Ancient artefacts unearthed in the highlands of Papua New Guinea provide some of the earliest evidence of human settlement of Sahul, the primordial landmass that once joined Papua New Guinea with Australia. Stone tools and plant remains indicate that, as early as 49,000 years ago, people lived 2,000 meters, or 1.2 miles, above sea level in Papua New Guinea's Ivane Valley, say archaeologist Glenn Summerhayes of the University of Otago in Dunedin, New Zealand, and his colleagues.
     By at least 50,000 years ago, modern humans occupied lowland rainforests and savannas of southeastern Asia's land mass known as Sunda. From there they crossed the open ocean to Sahul, presumably in seacraft of some kind. Rising sea levels separated Papua New Guinea from Australia roughly 10,000 years ago.
     Many researchers assume that modern humans spread from Africa to Sahul along the coast and preferred living at low altitudes. That idea gets drubbed by the new discoveries, Summerhayes says. Shortly after reaching Sahul's shores, settlers headed uphill to the Ivane Valley's thin air, cold temperatures and harsh habitat, the scientists conclude. "Early occupation of such adverse environments contributes to a model in which small numbers of foraging peoples moved around the Sahul landscape, colonizing new areas and then returning back to where they had been," Summerhayes says.
     Despite the challenges at high altitudes, prehistoric people had the mental savvy to survive, archaeologist Chris Gosden of the University of Oxford in England writes in a comment. Crucial survival skills in their intellectual arsenal included an ability to remember complex travel routes and to identify potentially edible and possibly lethal plants, Gosden says. Swift settlement of southern as well as northern Sahul occurred shortly after 50,000 years ago, proposes archaeologist Matthew Spriggs of Australian National University in Canberra. "Finding the first human sites is a bit of a needle-in-the-haystack problem," he says.
     Prior research on Papua New Guinea, conducted by Summerhayes and others, has located human occupations with radiocarbon dates as old as 41,000 years along the coast and at one Ivane Valley site. In 2007 and 2008, Summerhayes' team found seven more ancient camps in the highland valley. Each camp yielded various stone tools. Investigators found sharp implements indented in the middle, known as waisted axes, at four sites. Already known from later Stone Age sites on Papua New Guinea, waisted axes were used to clear trees and open patches of forest to sunlight so that edible and medicinal plants could grow faster, Summerhayes suggests. Sahul settlers made stone tools where they camped, he notes. Finds included large stones from which sharp flakes had been removed and shards of rock produced during toolmaking.
     Starch grains found on several stone tools came from yams, a food that must have been gathered in its natural range at lower altitudes, the researchers say. Charred nut shells from high-altitude Pandanus trees turned up at four sites. Ancient settlers ate these nuts and probably a pineapple-like fruit that grows on Pandanus trees, the scientists suspect. Excavations at Vilakuav also produced burned bone fragments from unidentified animals that had been hunted, in Summerhayes' view.
     Archaeologist Dr Andrew Fairbairn from the University of Queensland says this suggests early humans lived in small nomadic populations that moved up and down the mountains of Papua New Guinea in search of food. "They clearly were very mobile. We assume [they lived in] some form of egalitarian structure, but it's very difficult to say from the archaeological remains alone. It was a very cold period in history and these people were both resourceful and capable to be able to live at this altitude," he says.

Edited from ScienceNews (30 September 2010), Australian Geographic (1 October 2010)