The biology of first cousin marriages
That marriages between blood relations might lead to health issues for the child has been suspected for several years. Now, a detailed analysis of the issue involving over 11,000 children, born out of consanguineous marriages, revealed congenital anomalies in 386 of them. This figure of 3 per cent contrasts with the 1.6 per cent in children born of out of non-blood-relations unions. Dr Eamonn Sheridan and associates from leads, U.K. analysed these babies termed “Born in Bradford” to obtain these results. Bradford is a small area in the UK where Pakistani Muslims constitute 16.8 per cent of the population. A close knit group, they practice consanguinity; 75 per cent of them marry first cousins.
Babies born out of such wedlock could have a multiplicity of congenital problems. Heart problems top the list, followed by nervous disorders, limb anomalies and so forth. Sheridan and colleagues also studied the lifestyle, smoking and drinking habits, income and poverty and other factors that might contribute, and found that consanguinity is the leading culprit. They have published their analysis in the July 4 issue of The Lancet.
The problem in such close relative marriages surfaces when one of the partners carries a defect in any of the genes associated with some form of illness. When you marry within the community with one who may also have such a family defect, the child inherits two copies of this faulty gene, and thus has the defect. But when you marry outside the community, you bring in genes from a much larger gene pool, and the odds that the child will inherit the problem reduce remarkably.
Of course, the prevalence in Bradford is but 3 per cent. Most of the children are normal and as healthy as those born from non-cousin marriages. Also, lest someone conclude otherwise, this does not reflect against either Pakistan or Islam. The researchers found the Bradford group to be a large enough and inbred group where a study of this kind would have statistical significance. And while 37 per cent of Pakistani marriages in the U.K. were between cousins, it was only 1 per cent of all marriages in U.K. (A single swallow a summer does not make but here was a large flock of swallows). Similar studies, with smaller “catchment populations” have been done with Gypsies, the Arabs in Jerusalem, the Parsis and even on South Indians (largely Hindu) by Dr Kumaramanickavel (then at Sankara Nethralaya, Chennai) in 2002 (Community Genetics 2002, 5:180-185) with similar results.
We in South India too have communities that practise consanguineous marriages. Gotram (ancestral lineage) is taken seriously and marriage does not occur, generally, between a man and a woman of the same gotram. Thus a brother does not marry his own sister. But he can (if even used to be “should”) namely, first cousin. Using the same logic, an uncle-niece marriage is allowed and practised too. Recall what a daughter-in-law refers to her mother-in-law as in Tamil (Mamiyar, wife of my mother’s brother)
The gotram system is formally thought to keep a genetic distance, and thus thought to be “safer” from consanguinity point of view. True, the “genetic distance” is a little wider here than with own siblings, yet there is a genetic relationship, and thus thought to be “safer”. It is however not the same as a boy marrying “outside” the community or region form where the family never had a marital or genetic connection.
Social contracts
Marriages are social contracts. They are meant to produce genetic products or families. Families have practices, properties, fortunes, faiths, beliefs and biases. It is these that by and large determine who will marry whom. Think about why the Egyptian Pharaohs practised brother-sister marriage. Think for also for a minute about the marriages in the Parsi community, or the Ashkanazim Jews of Russia. If you marry outside the community, you are excommunicated (even there, gender bias is seen in some cases). And notice how the population of such communities has dropped over generations. The abhorrent, loathsome system called khap, practiced in certain parts of Haryana, sanctifies “honour” killing of a couple that marries against traditional practice. Are such sociological practices to propagate and maintain genetic purity, or property, beliefs and self-imposed ‘honour’ and exclusiveness’? What does biology have to say about this?
Making babies is easy for many microbes. You simply divide and make two, then four, eight and a whole generation is born. You do not need a partner, the whole thing is asexual. But when “sex” came in as a factor in evolution, variety was introduced. In essence, shorn of all romance, mating is mixing of genes. With new genes added, new traits are acquired. It is this variety that gave organisms newer abilities. Thus biology would like more and healthier genes in the offspring. That would mean no restrictions on who you mate with — it would simply suggest “go forth and multiply”. Variety is the spice of life. Marriage and conventions about it are however sociology. They establish traditions and rules about who you may marry and who you may not — these are facts of life!
http://www.thehindu.com/sci-tech/health/the-biology-of-first-cousin-marriages/article4902050.ece?utm_source=MostPopular&utm_medium=Health&utm_campaign=WidgetPromo
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