Genes reveal centuries of inbreeding, pathogens and isolation in a medieval community in northern Spain

In the necropolis of Las Gobas, in the northern Spanish town of Treviño, in Burgos province, 42 bodies were recovered that had been buried between the 7th and 11th centuries. The individual whose body was tagged as Number 29 had three children. One of them died as a newborn or was stillborn, another did not survive the age of four, and the third died young but had offspring, a child who died before his seventh birthday. The extent of this family drama is known thanks to the analysis of ancient DNA.

The study, published in the open-access scientific journal Science Advances, combines classical archaeology with genetics to uncover the secrets of a community that lived and died in isolation for five centuries. The sequencing of the genome of the buried bodies has revealed their high level of inbreeding, the pathogens they had, and even a case of smallpox that sheds light on the arrival of the disease to the Iberian Peninsula.

Las Gobas is a complex located in a gorge carved by the Laño River and which forms part of what some have called the Iberian Cappadocia. There is evidence that people have lived there since prehistoric times. But it was not until the 6th century when more than a dozen caves were excavated and repurposed. It must have been the refuge of a group of hermits who awarded the place a spiritual value. In the following century, two of these caves were converted into churches and a specific area was reserved for a cemetery.

From previous studies led by archaeologists such as the emeritus professor of the University of the Basque Country Agustín Azkárate, or Lourdes Herrasti from the Aranzadi Science Society, it is known that the beginnings of the community, formed by a population of Basque ancestors, must have been violent: two of its founders have sword wounds. “One of them has a perimortem injury, with a tangential cut in the brain,” Herrasti explains. “The other also has a sword wound in the head, but it healed, so he lived,” he adds. Now, a new investigation in the field of archaeogenetics has allowed researchers to learn that these two founders were cousins, to explore the family tree of individual number 29, and to certify that this group of people barely shared any genetic material with the groups that dominated the peninsula at that time.

The research, led by Ricardo Rodríguez Varela from the Centre for Palaeogenetics (CPG) at Stockholm University (Sweden), combines genetic, archaeological and historical data to reveal the high level of inbreeding in this northern community, which, as shown by its genes, remained relatively isolated despite the turbulence of those times. The first burials at the site date from a few decades before the Muslims arrived in the peninsula and the fall of the Visigoth kingdom. The Muslims managed to reach as far north as Pamplona, located just 100 km from Las Gobas, whose settlement was very close to the initial border between Christian and Muslim territory.

“Of the 41 individuals that they [the Azkárate team] excavated, we have obtained DNA from 39,” says Rodríguez Varela. From their analysis and genetic comparison with present and past populations, they were able to place the inhabitants of Las Gobas on a kind of genetic map of the peninsula. “We know that the Muslim border should not be too far away, so we wanted to see the impact of this Islamic conquest,” adds the researcher from Stockholm University. Much of the effort of conquering the new territory was was borne by Berber groups from northern Africa and only an elite were of Arab origin. “In the ancestry of these individuals, over time, we see an increase in the North African component, but the levels are much lower during these five centuries than in the medieval populations of the south [of the peninsula].”

This isolation from the rest of the world is confirmed by comparing the different genomes of those buried with each other. From previous archaeological studies, it was known that Las Gobas had two phases. In the first, until the 9th century, residents lived and were buried there. In the second period, the living abandoned the caves and went to the valley, leaving the caves only as a necropolis. “What we found is that in the first period there was a lot of endogamy, high consanguinity, with a lot of offspring between close relatives, such as first cousins. In the second period this also occurred, although to a lesser extent,” Rodríguez Varela points out.

Genetics has also made it possible to assess the presence of various diseases. Although pathologies of viral origin rarely leave their trace in the DNA of those who were affected, the same is not true for those of bacterial origin. Thus, they identified up to six conditions in the different remains. Almost all of them were zoonoses, originating from interaction with an animal, such as red fever, caused by the bacterium Erysipelothrix rhusiopathiae, or relapsing fever, caused by Borrelia recurrentis. “E. rhusiopathiae, a bacterium that causes a skin disease through contamination of open wounds, usually infects humans through contact with domestic animals, which suggests that animal husbandry was important for this community,” recalls CPG researcher and co-author of the study, Zoé Pochon, in a note.

Among those buried there is one person who had smallpox. The discovery is of great significance. It is the oldest case of smallpox detected by genetic analysis in southern Europe. Being one of the diseases that, until its eradication, caused the most deaths in the history of humankind, its entry into the Iberian Peninsula remains a subject of debate among scientists. This strain fits with those found in individuals of similar chronologies from Scandinavia, Germany and Russia, which suggests the pan-European presence of smallpox during the Middle Ages. Combined with the fact of the reduced North African genetic footprint, it would rule out the arrival of smallpox from the south through the Muslims, as some theories maintained.

For Professor Agustín Azkárate, Las Gobas is a special site: “The artificial caves of Las Gobas are located 20-30 km from the important Basque necropolises of Aldaieta and San Martín de Dulantzi. Despite the proximity, the cultural funerary habits are completely different.” While in the caves the deceased were buried, Azkárate points out that they did so “without any grave goods and the serious stab wounds to the skulls are striking (in two cases) that reveal undoubted confrontations, while the Aldaieta-type cemeteries present grave goods and the frequent presence of weapons inside the burials.”

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