[smrxx]

This could be due to population size. Isn't there a species of fish where a male becomes a female when there are no other females left? It seems plausible that some mechanism is in place to self regulate.

[meerab]

If this theory was correct the males in India and China would be affected more than males in the western world.

[djtriptych]

Not if population density is the trigger. How could the body evolve to be aware of national boundaries?

[maxerickson]

North America has low population density relative to most of the world.

Probably even more so if you do some sort of aggregation of the density that people live at rather than averaging population across land area. Suburbia and such.

[dom0]

> North America has low population density relative to most of the world.

Well the quotient N(north america) / A(north america) is low, but this value does not have to match the average or median population density in areas around samples.

In other words, yes, America is a big country, but it's big cities are just as densely populated as big cities anywhere else.

[maxerickson]

Well the quotient N(north america) / A(north america) is low,

It's infuriating that you choose to reply like this without accounting for both paragraphs of my comment. I mean, I'll just let it go, but c'mon.

I would say that US cities tend to be less dense and that Americans don't tend to live in urban centers as much as people in other countries.

[dom0]

Sorry, I must have misread it. Looking at some charts, you have a point there.

https://upload.wikimedia.org/wikipedia/commons/4/49/World_po... (1994)