This paper investigates the evolution of Differential Object Marking (DOM) in Abui and Teiwa, two Papuan languages of the Alor-Pantar family in Eastern Indonesia. In both languages, reflexes of the same proto-morpheme are used in the differential marking of P (the non-agentive argument in transitive constructions), but the languages contrast in the way Ps are differentiated. We compare the synchronic DOM patterns of Abui and Teiwa with each other as well as with the DOM patterns we reconstruct for their shared ancestor. We establish how different patterns of DOM in this family have evolved over time, and which semantic and morphological changes occurred in the process.
