Pathways to the interior: Human settlement in the Simbai-Kaironk Valleys of the Madang Province, Papua New Guinea

New Guinea has yielded some of the earliest evidence for a human presence in Sahul (Pleistocene Australia-New Guinea), with the north coast being one of the likely colonisation routes from Southeast Asia. Of the known pre-Last Glacial Maximum (>= 30kya) archaeological sites from New Guinea, only a handful come from the Highlands. Navigable pathways linking the north coast to the central cordillera, specifically 'grassland corridors', may have facilitated settlement, yet little is known about human settlement of fringe montane valleys within these corridors. A survey and excavation program within the Simbai-Kaironk Valleys (2,000-1,600 m asl) on the northern montane fringe identified 51 sites across a 21 km corridor. Radiocarbon dating suggests a possible human presence from 31 ka, clear evidence for landscape use from 17 to 15 ka, and an increase in site density from the Mid-Holocene. Most sites were from open settings, with Holocene settlements positioned at elevations optimising access to montane forests, grasslands and lowland resources. We argue that the Simbai-Kaironk grassland corridor has facilitated access to the central Highland valleys since the Late Pleistocene. Shorter and more direct pathways, transecting the river valleys via prominent spurs rising above the lowlands - and their associated insect-borne diseases - are likely to have facilitated coastal-Highland movement throughout the Holocene.