New research has revealed that the process of ‘peopling’ the entire continent of Sahul — the combined mega continent that joined Australia with New Guinea when sea levels were much lower than today — took 10,000 years.
Sophisticated models combined recent improvements in demography and models of wayfinding based on geographic inference to show the scale of the challenges faced by the ancestors of Indigenous people making their mass migration across the supercontinent more than 60,000 years ago.
The ancestors of Aboriginal people likely first entered the continent 75,000–50,000 years ago from what is today the island of Timor, followed by later migrations through the western regions of New Guinea.
According to the new research, this pattern led to a rapid expansion both southward toward the Great Australian Bight, and northward from the Kimberley region to settle all parts of New Guinea and, later, the southwest and southeast of Australia.
The research was led by the ARC Centre of Excellence for Australian Biodiversity and Heritage (CABAH) and saw international experts in Australia and the United States collaborate to investigate the most likely pathways and the timeframe needed to reach population sizes able to withstand the rigours of their new environment.
By combining two existing models predicting the routes they took – ‘superhighways’ – and the demographic structure of these first populations, the researchers were able to estimate the time for continental saturation more precisely. The new research has just been published in the international journal Quaternary Science Reviews.
Corey J.A. Bradshaw, Stefani A. Crabtree, Devin A. White, Sean Ulm, Michael I. Bird, Alan N. Williams, Frédérik Saltré. Directionally supervised cellular automaton for the initial peopling of Sahul. Quaternary Science Reviews, 2023; 303: 107971 DOI: 10.1016/j.quascirev.2023.107971
Reconstructing the patterns of Homo sapiens expansion out of Africa and across the globe has been advanced using demographic and travel-cost models. However, modelled routes are ipso facto influenced by migration rates, and vice versa. We combined movement ‘superhighways’ with a demographic cellular automaton to predict one of the world's earliest peopling events — Sahul between 75000 and 50000 years ago. Novel outcomes from the superhighways-weighted model include (i) an approximate doubling of the predicted time to continental saturation (∼10,000 years) compared to that based on the directionally unsupervised model (∼5000 years), suggesting that rates of migration need to account for topographical constraints in addition to rate of saturation; (ii) a previously undetected movement corridor south through the centre of Sahul early in the expansion wave based on the scenarios assuming two dominant entry points into Sahul; and (iii) a better fit to the spatially de-biased, Signor-Lipps-corrected layer of initial arrival inferred from dated archaeological material. Our combined model infrastructure provides a data-driven means to examine how people initially moved through, settled, and abandoned different regions of the globe.
