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Cousin marriages, including those between first cousins, are permitted by Islamic law and scriptures and were practiced by Muhammad himself as well as his companions. The Quran and Muhammad's practice of cousin marriage have cemented the legality of the practice in all Islamic legal schools, though some scholars said that marriage to non-relatives is preferable, and a few hadiths of contested authenticity discourage marriage to close relations.[1] Cousin marriages have been common throughout Islamic history[2] and remain so in Muslim-majority nations today, comprising a significant percentage of the total population of these nations.
Children born of cousin marriages face an increased risk of genetic disorders and childhood mortality[3][4] and are thus prohibited in some countries.[5][6] One study estimated infant mortality at 12.7 percent for married double first cousins, 7.9 percent for first cousins, 9.2 percent for first cousins once removed/double second cousins, 6.9 percent for second cousins, and 5.1 percent among non-consanguineous progeny. Among double first cousin progeny, 41.2 percent of pre-reproductive deaths were associated with the expression of detrimental recessive genes, with equivalent values of 26.0, 14.9, and 8.1 percent for first cousins, first cousins once removed/double second cousins, and second cousins respectively.
There is an increasing awareness in the Muslim world of the risks especially of multi-generational cousin marriage (which compounds the above dangers), and an increasing number of voices calling for it to be discouraged, even if it remains permitted.