Islam permits marriage between first cousins. (Judaism and Christianity do not.)
Add to that the desire to keep tribal wealth within the tribe (meaning, marriage within the tribe), and retain those practices for 80-100 generations,
and you have a massive problem with inbreeding and genetic inheritances.
Funny. California allows 1st cousin marriage as do many other states.
The husband is required to give the wife (more like the bride’s family) a “bride price”. If he marries his paternal first cousin, the money stays in the family.