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.
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All data are available for download at github.com/cjabradshaw/SahulHuman.
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Saltré, F. et al. Climate change not to blame for Late Quaternary megafauna extinctions in Australia. Nat. Comm. 7, 10511 (2016).
Johnson, C. N. et al. What caused extinction of the Pleistocene megafauna of Sahul? Proc. R. Soc. Lond. B 283, 20152399 (2016).
O’Connell, J. F. et al. When did Homo sapiens first reach Southeast Asia and Sahul? Proc. Natl Acad. Sci. USA 115, 8482–8490 (2018).
Birdsell, J. B. Some population problems involving Pleistocene man. Cold Spring Harb. Symp. Quant. Biol. 22, 47–69 (1957).
McArthur, N. Computer simulations of small populations. Aust. Archaeol. 4, 53–57 (1976).
Allen, J. & O’Connell, J. F. in Islands of Inquiry: Colonisation, Seafaring and the Archaeology of Maritime Landscapes, Terra Australis Vol. 29 (eds Clark, G., Leach, F. & O’Connor, S.) 31–46 (ANU E Press, 2008).
O’Connell, J. F. & Allen, J. The restaurant at the end of the universe: modelling the colonisation of Sahul. Aust. Archaeol. 74, 5–17 (2012).
Rasmussen, M. et al. An Aboriginal Australian genome reveals separate human dispersals into Asia. Science 334, 94–98 (2011).
Williams, A. N. A new population curve for prehistoric Australia. Proc. R. Soc. Lond. B. 280, 20130486 (2013).
Malaspinas, A.-S. et al. A genomic history of Aboriginal Australia. Nature 538, 207–214 (2016).
Clarkson, C. et al. Human occupation of northern Australia by 65,000 years ago. Nature 547, 306–310 (2017).
Clarkson, C. et al. Reply to comments on Clarkson et al. (2017) ‘Human occupation of northern Australia by 65,000 years ago’. Aust. Archaeol. 84, 84–89 (2018).
Roberts, R. G. et al. The human colonisation of Australia: optical dates of 53,000 and 60,000 years bracket human arrival at Deaf Adder Gorge, Northern Territory. Quat. Sci. Rev. 13, 575–583 (1994).
Turney, C. S. M. et al. Early human occupation at Devil’s Lair, southwestern Australia 50,000 years ago. Quat. Res. 55, 3–13 (2001).
Bowler, J. M. et al. New ages for human occupation and climatic change at Lake Mungo, Australia. Nature 421, 837–840 (2003).
Wood, R. et al. Towards an accurate and precise chronology for the colonization of Australia: the example of Riwi, Kimberley, Western Australia. PLoS ONE 11, e0160123 (2016).
Hamm, G. et al. Cultural innovation and megafauna interaction in the early settlement of arid Australia. Nature 539, 280–283 (2016).
Veth, P. et al. Early human occupation of a maritime desert, Barrow Island, north-west Australia. Quat. Sci. Rev. 168, 19–29 (2017).
Delannoy, J.-J. et al. in The Archaeology of Rock Art in Western Arnhem Land, Australia, Terra Australis Vol. 47 (eds David, B., Taçon, P. S. C., Delannoy, J.-J. & Geneste, J.-M.) 197–243 (ANU Press, 2017).
Maloney, T., O’Connor, S., Wood, R., Aplin, K. & Balme, J. Carpenters Gap 1: a 47,000 year old record of indigenous adaption and innovation. Quat. Sci. Rev. 191, 204–228 (2018).
McDonald, J. et al. Karnatukul (Serpent’s Glen): a new chronology for the oldest site in Australia’s Western Desert. PLoS ONE 13, e0202511 (2018).
Kealy, S., Louys, J. & O’Connor, S. Islands under the sea: a review of early modern human dispersal routes and migration hypotheses through Wallacea. J. Isl. Coast. Archaeol. 11, 364–384 (2016).
Kealy, S., Louys, J. & O’Connor, S. Reconstructing palaeogeography and inter-island visibility in the Wallacean Archipelago during the likely period of Sahul colonization, 65–45 000 years ago. Archaeol. Prospect. 24, 259–272 (2017).
Norman, K. et al. An early colonisation pathway into northwest Australia 70–60,000 years ago. Quat. Sci. Rev. 180, 229–239 (2018).
Bird, M. I. et al. Palaeogeography and voyage modeling indicates early human colonization of Australia was likely from Timor-Roti. Quat. Sci. Rev. 191, 431–439 (2018).
Kealy, S., Louys, J. & O’Connor, S. Least-cost pathway models indicate northern human dispersal from Sunda to Sahul. J. Hum. Evol. 125, 59–70 (2018).
