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, 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 another connected to noble families. The 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.
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. A large part of this is that 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. 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."
While extra limbs (polydactylism) and missing limbs do happen with children of incest, it's really not common. In fact, polydactylism doesn't seem to be more common in children of incest, according to some studies. However, fused limbs do seem to be more prevalent in children of incest. In this condition, toes and fingers grow with the skin and flesh around the limbs or digits fused together, making the limbs look webbed or even lacking definition altogether.
The Vadoma tribe in Zimbabwe has a high occurrence of fused limbs in their feet, giving them strange and birdlike toes. This has lead 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.
Lack of Fingernails
When you think of incest, you usually think of missing limbs, extra fingers, or a lack of teeth. Oddly enough, those things are not the most common signs of incest. However, in some rare cases, children are born with a few things missing.
The incestuous and rather cult-like Kingston family, a splinter clan of fundamentalist Mormons who practice polygamy, has been known to have children that are born without fingernails. That's right, a lack of fingernails on all of their fingers. This could be linked to any number of genetic disorders and conditions, and unless the children were given tests and exams, it would be impossible to determine exactly the cause. However, we can safely say that the widespread incest in the family has something to do with it.