Australia was first settled by between 1,000 and 3,000 humans around 50,000 years ago, but the population crashed during the Ice Age before recovering to a peak of some 1.2 million people around five centuries ago, a study said on Wednesday.
Estimating the early population of Australia is a source of debate in anthropology, partly because it touches on how European colonisation affected the country's indigenous people.
In an paper published by Britain's Royal Society, Alan Williams of the Australian National University in Canberra took a fresh look at investigations into ancient settlements where charcoal and other sources have been carbon-dated.
Using this data as a telltale of population change, Williams believes the first inhabitants of Australia arrived around 50,000 years ago and comprised a "founding group" of between 1,000 and 3,000 people.
This number is somewhat higher than previous estimates and suggests the first settlements were a result of deliberate migration rather than straggling, he says.
The newcomers crossed via a land bridge from Papua New Guinea, across a continental shelf that is now flooded, according to a common theory.
The numbers grew but then fell by as much as 60 percent between 21,000-18,000 years ago during the peak of the last Ice Age, when Australia became cooler and far drier than it is today, Williams believes.
At the end of the Ice Age, the population grew in fits and starts, reaching a peak of around 1.2 million 500 years ago.
It then went into slow decline to reach between 770,000 and 1.1 million by 1788, the start of British colonisation.
Europeans brought with them smallpox, measles, flu and other diseases that proved catastrophic for an indigenous population without immunity.
Information about the demographic impact of colonisation is sketchy, but anthropologists say a starting point is to have a reliable figure of the population before European contact.
Past attempts to chart Australia's population size before contact have given hugely varying figures. They include a founding population of fewer than 150 people, and by 1788 as few as 250,000 and as many as 1.2 million.
The study appears in Proceedings of the Royal Society B.