Bird, M. I. et al. Early human settlement of Sahul was not an accident. Sci. Rep. https://doi.org/10.1038/s41598-019-42946-9 (2019).
Nagle, N. et al. Aboriginal Australian mitochondrial genome variation—an increased understanding of population antiquity and diversity. Sci. Rep. 7, 43041 (2017).
Tobler, R. et al. Aboriginal mitogenomes reveal 50,000 years of regionalism in Australia. Nature 544, 180–184 (2017).
Siler, W. A competing-risk model for animal mortality. Ecology 60, 750–757 (1979).
Gurven, M. & Kaplan, H. Longevity among hunter-gatherers: a cross-cultural examination. Pop. Dev. Rev. 33, 321–365 (2007).
Fenner, J. N. Cross-cultural estimation of the human generation interval for use in genetics-based population divergence studies. Am. J. Phys. Anthropol. 128, 415–423 (2005).
Gould, R. A. Puntutjarpa Rockshelter and the Australian Desert Culture Anthropological Papers of the American Museum of Natural History Vol. 54 (American Museum of Natural History, 1977).
Durkheim, É. The Division of Labour in Society (Macmillan, 1984).
Reed, D. H., O’Grady, J. J., Ballou, J. D. & Frankham, R. The frequency and severity of catastrophic die-offs in vertebrates. Anim. Conserv. 6, 109–114 (2003).
Tallavaara, M., Eronen, J. T. & Luoto, M. Productivity, biodiversity, and pathogens influence the global hunter-gatherer population density. Proc. Natl Acad. Sci. USA 115, 1232–1237 (2018).
Finlayson, C. et al. The Homo habitat niche: using the avian fossil record to depict ecological characteristics of Palaeolithic Eurasian hominins. Quat. Sci. Rev. 30, 1525–1532 (2011).
Whyte, A. L. H., Marshall, S. J. & Chambers, G. K. Human evolution in Polynesia. Hum. Biol. 77, 157–177 (2005).
Hey, J. On the number of New World founders: a population genetic portrait of the peopling of the Americas. PLoS Biol. 3, e193 (2005).
Zlojutro, M. et al. Coalescent simulations of Yakut mtDNA variation suggest small founding population. Am. J. Phys. Anthropol. 139, 474–482 (2009).
Frankham, R. Effective population size/adult population size ratios in wildlife: a review. Genet. Res. 66, 95–107 (1995).
Moore, J. H. Evaluating five models of human colonization. Am. Anthropol. 103, 395–408 (2001).
Walker, R. et al. Growth rates and life histories in twenty-two small-scale societies. Am. J. Hum. Biol. 18, 295–311 (2006).
Hawkes, K., Smith, K. R. & Robson, S. L. Mortality and fertility rates in humans and chimpanzees: how within-species variation complicates cross-species comparisons. Am. J. Hum. Biol. 21, 578–586 (2009).
Hawkes, K. & Coxworth, J. E. Grandmothers and the evolution of human longevity: a review of findings and future directions. Evol. Anthropol. 22, 294–302 (2013).
Blurton Jones, N. G., Hawkes, K. & O’Connell, J. F. Antiquity of postreproductive life: are there modern impacts on hunter-gatherer postreproductive life spans? Am. J. Hum. Biol. 14, 184–205 (2002).
Bradshaw, C. J. A. & Brook, B. W. Human population reduction is not a quick fix for environmental problems. Proc. Natl Acad. Sci. USA 111, 16610–16615 (2014).
Bentley, G. R. Hunter-gatherer energetics and fertility: a reassessment of the !Kung San. Hum. Ecol. 13, 79–109 (1985).
Caswell, H. Matrix Population Models: Construction, Analysis, and Interpretation 2nd edn (Sinauer Associates, 2001).
Goosse, H. et al. Description of the Earth system model of intermediate complexity LOVECLIM version 1.2. Geosci. Mod. Dev. 3, 603–633 (2010).
Claussen, M. et al. Earth system models of intermediate complexity: closing the gap in the spectrum of climate system models. Clim. Dynam. 18, 579–586 (2002).
Timmermann, A. & Friedrich, T. Late Pleistocene climate drivers of early human migration. Nature 538, 92–95 (2016).
Friedrich, T., Timmermann, A., Tigchelaar, M., Elison Timm, O. & Ganopolski, A. Nonlinear climate sensitivity and its implications for future greenhouse warming. Sci. Adv. 2, e1501923 (2016).
