Sunday, August 18, 2013

Genetic Risks in Cousin Marriage

Alice C. Linsley

The Hebrew ruler-priests took wives only from within their caste. This is called "caste endogamy". The question often arises about the increased likelihood of genetic abnormalities or disorders. There is little evidence that the widely dispersed Hebrew clans, of which there were many, had a greater incidence of genetic abnormalities than exogamous populations. 

Several factors may account for this. 

1) The early Hebrew lived in Africa, the continent with the greatest genetic diversity.

2) The Hebrew were experts at animal husbandry and had learned from observation about breeding risks. The early Hebrew had a fairly sophisticated understanding of reproductive mechanisms. We find evidence for this in Jacob's expansion of his herd (Gen. 30) whereby he practiced genetic recombination.

3) There were many Hebrew clans, and they were geographically dispersed. The rulers took their wives from clans that resided a good distance away. Thus, environmental factors play a roll.

4) Hebrew men of lesser status likely married women who were not pure-blooded Hebrew. However, lesser status Hebrew men who were recognized as especially righteous were able to rise in status depending on attributed authority. 

The Hebrew Marriage and Ascendancy Pattern

Abraham's Hebrew people had a distinctive marriage pattern that involved marriage to half-sisters and patrilineal cousins. Typically, the high-ranking ruler-priest had two wives. The first wife, taken while the man was still young and not yet the ruler, was his half-sister, as Sarah was to Abraham. Shortly before the man ascended to rule over his father's territory, he took a second wife who was most often a patrilineal cousin, as was Keturah to Abraham. The two wives lived in separate households, usually on a north-south axis.

Many of the most famous biblical figures are the sons of cousin brides: Lamech the Younger, the father of Noah (Gen. 5); Joktan the Younger, son of Keturah and Abraham's first-born son (Gen. 25); Jacob, Isaac's son by his cousin Rebecca (Gen. 25), and Moses' son by his cousin Zipporah (Ex. 2).

The firstborn son of the sister wife ascended to the throne of his biological father. So Isaac ruled over Abraham's territory.  The first-born son of the cousin wife did not belong to the household of his biological father. Instead, he became a sort of prime minister in the territory of his maternal grandfather, after whom he was named. This is why it is necessary to speak of Lamech "the Elder" and Lamech "the Younger" or Esau "the Elder" and Esau "the Younger." This was the practice of E. A. Speiser in his Anchor Bible Commentary on Genesis.

This pattern of the cousin bride naming her first born son after her father is called the "cousin bride's naming prerogative." This naming practice makes it possible to trace Jesus' Horite Hebrew ancestry from Genesis 4 and 5 to the New Testament. The endogamous marriage practice of Jesus' ancestors does not appear to have had a negative effect on Jesus and his kinsmen.

Cousin marriage alone does not appear to significantly increase the risk of genetic defects in offspring. Geneticist Dr Eamonn Sheridan, from the University of Leeds, says: "It is important to note that the vast majority of babies born to couples who are blood relatives are absolutely fine, and whilst consanguineous marriage increases the risk of birth defect from 3% to 6%, the absolute risk is still small."

This risk is hardly greater than the risk for birth defects among white women over 34. Here the risk of bearing a child with a defect increases from 2% to 4% for them.

Poverty presents less risk than poor education and lack of information for expectant mothers. Research shows that higher levels of maternal education reduce by half the risk of having a baby with a defect across all ethnic groups.

Among Jewish descendants of the Hebrew, there are certain inherited tendencies. Among the Ashkenazi, genetic disorders include cystic fibrosis, Canavan disease, familial dysautonomia, Tay-Sachs disease, Fanconi anemia, Niemann-Pick disease, Bloom syndrome, mucolipidosis type IV, and Gaucher disease, among others.

Some have suggested that Leah's eye condition may be due to endogamous marriage. Though she is posed in Genesis as Jacob's cousin bride, it is more likely that she was his half-sister. A recent study of the Ultra-Orthodox Jews reveals a tendency to "lazy eye" in this smaller endogamous community, 

Today the incidence on some of these disorders has been minimized by genetic testing of Jewish couples considering marriage. The incidence of fatal genetic diseases is declining thanks to a technology-driven innovation: Matching by genetics.

The Early Hebrew Understanding of Reproduction.

The early Hebrew had a fairly sophisticated understanding of reproductive mechanisms. We find evidence for this in Jacob's expansion of his herd (Gen. 30) whereby he practiced genetic recombination.

From the biblical evidence it appears that the early Hebrew used a modular formula when selecting marriage partners from among their kinsmen. This is alluded to in the account of Laban's insistence that the older sister (Leah) must marry before the younger (Rachel). 

The deliberation about marriage partners likely involved a cycle of between 9 and 12 choices. In this equation X represents firstborn son, and the possible matches are between 9 and 12 blood related females, but they must be considered in a fixed order of rotation. There will never be a 13th possibility.

A bride must be selected from the 9-12 females and may be either a half-sister or a cousin, usually patrilineal, but sometimes matrilineal. The bride for the next son will be considered in the rotation, beginning with the next female in the rotation after the last match was made. Marriages were arranged.

The number 9 is based on the evidence that Abraham's ancestors were organized in groups of 3 clans and there were 3 groups of 3 clans, which means that there were 9 clans from which a consanguine bride could be chosen. The number 12 is based on the evidence of numerous 12 tribe sets, with celestial animal totems organized on the 12 moon phases.

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