Genome Analysis Points to Incest Among Ireland’s Prehistoric Rulers

Genome Analysis Points to Incest Among Ireland’s Prehistoric Rulers
Newgrange passage tomb in Ireland. (Image: L. M. Cassidy et al., 2020)

Evidence of incest and inbreeding has been uncovered at an elite prehistoric Irish burial site, in a new paper that reads like a Game of Thrones subplot.

New research published in Nature investigates the genetic profiles of 42 people from Ireland’s Neolithic period, along with two individuals from the preceding Mesolithic period. Dating back to between 5,500 and 4,000 years ago, this was a pivotal stage in the region’s history, as farming lifestyles gradually supplanted hunting, foraging, and fishing.

An adult male, buried at Newgrange passage tomb, had DNA consistent with first-degree incest, meaning his parents were siblings or possibly parent and child. The authors of the new study, led by Daniel Bradley from Trinity College Dublin, say this individual was likely a member of the ruling social elite, who used incest as a political tool.

“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 Lara Cassidy, also from Trinity and the first author of the paper, in a press release. “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.”

An interior portion of Newgrange passage tomb. (Image: L. M. Cassidy et al., 2020)An interior portion of Newgrange passage tomb. (Image: L. M. Cassidy et al., 2020)

Newgrange passage tomb is a 181,437 T Neolithic monument built roughly 5,000 years ago. It appeared some 500 years before Stonehenge and the Pyramids of Giza. Like other passage tombs, it featured a large chamber, a capped mound, and a long passageway into the structure’s interior, which hosts a crypt. Newgrange passage tomb — a United Nations World Heritage site — is famous for its annual solar alignment, in which the winter solstice sunrise lights up its interior chamber. Two similar tombs are found nearby in the Brú na Bóinne cemetery complex of Ireland’s Meath county.

Today, reproduction between closely related individuals — especially brothers and sisters — is a widespread taboo. Social mores during the Neolithic weren’t so terribly different, except among the ruling elites, who partook in these familial unions to distinguish themselves from the general population, to bolster their position atop the social hierarchy, and to maintain their regal authority. Similar arrangements were seen later among the Inca god-kings and Egyptian pharaohs, many of whom were inbred. Incest, when combined with the monumental tombs like Newgrange passage, drove home a powerful message about a royal family’s enduring political legitimacy.

Winter solstice sunlight shining into the sacred chamber of Newgrange passage tomb. (Image: L. M. Cassidy et al., 2020)Winter solstice sunlight shining into the sacred chamber of Newgrange passage tomb. (Image: L. M. Cassidy et al., 2020)

“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,” explained Bradley.

Fascinatingly, the new research also speaks to the power of oral tradition. A neighbouring tomb, now called Dowth passage tomb, was known as Fertae Chuile in the Middle Irish language (circa 900 to 1200 CE), which translates to “Hill of Sin” or possibly even “Hill of Incest,” according to the new paper. There’s also an 11th-century story from the region, in which a “builder-king restarts the daily solar cycle by copulating with his sister,” the authors write.

Genomes for the study were collected at other Irish sites, including Poulnabrone portal tomb, the oldest known burial structure in Ireland. Here, the researchers uncovered extraordinary genetic evidence from the remains of a male infant: trisomy of chromosome 21, otherwise known as Down syndrome. This finding, to the best of the authors’ knowledge, now “constitutes the earliest definitive discovery of a case of Down syndrome,” according to the study, in a find that predates previous evidence from the 5th to 6th centuries CE. Isotopic analysis suggests the infant was cared for, as evidenced by a signature consistent with breastfeeding. Interestingly, the infant’s genetic condition did not preclude a burial in a tomb reserved for elites.

DNA evidence from other individuals found at nearby tombs pointed to an extended kin group that stretched across some 500 years.

The new paper also shows how farming populations from mainland Europe gradually supplanted the indigenous hunter-gathers. Writing in an accompanying News and Views article, Alison Sheridan, a research associate at National Museums Scotland who wasn’t involved with the new research, said the appearance of novel genomic sequences “indicates the arrival in Ireland of people from elsewhere, from at least as early as 3800 [BCE], and is consistent with the idea that farming was brought to Ireland by immigrants. These people were genetically affiliated to the Neolithic population in Britain, and their roots lie in continental Europe.”

That said, the indigenous population was not wiped out but instead gradually absorbed into the incoming farming population, according to the new genetic evidence.

Sheridan said the new paper was “fascinating and invaluable,” but she believes the authors overreached by suggesting Ireland’s farmers sailed up from Iberia (Portugal and Spain), given resemblances in the DNA of both ancient groups. As she writes, however, there’s no archaeological evidence for this claim. Rather, “the archaeology points towards the Morbihan area of Brittany in northwest France, and the Nord-Pas de Calais region of northern France, as the ultimate areas of origin for Ireland’s immigrant farmers — with those from northern France probably arriving in Ireland via northern Britain.” Sheridan pointed to recent evidence in support of this scenario.

These issues aside, the new paper is providing a wealth of new data, casting new light on Ireland’s Neolithic period and the power structures at play during the dawn of the agricultural era.