Frontier Lapita interaction with resident Papuan populations set the stage for initial peopling of the Pacific.

The initial peopling of the remote Pacific islands was one of the greatest migrations in human history, beginning three millennia ago by Lapita cultural groups. The spread of Lapita out of an ancestral Asian homeland is a dominant narrative in the origins of Pacific peoples, and although Island New Guinea has long been recognized as a springboard for the peopling of Oceania, the role of Indigenous populations in this remarkable phase of exploration remains largely untested. Here, we report the earliest evidence for Lapita-introduced animals, turtle bone technology and repeated obsidian import in southern New Guinea 3,480-3,060 years ago, synchronous with the establishment of the earliest known Lapita settlements 700 km away. Our findings precede sustained Lapita migrations and pottery introductions by several centuries, occur alongside Indigenous technologies and suggest continued multicultural influences on population diversity despite language replacement. Our work shows that initial Lapita expansion throughout Island New Guinea was more expansive than previously considered, with Indigenous contact influencing migration pathways and island-hopping strategies that culminated in rapid and purposeful Pacific-wide settlement. Later Lapita dispersals through New Guinea were facilitated by earlier contact with Indigenous populations and profoundly influenced the region as a global centre of cultural and linguistic diversity.