There was a decline in consanguineous marriage rates in Lebanon between 1950 and 1970, from an overall rate of ca. 30% down to 20%.[1]

There has been an increase in consanguineous marriage rates since 1983-84 when the overall rate was 25%[2] to the 2000s (2008?) when the overall rate was 35.5%[3].

Reportedly, there has also been an increase in the wearing of headscarves in this period, i.e. since the 1980s:

The wearing of headscarves has risen since the 1980s, even though Lebanon is generally more liberal than other Mideast countries and also has larger Christian and secular communities. Women who support Hezbollah, the Shiite militant group, wear headscarves generally and some wear the Iranian-style chador, which covers the hair and body but not the face or hands.[4]

__________

[1] Parental consanguinity and congenital heart malformations in a developing country

[2] Consanguineous Marriage and Reproduction in Beirut, Lebanon

[3] Consanguinity in Lebanon: prevalence, distribution and determinants

[4] A Look At The Wearing Of Veils Across The Muslim World, International Herald Tribune, Oct 31, 2006.

Advertisements

From the Egypt Demographic and Health Survey 2005:

Total consanguineous marriages = 32.2%
Total first cousin marriages = 17.5%; inbreeding coefficient = 0.0109
Total second cousin marriages = 7.3%; inbreeding coefficient = 0.0011
Total “other blood relative” marriages = 7.4%

Total FBD marriages = 11%; inbreeding coefficient = 0.0069

Urban consanguineous marriages = 24%
Rural consanguineous marriages = 37.9%

Urban 1C = 13%; inbreeding coefficient = 0.0081
Urban 2C = 6%; inbreeding coefficient = 0.0009
Rural 1C = 20.6%; inbreeding coefficient = 0.0129
Rural 2C = 8.3%; inbreeding coefficient = 0.0013

Urban Governorates = 22.5%
Lower Egypt urban = 19.4%
Lower Egypt rural = 29%
Upper Egypt urban = 29.4%
Upper Egypt rural = 48.5%
Frontier Governorates = 41.4%

Urban Governorates = Cairo, Alexandria, Port Said, and Suez (no rural population)
Lower Egypt = 9 Lower Egypt governorates totally (Nile Delta)
Upper Egypt = 8 Upper Egypt governorates totally (Nile Valley)
Frontier Governorates = 5 governorates on eastern/western boundaries

Collection period: 2005
Study population: A nationally representative sample of ever-married women aged 15-49.
Sample size: 19,474
Location: Nation-wide.

From the Egypt Demographic and Health Survey 2008:

Total consanguineous marriages = 29.7%
Total first cousin marriages = 15.6%; inbreeding coefficient = 0.0098
Total second cousin marriages = 7%; inbreeding coefficient = 0.00109
Total “other blood relative” marriages = 7.1%

Total FBD marriages = 9.8%; inbreeding coefficient = 0.0061

Urban consanguineous marriages = 23.2%
Rural consanguineous marriages = 34.3%

Urban 1C = 12.4%; inbreeding coefficient = 0.0078
Urban 2C = 5.3%; inbreeding coefficient = 0.0008
Rural 1C = 17.9%; inbreeding coefficient = 0.0112
Rural 2C = 8.3%; inbreeding coefficient = 0.0013

Urban Governorates = 23.2%
Lower Egypt urban = 18%
Lower Egypt rural = 25.3%
Upper Egypt urban = 28.2%
Upper Egypt rural = 47.2%
Frontier Governorates = 34.2%

Urban Governorates = Cairo, Alexandria, Port Said, and Suez (no rural population)
Lower Egypt = 9 Lower Egypt governorates totally (Nile Delta)
Upper Egypt = 8 Upper Egypt governorates totally (Nile Valley)
Frontier Governorates = 5 governorates on eastern/western boundaries

Collection period: 2008
Study population: A nationally representative sample of ever-married women aged 15-49.
Sample size: 16,527
Location: Nation-wide.

