I miss a mention of male infertility. Wikipedia: "a 2017 meta-analysis found that sperm counts in Western countries had declined by 52.4 percent between 1973 and 2011". https://en.wikipedia.org/wiki/Male_infertility_crisis
Nobody is sure why, but some form of pollution is the likely culprit. It won't be heavy metals, as pollution by these has gone down. In marriages and other heterosexual reproductive partnerships, he man tends to be older. So if a woman delays childbearing for career reasons, she risks infertility not only from her own biological clock but from that of her partner.
I'll see your 1 billion and raise to 330,000. That's the population of Iceland. Iceland is admittedly very dependent on world trade, but the population is quite sufficient to support a sovereign state and a vibrant cultural scene, on not too much useable land. So I would say that the minimum population is whatever is needed to support our current community of engineering practices--probably just a few hundred million.
(I've taken the other side on previous threads. Our disagreement is about the transition costs of depopulating, not the end state once we get there.)
Reproductive strategies are determined by environmental conditions in every species that has a nervous system. As you note we are choosing fewer kids with a higher likelihood of survival, but if that changes in the future may revert. In the very longer term we may evolve more stable strategies, but that not relevant here. Demographics is not a matter of long trends though.
"If we manage to leave the planet in a habitable condition..." That is the very big IF.
Hans Gosling had alternative ideas:
https://www.youtube.com/watch?v=fTznEIZRkLg
I miss a mention of male infertility. Wikipedia: "a 2017 meta-analysis found that sperm counts in Western countries had declined by 52.4 percent between 1973 and 2011". https://en.wikipedia.org/wiki/Male_infertility_crisis
Nobody is sure why, but some form of pollution is the likely culprit. It won't be heavy metals, as pollution by these has gone down. In marriages and other heterosexual reproductive partnerships, he man tends to be older. So if a woman delays childbearing for career reasons, she risks infertility not only from her own biological clock but from that of her partner.
I'll see your 1 billion and raise to 330,000. That's the population of Iceland. Iceland is admittedly very dependent on world trade, but the population is quite sufficient to support a sovereign state and a vibrant cultural scene, on not too much useable land. So I would say that the minimum population is whatever is needed to support our current community of engineering practices--probably just a few hundred million.
(I've taken the other side on previous threads. Our disagreement is about the transition costs of depopulating, not the end state once we get there.)
Reproductive strategies are determined by environmental conditions in every species that has a nervous system. As you note we are choosing fewer kids with a higher likelihood of survival, but if that changes in the future may revert. In the very longer term we may evolve more stable strategies, but that not relevant here. Demographics is not a matter of long trends though.