Abstract On the basis of the constructs of evolutionary ecology, this article presents an explanation for political integration during the prehistoric-protohistoric period on Rotuma, Fiji. Archaeological, ethnohistorical, and environmental data are analyzed with a geographic information system (GIS) to define the natural and social constraints according to which specific behavioral strategies conferred benefits to the people who employed them. The analysis suggests that during the prehistoric-protohistoric period chiefs from the relatively less productive, eastern side of Rotuma dominated the political arena. The integration of the island into a single, loose polity provided the eastern chiefs with social and material benefits. Because of these benefits, the eastern chiefs sought to perpetuate the political structure. Individuals from other districts participated in the hegemonic political structure because they reaped long-term benefits, suffered minimal costs, and perceived relatively fewer advantages in obtaining pan-Rotuman positions. Given the specific environmental context of this relatively isolated island, the formation of an island-wide polity provided selective advantages to its members.