From the Egypt Demographic and Health Survey 2000:

Total consanguineous marriages = 37.8%
Total first cousin marriages = 21.8%; inbreeding coefficient = 0.0136
Total second cousin marriages = 10.3%; inbreeding coefficient = 0.0016
Total “other blood relative” marriages = 6.1%

Total FBD marriages = 13.2%; inbreeding coefficient = 0.0083

Urban consanguineous marriages = 29.7%
Rural consanguineous marriages = 43.9%

Urban 1C = 16.4%; inbreeding coefficient = 0.0103
Urban 2C = 7.9%; inbreeding coefficient = 0.0012
Rural 1C = 26%; inbreeding coefficient = 0.0163
Rural 2C = 11.4%; inbreeding coefficient = 0.0018

Urban Governorates = 29.1%
Lower Egypt urban = 25.2%
Lower Egypt rural = 36.6%
Upper Egypt urban = 35.3%
Upper Egypt rural = 53.5%
Frontier Governorates = 46.2%

Urban Governorates = Cairo, Alexandria, Port Said, and Suez (no rural population)
Lower Egypt = 9 Lower Egypt governorates totally (Nile Delta)
Upper Egypt = 8 Upper Egypt governorates totally (Nile Valley)
Frontier Governorates = 5 governorates on eastern/western boundaries

Collection period: 2000
Study population: A nationally representative sample of ever-married women aged 15-49.
Sample size: 15,573
Location: Nation-wide.

Genetic relatedness affects social behavior due to kin selection and inclusive fitness.  For instance, organisms are more likely to be altruistic toward genetically related individuals rather than unrelated ones since they share a greater number of genes in common with them and are, therefore, more likely to share in common with them the same gene(s) for altruistic behavior.

Another social behavior likely influenced by inclusive fitness is control of reproduction.  Individuals, and groups of individuals, frequently attempt to control the reproductive activities of other individuals with whom they share genes in common.   Such actions might clearly affect the inclusive fitness of “the influencers.”

In many species, this control often takes the form of the reservation (or attempted reservation) of breeding rights for certain members of a group (e.g. the alpha pairs in wolves and meerkats, or the queen in some of the social insects such as group-living ants).  The ultimate aim, however, is the regulation of which genes get passed on to the following generation and via whom.

It is not difficult to imagine that social behaviors related to the control of reproduction might evolve in many species since inclusive fitness is really all about reproduction.  Just as there is likely an “altruism gene” (or complex of genes), there is probably a complex of genes affecting behaviors related to the social control of reproduction.

In humans, social control of reproduction is frequently achieved via social mores related to mating practices (it is also frequently achieved via more direct means); and the relative stringency of these mores in various societies appears to be connected to the levels of genetic relatedness between the members in each society.  This follows when considered from an inclusive fitness point-of-view.  For instance, if one’s daughter is also one’s cousin in terms of genetic relatedness, the price to one’s inclusive fitness would be greater if she failed to mate successfully than if she is only a daughter.

In Western society, which has for a long time has been characterized by relatively loose genetic relatedness between its individual members, this social control of reproduction has manifested itself in the recent past, for example, in the desire of parents to give formal approval of their children’s (especially daughters’) choice of spouse.

In societies with relatively higher levels of genetic relatedness between family members, social control of reproduction has manifested itself in restrictions of interaction between unrelated men and women. In the Muslim world, for example, this has taken various forms of purdah. In other societies (mainly some sub-Saharan African societies but also in places such as Egypt and Sudan), the social control of reproduction has taken the form of female genital mutilation (FGM). The Chinese practice of foot binding may also have been a way to limit the reproductive options of members of that society.

Below is a map indicating the “global distribution of marriages between couples related as second cousins or closer (F≥0.0156).”  Those societies that today have strong practices of social control of reproduction (i.e. purdah and FGM) are also those societies with the highest levels of genetic relatedness within families, e.g. Saudi Arabia, Sudan, Pakistan, Afghanistan.

Consanguineous marriage (%)

Additionally, those societies which practice FBD (father’s brother’s daughter) or patrilineal parallel cousin marriage (e.g. Saudia Arabia, Pakistan, Afghanistan) possess the most stringent social controls of reproduction. Lineages which consistently practice FBD marriage are even more genetically related than those which simply practice general cousin-marriage since all of the males in the FBD lineages will share the same Y-chromosome.

Korotayev has noted that a majority of societies which practice FBD marriage are Islamic. FBD marriage enables families to keep property and wealth in the paternal family while at the same time fulfilling Islam’s requirement entitling women to a share of any inheritance. It is not unlikely, therefore, that those societies in the past which adopted Islam subsequently adopted FBD marriage practices.

However, FBD marriage practices likely pre-date Islam, at least in the Levant. I suggest that many aspects of Islam, such as its call for submission to an ultimate authority, arose in response to the mating practices and levels of genetic relatedness in these societies.  With greater levels of relatedness comes a greater urgency to control who mates with whom.  Many Muslim mores (like many religious and social mores around the world) are simply social controls of reproduction and reflect the levels of genetic relatedness of the societies from which they emanate.

Update:  05/21/10 – edited for clarity.