I submit that it is physical:
1) Turbans restrict blood circulation in the head/cranial region.
2) Brain damage from all the rocking back and forth when they are learning lessons and studying Koran.
3) Lack of chairs. They have to sit and bend over to write which causes what blood is there to stagnate;
4) Ululation. Exposure to the sound causes sonic damage to ears, impeding ability to listen and learn.
Add to this the dictatorial nature of gov't/religion, general societal poverty, and a class system, and you have the makings of underachievers.
parsy, who wishes they wanted the benefits of freedom