Our species passed through Laos in its expansion to Australia

June 13 () –

Fossils found in Tam Pà Ling, a cave in Laos, have revealed that between 86,000 and 68,000 years ago modern humans passed through it on their way through Asia to reach Australia.

In about seven meters of sediment from the cave, evidence of a human presence in this region dating back at least 56,000 years was found. When our first Homo sapiens ancestors arrived in Southeast Asia on their way from Africa to Australia, they left evidence of their presence in the form of human fossils that accumulated over thousands of years in the depths of a cave.

The latest evidence from the Tam Pà Ling cave in northern Laos, discovered by a team of Laotian, French, American and Australian researchers, proves beyond doubt that modern humans spread from Africa through Arabia and into Asia. much sooner than previously thought. These results are published in Nature Communications.

It also confirms that our ancestors did not just follow coasts and islands but traveled through forested regions, most likely through river valleys as well. Some moved through Southeast Asia to become the first settlers of Australia.

“Tam Pà Ling plays a key role in the migration story of modern humans through Asia, but its importance and value have just been recognized“, says Fabrice Demeter, associate paleoanthropologist at the University of Copenhagen and one of the lead authors of the paper.

Three Australian universities have contributed to the project: Macquarie University and Southern Cross University dated samples using multiple techniques and Flinders University demonstrated that the cave sediments they had been deposited in different layers over tens of thousands of years.

Since the first excavation and the discovery of a skull and jaw in 2009, the cave has been the subject of controversy. Evidence from our early voyages from Africa to Southeast Asia is often dominated by island locations such as Sumatra, the Philippines, and Borneo.

This was before Tam Pà Ling, a cave located more than 300 kilometers from the sea in northern Laos, began to reveal its secrets. The skull and mandible were identified as belonging to Homo sapiens that had migrated through the region, but the question is when they did and, as usual in questions of human dispersal, the debate boils down to chronology, although these tests were difficult to date.

Human fossils cannot be directly dated, as the site is a World Heritage Site and is protected by Laotian law. There are very few suitable animal bones or rock decorations to date, and it is too old for radiocarbon dating. For this reason, the dating by luminescence of the sediments constitutes the backbone of the chronology.

Luminescence dating relies on a light-sensitive signal that resets to zero when exposed to light, but accumulates over time when protected from light during burial. Initially, it was used to delineate the sediments that covered the fossils.

“Without luminescence dating, this vital evidence would lack chronology and the site would be missed on the accepted route of dispersal through the region,” explains Macquarie University geochronologist Kira Westaway. Luckily, the technique is versatile and can be adapted to different challenges.”

These techniques yielded a minimum age of 46,000 years, a chronology consistent with the predicted time for the arrival of Homo sapiens in Southeast Asia.

From 2010 to 2023, annual excavations (delayed by three years of closure) increasingly revealed evidence that Homo sapiens had passed through on their way to Australia. Seven pieces of human skeleton were found at intervals through 4.5 meters of sediment, which pushed the possible chronology much further back in time, in the scope of the first migrations of Homo sapiens to this region.

In this study, the team overcame these problems by creatively applying strategic dating techniques wherever possible, such as uranium series dating of a stalactite tip that had been buried in sediment, and using uranium series dating. uranium along with electron spin resonance dating techniques for two rare but complete bovid teeth unearthed to 6.5 meters.

“Direct dating of the fossil remains confirmed the sequence of ages obtained by luminescence, which allowed us to propose a complete and secure chronology of the presence of Homo sapiens in Tam Pà Ling“, says Renaud Joannes-Boyau, associate geochronologist at Southern Cross University.

The team supported the dating tests with detailed analysis of the sediments to assess the origin of the fossils using micromorphology, a technique that examines sediments under a microscope to establish the integrity of the layers. This key component of the new chronology helped establish that there was a constant accumulation of sedimentary layers over a long period.

“Far from reflecting rapid sediment dumping, the site represents a consistent, seasonally deposited pile of sediment,” explains Flinders University geoarchaeologist Mike Morley, who worked with PhD students Vito Hernandez and Meghan McAllister-Hayward.

The new chronology revealed that there had been a human presence in this area for more than 56,000 years. In addition, the age of the lowest fossil at seven meters — a leg bone fragment — provides a chronology for the arrival of modern humans in this region between 86,000 and 68,000 years ago. This delays the arrival in mainland Southeast Asia by about 40,000 years. Although, based on genetics, these early migrations did not contribute significantly to our current populations.

“This is really the clincher for the Tam Pà Ling evidence,” says Associate Professor Westaway. “We finally have enough dating evidence to say for sure when Homo sapiens first arrived in this area, how long they were there and what route they were able to follow”.

The Tam Pà Ling cave is very close to the recently discovered Cueva de la Cobra, frequented by Denisovans approximately 70,000 years earlier. Despite the lack of evidence for an early arrival in mainland Southeast Asia, this area could be a dispersal route previously used by our ancestors, long before Homo sapiens.