The reason Christian Arabs from Lebanon/Syria/Jordan are smarter than Muslim Arabs or why Hindus from places like Bangladesh are smarter than Muslims is because of the Jaziya tax. Dhimmis or non-Muslims in Islamic lands had to pay a Jaziya tax or they would be killed, only escape from this is conversion to Islam. Thus the poorest low IQ sections of the population who could not pay the tax converted early.The smarter populations (and in the case of South Asia, the higher castes) used money to prevent conversion as much as possible. Thus the Muslims in these areas are predominantly low IQ genes while high IQ populations got separated into a different gene pool. Islam is dysgenic. Even Lew Kyan Yew of Singapore berated Malay Muslims for being dysgenic by the tendency of Muslims to marry even if the people involved were either very stupid of full of genetic diseases.
Do you think there is any truth to this? Interesting notion from the comments.