Modeling water crossings leading to the arrival of early Homo in Sulawesi, Indonesia, via paleoclimate drift experiments

Abstract Lithic tools found at Talepu, Sulawesi, in Wallacea suggest that an unknown hominin occupied Sulawesi between ∼ 118–194 ka. The Philippines, Borneo, and Flores are identified as possible sources of the colonizing hominin. Climatic reconstructions indicate that the period between ∼ 118–194 ka was marked by large variation in sea level in Wallacea, with portions of the Sunda shelf exposed at low sea level but with coastlines and land extent comparable to that of the present day at high sea level stages. A series of simulated 30-day oceanic drift experiments are conducted to determine which of the three proposed regions would be the most likely origin for hominin dispersal to Sulawesi. Drifts are simulated for low and high sea level cases. Present day sea level, winds and currents from atmosphere and ocean reanalysis products are used as proxy of environmental conditions during high sea level states. Output from Last Glacial Maximum (∼21 ka) simulations generated by three paleoclimate models is used to reconstruct the environment during low sea level conditions. Simulated drifters are released from multiple locations within three possible source regions: Borneo, Mindanao (Philippines) and the Banda Arc (including Flores). Probabilities of success and trip durations of direct arrivals as well as island-hops to Sulawesi are calculated. Results indicate that crossings are facilitated by low sea level, but the possibility of crossings at high sea level cannot be discarded. All of the three analyzed departure areas could be considered feasible sources for arrivals at Sulawesi but, Borneo is by far the most likely source area and Mindanao departures more likely to arrive in Sulawesi than those from the Banda Arc. The shortest simulated period voyagers would have to survive at sea are 3–8 days, 14–19 days and 12–20 days for Borneo, Mindanao and Band Arc departures respectively. These results have implications for the trajectory of hominin evolution in the region, including inputs to modern human diversity.