The skull, though weathered from millennia of brutal heat and scouring sands, is unmistakably human. Unmistakable, too, are the signs of a violent death: massive fractures from the blunt force of a weapon wielded by another human. The shattered cranium is one of several from a site in Kenya known as Nataruk, where, long ago, a band of hunter-gatherers met its end. Described in Nature in 2016, the remains are believed to be among the earliest evidence of human warfare. Although the terrain is ari…