Wolfgang Kaehler, Corbis
Children attend an elementary school in Papua New Guinea.
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.