Maybe a good place to start: https://www.thelancet.com/journals/lanpsy/article/PIIS2215-0366(16)30348-0/fulltext https://www.thelancet.com/journals/lanpsy/arti

Maybe a good place to start: https://www.thelancet.com/journals/lanpsy/article/PIIS2215-0366(16)30348-0/fulltext https://www.thelancet.com/journals/lanpsy/article/PIIS2215-0... It cites many sources including biological and social, however: > ... we still do not really understand the causes of these differences, and comparatively little research has been done to explain them.