following your innate sense of self. Intelligent people can be dishonest with themselves, not know themselves and be (more) capable of lying to themselves and coming up with justifications to do what they mentally want (rather than following their innate sense), thereby trapping themselves in endless dishonest but justified loops.
This tracks with what I've seen. Greater "capability" can imbue a greater ability to lie, cheat, deceive oneself, or others, and generally create all sorts of complicated problems, be them internal or external
Now in modern times many people have moved away from religion, yet most aren't replacing that philosophical void with anything comparable. And I think this naturally leads to things like hedonism which is completely unsatisfying over time, or even nihilism which is even less satisfying. One could even argue this issue is directly related to the collapse of fertility in developed nations.
I think that a personal life philosophy is absolutely critical for having a contended life. And I use contended instead of 'happy' as part of my own philosophy of life. I don't think happiness is or should be a goal. Happiness is a naturally liminal emotion. And seeking to extend it is only likely to leave one 'unhappy', so to speak. So instead I think we should pursue contentedness. Being satisfied or pleased with one's life does not mean one is necessarily happy, but it certainly means you're content with it.