DNA study reveals Ireland's age of 'god-kings'
DNA was used to confirm the existence of an elite social class in the Stone Age residents of Ireland.
It is one of the earliest examples of such a hierarchy in human societies.
An important piece of evidence comes from an adult man who was buried at the 5,000-year-old Newgrange Memorial. His DNA revealed that his parents were first-degree relatives, possibly brother and sister.
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He was a member of an expanded "clan" buried on impressive stone monuments across Ireland.
The Irish elites were founded in the Neolithic period when people started farming. The researchers extracted DNA from 44 ancient individuals from across Ireland and sequenced their genomes (the complete complement of the genetic material contained in the cell nuclei).
References to incestuous unions like those found in Newgrange are rare in human history. They are taboo for interconnected biological and cultural reasons. Wherever they occur, they were often given divine status within royal dynasties.
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Brother-sister marriages are found among the pharaohs of ancient Egypt and the "god kings" of the South American Inca Empire. Tutankhamun's parents, for example, are viewed by some as full siblings. Among these cultures, rulers relied on aspects of religion to legitimize their power and exercised it by building extravagant monuments.
Lara Cassidy, assistant professor at Trinity College Dublin, commented on the genetic pattern of the Newgrange man as follows: "I had never seen anything like it.
"We all inherit two copies of the genome, one from our mother and one from our father. Well, the copies of that person were very similar, a tell-tale sign of close inbreeding. Our analysis allowed us to confirm that his parents were relatives first degree. "
The Newgrange Memorial in County Meath is a kidney-shaped hill that covers an area of more than one acre. It is part of a tradition of artistic monuments built with large stones or megaliths during the Neolithic in Atlantic Europe.
The place is older than Stonehenge and the Pyramids of Giza and is famous for its annual sun exposure, where sunrise at winter solstice illuminates the inner chamber with a beam of light. The man's remains were placed in an ornate recess in the inner chamber.
"The prestige of the funeral makes this very likely a socially sanctioned union and speaks of a hierarchy so extreme that the only partners worthy of the elite are family members," said Prof. Dan Bradley, also of Trinity College .
Dr. Cassidy, the lead author of the new study published in Nature, told BBC News: "It is an extreme of what elites do. If you marry within your kinship group, you can keep power in your 'clan'."
"But elites also break a lot of rules to separate themselves from the rest of the population ... it's a bit of chicken and egg: if you break those rules, you will probably make yourself appear even more divine."
Remarkably, a local myth resonates with both the DNA results and the Newgrange solar phenomenon. The story was first recorded in the 11th century AD - four millennia after the construction of Newgrange - and tells of a builder who restarted the daily solar cycle by sleeping with his sister.
The Middle Irish place name for the neighboring Dowth passage grave Fertae Chuile is based on this tradition and can be translated as "hill of sin".
Dr. Tom Booth, senior scientist at London's Francis Crick Institute, who was not involved in the study, described the study as "impressive" and described it as "the most detailed picture of the genetics of people who lived in the UK and Ireland during the year to date" Neolithic ".
He added, "Given the distance of these societies from our own, I'm cautious when speaking about dynasties or monarchs as we understand them today, and people who expect a Neolithic Game of Thrones may need to take a cold shower.
"But surely the evidence is pretty convincing that certain megalithic tombs in Ireland were reserved for people who were more closely biologically related, including potentially prestigious groups of families who married together."
The team discovered a network of distant family connections between the Newgrange man and other people from passage graves across the country, including the "mega-cemeteries" of Carrowmore and Carrowkeel in County Sligo.
The genetic ties between elite individuals in distant locations have not been seen in contemporary burials in less prestigious locations.
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"It appears that we have a powerful extended kinship group here that has had access to elite tombs in many regions of the island for at least half a millennium," said Dr. Cassidy.
Tom Booth said: "In the UK, recent discoveries that some graves were built over the remains of wooden houses have been used to indicate that these places were associated with certain families, but solid evidence of who ended up in those graves and why always elusive. "
The old genomic study also uncovered the earliest diagnosed case of Down syndrome - in a male infant who was buried 5,500 years ago in the portal grave of Poulnabrone, County Clare.
"He was buried in a sacred place; he was breastfed before his death," said Dr. Cassidy. "It is an interesting insight into the social values of this society.
"People with disabilities can sometimes be invisible in the archaeological record. I think it's really nice that we can now shed light on this with ancient genomes."
Ireland's Neolithic residents trace their origins to an expansion of people from Anatolia (modern Turkey) around 6,000 to 7,000 years ago. This migration changed the way of life in Europe from hunting to agriculture. Genetically speaking, Ireland's first farmers were most closely related to people who, by and large, lived in Iberia (today's Spain and Portugal) at the same time.
For generations, farmers crossed the Mediterranean from Anatolia to Iberia and meandered up the French coast before reaching Ireland by sea.
When the new migrants reached the coast of this North Atlantic landmass, they quickly drove out the local Mesolithic hunters and gatherers who were genetically similar to the pre-agricultural peoples across Europe. However, their DNA shows that they have developed a special character after centuries of isolation.
Their genetic code shows little evidence of interaction with similar populations in the UK, suggesting that the Irish Sea was a formidable contact barrier in the centuries before agriculture.
DNA predicts that Ireland's hunters and gatherers had a striking combination of dark skin and blue eyes. In contrast, the Anatolian farmers probably had pale skin with brown eyes.
The small hunter population may have been overwhelmed when the peasants arrived in greater numbers. But they haven't completely disappeared.
Two people from a wedge tomb in Parknabinnia, County Clare, showed a high level of Mesolithic descent. Obviously, Neolithic farmers sometimes integrated the hunters into their communities.
Regarding whether the results could apply to other geographic areas, Tom Booth said: "The evidence we have from earlier Neolithic periods in the UK and Ireland suggests that there was a loose connection between graves and families.
"People belonging to certain paternal lineages were more often buried in megalithic tombs during these periods, but fewer occurrences of close biological relatives suggest that family connections do not tell the whole story. Social developments that could lead to strong associations between families and megalithic tombs specific to later Neolithic societies in Ireland. "
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