An ongoing Austronesian expansion in Island Southeast Asia

The Austronesian expansion into Island Southeast Asia and the Pacific was the last and most far-reaching prehistoric human migration. Austronesian languages replaced indigenous languages over nearly half the globe, yet the absolute number of Austronesian colonists was small. Recently, geneticists have identified large geographic disparities in the relative proportions of Asian ancestry across different genetic systems (NRY, mitochondrial DNA, autosomes and X chromosomes) in Austronesian-speaking societies of Island Southeast Asia and the Pacific. Surprisingly, a substantial genetic discontinuity occurs in the middle of a continuous chain of islands that form the southern arc of the Indonesian archipelago, near the geographic center of the Austronesian world. In the absence of geographic barriers to migration, this genetic boundary and swathe of Austronesian language replacement must have emerged from social behavior. Drawing on decades of comparative ethnological research inspired by F.A.E. van Wouden’s structural model of Austronesian social organization, later codified by Claude Lévi-Strauss as “House societies” (“sociétés à maison”), we propose a two-stage ethnographic model in which the appearance of matrilocal “House societies” during the initial phase of the Austronesian expansion, and the subsequent disappearance of “House societies” in lowland rice-growing regions, accounts for the observed linguistic, genetic and cultural patterns.