What’s your best guess about cause?
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0055387
Just one of many things we do differently than previous generations. If you have access to HS yearbooks from the 1930’s in rural America somewhere take a look at them. Notice how the HS senior boys look like men? The HS senior girls look like women? Take a look now. The boys have effete features and the square jaws are on the girls.