12 Genetic Mutations That Can Arise from Incest


Incest is a taboo in pretty much every culture around the world, but it wasn’t always so. Nobles and royals used to try to keep royal blood pure by marrying people they were related to; Egyptians rulers, in particular, would often marry their siblings or even their own children. This gave us a glimpse of the serious genetic mutations that can arise from incest. But how exactly do you get genetic problems from incest?

Even if there’s not always a mutation, inbreeding with someone you’re related to brings up a lot of problems involving recessive traits. Because the two of you have similar genes, any recessive abnormalities you have can be passed on more easily and expressed more visibly in your offspring. This also means that, even if you don’t show any signs of genetic disorders yourself, your child may show incest-related genetic mutations. It is important to note that these traits and mutations don’t always arise from incest, but they can show up more frequently through incestuous breeding.

If you’re still morbidly curious as to how incest affects your genes or what inbred people look like, look no further. Here are just a few of the genetic mutations that come from incest, as well as the expression of recessive genes you might never see otherwise.

The Habsburg Jaw

This genetic condition, also called prognathism, is connected to noble families. The Spanish House of Habsburg came to power during the mid-1400s and remained there until the mid-1700s, but during that time, there was quite a bit of inbreeding. Rather than marrying outside the family, the Habsburgs arranged close marriages to protect their interests. Unfortunately, their genetics paid the price. Their children started to show long, jutting lower jaws, with severe under-bites.

The worst case of this was found in Charles II of Spain, who had an under bite so severe that he could not speak properly, could not chew, and had problems with drooling. (In addition, he was infertile and had cognitive disabilities: he learned to talk when he was 4, and to walk when he was 8.)

Even modern ancestors of this family show slight variations of this genetic problem, showing just how long-lasting the results of genetic mutations from incest can be.

Misshapen Skulls

If you look at many ancient Egyptian busts, you may notice that their heads look a little funny – in particular, they are often elongated in the back. This wasn’t just a stylistic choice on the part of the artist; many Egyptian royalty actually had skulls shaped like that. After all, Egyptian royal customs depended heavily upon incest. Brothers married sisters; mothers married sons; and cousins often married cousins. The result was that their skulls were often deformed, though it should be noted that most royalty wrapped their heads to get that particular deformed shape as they grew, as it was also a sought-after style. King Tut, for example, suffered from such a skull deformation, in addition to “a cleft palate, a club foot (as well as missing bones in his feet), and scoliosis.”

Fused Limbs

The Vadoma tribe in Zimbabwe, which exists in relative isolation and procreates largely in pairs from its small ingroup, has a high occurrence of fused limbs in their feet, giving their feet a unique, birdlike appearance. This has led to them sometimes being called “the ostrich people.” Because their gene pool is small, and because the gene is both dominant and common, the trait lives on.


Several major European royal families were absolutely riddled with incest. Queen Victoria, in particular, saw the negative impact of inbreeding. During the 1850s, Victoria and Albert had a child who had trouble with his blood clotting. While that child, Leopold, did not commit incest with any of his siblings, many of his brothers and sisters did marry into the family, even indirectly, and more of their offspring started to show signs of trouble with bleeding. This is because they were carriers of hemophilia (sometimes called “the royal disease”), a recessive genetic disorder.

Hemophilia plagued the Russian royal family, the Romanovs, and it was fear for the hemophiliac Prince Alexei Romanov, Queen Victoria’s grandson and heir to the Russian throne, that led his mother Alexandra to fall under the spell of Rasputin.

Hemophilia happens when the blood does not clot properly. This means that even small injuries like a simple cut, bruise, or nosebleed, can result in a serious loss of blood, and that injuries do not heal correctly. This can lead to infections and even death.


Based on social mores, among Pakistani Muslims, intermarrying with close blood relatives, like first cousins, still takes place, and the impact is becoming visible. A 1998 study demonstrated that about 63% of Pakistanis participate in blood-relative marriages, which contributed to a rise in a condition called microcephaly, where a child is born with an unusually small head. This often means that the brain does not fully develop, either. As such, mild to severe mental disabilities are a major risk. The inbreeding in Pakistani culture means that 1 in 10,000 Pakistanis have this problem, compared to the 1 in 1,000,000 people who have it in the general global population.

