>>10568283First, I would question the statistics, as 8.5% seems way too high.
This is just my hypothesis, so take it with a huge grain of salt.
The reason is, that there are two brains in our body - the cerebral cortex, and the cerebellum.
The cerebral cortex spots correlations and can learn things mechanically.
The cerebellum checks if these correlations make sense and guides the cerebral cortex.
The problem is that the cerebral cortex has no ability to tell what makes sense and what doesn't, so if it overtakes the cerebellum and becomes the part of the brain that makes the final decisions, the result is insanity.
People solved this problem by evolving away from large cerebral cortex, and towards more powerful cerebellum. Asians, however, seem to have some additional adaptation that prevents this from happening, which is why they have such low rates of mental illness and coudl afford to either keep, or re-evolve the bigger cerebral cortex.
However, if you combine the big cerebral cortex with the weak cerebellum that cannot keep it in chceck, the result is insanity.
It might also be ther reason for why trepanations were common, as people learned that insane people sometimes recover after head injury, and learned to treat the insanity by destroying (possibly a part of) one hemisphere.
