FACT SHEETS

Retracing our ancient routes

17.07.19

The size of the first population of people needed to arrive, survive and thrive in what is now Australia has been revealed in two studies by CABAH researchers.

We know that people have been in Australia for a very long time — at least for the past 50,000 years, and probably substantially more than that.

We also know that people ultimately came to Australia through the islands to the northwest. Many Aboriginal communities across northern Australia have strong oral histories of ancestral beings arriving from the north.

But under what circumstances did the ancestors of Aboriginal, Torres Strait Islander, and Melanesian peoples first make it into Australia?

The continent of Australia that the first arrivals encountered wasn’t what we know as Australia today. Instead, New Guinea, mainland Australia, and Tasmania were joined and formed a mega-continent we know as Sahul.

 

Wave-cut island off of northwest coast of Seram near Waeyoho. Image credit: Bert Roberts
How did people arrive?
Via complex and planned maritime voyages through a northern route
How many were needed to survive?
At least 1,300 in a single event, or multiple waves of more than 130
Modern coastline over former mega-continent Sahul

This mega-continent existed from the time the first people arrived right up until about 8,000 to 10,000 years ago.

So when we talk about how and in what ways people first arrived in Australia, we really mean in Sahul.

But how can we possibly infer what happened when people first arrived tens of millennia ago?

It turns out there are several ways we can look indirectly at both where people likely entered Sahul from the island chains we now call Indonesia and Timor-Leste, and how many people were needed to enter Sahul to survive the rigours of their new environment.

Our studies — published in Scientific Reports and Nature Ecology and Evolution — show the most likely places where people would have made landfall in Sahul, and the numbers needed to create a viable population.

We developed what are known as demographic models (mathematical simulations) to see which island-hopping route these ancient people most likely took.

It turns out that the northern route connecting the current-day islands into West Papua would probably have been easier to navigate than the southern route from Timor to the now-drowned Sahul Shelf off the modern-day Kimberley coastline.

While the southern route is less likely, it would still have been possible.

Next, we extended these demographic models to work out how many people would have had to arrive to survive in a new island continent. It turns out it was probably a lot.

We applied a unique combination of:

  • fertility, longevity, and survival data from hunter-gatherer societies around the globe
  • “hindcasts” of past climatic conditions from general circulation models very much like what we use to forecast future climate changes
  • well-established principles of population ecology.

We used this combination of factors to estimate the number of people the landscape could support and to predict how many people first arrived in Sahul.

Next, we extended these demographic models to work out how many people would have had to arrive to survive in a new island continent. It turns out it was probably a lot.

We applied a unique combination of:

  • fertility, longevity, and survival data from hunter-gatherer societies around the globe
  • “hindcasts” of past climatic conditions from general circulation models very much like what we use to forecast future climate changes
  • well-established principles of population ecology.

We used this combination of factors to estimate the number of people the landscape could support and to predict how many people first arrived in Sahul.

Our simulations indicate that at least 1,300 people likely arrived in a single migration event to Sahul, regardless of the route taken. Any fewer than that, and they probably would not have survived, for the same reasons that it is unlikely that an endangered species can recover from only a few remaining individuals.

Alternatively, the probability of survival was also large if people arrived in smaller, successive waves, averaging at least 130 people every 70 or so years over the course of about 700 years.

A planned arrival

This suggests that the peopling of Sahul could not have been an accident or random event. It was very much a planned and well-organised maritime migration.

Our results are similar to findings from several studies that also suggest this number of people is required to populate a new environment successfully, especially as people spread out of Africa and arrived in new regions around the world.

The overall implications of these results are fascinating. They verify that the first ancestors of Aboriginal, Torres Strait Islander, and Melanesian people to arrive in Sahul possessed sophisticated technological knowledge to build watercraft, and they were able to plan, navigate, and make complicated, open-ocean voyages to transport large numbers of people toward targeted destinations.

Our results also suggest that they did so by making many directed voyages, potentially over centuries, providing the beginnings of the complex, interconnected Indigenous societies that we see across the continent today.

These findings are a testament to the remarkable sophistication and adaptation of the first maritime arrivals in Sahul tens of thousands of years ago.

This article was originally published on The Conversation by Corey Bradshaw, Laura Weyrich, Michael Bird and Sean Ulm.

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