Except in [0] the birth rate is relatively flat between 1950-1970 and then suddenly starts a rapid reduction. Developed countries have already been industrialized for 100 years by that point. The modern work day and access to many modern fun and rewarding activitys have been available for literal decades. Mass urbanization already occurred. Many of the modern household appliances have been in use for decades. Antibiotics, vaccines, and childhood mortality had already been dramatically reduced to within the vicinity of modern norms. In developed countrys female workforce participation, education, and political activity were material with no clear fundamental shift in those metrics in the 1960s-1970s.

But you know what did occur in the 1960s-1970s? The invention and popularization of the birth control pill. Here is the US birth rate [1]. Rising from 1950-1960 then a sudden and precipitous drop in the 1960s until stabilization in the 1970-now range. This coincides with the global drop in fertility rate. How about Germany [2]? Growth from 1950 to late 1960s then a sudden drop until stabilization in the mid 1970s. France [3]? Flat and high until mid-1960s then a sudden drop until stabilization in 1980. UK [4]? Growth from 1950 to mid 1960s then a sudden drop until stabilization mid 1970s. Australia [5]? Growth until 1960 then drop until stabilization in 1980.

Every single developed country in the world is flat to growing and then sees a sudden and rapid decline in birth rate just a few years after mass availability of the birth control pill until stabilization around the time that the pre-birth control cohort ages past reproductive years. The birth control pill is so new that the reproductive cohort that lived prior to its invention is still alive.

My hypothesis is that fertility is just a function of access to cheap, effective contraceptives. The fertility rates we see today are the natural rates when pregnancy is a choice.

[1] https://www.macrotrends.net/global-metrics/countries/usa/uni...

[2] https://www.macrotrends.net/global-metrics/countries/deu/ger...

[3] https://www.macrotrends.net/global-metrics/countries/fra/fra...

[4] https://www.macrotrends.net/global-metrics/countries/gbr/uni...

[5] https://www.macrotrends.net/global-metrics/countries/aus/aus...

I think that is it. We have somewhat of a confirmation with Romania and Decree 770, which led to an increase in children (though that might have been temporary I'm not well versed in the history). I think there is no inherent desire to have children or if there is, it is far weaker than a lot of people think. And it makes sense, evolutionary. If you have a desire for self-preservation, a desire for the preservation of those close to you, a desire to nurture the young (once they are there, which also shows in seeing 'cuteness') and a desire for sex, then you don't really 'need' a desire for children directly, because the children will naturally follow from that chain of desires. It just fits with how evolution seems to works (I think at least), which often causes these daisy chains of things that work intermittently to cause something else.

Yeah, the big secret out there is that half of people once born might have been unwanted and "accidental", if not more.

it’s funny how much mental gymnastics people will do to avoid this obvious answer

birth control and its consequences have been a disaster for the human race

in addition to the obvious birth rate effects, i think there are a lot of other sociological effects from everyone being on hormonal birth control that people don’t want to admit