In the mountains of Asturias, northern Spain, El Sidron cave has kept an extraordinary secret for nearly 50,000 years: the remains of thirteen NeanderthalsNeanderthalsA fossil humanity of Eurasia, robust and cold-adapted, extinct around 40,000 years before present.→, members of the same family group, massacred and consumed by their contemporaries. It is one of the best-documented Neanderthal assemblages in the world - and one of the most troubling. Since 1994, meticulous excavations have recovered more than 2,500 bone fragments, whose DNADNAThe molecule carrying genetic information, used to reconstruct kinship between species.→ analyses have revealed a social organisation of unprecedented precision.

Entrance to El Sidron cave in Asturias, Spain
El Sidron cave, in Asturias (Spain), has yielded since 1994 the remains of 13 Neanderthals dating to around 49,000 years ago. Analysis of their mitochondrial and nuclear DNA has enabled the reconstruction of the group's family structure and the discovery of evidence for ritual cannibalism.

The remains derive from a single episode: the bodies of seven adults (four males, three females) and six children and adolescents were thrown into the cave at the same time, approximately 49,000 years ago[1]. The bones bear unambiguous traces of systematic butchery - the same marks Neanderthals left on hunted animal bones. Skulls opened by percussion, long bones broken for marrow extraction: the cannibalism at El Sidron was not accidental. Was it for food, ritual purpose, or both? The debate remains open.

A family structure decoded by DNA

In 2010, a study published in PNAS delivered the conclusions of the genetic analysis[2]. Mitochondrial DNA - transmitted only through the mother - shows that the thirteen individuals belonged to three distinct maternal lineages. Cross-referencing with nuclear DNA (transmitted by both parents), researchers reconstructed the kinship links: the males were closely related to each other (brothers, uncles, nephews), while the females came from different lineages, with no evident relationship among themselves.

This pattern corresponds exactly to what is known as patrilocal exogamy: men remain in their birth group while women join from outside - from other groups, other territories. This social organisation, found among many contemporary hunter-gatherer societies and among our closest primate relatives (chimpanzees, gorillas), was therefore already present in Neanderthals 50,000 years ago. It is a unique window into the social structure of our vanished cousins.

Right-handed Neanderthals and caregivers

The analyses did not stop there. Study of the teeth and bones at El Sidron revealed further information. The characteristic dental wear of one adult male individual suggests he was right-handed - a trace left by the habit of gripping hide or fibre with the teeth while working it with the right hand, a gesture still seen among some traditional craftspeople. The presence of birch-bark resin and dental calculus containing medicinal plant remains (chamomile, yarrow) indicates that these Neanderthals self-medicated or tended the sick with plants[3].

One individual bore the marks of a rare genetic disorder - cleidocranial dysostosis - affecting bone development. This malformation, visible on the skull and clavicles, would not have prevented the individual from living, but would have required care or special attention from the group. That a Neanderthal affected by such a condition survived to adulthood in the harsh environment of the Upper PalaeolithicUpper PalaeolithicThe final phase of the Palaeolithic (c. 45,000 to 10,000 years ago), marked by Homo sapiens in Europe, art, ornaments and a succession of cultures (Aurignacian, Gravettian, Solutrean, Magdalenian).→ testifies to genuine social solidarity.

El Sidron and the portrait of Neanderthal

El Sidron has become one of the reference sites for understanding Neanderthal not as a crude and solitary creature, but as a member of an organised society with kinship rules, medical practices, and perhaps complex funerary rituals. Even the cannibalism does not contradict this image: many historical human societies practised ritual cannibalism, sometimes precisely to honour the dead or absorb their strength. The family of El Sidron - these men, women and children, killed and consumed in an Asturian cave - has become one of our clearest windows onto what it meant to be a Neanderthal.