In the southern Melanesian islands of Vanuatu, as in New Caledonia, Fiji, and West Polynesia, the archaeological record indicates significant shifts in aspects such as patterns of settlement and mobility, landscape use, and pottery production, some 500 years (2500 BP) after initial colonization. The relatively uniform Lapita Cultural Complex, the first manifestation of human activity on these islands, was transformed in each archipelago into various distinctive cultural entities. Using dietary (δ13C and δ15N values measured in collagen) and mortuary data recorded in 43 Lapita and seven immediately Post-Lapita adult burials from the site of Teouma (Efate, Vanuatu), we demonstrate that these medium-term, transformative processes also affected the economic component of the social system as well as its symbolic and religious structures. Evolutionary change adapting to changing local conditions is envisioned as the likely dominant factor influencing this cultural trajectory, while environmental/climatic change, secondary migration, and internal social changes unrelated to adaptive processes could have interacted to produce the recorded patterns.