A Mixed Coastal–Terrestrial Model of Adaptation in ISEA Reflecting on the Two Southern Routes of Early Modern Human Migration

Abstract This study revisits models of early modern human–coastal adaptation in Island Southeast Asia, a region central to understanding two major dispersal events: the initial Out of Africa movement towards southern Asia and the subsequent colonisation of Sahul via Wallacea. We distinguish episodic or opportunistic pre-Last Glacial Maximum (LGM) sea crossings from sustained, year-round coastal subsistence, which appears to have intensified only after the LGM. Focusing on archaeological evidence from the Lesser Sunda Islands, we propose an alternative model that somewhat reconciles both the traditional view of systematic marine exploitation emerging in the Mid- to Late Holocene and the revisionist claims of intensive coastal use as early as 160,000 years ago. Instead, our findings suggest a more gradual trajectory of adaptation following the LGM, structured into four phases: early occupation (50–23 ka) characterised by a focus on terrestrial subsistence supplemented with aquatic resources; post-LGM adaptation (22–16 ka) marked by increasing coastal resource use; a peak maritime phase during rapid sea-level rise (15–8 ka); and Mid- to Late Holocene settlement (7 ka–present) when terrestrial and marine resources became more integrated. Isotopic data and faunal assemblages reflect flexible, context-dependent subsistence strategies across Wallacea. The northern corridor likely supported denser populations and functioned as a key migration hub, while the southern route became more viable post-LGM due to expanding intertidal zones. This model reframes coastal resources not as a singular driving force but as complementary elements in a dynamic, environmentally mediated adaptive process during early modern human migration through Southeast Asia.