Tag Archives: characteristics of inbred humans

Human inbreeding: examples

In a genetics class I attended recently, Professor Scott Weitze recommended a few books including The Family That Could Not Sleep by D.T. Max and Mutants: On genetic Variety and the Human Body by Armand Marie Leroi. I thought I should mention both these books because both deal with mutations that probably arose due to human inbreeding.

The Family… lists many prion related symptoms which seem interesting from the perspective of inbreeding. The Italian family referred to in the title is haunted by progressive insomnia that kills the victims within months due to sleep deprivation. Although this condition is due to prions, the fact that this condition is inherited makes me believe that some inbreeding may be involved. A mutation that promotes the incorrect folding of the protein which creates the prions may have arisen in an ancestor in the family. Due to consanguineous marriages the incidence of the mutation may have increased to the current status within the family. Mutants, too, is a wonderful book that links myth, reported cases, and medical cases of human deformities that have lingered since ancient ages.

While The Family…. consists of many prion related diseases, Mutants starts with the description of the mythical Monster of Ravenna that remarkably resembles patients with Roberts’s Syndrome. Then leading the readers from the battle of preformationists and epigeneticists the book delves into the modern day developmental biology to explain various irregularities during the development of an embryo that leads to deformities. While some developmental irregularities could be due to the environment and chemical agents, others such as ectrodacytly (previously also known as Cleppie Bells or lobster claws) could be due to inbreeding because they seem to be in the individuals that seem to have shared ancestors. Cleppie Bells in a few Scots family, Lobster claws in a British family, Ostrich foot in an African family, and the aleijadinhos of Brazil are some of the examples of ectrodacytly listed by the author. All these deformities are in very small populations sharing a common ancestor. I thought this would probably be interesting especially to those who refute the negative implications of consanguineous marriage.

I would not want to summarize the books because the authors have spent a lot of time and effort to write them. I would suggest though that readers interested in deciphering more about the implications of human inbreeding read both of these books.


Filed under Human Evolution

Human Inbreeding: A better understanding

Unions contracted between persons biologically related as second cousins or closer (F ≥ 0.0156) are categorized as consanguineous. It is very confusing whether children of consanguineous marriages are genetically predisposed to any developmental defects. In my previous article ‘Human Inbreeding: What are the consequences?’ I tried to explain the deleterious effects inbreeding may cause. The articles I read at that time were not very conclusive whether inbreeding is beneficial or deleterious. So, I decided to dig up some more scientific journals to find out the effects of inbreeding.

One article I found, reasserted the former argument that inbreeding does not have any effect on fertility (spontaneous abortions and stillbirths) of women. However, higher rates of neonatal and post-neonatal deaths, and deaths of children younger than 5 years were observed in consanguineous couples. I then thought, does inbreeding affect the fertility of men? A study involving Middle-Eastern Males demonstrated that consanguinity and the familial clustering increased the chances of having infertility problems 2.6 times higher in cases than controls. So, I am thinking even though inbreeding does not cause any aberrant pregnancies, inbreeding does have adverse effects on male fertility and on survival of newborn children.

I have also wondered whether inbreeding plays a role in other diseases. While searching for answers to satisfy my curiosity, I found that researchers who have looked at Middle East and North Africa region have pointed out that in the Islamic Arabs residing in these regions, there is a high prevalence of first-cousin consanguinity. Hemoglobin disorders, inherited metabolic disorders, neurogenetic disorders, and birth defects are also relatively common in this part of the world. One can thus ask a question that may be these diseases can be credited to, at least in part to the inbreeding?

Also, medical professionals have found “significant association between parental consanguinity and congenital hypothyroidism.” Congenital hypothyroidism seems to correlate with the degree of consanguinity—children of first cousins are more prone to than those of second cousins.

Amid all the confusions, it is very well accepted that among genetic disorders, only autosomal recessive disorders are strongly associated with consanguinity. However, there are ample of studies showing that in a population with a high rate of consanguinity, there is a significant increase in the prevalence of common adult diseases like mental disorders, heart diseases, gastro-intestinal disorders, hypertension, hearing deficit, and cancer. Interestingly though, a study in Arab populations, however demonstrated that reduction of overall cancer risk was associated with increased coefficient of inbreeding (F). Both older and younger healthy men had significantly higher F but only women over 30 years of age with higher F had reduction of overall cancer risk. This study showed that being more inbred was associated with a reduction in overall cancer risk by about 25%.

