Consanguinity refers to the union between two individuals sharing one or more common ancestors. In genetics, it is measured by the coefficient of consanguinity (F), which assesses the probability that an individual inherits two identical copies of the same gene through ancestry. The higher this coefficient is in a population, the greater the frequency of unions between relatives.
Coefficient of consanguinity: how the phenomenon is measured between populations
The F coefficient ranges from 0 (no kinship between parents) to 0.25 (union between siblings or parent-child). For marriages between first cousins, the theoretical value is 0.0625. Population genetics studies aggregate these individual coefficients to obtain an average rate by country or region.
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This average rate masks very different realities. In the same country, some rural areas or isolated communities show levels well above the national average, while large urban areas present lower rates. International rankings simplify a geographically fragmented reality.
Viral maps circulating on social media, particularly those shared on forums like MapPorn, often mix old data, heterogeneous sources, and varying definitions of consanguineous marriage. Creating a top 10 of the most consanguineous countries requires relying on a methodology comparable between countries, which remains a challenge for research.
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Countries with high consanguinity: the most affected regions of the world
The highest rates of consanguineous marriages are concentrated in several geographical areas. The Middle East, North Africa, and certain parts of South Asia are the main affected regions.
In the Middle East, countries like Saudi Arabia, Iraq, Jordan, Qatar, and the United Arab Emirates exhibit particularly high rates of cousin marriages. In North Africa, Sudan, Algeria, and Tunisia are regularly among the most cited countries. Pakistan and Afghanistan often complete these rankings for the South Asian region.
The practice of cousin marriage overwhelmingly dominates these unions. In several of these countries, marriage to a paternal cousin (son or daughter of the paternal uncle) is the most common form. Unions between more distant cousins (second degree) or other relatives are also included.
Why these geographical areas concentrate the highest rates
Several factors accumulate in these regions:
- Ancient matrimonial traditions encouraging unions within the same lineage to preserve land or family heritage
- Tribal or clan social structures where marriage outside the group is seen as a loss of alliance
- Economic factors, as marriage between relatives reduces dowries and financial compensations between families
- Geographical isolation of certain rural communities, limiting the choice of spouse
These motivations are not fixed. Urbanization and access to education are gradually changing matrimonial practices in several of these countries, although progress remains slow in rural areas.
Genetic and health consequences of consanguineous unions
Recent medical research treats consanguinity as a health risk indicator rather than just a cultural marker. The increase in homozygosity (the presence of two identical copies of a gene) in consanguineous populations raises the probability of expression of autosomal recessive diseases.
In Tunisia, autosomal recessive diseases account for a majority of reported genetic diseases, with consanguinity found in most families affected by a specific pathology. This observation illustrates the extent of the phenomenon in populations where marriages between relatives have been common for several generations.
Beyond rare diseases: effects on reproductive health
The consequences are not limited to rare genetic diseases. Studies conducted in Algeria, particularly in the Sabra region, have analyzed the impact of consanguinity on abortion rates and infant mortality. Consanguineous couples have an increased risk of reproductive complications compared to non-related couples.
The accumulation of deleterious genetic variants in the homozygous state can also lead to the expression of comorbidities, meaning the simultaneous presence of multiple pathologies in the same individual. This mechanism explains why some consanguineous families are affected by a range of disorders rather than a single isolated disease.
Limits of rankings and shifting scientific debate
Lists of “most consanguineous countries” circulate widely online, but the scientific community is wary of them. Methodologies vary from study to study: some rely on marital declarations, while others use direct genomic analyses. The periods of data collection also differ, making comparisons between countries fragile.
The scientific debate has shifted in recent years. Rather than ranking countries, researchers are more interested in the dynamics of the genome in consanguineous populations: how deleterious variants accumulate, transmit, and interact over generations.
- Genomic analysis now allows for the actual measurement of an individual’s homozygosity, without relying on family declarations
- Longitudinal cohort studies are gradually replacing one-time cross-sectional surveys
- Fine mapping by region (rather than by country) provides a more accurate picture of the reality of practices
This genomic approach offers a more precise insight than simplified rankings. It also shows that consanguinity is not a binary phenomenon: between a country where cousin unions represent a minority and a country where they involve a large fraction of marriages, the biological consequences differ significantly.
Understanding the phenomenon benefits from going beyond a simple ranking to focus on the underlying genetic mechanisms and their concrete effects on the health of the affected populations.