This is the fourth and final segment in a series on incest; you can go back and read the previous segments on incest in ancient Egypt, incest in the Hapsburg family, and incest in nature.

As surprising as it may seem, consanguineous marriages are nowadays respected and practised among more than one billion of the world’s population, in particular in the Muslim countries of North Africa, Central and West Asia, and in most parts of South Asia (Jalal Abbasi-Shavazi 2008) with consanguinity rates reaching 20–50% (Hamamy 2016). It has been shown (Bittles 1994, 2001) that sociocultural factors, such as the maintenance of family structure and property, ease of marital arrangements, better relationships with in-laws, and financial advantages relating to dowry, seem to be strong contributory factors in the preference for consanguineous unions.

In countries with civil unrest, consanguineous marriages are preferred because close-kin marriage is regarded as safeguarding for personal and family. It has also been suggested that marriage dissolution and divorce is lower among cousin couples. Studies have indicated that women in first-cousin marriages are protected against intimate partner violence. In another study focussing on cases of consanguinity in Iran (Jalal Abbasi-Shavazi 2008), the authors also demonstrate that in this country the ethnicity, province and area of residence have remained by far the most important determinants of the practice of marriage to biological relatives. In contrast, the modernization variable, education, had no significant effect upon behaviour, the effect being only for those with tertiary education.

Figure 1: Global prevalence of consanguinity (Bittles 2009)

In other countries, the genetic risk associated to consanguineous relations is taken very seriously and all is done to avoid it. This is the case with Iceland. With a population of only 320.00 inhabitants, the risk of incest is really high. De facto, in Iceland everyone shares at least one family relationship. It is said that one of the most asked questions during a first date is: “Hverra manna ert þú?” Which means “ Who are you, who is your family?” To avoid any chance to end up dating your cousin, 3 engineers have recently created a smartphone app called ÍslendigaApp in which people can check the family genealogy and any family relationship with their intended in a few seconds. It even has a “bump” option which gives the info on family relationships when the partners’ phones are clashed and can even send an “incest alert” when the two partners are close family members.

At the origin of this app, there is a genealogy website called Íslendingabók (i.e. Book of Icelanders). Launched in 2010, the database lists the family relationships between Icelanders going back 1200 years. To check the information related to your family, any inhabitant of the Island only needs to provide his/her name and national identity number. Quickly, the website starts to be much more than just a catalogue of genealogy trees and people started to use it to check any possible family connections to their partner.

Here the series on Incest ends. Through the different articles of this series, I have tried to elucidate the incest taboo, find its sources, and understand its origins through different historical cases — Tutankhamun or the Habsburg family — but also through scientific cases.  All these examples have shown us that this taboo seems deeply anchored in nature and culture but that neither nature nor some cultures totally prohibited it. So where to find its source? The questioning hits some dead-end; the answers provided are always partial. Psychology has tried to stick its nose into it while some scientists are waiting for the discovery of a possible “incest” gene. While we wait for answers, I would like to ask you: “Why do you find incest disgusting?” I hope these articles gave you some food for thoughts and starting points for further questioning.

“There is nothing either good or bad, but thinking makes it so” (Hamlet by W. Shakespeare).

References

Bittles A. H. (1994). ‘The role and significance of consanguinity as a demographic variable.’ Population and Development Review 20(3):561-583.

Bittles A. H. (2001). “A Background summary of consanguineous marriage.” Center for Human Genetics, Edith Cowan University, Perth.

Bittles, A. H. and M. L. Black. “Consanguinity, Human Evolution, and Complex Diseases.” Proceedings of the National Academy of Sciences 107.Suppl 1 (2010): 1779-86. Web.

Hamamy, Hanan, and Alwan, Sura. “Chapter 18 – The Sociodemographic and Economic Correlates of Consanguineous Marriages in Highly Consanguineous Populations.” Genomics and Society, 2016, pp. 335–361.

Jalal Abbasi-Shavazi, Mohammad, et al. (2008). “modernization or cultural maintenance: the practice of consanguineous marriage in Iran.” Journal of Biosocial Science, 40(6):911–933.

This is the third segment in a series on incest; you can go back and read the previous segments on incest in ancient Egypt and incest in the Hapsburg family.

Firstly, did you know that despite the earliest forms of life emerging around 3.8 billion years ago, sex has only existed for 1.2 billion years? Before that, asexual reproduction was the only form of reproduction to evolve. When you think about it, this is the most extreme type of incest, reproducing yourself with …yourself, cloning yourself. Nowadays, most mammals tend to not engage in inbreeding. If they do, we have seen that incest can lead to depression inbreeding with offspring experiencing health problems. For this reason, scientists used to think that Nature might have weeded out incestuous behaviour through natural selection.

However, recent studies have actually shown that incestuous behaviour has not completely disappeared and that it is more common than generally thought. Some species are asexual or still breed with themselves in situations where there is no advantage to sex; others commit incest where there is no penalty to inbreeding. And guess where those incestuous species are mostly found? Islands and mountaintops. In these isolated places, it is difficult to find someone who does not fit somewhere in your family tree.

