Over the years there has been a raging debate in the world society of late regarding the cousin and same clan marriages. The south Asian societies usually had a traditional system where it was avoided to be married into one’s own clan and that too of your mother, thereby propagating conventional wisdom that cousin marriages are absolutely NO-NO.
Same is the case for the American society where cousin marriages are frowned upon baring President Roosevelt who married his distant cousin (one doubts however that there has been some other, with cousin marriage who may have become president of United Sates of America). Though, the phenomenon of cousin marriages was usually among the royals of Europe, who use to use it to keep the bloodline “PURE”.
Similarly the tribes of Middle East have massive levels of cousin marriages which is no way related with Islamic practice in particular or is in Quran but a lot to do with the tribal norms of certain tribe (particularly of Arab societies). When a certain group becomes socio-economically powerful then they exert their own “ideologies” on others without understanding the consequences of it. Thereby, trying to institutionalize it via a religious norm in order to propagate authority. Though now with introduction of genetic research being carried out in Arabian countries, the lawmakers of the region understand the fallacy of such unions.
Over the years, scientists have performed genetic evaluations and research in order to find the answers regarding Spanish Habsburg Dynasty’s EXTINCTION.
Habsburg Dynasty was one of the most powerful dynasties in the world who commanded large amount of Europe for over 200 years since 1516–1700. The members of the dynasty frequently married close relatives in such a way that uncle-niece, first cousins and other consanguineous unions were prevalent in that dynasty. In the historical literature, it has been suggested that inbreeding was a major cause responsible for the extinction of the dynasty when the king Charles II, physically and mentally disabled, died in 1700 and no children were born from his two marriages. When Charles II died in 1700 the line of the Spanish Habsburgs died with him and a new dynasty- the French Bourbons- was installed in Spain.
Though many in Spain never got to analyze the genomes of the members of dynasty but there was a widespread belief that it was something rotten in their bloodline which resulted in their end (as staunch Roman Catholics donot like the concept of cousin marriages).
The issue of incestuous or cousin relationship could be seen in the book by Gabriel García Márquez named One Hundred years of solitude (my guess is that Spanish society still is fascinated about the entire Habsburg Dynasty extinction issue and writers try to experiment or play and test with the issue.) . However the book is not only that, it offers an in-depth account to settlers of Europe in South America, a must read and one recommends it with two thumbs up.
Coming back to topic of Habsburg Dynasty. Charles II, was dubbed El Hechizado (“The Hexed”), was the produce of an uncle-niece marriage — Phillip IV with his niece Mariana of Austria. His grandfather Philip III was also born of an uncle-niece marriage — Philip II with his niece Anna of Austria.
According to contemporary writings, he was short and weak and suffered from intestinal problems and sporadic hematuria (the presence of red blood cells in the urine). He did not speak until age 4 and did not walk until age 8.Such detrimental health effects are often seen in children of consanguineous marriage because they are more likely to inherit rare deleterious recessive versions of genes. Charles II’s disorders and illnesses are also evidence of the inbreeding of the line.
The high degree of relatedness of these rulers’ parents combined with the remote inbreeding in the lineage likely had a significant impact on the eventual extinction of the line.
There was a stark rate of infant and child mortality in the Habsburg families. Only about 60 percent of infants survived to age 1, and only half of the children born to the dynasty survived to age 10, compared with about 80 percent survival of infants in Spanish villages at the time.
Gonzalo Alvarez from the University of Santiago de Compostela has confirmed that inbreeding indeed was the reason for the extinction of this dynasty. He traced the pedigree of the entire line back through 16 generations, including over 3,000 people.
For each person, he calculated a figure called the “inbreeding coefficient”, symbolised by the letter F. It measures the probability that a person with two identical copies of a gene inherited both from the same ancestor. For example, a child born to cousins has an F value of 0.0625, but it becomes much higher if the parents come from a long line of inbred couples. The higher the value, the greater the degree of inbreeding in that lineage.
It is more like this suppose paternal grandfather has certain issue in his immune system; say Hemophilia genetic disorders which mean the body’s inability to control bleeding. The bleeding might be exterior, if the skin is broken by a cut, scrape, or abrasion, or it can be interior, into joints, muscles, or organs which are hollow. Here after a wound the body does not heal easily.
If a grandfather has that gene, the same will be passed onto the sons and daughters. If the grandchildren marry ie perform cousin marriages then it would lead to exponential increase in the faulty genome which would aggravate the problem of Hemophilia in the offspring.
There has been research going on in Arab world, wherein after the economic rise of middle east owing to the success of Oil wealth, the sheiks are trying to solve the genetic disease parameters and the young are resisting the age old tradition of cousin marriages.
The inbreeding coefficient of the Spanish Habsburg kings increased strongly along generations from 0.025 for king Philip I, the founder of the dynasty, to 0.254 for Charles II and several members of the dynasty had inbreeding coefficients higher than 0.20. In addition to inbreeding due to unions between close relatives, ancestral inbreeding from multiple remote ancestors makes a substantial contribution to the inbreeding coefficient of most kings. A statistically significant inbreeding depression for survival to 10 years is detected in the progenies of the Spanish Habsburg kings. The results indicate that inbreeding at the level of first cousin (F = 0.0625) exerted an adverse effect on survival of 17.8% 612.3. It is speculated that the simultaneous occurrence in Charles II (F = 0.254) of two different genetic disorders: combined pituitary hormone deficiency and distal renal tubular acidosis, determined by recessive alleles at two unlinked loci, could explain most of the complex clinical profile of this king, including his impotence/infertility which in last instance led to the extinction of the dynasty.
The formula for F, the inbreeding coefficient is: FI = Σ (0.5)i X ( 1 + FA )
If drift becomes powerful enough it can lead the population toward extinction through mutational meltdown.
When miscarriages, stillbirths and neonatal deaths were removed from the analysis, the inbreeding effect on survival to 10 years was found more consistent and both multiple and logistic regressions show a clear inbreeding depression in the inbred offspring.
In short cousin marriages is an issue, however the laws of the Europe still do not prohibit incestuous relationship (a byproduct of ultra-liberalism which does not takes into account scientific evaluation), though it is been said that having children is a cause since grown up adults can have any form of sexual relation. There are certain states in Unites States too where incest has been legalize but the offspring of such a union is without doubt not considered healthy by the genetics scientists.
Therefore certain societies prohibit cousin marriages or marrying into the same clans. It has been prevalent among south Asian and central Asian societies but with arrival of Islam and with influence of Arabic culture things started changing in south and central Asia. Even for that matter Prophet Mohammad himself said on many occasions that if you want to have fit and strong child do not marry into your own clan.
It has been found in many of the Pakistani British families that they exists an inbreeding depression syndrome which have led to pre mature deaths of many kids. The govt of Britain chooses not to interfere as it may turn into a political fight where they may be accused of islamophobia but fact and rationality of genetics give credibility to practice of not marrying your cousins and into your clan.
I must say that one found very interesting statistics on razib Khan’s blog that
The highest levels of inbreeding in major populations have been found in urban Pondicherry (South India) and among army families in Pakistan where 54.9% and 77.1% of marriages are consanguineous, respectively…In Pondicherry 20.2% of marriages are uncle-niece and 31.3% first cousins, whereas in the Pakistan study 62.5% of marriages are between first cousins.
The question finally boils down to that should we be so selfish that it may affect our future generations or using words like liberalization or modernization we are trying to live in a world of self denial and illusion. As passing of law prohibiting such unions is always considered to be regressive but having children out of close relatives or within ones own clan which sets in regressive gene is not consider regressive.
References for people who wish to read more on this topic and wish to have a look at original research :