from what I've read the male:female birth ratio in the US has been steadily declining, though still leans slightly male heavy. and the expected gain of male births from higher average temps due to climate change won't be significant enough to make up the difference. besides, a normal birth ratio is only like a 2.5% diff historically, and modern-day rates are lower than that average.

but this is about total extant males, not the birth rate. so I'll list a few potential factors I see:

• as a cohort ages, the population naturally flips to more female dominant due to higher male mortality rates. very relevant when we're talking population-wide rather than at-birth

• major war abroad would reduce the amount of men, but an invasion or civil war could potentially lead to a greater rate of female losses (e.g. as refugees) than male combat losses. I don't have numbers to know if it's significant enough but you can see this effect today in Ukraine. obviously this gets extra complicated in a world where women can be frontline combatants and the majority of the male population might be non military

• IF the current trendline of the US returning to isolationism holds AND that causes a demonstrable economic downturn, you MIGHT see a shift toward men seeking employment abroad en masse

• however, from what I've heard from genetics, archaeology, and sociology, on average a given female population moves "away" much more than its male counterpart does. afaik this more-or-less averages out to a net-zero effect in the long run that contributes to genetic and cultural mixing, but we do see something similar today that shows an unbalanced rate of female migration: rural -> urban populations. I don't know if that effect would play out across international borders without a strong stressor like war or famine

all told, even though I think trendlines indicate a high chance of conflict and upheaval at this timescale, I really don't think this market's level of disparity is likely, so I'm in the strong NO camp

Why would this happen?

@Jack1 perhaps through techocapital advantages, the base population starts to look more like manifolders