Twenty-five kilometers north of Dublin, a masterpiece of Stone Age engineering rises from the hills: a circular structure 12 meters high, almost the area of a U.S. football field, and made up of more than 200,000 tons of earth and stone. Some of the first farmers to arrive in Ireland erected this monument, called Newgrange, nearly 1000 years before Stonehenge or Egypt’s first pyramids were built. Archaeologists have assumed it was a ceremonial site and communal tomb—an expression of an egalitarian society.
Now, DNA from a middle-aged man buried in 3200 B.C.E. at the center of this mighty mound suggests otherwise. His genes indicate he had parents so closely related they must have been brother and sister or parent and child.
Across cultures, incest is almost always taboo—except in inbred royal families. Its genetic traces at Newgrange suggest social hierarchy took hold in Ireland earlier than thought, according to a new study. “Maybe we’ve been arguing too far that [these people were] egalitarian,” says Jessica Smyth, an archaeologist at University College Dublin who was not part of the team.
The newly sequenced genomes from Newgrange and other Irish tombs are part of a wider re-evaluation of the Neolithic era, which is marked by the advent of agriculture. Over the past decade, researchers have used ancient DNA to track a slow-motion, 5000-year expansion of ancient farmers from Anatolia across Europe. The Neolithic settlers who arrived in Ireland around 3700 B.C.E. were the westernmost limit of that expansion.
Most Irish Neolithic settlements are small scale, with houses of roughly equal size. As seen in Neolithic graves across Europe, their burials show little sign of hierarchy. Even in major monuments like Newgrange, human remains were jumbled together, as if in a communal tomb. “Archaeologists [have] argued for a long time for a more egalitarian Neolithic,” says co-author Thomas Kador, an archaeologist at University College London.
Newgrange is pierced by a passage that leads to a central chamber; its entrance is oriented so a ray of sunlight illuminates the chamber at dawn on the shortest day of the year. “It’s clearly a place of public ritual and must have taken a lot of manpower to construct,” says geneticist Lara Cassidy of Trinity College Dublin. Hundreds of such passage tomb monuments are found across Ireland.
Most of the bodies in those tombs were cremated. But at the heart of Newgrange, excavators in the 1970s found the unburnt bones of one man, labeled NG10, in a niche decorated with elaborately carved stones. Cassidy and her team were able to extract DNA from NG10’s petrous bone, a dense part of the inner ear.
Comparing NG10’s DNA and that of other Neolithic burials with DNA from people living on the island centuries earlier shows Neolithic farmers arrived in Ireland as part of a mass migration, and soon swamped or eliminated the genetic legacy of earlier hunter-gatherers, says geneticist Daniel Bradley, a co-author also at Trinity College Dublin.
NG10’s DNA also reveals his unusual parentage. In a paper published today in Nature, Cassidy’s team draws on parallels in the historical record to argue that the son of an incestuous union buried in such a prominent tomb points to a hereditary ruling class. “Matings like that are taboo pretty much universally, with very few exceptions,” he says.
Those exceptions include Egyptian pharaohs, who were considered deities who needed to marry each other. Royal siblings in Hawaii and the Incan empire were also known to marry, concentrating power in one family. “I believe we’re seeing a similar social dynamic at play among colonists of Neolithic Ireland,” Cassidy says.
Additional DNA from more than 40 people buried at other Neolithic sites, including three passage tombs, supports the existence of a close-knit elite. People buried in passage tomb sites were more closely related to each other than to people buried in other types of tombs, even though the passage tombs were separated by hundreds of kilometers and spanned more than 500 years. Some individuals in the far-flung passage tombs could have been second or third cousins or great-great-great-great-grandparent and child.
Chemical isotopes in their bones show the people in the passage tomb burials ate more meat and animal products than their contemporaries. The burials also include women and children, suggesting social status was inherited rather than won in a single lifetime, for example in battle. “We’re not talking about strong men, we’re talking about something that could be inherited and maintained over several generations,” Kador says. “A small [related] elite called the shots, like in Egypt.”
But other archaeologists are cautious. “To go from [NG10] to saying these are proto-state societies where you have a godlike elite is pushing it a bit far,” says University of Manchester archaeologist Julian Thomas. “It’s one guy.” He notes Newgrange was a burial place for almost 1000 years, too long to make generalizations from a single burial.
Monuments like Newgrange may have been used communally at certain times and co-opted as personal tombs for brief periods, says Alasdair Whittle, an archaeologist at Cardiff University. “It’s a really stunning discovery,” he says of NG10 parentage. But “social difference in the Neolithic, when it occurs, was often relatively short lived.”
He suggests that in the years before NG10 was born, an elite may have emerged temporarily in response to crisis. A climate downturn in the middle of the fourth millennium B.C.E., around the time the passage tombs reach their peak, could have led to famine, prompting dramatic but temporary change in the way society was organized.
One way to settle the debate is to look at similar passage tombs built on the Orkney Islands and in Wales and France. “The question is whether this arose in Ireland or whether they were importing existing social structures into the island,” Cassidy says. “It’s going to be very exciting to see if this is a pattern we see in other areas.”