The thick 7-meter-deep sediment forms the Tam Pa Ling Cave floor. (KRIA WESTAWAY FOR CHINA DAILY)

Deep in the lush green hills of northern Laos, a group of international scientists has been piecing together the evolution of man's migration from Africa to Southeast Asia and, eventually, Australia.

For decades now, scientists have been working in a limestone cave called Tam Pa Ling, which translates to "Cave of the Monkeys", brushing away sediment around fossil remains that over time have been adding pieces to solving the puzzle.

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The latest find by a team of Laotian, United States, French, and Australian scientists is a collection of fossil bones dating back 86,000 years.

These tiny fragments are the oldest example of our ancestors yet found in Southeast Asia.

In 2012, scientists uncovered parts of a skull dating back 46,000 years in the same cave.

A paper published on June 13 in the scientific journal Nature Communications said the "find demonstrated beyond doubt that modern humans spread from Africa through Arabia and to Asia much earlier than previously thought"

A paper published on June 13 in the scientific journal Nature Communications said the "find demonstrated beyond doubt that modern humans spread from Africa through Arabia and to Asia much earlier than previously thought".

"It also confirms that our ancestors didn't just follow coastlines and islands. They traveled through forested regions, most likely along river valleys, too. Some then moved on through Southeast Asia to become Australia's first people."

Fabrice Demeter, a paleoanthropologist at the University of Copenhagen who was one of the paper's lead authors, said in a media release that coincided with the release of the paper that "Tam Pa Ling plays a key role in the story of modern human migration through Asia, but its significance and value is only just being recognized".

Kira Westaway, a geochronologist with Australia's Macquarie University and one of the lead scientists involved in the project, said the significance of the fossil find at the Tam Pa Ling cave should not be underestimated.

"Human fossil evidence is very rare in Southeast Asia, so a site that contains seven individual skeletal parts over a 56,000-year period is incredible," she told China Daily.

"But another fascinating part of this research is the location of the cave — it's not a coastal location, it's not on an island, but right in the middle of mainland Southeast Asia at least 300 kilometers from the sea.

An extensive array of decorations can be seen on the cave roof and floor; scientists take sediment samples from the excavation pit in Tam Pa Ling cave. (VITO HERNADEZ FOR CHINA DAILY)

"It is also in an upland region and would have been heavily forested."

Westaway added: "We know that hominids (the group consisting of modern humans, extinct human species and all our immediate ancestors) tended to move along river valleys inland, but this location confirms our suspicions that early Homo sapiens had the capacity to adapt and disperse through upland forested regions much earlier than anticipated."

"Surviving in forested regions requires a very different skills set than coastal living and the fact that they had acquired these skills by such an early time is surprising and significant," she said.

Another geochronologist, Renaud Joannes-Boyau from Australia's Southern Cross University, has spent the best part of 10 years working with colleagues from around the world at the site.

"The cave is really quite beautiful," he told China Daily.

"It is painstaking work. When you look around the cave there are various levels where fossil fragments have been found over the years.

"You spend so much time brushing away sediment that has been laid down for thousands of years to eventually uncover a fragment of bone, but it is an incredible moment in time," he said.

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He believes Homo sapiens started leaving Africa as early as 200,000 years ago.

"The Tam Pa Ling fossils suggest an earlier presence of modern humans in Asia, but further research is needed to establish their specific relationship to the migration into Australia."

The presence of modern humans in Australia dating back 60,000 years is supported by various lines of archaeological evidence, including the discovery of stone tools and ancient human remains.

Johannes-Boyau said what has been found so far in the cave is another piece in the evolution of man in Southeast Asia.

Nothing has been found in the cave such as drawings of stone tools to suggest it was a settlement.

"If anything, it was probably a transit route," he said.

"The remains are significant in that little is known about our journey (out of Africa). Every time we find new fossils we basically rewrite what the human evolution journey has been," he said.

Macquarie University's Westaway said that when trying to reconstruct the migration of Homo sapiens, it always comes down to a question of timing.

"We know what happened; we just don't know exactly when it happened," she said.

The deepest excavation pit is found at the rear of the cave close to a wall. (KIRA WESTAWAY FOR CHINA DAILY)

"Sites like Tam Pa Ling help us to place Homo sapiens at a certain location at a certain time and this helps to reconstruct how and when they dispersed."

She said finding earlier-than-expected arrival sites in unanticipated locations helps to appreciate the ability of Homo sapiens to adapt to different conditions and to exploit varied and often extreme environments.

Finding evidence of Homo sapiens in Southeast Asia 86,000 years ago also poses a problem for scientists.

Westaway said it calls into question "the accepted timing for the exit out of Africa … at least according to genetic evidence".

"Human dispersal across the globe is not a simple linear path — we believe it's a more complex spread of different migrations; some very early and some much later," she said.

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The fossil finds in Laos suggest that the prevailing theory of modern humans moving out of Africa in a single wave about 50-60,000 years ago was incorrect.

"The 50-60,000 years migration across Southeast Asia that contributes to our current gene pool may not have been the first — there may well have been earlier migrations that were not successful and therefore did not contribute their genetics to our modern populations," Westaway said.

"Sites like Tam Pa Ling, Lida Ajer (Sumatra) and Madjedbebe (northern Australia) may well represent these early unsuccessful migrations, but this does not discredit the fact that they had arrived in this region by this time — a truly remarkable achievement."

Westaway added: "This really is the decisive paper for the Tam Pa Ling evidence. Finally, we have enough dating evidence to confidently say when Homo sapiens first arrived in this area, how long they were there and what route they may have taken."

Tam Pa Ling cave is very close to the recently discovered Cobra Cave, which was frequented by Denisovans approximately 70,000 years earlier.

Despite the previous lack of evidence for early arrival in mainland Southeast Asia, this area might have been a dispersal route among our ancestors, long before Homo sapiens.

"We have much to learn from the caves and forests of Southeast Asia," Westaway said.

Prime Sarmiento in Hong Kong contributed to this story.

Contact the writer at karlwilson@chinadailyapac.com