Cleft Palate

King Tut, who was born of incest, showed a surprising number of medical problems when his body was examined, including cleft palate. A cleft palate occurs when the roof of the mouth does not form fully, and is thus left open to the sinus passage. This makes eating, swallowing, breathing, and even speaking difficult.


This is another disorder found in King Tut, and it is yet another example of how incest can impact the genetics of children. Club foot describes a broad range of different foot abnormalities, but it generally can be noted by the tendons that connect the foot to the body being too short to allow the foot to rest flat. These conditions are present at birth, and are certainly not solely caused by incest. However, close genetic linkages between parents can increase the risk of the condition.


Albinism is a condition where your body lacks melanin, a substance that causes your hair, skin, lips, and other body parts to have color. People with albinism tend to have light eyes, pale skin, and near-white hair, even if they come from a dark-skinned heritage. This condition is an autosomal recessive disease, which means that when people with similar genes breed, their children are more likely to have it. Cousins, siblings, and parent/children unions are far more likely to express this type of condition, as evidenced by what happens in small breeding pools.

Puerto Rico, for example, contains small pockets of people that rarely get much genetic diversity, and it has the highest density of albinism in the world.

Severe Asymmetry

Generations of inbreeding can give rise to congenital birth defects, which include drastic facial asymmetry. When you’re born, both sides of your face tend to be pretty much identical (with some minor asymmetry), including your ears, your eyes, your nose, and mouth. With incestuous offspring, particularly after many generations of incest, we start to see that both sides of the face don’t exactly look the same. Eyes can be higher or lower, and may be different sizes. Ears may be uneven, and the mouth may have a slant to it.


Dwarfism isn’t something you see after only one generation of incest, but it has been linked to incestuous breeding over generations. In the 1700s, there was a very close-knit settlement in Pennsylvania called Lancaster, which had offspring produced by inbreeding. Young children failed to thrive, there were issues with infertility, and eventually they saw an emergence of Ellis-van Creveld disease. This disease is associated with dwarfism, as well as the stunting of the extremities and issues with the heart. The eventual emergence of this disease is likely due to a lack of diversity in the Lancaster gene pool.


The children produced from incestuous unions are not always viable. In that situation, either the fetus fails to thrive, or the children are stillborn. In this way, incestuous relationships are often infertile ones. However, even if you do manage to have a child through incest, infertility may be passed on to your offspring. The viability of both sperm and eggs may be negatively impacted, or the reproductive system may simply not function normally. Historically, this infertility has given royal incestuous families no end of trouble, especially given the importance of producing heirs.


This genetic condition is fairly common, regardless of incest. Scoliosis happens when the spine shows abnormal curvature towards one side of the back. In severe cases, this can impact a person’s ability to walk and sit comfortably, and it may require surgery or years of corrective braces to fix. A surprising 2-3% percent of American have scoliosis by the time they reach age 16. Experts also know this condition can be passed on through genetics. When incest occurs, even if neither parent expresses the gene, they may have a child who has the condition due to the similarity of the parents’ genes. Because of this, incest makes scoliosis more likely to occur.

Immune System Disorders

Children born of incest tend to be very sickly. While this may have to do with malformations of the skeleton, muscles, or organs, a major factor is a faulty immune system. In a properly functioning immune system from a non-incestuous pairing, there’s a wide range of different alleles that fight off different diseases – the wider the variety, the more diseases you can combat. When you breed with a close blood relative, though, the resulting immune system has far fewer unique alleles and can only protect itself from a smaller set of diseases. This lack of diversity makes a child much more susceptible to diseases, and can effectively stunt the immune system.

We may not fully understand how the body passes on immunity from parent to child, but historically speaking, it’s pretty obvious that incest does not help. Our DNA needs diversity in order to build a strong immune system.

Leave a Reply