Cousin Marriage in Islamic Law

Due to the actions of Prophet Muhammad and the Rightly-Guided Caliphs, marriage between cousins is explicitly allowed and even encouraged in Islam. The Qur'an itself does not discourage or forbid this practice in any way. In fact it implicitly allows it, as seen in chapter 4 verse 23:

So everyone besides these relatives named can be married. Such marriages in Muslim majority countries are often preferred and even encouraged in some regions. This is in contrast with China, India, most of the United States and some other nations where cousin-marriage is against the law and regarded as incest.

Even though there is some debate on this issue, scientists tend to agree it is genetically unhealthy. There are other problems with cousin marriages.

Muhammad

Prophet Muhammad himself married cousins, as he did with Zaynab bint Jahsh, who was not only the daughter of Umaimah bint Abd al-Muttalib, one of his father's sisters,^[1] but was also divorced from a marriage with Muhammad's adopted son, Zayd ibn Haritha. It was this last issue that caused the most controversy, with traditional Arab norms at the time being opposed, though not the Qur'an (Sura Al-Ahzab 33:37).^[2]

According to Ibn Sa'd, after Zaynab's marriage to his adopted son Zayd, Muhammad went to visit him, but instead found a hastily clad Zaynab. Though he did not enter the house, the sight of her pleased him. Tabari states that Zaynab was only wearing a single slip, and the wind pushed away a curtain when Muhammad entered, revealing her "uncovered." Thereafter Zayd no longer found her attractive and thought of proposing divorce, but Muhammad told him to keep her. Eventually, however, Zayd did divorce her.

Ali

Muhammad also allowed the marriage of his daughter, Fatimah, to his cousin, Ali ibn Abi Talib, who would later go on to become the fourth Rightly-guided Caliph of Islam.

Umar

The second Caliph, Umar ibn al-Khattab, also married his cousin, Atikah bint Zayd ibn Amr ibn Nufayl.^[3][4]

From a biological point of view it becomes clear that first cousin marriage is not recommended because close relatives have a higher than normal consanguinity which means an increased chance of sharing genes for recessive traits. With this high amount of shared DNA, you have a higher risk of birth defects in a baby. Even if cousin marriages are not performed, you can still have such genetic defects in populations where there is a restricted social structure.

In Pakistan, where there has been cousin marriage for generations, and according to professor Anne-Marie Nybo Andersen from South Danish University, the current rate is 70%,^[5] 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.

A BBC report discussed Pakistanis in the United Kingdom, 55% of whom marry a first cousin. Given the high rate of such marriages, many children come from repeat generations of first-cousin marriages. The report states that these children are 13 times more likely than the general population to produce children with genetic disorders, and one in ten children of first-cousin marriages in Birmingham either dies in infancy or develops a serious disability.^[6]

The BBC also states that Pakistani-Britons, who account for some 3% of all births in the UK, produce "just under a third" of all British children with genetic illnesses. Published studies show that mean perinatal mortality in the Pakistani community of 15.7 per thousand significantly exceeds that in the indigenous population and all other ethnic groups in Britain. Congenital anomalies account for 41 percent of all British Pakistani infant deaths.^{[7][8][9][10]}

Worldwide, it has been estimated that almost half of all Muslims are inbred:

The British geneticist, Professor Steve Jones, giving The John Maddox Lecture at the 2011 Hay Festival had stated in relation to Muslim inbreeding, "It is common in the Islamic world to marry your brother’s daughter, which is actually [genetically] closer than marrying your cousin."^[14]

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• Incest in Islam - Islam Monitor (archived), http://islammonitor.org/index.php?option=com_content&view=article&id=3921:incest-in-islam&catid=294:social-practices-interactions&Itemid=61