Tigchelaar, M., Timmermann, A., Pollard, D., Friedrich, T. & Heinemann, M. Local insolation changes enhance Antarctic interglacials: insights from an 800,000-year ice sheet simulation with transient climate forcing. Earth Planet. Sci. Lett. 495, 69–78 (2018).
Stockhecke, M. et al. Millennial to orbital-scale variations of drought intensity in the Eastern Mediterranean. Quat. Sci. Rev. 133, 77–95 (2016).
Lorenz, D. J., Nieto-Lugilde, D., Blois, J. L., Fitzpatrick, M. C. & Williams, J. W. Downscaled and debiased climate simulations for North America from 21,000 years ago to 2100 ad. Sci. Data 3, 160048 (2016).
Wilby, R. L. & Wigley, T. M. L. Downscaling general circulation model output: a review of methods and limitations. Prog. Phys. Geogr. Earth Environ. 21, 530–548 (1997).
Coe, M. J., Cumming, D. H. & Phillipson, J. Biomass and production of large African herbivores in relation to rainfall and primary production. Oecologia 22, 341–354 (1976).
Krausmann, F. et al. Long-term trajectories of the human appropriation of net primary production: lessons from six national case studies. Ecol. Econ. 77, 129–138 (2012).
Whittaker, R. H. & Likens, G. E. Primary production: the biosphere and man. Hum. Ecol. 1, 357–369 (1973).
Phillipson, J. Rainfall, primary production and ‘carrying capacity’ of Tsavo National Park (East), Kenya. Afr. J. Ecol. 13, 171–201 (1975).
Cao, M., Ma, S. & Han, C. Potential productivity and human carrying capacity of an agro-ecosystem: an analysis of food production potential of China. Agric. Syst. 47, 387–414 (1995).
Williams, M. et al. Glacial and deglacial climatic patterns in Australia and surrounding regions from 35 000 to 10 000 years ago reconstructed from terrestrial and near-shore proxy data. Quat. Sci. Rev. 28, 2398–2419 (2009).
Petherick, L. M., Moss, P. T. & McGowan, H. A. Climatic and environmental variability during the termination of the Last Glacial Stage in coastal eastern Australia: a review. Aust. J. Earth Sci. 58, 563–577 (2011).
Williams, A. N., Ulm, S., Cook, A. R., Langley, M. C. & Collard, M. Human refugia in Australia during the Last Glacial Maximum and terminal Pleistocene: a geospatial analysis of the 25–12 ka Australian archaeological record. J. Archaeol. Sci. 40, 4612–4625 (2013).
Williams, A. N. et al. A continental narrative: human settlement patterns and Australian climate change over the last 35,000 years. Quat. Sci. Rev. 123, 91–112 (2015).
Ellerton, D., Shulmeister, J., Woodward, C. & Moss, P. Last Glacial Maximum and Last Glacial–Interglacial Transition pollen record from northern NSW, Australia: evidence for a humid late Last Glacial Maximum and dry deglaciation in parts of eastern Australia. J. Quat. Sci. 32, 717–728 (2017).
Hesse, P. P. et al. Dramatic reduction in size of the lowland Macquarie River in response to Late Quaternary climate-driven hydrologic change. Quat. Res. 90, 360–379 (2018).
Shulmeister, J., Kemp, J., Fitzsimmons, K. E. & Gontz, A. Constant wind regimes during the Last Glacial Maximum and Early Holocene: evidence from Little Llangothlin Lagoon, New England Tablelands, eastern Australia. Clim. Past 12, 1435–1444 (2016).
Mueller, D. et al. Revisiting an arid LGM using fluvial archives: a luminescence chronology for palaeochannels of the Murrumbidgee River, south-eastern Australia. J. Quat. Sci. 33, 777–793 (2018).
Hope, G. et al. History of vegetation and habitat change in the Austral-Asian region. Quat. Int. 118-119, 103–126 (2004).
Johnson, B. J. et al. 65,000 years of vegetation change in central Australia and the Australian summer monsoon. Science 284, 1150–1152 (1999).
Fitzsimmons, K. E. et al. Late Quaternary palaeoenvironmental change in the Australian drylands. Quat. Sci. Rev. 74, 78–96 (2013).
Barrows, T. T., Stone, J. O. & Fifield, L. K. Exposure ages for Pleistocene periglacial deposits in Australia. Quat. Sci. Rev. 23, 697–708 (2004).
Barrows, T. T., Stone, J. O., Fifield, L. K. & Cresswell, R. G. The timing of the Last Glacial Maximum in Australia. Quat. Sci. Rev. 21, 159–173 (2002).
