The practice of zawaaj al aqaarib, the marriage between relatives, is relatively common within the societies of the Arabian Peninsula. A 2009 study published in the journal Intelligence looked at rates of consanguineous marriage - that is, the marriage of blood relatives - across 72 nations; it found that very few of them had rates higher than those reported in the Arabian Peninsula.
The region's highest rate of kin-marriage appears to be in Qatar. There, according to a 2006 study published in the Journal of Biosocial Science, the rate is 54.5 per cent. That study's authors attribute this relatively high rate to traditions, in that Qatari society is more culturally homogenous than other populations, and shows particularly strong attachment to Bedouin marital traditions.
The same study also reported an increasing trend towards kin-marriage, with the rate increasing from 41.8 per cent to 54.5 per cent across a single generation. A UAE study in the late 1990s found an increase from 39 per cent a generation earlier to 50.5 per cent when the study was done.
This apparent increase may be explained in terms of how the research was designed and of the sampling methodology, but there are also strong arguments suggesting that kin-marriages actually have increased in recent decades.
Several authors argue that the practice has persisted or increased because such couples are considered more stable than those involving unrelated individuals, and also economically beneficial in consolidating, rather than fragmenting, familial wealth.
Another possible explanation is "demographic imbalance". In at least three Gulf nations (Kuwait, Qatar and the UAE) citizens are a minority. Several international studies have noted increasing rates of kin-marriage among North African and Pakistani immigrant populations in Europe, obviously minorities. Perhaps similar minority dynamics are at play here.
The data seem to support these arguments. Qatar, with the highest rate of kin-marriage, is also frequently reported as having the Gulf's highest per-capita GDP, as well as the biggest demographic imbalance.
Whatever the exact reasons for it, kin-marriage has important health implications, starting with increased risk of illnesses associated with recessive genetic traits. This is particularly true if the partners' degree of kinship is high.
Generally, a marriage is considered "consanguineous" if the partners are second cousins - if they share a common great-grandparent - or closer. In Gulf societies the most common form of kin-marriage has traditionally been between paternal first cousins - for a man to marry his father's brother's daughter (bint 'amm).
The published data for Qatar, Saudi Arabia and the UAE suggest bint 'amm marriage remains the most popular form of kin-marriage. But some studies also report relatively high rates of "double first cousin marriage". This involves the sons of two brothers marrying two sisters (of another family) when all share grandparents. Double first cousins share the same degree of genetic relatedness as half brother and sister.
The physical health problems that can arise from kin-marriage are well-documented. Increased thalassaemia risk, for example, has been widely reported regionally.
But recent research on kin-marriage in Egypt has shed light on potential psychological risks, too. In two studies led by the University of Pittsburgh's School of Medicine, kin-marriage was found to greatly increase the risk of bipolar disorder. The larger of the two studies, published in 2009 in the American Journal of Medical Genetics, looked at 1,584 individuals and found that those who screened positive for bipolar disorder were at least four times more likely to be the offspring of kin-marriages than those who did not.
Psychological problems arise in response to social circumstances. But we should also consider the possibility of a genetic contribution - perhaps an inherited vulnerability. When the world was less stressful, a high rate of kin-marriage would not have been an issue in psychological health. But times have changed, and the Egyptian studies suggest that kin-marriage increases the risk of a particularly debilitating psychological disorder.
This is certainly a question worthy of further research, and worthy of careful consideration when weighing matrimonial options.
Justin Thomas is an assistant psychology professor at Zayed University in Abu Dhabi
On Twitter: @jaytee156
