Murder scene might reveal why Neanderthals went extinct

49,000 years ago in a cave in northern Spain, twelve Neanderthals were murdered and eaten by another group of Neanderthals. This grisly scene may tell a larger story about the reasons why our humanoid cousins ultimately died out.

There are a bunch of competing theories as to why Neanderthals went extinct. One idea is that Neanderthals had less genetic diversity than our human ancestors, making them less able to survive deadly viruses. Another possibility is that Neanderthals lived in smaller, simpler social groups than humans did, which made establishing reliable trading networks far more difficult and leaving groups at greater risk of being suddenly wiped out in a catastrophe.

The so-called "tunnel of bones" in a cave in El Sidrón, Spain provides the best chance yet to test these ideas. The twelve Neanderthals in the caves include men, women, and children, and they were killed and cannibalized 49,000 years ago. Their murderers had split open their bones to get at the marrow inside. Modern researchers are again taking bits of the dead Neanderthals away, but this time it's mitochondrial DNA and Y chromosome fragments for scientific study.

The new data has revealed that the twelve Neanderthals in the cave were all very similar genetically, far less than what's now observed in modern humans. Three adult males, two teenage males, and a child all shared the same mitochondrial DNA, which can only be inherited from one's mother, which suggests they all shared a fairly recent common female ancestor, perhaps a grandmother. The three adult females in the cave all had different mtDNA, and a teenager, child, and infant shared another common type of mtDNA.

Researcher Carles Lalueza-Fox explains what we're looking at here:

"This looks like a family. It's similar to what you would find if you went to a wedding and sampled the people in the wedding party. If you sample 12 people in the street, you would never find so many people with the same mtDNA."

He believes the familial links on display here are evidence of patrilocality, in which the Neanderthals lived together in groups of close male relatives and females joined from other clans. That type of arrangement suggests some reasonably strong associations between neighboring groups, but the family's grisly end paints a very different picture. Lalueza-Fox argues both events are indicative of the Neanderthal social structure:

The world of the Neanderthal was a very small world. They were in these small family groups. When they met each other, things could go from exchanging females to killing each other-even eating each other."

We can't know exactly who killed these twelve Neanderthals, although whoever did it was obviously incredibly hungry. All the bones had been smashed open, with even the tiniest bones split open for whatever marrow could be found inside. Even the skulls were split apart in order to extract edible brain parts.

The conditions that drove the murderers to such lengths might say more about the weaknesses of Neanderthal society than the murders themselves. These were clearly the direst of circumstances, and apparently the murderous Neanderthals did not have access to any larger trade networks that might bring in fresh supplies.

With no other options - and the fact that they took everything suggests the killers waited until they were on the brink of starvation - the Neanderthals had no choice but to start eating each other. It's a grim picture, and it might help explain just why Neanderthals died out and our human ancestors survived.

[Proceedings of the National Academy of Sciences via ScienceNow]