Depending on your perspective, it was a war or just a violent encounter between two groups. Left in the shallow waters of a lagoon in Nataruk, Kenya, the victims' skeletons were preserved for 10,000 years in the positions they held in death. There were 21 adults and six children. Some still had stone weapons lodged in their bones. Their skulls were fractured by blunt force trauma. A pregnant woman appears to have been bound, her hands and feet tied together, and left to die. Another woman's knees were broken, one of her feet fractured, and her hands bound. Her skeleton was surrounded by fish, as if her attackers decided to cover her in garbage.

Due to a fluke of geology, the aftermath of this massacre was preserved in lagoon sediments until 2012, when several of the skeletons were exposed by winds on a long gravel bar running parallel to the dunes that now blanket the area. The victims were killed at the edge of Lake Turkana, whose shores have today shrunk by 30km. In the early Holocene, when these people were still alive, the region was full of hunter-fisher groups living on the bounty of the lake and its surrounding land.

Archaeologists have little evidence of war during this period in human history, when Homo sapiens was still largely a nomadic animal. Many would argue that war is an outgrowth of the settled life, when people began to stockpile foodstuffs in their homes, thus making themselves targets for groups who needed or wanted more. The famous historian Lewis Mumford once argued that cities were originally built as war machines. Conflicts that occurred before we raised city walls and armies, he believed, could not truly be called warfare. But the authors of a new paper in Nature call that assumption into question. They chronicle the violent deaths of these 27 people in ancient Kenya and ask whether it might not be one of the first records of human warfare in history.

We know that humans have engaged in interpersonal violence going back hundreds of thousands of years. But this scene in a vanished lagoon isn't just interpersonal, where one person kills another one in some kind of dispute. Too many people were killed, systematically and simultaneously. Depending on how you analyze these skeletons, there is even evidence for torture. They were obviously set upon by an organized group that aimed to kill as many people as possible. When two groups meet in conflict, no matter how small, it might indeed be a war.

The researchers suggest that it's possible this was a war over resources. There is some evidence that people were moving into settlements in the area. Fragments of clay pots in the region suggest that people may have been storing food and claiming land. "The massacre at Nataruk could be seen as resulting from a raid for resources—territory, women, children, food stored in pots," write the scientists. Or it might just be "a standard, antagonistic response to an encounter between two groups."

Either way, the find is unusual. There is only one other known example of this kind of massacre in early human history, from a graveyard in Jebel Sahaba, Sudan, where 23 of the people appear to have died violently over 12,000 years ago. But those victims were buried by their community in graves, suggesting that they lived in settlements that were raided. The victims at Nataruk in Kenya were not buried in graves. Instead, they were left in the open to decay. And just by chance, plus a layer of sediment, their bones survived to testify that war may have started much earlier than anyone knew.

Nature, DOI: 10.1038/nature16477

Listing image by Marta Mirazon Lahr