Ireland’s ancient kings married their sisters and fathered inbred children to maintain their dynasty

Ireland’s ancient kings married their sisters and fathered inbred children to maintain dynastic bloodlines, 5,000-year-old genomes found in Newgrange tomb revealed. 

Experts from Trinity College Dublin came to this conclusion after studying the DNA of a man who was buried in the famous passage tomb in Ireland’s County Meath.

The individual appears to have been the product of ‘first-degree’ incest — meaning that his parents were likely either siblings, or even a parent and their child. 

Breaking such deep-rooted taboos while maintaining social acceptance is normally only tolerated among those are considered to be above the rules, or even godlike.

This suggests that the dynasty of Ireland’s ancient kings saw themselves as a rarefied elite akin to that of the similarly inbred Inca kinds and ancient Egyptian pharaohs.

In addition, the researchers also found the earliest known case of an individual with the genetic disorder Down’s Syndrome at a separate tomb.

Older than both the pyramids and Stonehenge, the Newgrange tomb is an imposing, 200,000 tonne Neolithic monument built more than 5,000 years ago.

The large circular mound — which harbours an inner stone passageway and chambers — is renown for its annual ‘solar alignment’, in which the sunrise on the winter solstice illuminates its sacred inner chamber in a golden blast of light.

Little had been known, however, about the prehistoric society that assembled this monument and other — prompting archaeologists and geneticists to analyse the genomes of 44 neolithic individuals from sites across Ireland.

Among these was the inbred individual that had been found buried in the most ornate recess of the Newgrange tomb — and likely belonged to a dynastic elite.

‘I’d never seen anything like it. We all inherit two copies of the genome, one from our mother and one from our father,’ said paper author and geneticist Lara Cassidy of Trinity College Dublin.

‘Well, this individual’s copies were extremely similar, a tell-tale sign of close inbreeding.’

‘In fact, our analyses allowed us to confirm that his parents were first-degree relatives.’

Such relationships — which include a brother and sister having a baby together — are a near-universal taboo for both biological and cultural reasons, Dr Cassidy said.

However, she added, there is one known exception — first-degree incest sometimes is seen as acceptable among social elites, typically within a deified royal family.

By establishing themselves as being above this most cardinal of rules, this allows elite families to simultaneously maintain their separation from the general public while reinforcing the social hierarchy and their power.

In fact, dynastic incest often goes hand-in-hand with public ritual and extravagant monumental architecture — because they achieve the same ends, Dr Cassidy added.

‘Here the auspicious location of the male skeletal remains is matched by the unprecedented nature of his ancient genome,’ added paper author and population geneticist Dan Bradley, also of Trinity College Dublin.

‘The prestige of the burial makes this very likely a socially sanctioned union and speaks of a hierarchy so extreme that the only partners worthy of the elite were family members.’

The team’s genetic analysis also revealed a web of distant familial relations between the man from the Newgrange site and other passage tombs across Ireland — including the mega-cemeteries of Carrowmore and Carrowkeel, in County Sligo.

‘It seems what we have here is a powerful extended kin-group, who had access to elite burial sites in many regions of the island for at least half a millennium,’ Dr Cassidy explained.

In addition, the researchers found that the results of their genetic analysis resonated with both the Newgrange solar phenomenon and a piece of local mythology.

The tale — which was first written down in the 11th Century AD, some 4,000 years after Newgrange was erected — tells of King Bresal Bródíbad who commissioned ‘the men of Ireland from every quarter’ to build a tower to take him to heaven.

The king’s sister offered to halt the course of the sun in the sky, as to allow the construction to be completed within ‘a long day’ — but her magic was broken when Bresal slept with her, and the heaven-reaching tower left unfinished.

In fact, the name in Middle Irish for the nearby Dowth passage tomb — ‘Fertae Chuile’, which translates as ‘Hill of Sin’ — is derived from the folklore.

‘Given the world-famous solstice alignments of Brú na Bóinne [the Irish name for Newgrange], the magical solar manipulations in this myth already had scholars questioning how long an oral tradition could survive,’ said Ros Ó Maoldúin.

‘To now discover a potential prehistoric precedent for the incestuous aspect is extraordinary,’ the Trinity College archaeologist and paper author added.

The genome survey stretched over more than 2,000 years and unearthed other unexpected results.

Within the oldest known burial structure on the island, Poulnabrone portal tomb, the earliest yet diagnosed case of Down Syndrome was discovered in a male child who was buried there 5,500 years ago.

Isotope analyses of the child showed a dietary signature of breastfeeding. In combination, the research team said it provides an indication that visible difference was not a barrier to ‘prestige burial’ in the deep past.

The study also revealed that the monument builders were early farmers who migrated to Ireland and replaced the hunter-gatherers who preceded them.

But the researchers said that the replacement was not absolute as a single western Irish individual was found to have an Irish hunter-gatherer in his recent family tree, pointing toward a ‘swamping’ of the earlier population rather than an extermination.

Genomes from the rare remains of Irish hunter-gatherers themselves showed they were most closely related to hunter-gatherer populations from Britain – such as ‘Cheddar Man’ – and mainland Europe.

However, unlike British samples, the earliest Irish had the genetic imprint of a prolonged island isolation.

The research team said that fits with what was known about prehistoric sea levels after the Ice Age when Britain maintained a land bridge to the continent long after the retreat of the glaciers, while Ireland was separated by sea and its small early populations must have arrived in primitive boats. 

The full findings of the study were published in the journal Nature.