Coasting out of Africa: The potential of mangrove forests and marine habitats to facilitate human coastal expansion via the Southern Dispersal Route

Based primarily on genetic data, it has been proposed that Homo sapiens followed a coastal ‘Southern Dispersal Route’ from Africa to Island Southeast Asia and Australia between ∼100,000 and 50,000 years ago. Geographic Information System (GIS)-based modelling has suggested that humans followed coastlines and rivers through the region, with the large Indus and Ganges river deltas providing formidable barriers to human migration. Archaeological evidence for such a coastal dispersal is virtually absent in East Africa, the Arabian Peninsula, and south-central Asia, however, creating a lively debate about the potential of coastal versus interior dispersal routes. We analyze south Asian coastlines and consider the potential effects of post-glacial sea level rise on the preservation of Pleistocene coastal sites to identify areas where archaeologists might search for evidence of early human dispersals along Asia's south coast, including the Arabian Peninsula and the Indian subcontinent. We also explore the ecology of mangrove and other coastal ecosystems from East Africa to Australia, where the Indian Ocean gyre facilitates the broad dispersal of marine organisms, including biologically rich and diverse mangrove forests. The presence of similar ecosystems and species around much of the Indian Ocean margins may have facilitated the dispersal of coastal peoples. Rather than a barrier, large mangrove forests may have attracted coastal groups, whose foraging in such ecosystems could have spurred the development of the sophisticated watercraft needed to colonize the island arcs of Southeast Asia and western Melanesia.