Two teams of Australian researchers working independently have found that there were likely more first arrivals to Australia and New Guinea than previously thought—and it was not by accident. The first team created a model showing that a large number of people must have made the trip to have survived the migration. They have published their results in the journal Nature Ecology and Evolution.
The second team found that multiple crossings must have taken place for the population to survive in their new home. They published their results in the journal Scientific Reports. Michael Westaway with the University of Queensland has published a News and Views piece outlining the work by the two teams in Nature Ecology and Evolution.
Corey J. A. Bradshaw et al. Minimum founding populations for the first peopling of Sahul, Nature Ecology & Evolution (2019).
The timing, context and nature of the first people to enter Sahul is still poorly understood owing to a fragmented archaeological record. However, quantifying the plausible demographic context of this founding population is essential to determine how and why the initial peopling of Sahul occurred. We developed a stochastic, age-structured model using demographic rates from hunter-gatherer societies, and relative carrying capacity hindcasted with LOVECLIM’s net primary productivity for northern Sahul. We projected these populations to determine the resilience and minimum sizes required to avoid extinction. A census founding population of between 1,300 and 1,550 individuals was necessary to maintain a quasi-extinction threshold of ≲0.1. This minimum founding population could have arrived at a single point in time, or through multiple voyages of ≥130 people over ~700–900 years. This result shows that substantial population amalgamation in Sunda and Wallacea in Marine Isotope Stages 3–4 provided the conditions for the successful, large-scale and probably planned peopling of Sahul.
Michael I. Bird et al. Early human settlement of Sahul was not an accident, Scientific Reports (2019).
The first peopling of Sahul (Australia, New Guinea and the Aru Islands joined at lower sea levels) by anatomically modern humans required multiple maritime crossings through Wallacea, with at least one approaching 100 km. Whether these crossings were accidental or intentional is unknown. Using coastal-viewshed analysis and ocean drift modelling combined with population projections, we show that the probability of randomly reaching Sahul by any route is <5% until ≥40 adults are ‘washed off’ an island at least once every 20 years. We then demonstrate that choosing a time of departure and making minimal headway (0.5 knots) toward a destination greatly increases the likelihood of arrival. While drift modelling demonstrates the existence of ‘bottleneck’ crossings on all routes, arrival via New Guinea is more likely than via northwestern Australia. We conclude that anatomically modern humans had the capacity to plan and make open-sea voyages lasting several days by at least 50,000 years ago.