Probably it is that we are not hunter gatherers any more.

Some people react differently to urbanization because its not natural.

The number one thing natural thing that is missing most of the time is exercise.

When you are a hunter gather society you must forage and hunt to survive.

This requires lots of exercise and you are in the sun all day.

So to me its more a form of atrophy that leads to mental illness most of the time.

Lack of exercise.