I don't believe that's true across cultures. Even in North America you've got social groups and organizations that are continuing to make babies like crazy.
The number 2 comes from the current world wide trend. In developed countries the fertility rate tumbles down but stops at around 2. So it is believed this is the average bottom.
Maybe you like this talk from Hans Rosling: https://www.ted.com/talks/hans_rosling_religions_and_babies
See Hans Rosling's talk on this [1] or see it yourself in data [2]. As soon as education, medicine, economic situation improves, you get a drop to ~2 children per woman across all cultures.
[1] https://www.ted.com/talks/hans_rosling_religions_and_babies
[2] https://www.google.com/publicdata/explore?ds=d5bncppjof8f9_&...
Most likely answer, religion. Successful religions grow one of two ways, and generally have encodings for both. That is they tend to have means to convert the non-religious, and secondly, and importantly in this case, have 'strong' rules on having kids. For example, in the old testament Onan was killed for 'spilling his seed' and not impregnating his dead brothers wife.
That said, even in ancient times it appeared that birthrates did go down, as in Greces case, their city state succeeded. This left them open from attack and cultural take over by outside nations and ideals with higher birthrates.
In the modern world we are coming to the point where human labor is not as necessary and has been supplanted by machine labor. Also machine protection, in our weapons of war. This could allow a nation/culture to shrink dramatically while still being able to defend against outside threats. If such a shrinking culture were one that 'grew' by spreading its message to other cultures it may succede to grow and shrink the entire worlds population at the same time. These ideas of disappearing utopia cultures are often touched by science fiction.
"Many more". Israel: 3.11 (down from 4 in 1960s), Faroe Islands: 2.6 (down from 3.2 in 1970s).
Compare to Niger: 7.24.
And especially compare to muslim countries which just love having kids, don't they? Oh, look dropping from 8 kids per woman to around 2 for most of them (some are understandably lagging behind, like Yemen, Iraq, Gaza)
> That seems to indicate that 2 is not in fact a magic number at all.
I said ~2 kids, i.e. about two kids, not exactly 2 kids. There's nothing magic about this number, it's sub-replacement fertility [1]. 2.1 for developed countries, 3.4 for some developing countries. Yes, some nations will dip below 2, can't see how that disproves my words. Neither culture nor religion have anything to do with it. Give people quality of life, education, access to modern medicine, and they stop having 8 kids per woman, and quickly dip to about replacement fertility rates.
> On average most woman want two children. But when a lot of them die they will get more (average of 6 around 1800).
and that doesn't seem to be the case.
And you said that culture had nothing to do with it, but clearly the variation in the birth rates (50% to 150% of the ~2) in countries with roughly the same standard of living is due to something.
Once again. Slowly.
As people gain access to medicine and education, and as quality of life increased, traditions and religion fly out of the window. Even deeply religious countries like the Gulf states go from 7-8 kids per woman to roughly 2 kids per woman.
These factors trump any other factor in determining how many kids a woman will have.
Once the countries get on more or less the same level in terms of these factors, only then will you see variations due to other things like culture, religion, what not.
Israel is 1.5 times more than other developed countries (and the difference is slowly but surely dropping)? So? Niger is almost 4 times more than other countries.
Medicine, education, quality of life. These three universally affect rates regardless of tradition, religion or what not.