In the current world of sub replacement reproduction, a phenomenon occurring primarily in developed countries with large governments, sick with individualism and fading traditions of family and marriage, policies are implemented to financially incentivize reproduction or replace lost population with imported people.
In most cases populations still decline, perhaps approaching a lower and sustainable equilibrium where surviving families are those more inclined to meet replacement rates. But it’s not likely that reducing populations will achieve a stable equilibrium because the low birth rates seem related to cultural trends rather than resource constraints. In particular, the glorification of individual rights and freedoms over community obligations and a rising disdain for traditional families. Child rearing is no longer viewed as one of the central and necessary reasons for human being.
These cultural trends have immense momentum and long time scales, and no entity has the resources and patience to change affect them. In search of solutions to population decline, and betting that the current trends in women's choices will continue to reduce fertility rates, I propose decreasing the necessary population replacement rate by selectively birthing more women to match the current fertility rate.
Current fertility rates in the developed world are in the range of 1 to 2. The natural replacement rate for humans is about 2.1 children per women to account for sex ratio and child mortality. If women want to have an average of one to two children, less than the natural replacement rate, we simply need more women than men. If the population were made up entirely of women (sex ratio is female to male births, so close to 0), we’d only need a fertility rate of about 1.1 for a stable population.
Reducing the sex ratio to have more women may solve the depopulation crisis, but may introduce serious societal questions. For example, men staff most jobs in construction, infrastructure, agriculture, and IT. Can they be replaced by females? It is not clear that a an exclusively female, or for that matter, an exclusively male society, could operate at a similar level as the current one. There is also the question of marriage. Such a society would require artificial reproduction or a more prominent form of polygamy. Polygamy is usually an unstable configuration as it leaves a large population of dissatisfied males with time and energy to cause problems and mayhem. But a low sex ratio society could allow for a stable and fully polygamous society without unhitched males.
There are various artificial methods to choose the sex of a baby, some worse than others. I also suspect natural mechanisms already exist in humans. For example, some mechanism has caused the sex ratio (female to male births) to drop in many western countries since the 1950s.2 It is suggested that sex ratios decline (more females) in high stress environments or as male fertility drops.3 And we also know that male fertility is declining across North America, Europe, Australia, and New Zealand. Many suspect that declining male fertility is linked to environmental changes like reduction in physical activity and related testosterone, chemical pollutants, and nutrition etc. This would be some sort of poisoning or hormone disruption effect. It could also be an evolved human response to increasing stress or increasingly non-physical human work. In the case of latter, it could be that reduced physical needs reduce male fertility because it shows that physical activity is not important in the current environment and males are less needed. If men cannot contribute in the traditional ways, women stop producing them and instead produce more women to increase the population so that men can be useful again.
Another example of naturally changing sex ratio are submariners, military folks that serve on nuclear submarines, who produce offspring with an unusually low sex ratio (more females than males).1 Submariners live underwater, for extended periods of time surrounded almost exclusively by men. Some mechanism, not likely to be related to the nuclear power source, leads to lower sex ratio, though it's unclear whether it's a change in the sperm or something else with latent effects. A Darwinian explanation would be that in an environmental catastrophe where most of the female members of the group have died, it is beneficial to immediately start producing new female members instead of more males. It makes sense that humans would have mechanisms that encourage different sex ratios for different environmentals and population conditions. Sometimes you just need more females.
- [Davis D, Gottlieb MB, Stampnitzky JR.: Reduced ratio of male to female births in several industrial countries: a sentinel health indicator? JAMA]↩
- [James WH.: Proximate causes of the variation of the human sex ratio at birth. Early Hum Dev 2015; 91(12): 795–799, James WH.: Offspring sex ratios at birth as markers of paternal endo- crine disruption. Environ Res 2006; 100(1): 77–85.]↩
- [@Kramer2019, Altered sex ratios in offspring of U.S. submariners urban legend or fact-do submariners have more daughters?]↩