In 1938, a biological expedition under Richard Archbold arrived in western New Guinea to survey the area by air. On June 23, after hours of flying over near-impenetrable jungle, Archbold's plane passed over the Grand Valley of the Baliem River. The valley was occupied by 50,000 Papuans, until that point unknown to—and unknowing of—the outside world. After six weeks, patrols from the Archbold expedition finally met with the inhabitants. That was the last substantial first contact in history.

At the time of first contact, residents of the Grand Valley were living a Stone Age existence. Early estimates of infant mortality were as high as 20 or 30 percent. Despite those very high natural mortality rates, female infanticide and the killing of twins were common. More lives were claimed from warfare and cannibalism, with war casualties accounting for as much as 10 to 30 percent of all male deaths.