Incestuous species

• Mongoose

Mongoose live in close-knit groups with a median size of 18 adults. Each group has both male and female dominant members, who do most of the breeding and reproducing—those on the periphery only reproduce occasionally. Most group members remain with their group for their entire lives. This close-knit living arrangement has led to a high incidence of incest. A study has found that 64% of newborn pups were the result of mating between members of the same natal group (Nichols, 2014). Father/daughter incest was documented eight times over the course of the study run over 16 years; no mating attempts between mother/son were reported. The researchers point out that females tend to have short lives and generally die before their sons are old enough to mate with them.

Yellow mongoose, Cynictis penicillata

• Whiptail lizards

This one is with no doubt my favourite.

Some women might have dreamed of a world with no men. Whiptail lizards have done it. Females whiptail lizards are able to clone themselves. And this is not the only species with this capability. There are actually quite a few, 80 groups to be precise, which include amphibians, reptiles, and even fish. But the specificity of these female lizards is that though they don’t need to have sex to survive, they still display mating behaviours, meaning that females sometimes mount other females. Scientists think this behaviour is hormonally driven; high progesterone levels may cause females to mount others. But they probably don’t just bump cloacal regions for fun. Studies have shown that females who are mounted by another female are more fertile than those who go it alone, likely because the mounting behaviour promotes ovulation (Wade, 2013).

Mating behaviour among whiptail lizards: female lizard mounting another female.

• Spotted salamanders

Among spotted salamanders, DNA analysis shows inbreeding at the level of first cousins, on average. Despite having hundreds of possible mates to choose from, females tended to fertilize their eggs with sperm from related males.

Spotted salamander

Interestingly, in some cases, the natural selection mentioned earlier seems to contradict other studies showing that for some animal or insects, inbreeding within first cousins or brother/sister gives better chance of survival to the offspring. Inbred ambrosia beetles, for example, fared no worse than outbred insects, and the eggs produced by brother-sister pairs are likelier to hatch than the eggs of unrelated pairs (Andersen 2012). Similarly, another study has found that for at least one fish species, fathers from brother-sister couples spent more time, on average, defending their caves and that both parents tended to pay more attention to their kids than unrelated couples.” How to explain this? The ecologist who supervised the study reports, “Couples which are full siblings are more cooperative in brood care. … [T]he males and females stay with the offspring for several weeks and guard them—they defend them—and there’s less aggression between full siblings.”

Stay tuned for next and final segment in a series on incest. We will talking about the practice of incest in modern societies: Modernization or cultural maintenance?

 References

Andersen, H., Jordal, B., Kambestad, M., & Kirkendall, L. (2012). Improbable but true: The invasive inbreeding ambrosia beetle Xylosandrus morigerus has generalist genotypes. Ecology and Evolution, 2(1), 247-257.

Nichols, H., Cant, M., Hoffman, J., & Sanderson, J. (2014). Evidence for frequent incest in a cooperatively breeding mammal. Biology Letters, 10(12), 20140898.

Wade, J., Huang, J., & Crewst, D. (1993). Hormonal Control of Sex Differences in the Brain, Behavior and Accessory Sex Structures of Whiptail Lizards ( Cnemidophorus Species. Journal of Neuroendocrinology, 5(1), 81-93.

My curiosity was piqued during one of my turns at the Petrie Museum. Facing all these artefacts, traces of dynasties of pharaohs, I was suddenly reminded of the stories of incest and marriages between brother and sister which were common in ancient Egypt among the ruling class. More recently, the topic was brought up again by another visitor. I was then told about Akhenaton’s androgynous appearance that could have been a result of the incestuous practices of the time. This practice seems to be a common thing and these stories made me immediately think of the Greek and Roman gods and their intricate family-love relationships. With this thought came then one question: why would pharaohs marry their sister, mother and other relatives? To act as living gods? To preserve the purity of their blood?

Fig. 1: Limestone statuette of Akhenaten, Nefertiti and Princess (Tell el Amarna). [Petrie museum, UC004]

Many others questions followed: If incest was accepted in ancient Egypt among the ruling class, was it tolerated by the whole population? What makes it unacceptable in Western countries today? Health? Morality? Are marriages among siblings and/or first cousins still allowed nowadays in some countries? And what are actually the risks of incestuous relations?

From ancient Egypt to the Habsburg family in Europe, throughout history cases of consanguinity — mainly among members of the ruling classes — are numerous. It is surprising that the practice continued for as long as it has when religious and civil laws started to forbid it and when the risks associated to this practice started to be known; from the 5th century BCE, Roman civil law already forbade couples from marrying if they were within four degrees of consanguinity (Bouchard 2010). From the half of the 9^th century CE, the church even raised this limit to the seventh degree of consanguinity and the method of calculating degrees was also changed. More recently, modern philosophers and thinkers argued that the prohibition against incest was a universal phenomenon, the so-called incest taboo . But this theory seems contestable in view of the Egyptian case.

