In Newgrange, Ireland, there is a 5,000-year-old Neolithic-era monument, carved with mysterious symbols, marking the elaborate tomb of an important ancient man. These kinds of tombs are found all over Ireland but the one in Newgrange is the most famous and, most think, belonged to a king. Now, new research into the man’s genetics reveals that that his parents were likely to have been siblings. The discovery suggests that those who ruled Ireland thousands of years ago were practitioners of incest, one of human society’s most consistent taboos. This would place them among a cluster of famous dynasties that preferred to shun social norms and reproduce with close relatives.
The study, published last week in the prestigious scientific journal Nature, was produced by a team of scientists at Trinity College Dublin led by geneticist Lara Cassidy. The study examined the remains of 42 individuals buried at Neolithic sites throughout the country. The purpose of the study was to try to understand the social hierarchies and structures that were at work at the time. Passage tombs—earth-covered burial chamber(s) accessible only via narrow passageways—like the one at Newgrange, took a great deal of labor to build. Understanding for whom these tombs were constructed is one step towards understanding the social world of Neolithic Ireland.
The analysis of the genetic information from the sample at Newgrange (which you can view online and was built ca. 3200 B.C.) revealed that the parents of the king buried there were first-degree relatives. Cassidy explained to Tom Metcalfe at Livescience that “We inherit one copy of the genome of our mother, and one from our father, and we can compare these two copies of the genome in this individual,” and that in this case “what we saw was that they were extremely similar.” Other relatives of the king were discovered buried in passage tombs 150 km to the west of Newgrange.
The discovery is interesting precisely because it is so taboo. Incest among members of the same “nuclear family” is remarkably rare (unless family members have been raised apart). In the modern world when incest occurs it usually takes place and is understood as an abuse of power by older, more authoritative, and usually male family members.
Where this almost universally agreed-upon taboo is most regularly flaunted, however, is among members of the socio-political elite. Among royal families, especially families who claimed divine ancestry, brother-sister unions were common. Arguably the most famous example of this is the Pharaohs of Egypt. A controversial 2015 University of Zurich study of the remains of elite ancient Egyptians suggested that incest was very common among the pharaohs. Literary evidence alone seems to confirm this. Amenhotep I, one of the most famous of the kings of Egypt, was the product of three generations of sibling incest. Similarly, the boy-king Tutankhamun, son of Akhenatan, was the product of a brother-sister relationship and later married his half-sibling Ankhesenpaaten. Cleopatra, too, was the product of a sibling union. The effects of multi-generational incest appear to have taken a toll on the royal family: Tutankhamun suffered from a genetic bone disease.
Relationships like this were permissible for the Pharaoh’s precisely because of their extraordinary bloodline. As Egyptologist Zahi Hawass has explained “A king could marry his sister and his daughter because he is a god, like Iris and Osiris, and this was a habit only among kings and queens.” In some ways it’s about preserving the purity and strength of their divine blood.
Cassidy argues that something similar was happening among Neolithic Irish elites: It’s “a way that elites can separate themselves — they get to break a taboo, they get to break a social convention that others aren't allowed to.”
Inbreeding, as the Hapsburg family found out to their detriment, can have some unintended consequences. Too much inter-marriage among the royal families of Europe has led to the emergence of less than desirable physical qualities including, allegedly, the Hapsburg lip, and, more seriously, the prevalence of the blood clotting disorder hemophilia among descendants of Queen Victoria.
One problem with the commonly believed “royals only” exception to incest is the data from Ptolemaic and Roman era Egypt (second to third century B.C.). As Keith Hopkins showed in 1980, during this period most full brother-sister marriages were non-royal marriages. In the Roman period, censuses reveal, brother-sister unions were common in Egypt for the first three centuries A.D. (they constitute about 15-20 percent of marriages). Naphtali Lewis further notes that far from being taboo such marriages were celebrated, publicly announced, and in all respects ‘ordinary.’ There is no ancient commentary on genetic flaws or unsuccessful relationships. From the third century onwards, however, they disappear entirely from papyrological records. This is likely due to an edict, published in 295 A.D. by the Emperor Diocletian, that specifically forbade incestuous relationships throughout the empire. In the rest of the Roman empire these kinds of unions were a social taboo; accusations of incest were levied against outsiders, including early Christians, as a sign of their moral depravity and barbarian nature.
There are a number of socio-economic reasons that for four centuries elite (but not royal) Egyptians chose to marry their siblings or half-siblings. One explanation is that they were elite Greeks who wanted to preserve their sense of ethnic identity and elite status by avoiding intermarriage with those deemed “not Greek.” A second, that has been relevant throughout history, is that marriage within familial groups helps preserve wealth because of the condensed lines of inheritance.
UNC-Charlotte anthropologist Jon Marks, author of Tales of the Ex-Apes, explained to the Daily Beast that a lot comes down to our definitions of incest. Even though it is banned in many US states, marriage among first cousins, he said, is still the “the most popular union in our species” and comprises about 10 percent of marriages globally. A recent genetic study of Iceland revealed that the most fertile marriages were between fourth cousins. The prevalence of marriage among cousins could, in fact, be at work in the case of the Neolithic Irish king. Marks told me, that the study’s “inference of a brother-sister union from how very inbred the subject was, is a reasonable one, but it isn’t entirely clear that they could differentiate that from, say, the result of several generations of cousin-marriage.”
If this seems like a bad idea for the evolution of our species it might strike you as somewhat ironic to learn that Charles and Emma Darwin were first cousins (as Adam Kuper shows in Incest and Influence, this was a great way for Victorians to protect familial wealth). What the historical evidence—from ancient Egypt all the way into the present—shows is that when it comes to marriage lots of people like to keep things in the family.
