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Comment by bdamm | Hacker News Reader

Can anyone explain the population reversal? There's vague references to changing fertility rates, but that doesn't explain the reversal. There are complex economic factors at play and so just observed changes to fertility aren't enough to make the prediction of population reduction. For example, does the model include expected advancements in agriculture, or does the model assume there is some challenges in growing our food supply? Also, China used to have a one-baby policy but I don't think that is still in effect. Does the model include that?

These kinds of models are pretty to look at but rapidly fall apart when you play with base assumptions. The only way to absorb this data is to have an interactive set of adjusters to base data possibilities.

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One child policy was in effect and Chinese people got used to it. It's been enforced as a social norm and the subsequent generations seldom have more than two kids. You can add China's increased urbanisation, increased work hours and smaller houses/apartments into the mix.

Are the work hours very different between working extremely long hours in a factory and working extremely long hours on a farm 70 years ago?

One Child Policy was certainly a huge factor. So is probably a strong rise in wealth and education, which are both linked to lower birth rates.

A lot of families are split up as a result of migrant factory work and the factory dorms, so it's probably a drag in multiple ways compared to farming.

Good point. It's hard to have children when you're physically apart for most of the year, and it's even harder to raise them when you're not home. Do children generally stay with family in the rural areas, or do they stay with one or both parents in the industrial zones?

Absolutely. More children meant more farmhands. In the city, it's a net negative.

It's not to say you're wrong, it's just the one child policy is a compounding factor.

True, there's less incentive to have large families, and it's a practical issue as well, I suppose. You can have your child around and keep an eye on them while you're working on the family farm, but you can't take them with you into a factory and sit them down next to the assembly line.

Are there plans to do the opposite of OCP? I suppose it's easy-ish to forbid people to have multiple children, but to force them because you now need them?

Forcing can be in terms of incentives like tax rebates etc.

It might be that the incentives offered in Western European countries aren't large enough, but it seems counter-intuitive - we had much larger families when the incentives were much smaller. The long established population has very few children, recent immigrants (from poorer countries) have more, but also show falling birth rates within a few generations. And that's in countries with free education, usually free healthcare for children, tax rebates, financial support from the government et cetera.

Farmers sustain their families where they work. Factory workers are separated from their families. China is full of villages with only grand-parents and small children left.

China went from forced to proper demographic transition.

There are lots of reasons - as populations become more educated/urban/rich/able to access contraception, fertility rates decline.

https://en.wikipedia.org/wiki/Sub-replacement_fertility#Caus... describes many associations.

A short-ish read on how the UN does population projections and major factors contributing to the expected population decline:

https://esa.un.org/unpd/wpp/Publications/Files/Key_Findings_...

This is a nice explanation of different models: https://youtu.be/QsBT5EQt348

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