However this plays out, it's going to be a monumental shift in what constitutes human civilization. I see a few possibilities: Optimistic: falling population l

However this plays out, it's going to be a monumental shift in what constitutes human civilization. I see a few possibilities: Optimistic: falling population levels make automation a top priority and we replace almost all labour both physical and mental with robots/AI. The prospect of extinction drives research into life extension, healthspan extension, and fertility extension and we find a balance where we are able to live long, fulfilling lives and still have enough children to avoid regression or extinction. Business as usual, sort of: we find the magic mix of incentives and social programs to keep the replacement rate steady at 2.1. We deal with whatever weird effects the previous fluctuations have induced and hold population levels steady. This might be stranger than it sounds since you would either end up in a situation where some people choose not to have children while others have many children to balance things out or you have some kind of tight social control where everyone has the "correct" number of children. I'm honestly not sure how this would work at all since both cases have an air of planned economy about them. Pessimistic: economic and legislative collapse destroy all existing forms of trade and governance. Population craters due to war, famine, and disease. We regress to a pseudo-industrial level that can be maintained by a greatly reduced population hindered by depleted resources and corrupt local warlords. Who knows how long we could be stuck in this state or if we could ever crawl our way back out of it before completely stripping the Earth. Horrific: global crisis results in the abolition of women's rights and the enslavement of populations to perform the necessary labour to keep everything running.