The original seafarers

The settlement of Australia is the first unequivocal evidence of a major sea crossing and rates as one of the greatest achievements of early humans. However the motive and circumstances regarding the arrival of the first Australians is a matter for conjecture. It may have been a deliberate attempt to colonise new territory or an accident after being caught in monsoon winds.

The lack of preservation of any ancient boat means archaeologists will probably never know what kind of craft was used for the journey. None of the boats used by Aboriginal people in ancient times are suitable for major voyages. The most likely suggestion has been rafts made of bamboo, a material common in Asia.

The size of the first population of people needed to arrive, survive, and thrive in what is now Australia is revealed in two studies published today.

It took more than 1,000 people to form a viable population. But this was no accidental migration, as our work shows the first arrivals must have been planned.

Our data suggest the ancestors of the Aboriginal, Torres Strait Islander, and Melanesian peoples first made it to Australia as part of an organised, technologically advanced migration to start a new life.

Changing coastlines

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 referred to as Sahul.

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

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

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

We also know 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 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:

• where people most likely entered Sahul from the island chains we now call Indonesia and Timor-Leste

• how many people were needed to enter Sahul to survive the rigours of their new environment.

First landfall

Our two new studies – published in Scientific Reports and Nature Ecology and Evolution – addressed these questions.

To do this, we developed demographic models (mathematical simulations) to see which island-hopping route these ancient people most likely took.

It turns out the northern route connecting the current-day islands of Mangoli, Buru, and Seram into Bird’s Head (West Papua) would probably have been easier to navigate than the southern route from Alor and Timor to the now-drowned Sahul Shelf off the modern-day Kimberley.

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

Modelled routes for making landfall in Sahul. Sea levels are shown at -75 m and -85 m. Potential northern and southern routes indicated by blue lines. Red arrows indicate the directions of modelled crossings. Michael Bird

Next, we extended these demographic models to work out how many people would have had to arrive to survive in a new island continent, and to estimate the number of people the landscape could support.

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.

Our simulations indicate 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.