Barrows, T. T., Stone, J. O., Fifield, L. K. & Cresswell, R. G. Late Pleistocene glaciation of the Kosciuszko Massif, Snowy Mountains, Australia. Quat. Res 55, 179–189 (2001).
Reeves, J. M. et al. Climate variability over the last 35,000 years recorded in marine and terrestrial archives in the Australian region: an OZ-INTIMATE compilation. Quat. Sci. Rev. 74, 21–34 (2013).
Petherick, L. et al. Climatic records over the past 30 ka from temperate Australia—a synthesis from the Oz-INTIMATE workgroup. Quat. Sci. Rev. 74, 58–77 (2013).
Gautney, J. R. & Holliday, T. W. New estimations of habitable land area and human population size at the Last Glacial Maximum. J. Archaeol. Sci. 58, 103–112 (2015).
Smith, M. The Archaeology of Australia’s Deserts (Cambridge Univ. Press, 2013).
Attenbrow, V. & Hiscock, P. Dates and demography: are radiometric dates a robust proxy for long-term prehistoric demographic change?Archaeol. Oceania 50, 30–36 (2015).
Hiscock, P. & Attenbrow, V. Dates and demography? The need for caution in using radiometric dates as a robust proxy for prehistoric population change. Archaeol. Oceania 51, 218–219 (2016).
Smith, M. The use of summed-probability plots of radiocarbon data in archaeology. Archaeol. Oceania 51, 214–215 (2016).
Williams, A. N. & Ulm, S. Radiometric dates are a robust proxy for long-term demographic change: a comment on Attenbrow and Hiscock (2015). Archaeol. Oceania 51, 216–217 (2016).
Bradshaw, C. J. A. et al. More analytical bite in estimating targets for shark harvest. Mar. Ecol. Prog. Ser. 488, 221–232 (2013).
Frankham, R., Bradshaw, C. J. A. & Brook, B. W. Genetics in conservation management: revised recommendations for the 50/500 rules, Red List criteria and population viability analyses. Biol. Conserv. 170, 56–63 (2014).
Traill, L. W., Bradshaw, C. J. A. & Brook, B. W. Minimum viable population size: a meta-analysis of 30 years of published estimates. Biol. Conserv. 139, 159–166 (2007).
Traill, L. W., Brook, B. W., Frankham, R. & Bradshaw, C. J. A. Pragmatic population viability targets in a rapidly changing world. Biol. Conserv. 143, 28–34 (2010).
Harpending, H. C. et al. Genetic traces of ancient demography. Proc. Natl Acad. Sci. USA 95, 1961–1967 (1998).
Murray-McIntosh, R. P., Scrimshaw, B. J., Hatfield, P. J. & Penny, D. Testing migration patterns and estimating founding population size in Polynesia by using human mtDNA sequences. Proc. Natl Acad. Sci. USA 95, 9047–9052 (1998).
Tenesa, A. et al. Recent human effective population size estimated from linkage disequilibrium. Genome Res. 17, 520–526 (2007).
Liu, H., Prugnolle, F., Manica, A. & Balloux, F. A geographically explicit genetic model of worldwide human-settlement history. Am. J. Hum. Gen. 79, 230–237 (2006).
Zollner, P. A. & Lima, S. L. Search strategies for landscape-level interpatch movements. Ecology 80, 1019–1030 (1999).
Eller, E., Hawks, J. & Relethford, J. H. Local extinction and recolonization, species effective population size, and modern human origins. Hum. Biol. 81, 805–824 (2009).
Wainwright, H. M., Finsterle, S., Jung, Y., Zhou, Q. & Birkholzer, J. T. Making sense of global sensitivity analyses. Comput. Geosci. 65, 84–94 (2014).
Prowse, T. A. A. et al. An efficient protocol for the global sensitivity analysis of stochastic ecological models. Ecosphere 7, e01238 (2016).
Elith, J., Leathwick, J. R. & Hastie, T. A working guide to boosted regression trees. J. Anim. Ecol. 77, 802–813 (2008).
Hijmans, R. J., Phillips, S., Leathwick, J. & Elith, J. dismo: Species distribution modeling. R package version 1.1-4 https://cran.r-project.org/web/packages/dismo/index.html (2017).
This study was supported by the Australian Research Council through a Centre of Excellence grant (CE170100015) to R.G.R., S.U., M.I.B., Z.J., C.J.A.B. and L.S.W., fellowships to S.U. (FT120100656), M.I.B. (FL140100044), R.G.R. (FL130100116), Z.J. (FT150100138) and L.S.W. (FT180100407), and an Australian Government Research Training Program Award to K.N.
The authors declare no competing interests.
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