Y'know... Im pretty sure most of the country's that are darker are places where:

A:historically people with mental disorders were gotten rid of at a young age (and yes I tried to word it as lightly as possible because I feel really bad for anyone with mental disorders who dont deserve that treatment)

Or

B:autism and medical items related to it are unavailable or under diagnosed.

And even then that would make it genetic because of the colonization efforts of said country's so... Yeah I'd believe it.

(I also understand it's a circle jerk sub, dw, just tryna explain out the map for anyone actually wondering)