In figure 1.6 we have modern day Japan, Italy of 1921 and Cisalpine Gaul as examples of how mortality affects breeding space. From it we can see that while in modern day Japan almost all born women are also alive to be mums and thus 2 children is breaking even, in 1921 Italy only 71% of the available fertile years for women can be used. So you need about 3 children per mother just to stay even in Italy 1921. And for Cisalpine Gaul you have a mere 29%, so you need about 6 children per mother to stay even.

I would say it is the six children family that is more representative of pre-19th century agricultural society. Add 19th century food and hygiene to get to Italy 1921 and you have a population that doubles per generation. Add 20th century medicine and you have a population that triples per generation.

The good news is that we have a functioning feedback to have fewer children in an increased societal position for women, which has brought and is bringing births in most of the world down to or below reproduction levels. Births started going down in the areas that first saw the decrease in deaths already a hundred years ago. That was at the same time as the European empires were at their heights and industrialism was taking off. It is hard to fit that with some precognition of future resource hardships, in particular as other societies were just entering the same pattern. So to fit it with resource scarcity the richest societies must have felt that we were heading into poverty while poorer thought they were heading for expansion.

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