So why is it that incest was accepted and practised in ancient Egypt and more recently among members of the royal family such as the Habsburg (16^th-18^th century)? And how did science shed the lights on family relationships, incestuous practices and the diseases resulting from them?

Let’s first take the case of the 18^th dynasty, the first dynasty of the New Kingdom of Ancient Egypt.

Incest in Ancient Egypt: the case of the 18th Dynasty

There is an abundance of evidence showing that marriages or sexual relations between members of the “nuclear family“ (i.e. parents, children) were common among royalty or special classes of priests since they were the representatives of divine on Earth. They were often privileged to do what was forbidden to members of the ordinary family. During the Ptolemaic period (305 to 30 BCE) the practice was even used by King Ptolemy II as “a major theme of propaganda, stressing the nature of the couple, which could not be bound by ordinary rules of humanity” (Chauveau, M.).

Fig. 2: Alabaster sunken relief depicting Akhenaten, Nefertiti, and daughter Meritaten. Early Aten cartouches on king’s arm and chest. From Amarna, Egypt. 18th Dynasty. [Petrie Museum, UC401]

But let’s go back to the 18^th dynasty (1549/1550 BCE to 1292 BCE). In 2010, a team of Egyptian and German researchers analysed 11 mummies dated from the 18^th dynasty which were closely related to Tutankhamun (Hawass, Zahi, et al.). The mummies were scanned and DNA extraction on bone tissues was carried out. The information they could get from these analyses enabled them to identify the mummies, determine the exact relationships between members of the royal family, and to speculate on possible illnesses and causes of death.

The results of the DNA analyses show that Tutankhamun was, beyond doubt, the child born from a first-degree brother-sister relationship between Akhenaten and Akhenaten’s sister (see Fig. 3). Moreover, the authors provided an answer to the androgynous appearance of Akhenaten. They actually showed that the feminized appearance exhibited by the art of the pharaoh Akhenaten (also seen to a lesser degree in the statues and reliefs of Tutankhamun) was not related to some form of gynecomastia or Marfan syndrome as suggested in the past. Neither Akhenaten nor Tutankhamun were likely to have displayed a significantly bizarre or feminine physique. The particular artistic representation of persons in the Amarna period is more probably related to the religious reforms of Akhenaten.

However, the incestuous relationship between Akhenaten and his sister may have had other consequences. Pharaoh Tutankhamun suffered from congenital equinovarus deformity (also called ‘clubfoot’). The tomography scans of Tutankhamun’s mummy also revealed that the Pharaoh had a bone necrosis for quite a long time, which might have caused a walking disability. This was supported by the objects found next to his mummy. Did you know that 130 sticks and staves were found in its tomb?

Fig. 3: Genealogical tree showing the relationship between the tested mummies dating from the 18th dynasty (Source: Hawass, Zahi, et al.).

Fig. 4: Scans of Tutankhamun feet (Hawass, Zahi, et al.)

Incest and common people

This article on consanguinity and incestuous marriages could easily finish here. We learned that incest was practised in ancient Egypt for strategic reasons, in order to preserve the symbolism which associates the pharaoh to a living god. We also saw how science could help us in unravelling the true stories lying behind myths, speculations and rumours.

This could be almost perfect but the incest taboo is more complex than this. As observed by Paul John Frandsen, “in a society (such as ancient Egypt) where nuclear family incest is practised there is no discrepancy between what is licit among royalty and in the populace”. Indeed, contrary to what is often admitted incest was not only reserved to the ruling class. In Persia and ancient Egypt, incestuous relationships between members of non-royal nuclear families also existed (Frandsen P. J.). This shows that incestuous relationship in the nuclear family could be more than just propaganda and that other reasons might have motivated this practice. It has been argued that this was done for economic reasons as endogamy could have been a means to keep the estate undivided and/or avoiding paying bride price. However, these arguments have been dismissed. Up till now, there is thus no reasonable explanation for the lack of incest taboo in ancient Egypt and Persia.

Keep an eye out for my next post, where I’ll talk about incest in the Habsburg royal family and King Charles II of Spain (also called “the Bewitched”)!

References (and read more!)

Bouchard, Constance Brittain. Those of My Blood : Creating Noble Families in Medieval Francia. University of Pennsylvania Press, 2001.

Chauveau, Michel.MmNm. Egypt in the Age of Cleopatra : History and Society under the Ptolemies. Cornell University Press, 2000.

Hawass, Zahi, et al. “Ancestry and Pathology in King Tutankhamun’s Family.” JAMA, vol. 303, no. 7, 2010, pp. 638–647.

Frandsen, Paul John,MmNm. Incestuous and Close-Kin Marriage in Ancient Egypt and Persia : an Examination of the Evidence. Museum Tusculanum Press, 2009.