The scene was a lagoon on the shore of Lake Turkana in Kenya. The time about 10,000 years ago. One group of hunter-gatherers attacked and slaughtered another, leaving the dead with crushed skulls, embedded arrow or spear points, and other devastating wounds. A woman was killed by a blow to the head and the position of her hands and feet suggest that she may have been tied up before she was killed. Violence has always been part of human behavior, but the origins of war are hotly debated. Some experts see it as deeply rooted in evolution, others emphasize the influence of complex and hierarchical human societies. No one is suggesting that this discovery will settle this argument, but it may be the first instance of a massacre in a foraging society.