Cousin marriage, known as “consanguinity,” is prevalent in many Sub-Saharan groups. In Nigeria it is practiced by the 18 million members of the Hausa tribe, preferentially in marrying patrilateral parallel cousins. The custom is also common among the Yoruba. Cousin marriage increases the risk of birth defects, due to sharing of the genes. In 1993, an Aligarh Muslim University report from India study showed an IQ drop of 11.2 points (from 99.6 to 88.4) in the offspring of cousin marriages.