In 2012, archaeologists stumbled across something disturbing in Nataruk, near Lake Turkana in Kenya: the remains of at least 27 people, unburied and exposed to the elements. Twelve were relatively complete skeletons, whereas the others were a jumble of bones. Out of those best preserved, the archaeologists could tell 10 had died violent deaths—five from blunt-force trauma to the head (pictured), and five from sharper wounds to the head and neck, likely from arrows. The hand position of a couple of the bodies suggested they had been bound when they died. The archaeologists determined that they were likely looking at evidence of warfare, in which one group of people systematically killed members of another. A massacre like this one wouldn’t be that unusual, except for one thing: The Nataruk site is really old. Based on radiocarbon dates from shells near the skeletons as well as an examination of tools from Nataruk and nearby sites—including some obsidian blades still embedded in the skeletons—the massacre occurred about 10,000 years ago, the team reports online today in Nature. This is back when people around Nataruk were still living in hunter-gatherers bands, rather than in settled communities. The problem? Many anthropologists believe that prehistoric hunter-gatherers didn’t engage in the kind of systematic warfare on display at Nataruk, because they didn’t have land or stores of food to fight over. The team proposes two explanations: Either the Nataruk people lived a more settled lifestyle than scientists thought, or organized warfare arose much earlier. The only way to know for sure, the scientists say, is to find evidence of more prehistoric massacres.