I am not sure what to make of the relationship between inbreeding and cancer but I am certain that in breeding may have adverse affects in humans and it should not be encouraged.

More readings
Examples of inbreeding in humans
Probability of inbreeding


Kobeissi and Inhorn; Health issues in the Arab American community. Male infertility in Lebanon: a case-controlled study.
Kerkeni et. al.; Interplay of socio-economic factors, consanguinity, fertility, and offspring mortality in Monastir, Tunisia.
Saadallah and Rashed; Newborn screening: experiences in the Middle East and North Africa.
Hashemipour, et. al.; Parental consanguinity among parents of neonates with congenital hypothyroidism in Isfahan.
Hamamy, et. al.; Consanguinity and genetic disorders. Profile from Jordan.
Bener, et. al.; Consanguineous marriages and their effects on common adult diseases: studies from an endogamous population.
Denic et. al.; Risk of cancer in an inbred population.


Filed under Evolution, Human Evolution, My Life My Thoughts

Human Inbreeding: What are the consequences?

“Inbreeding is breeding between close relatives, whether plant or animal” (1). Inbreeding can occur naturally in plants via self pollination. It is also carried out in animals by breeders to produce pure strains or to amplify a desirable trait. Inbreeding limits genetic diversity in addition to increasing the probability of inheriting any deleterious recessive genes from a parent or ancestral population. The level of inbreeding is determined by ‘inbreeding coefficient’ meaning that the closer the relatives are the higher the inbreeding coefficient is and thus riskier.

Inbreeding is not only limited to plants and animals. Inbreeding was practiced in western societies (before 19th and 20th centuries) and it is still common in some parts of the world. While Muslims of India, Middle-East, and Africa practice inbreeding for cultural and religious reasons, Amish, Mennomites and Hutterites may have practiced it because they were isolated. The high inbreeding coefficient in Dammam, Saudi Arabiais (0.0312) an be attributable to beliefs, traditions, and the desire to keep property within the family. The practice of endogymy in Hindus may arguably produce similar effects as inbreeding over long periods of time. Another reason responsible for persistence of inbreeding practices is socioeconomic status—the rich wanting to marry only the rich to maintain their status and thus looking in their own families for partners and poor only being able to afford a marriage among themselves. Interestingly, some royal societies have also been known to practice inbreeding to protect royal blood lines. For example, the English Royal family has had many hemophiliac members due to inbreeding. Inbreeding was common in Spanish Royal family as well. Historical events also promote inbreeding. After the United States devastated Hiroshima and Nagasaki in Japan, “there was an increase in the number of consanguineous marriages (first cousin level) in the areas surrounding Hiroshima and Nagasaki.”

While some propose that long-term practice of inbreeding can be beneficial to a population as harmful genes are elimination by selection, there have been ample studies suggesting that inbreeding poses threats to a population in a variety of ways such as reduced fertility and increased child mortality/morbidity. A study investigating the effects of inbreeding on the fertility of adult women demonstrated that deleterious recessive alleles received from inbreeding can lower the fertility rates of adult woman. Another study investigated five effects of inbreeding: fertility, mortality and morbidity of the offspring, reproductive performance of the offspring, and characteristics of the offspring. In thus study inbreeding did not have an adverse effect on the fertility of the marriages; however, results showed that inbreeding significantly increases childhood mortality in the first year of life, increases morbidity, and significantly increases numbers of disabled offspring. Moreover, development also seemed to be affected for “the children of consanguineous marriages were significantly older than the control group when they first walked and talked.” However, inbreeding seemed to be beneficial when examining some aspects of health. Offspring from the inbreeding group showed a 14.3% decrease in allergies and a 23.9% decrease in nephritis, a rare genetic disorder that causes inflammation of the kidneys. While these are a studies that investigate effects of human inbreeding, many more animal studies have demonstrated that inbreeding creates health problems. For example, all pure bred dogs have significantly higher and devastating medical conditions.


Human inbreeding and cancer
How cancer is formed
Read More


Filed under Human Evolution