is it so hard to understand? the material wealth of the developed world has dropped by quite a large amount (at least for shelter, medical insurance, education). Don't trust those GDP per capita figures (even adjusted for PPP), they don't tell you the true story because inflation isn't being counted correctly and the basket of goods used is questionable at best. there's a lot of subsitutions going on in those figures that understate inflation.

On an interview with an older guy from the 50s, he was explaining how a painter could have support a family and 6 kids and a house, all on a single income. Try doing that today. These days, it would be hard for a painter to just support himself, much less a wife, a house and six kids.

In the US, in blue states, millenials are now spending upwards of 40 to 50% of their incomes just on shelter.

In the bay area, it's not uncommon for couples in the highest income brackets to rent out rooms in their townhouse (notice i said townhouse) to make ends meat ( at least for those who bought recently). and that's just the top 2-3%. you can imagine how everyone else lives.

We need to get away from using GDP per capita as a measure of wealth and instead use number of hours worked to earn necessities (shelter, food, water, transportation, education and medical).

> It's still not really understood.

Is it really not that well understood? In countries and regions that are highly industrialized (like the societies you mention), having more than 2-3 children doesn't provide any more economic security like it does for largely agrarian and manual-labor based societies.

IMHO education plays huge role. More often people decide to go to collage, then have a career, people also learn what a huge effort have to be put into rising child. On top of that there is so many fantastic things that person can do and have to give up at least to some extend if having a baby. In my opinion those are huge factors. This is a reason why on average successful, well educated people tend to have less children even though they have all the resources to have a lot of them.

Agreed, the best way to raise the standard of living is to educate women and loan them money. They now have options. They are stuck being baby factories. When this happens, population growth quickly follows.

Citation to back up your comment: https://ourworldindata.org/fertility-rate#what-explains-the-...

Urbanization alone has long been observed as causing a drop in observed ferility rates as they no longer get the useful free labor investment, space is more expensive and they are no longer self sustaining.

Low sperm count is not the reason why most people do not have three plus kids - it isn't like people give up on birth control at 30 or 40 and never have any kids again. Most of is "won't have more kids" as opposed to "can't have more kids".

I think it might be caused by the modern pension system. There's no need for children if pension is provided by other means.