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Fossils reveal early modern humans in southeast Asia 77,000 years ago
Our ancient relatives may have reached southeast Asia over 10,000 years earlier than thought.
While it’s not yet known what happened to these early humans, their presence adds to an increasingly complex picture of early migration.
New ancient human fossils are shedding light on the first modern humans in southeast Asia.
While it’s generally agreed that Homo sapiens evolved in Africa, the timing of its migration across the world is open for debate. Fossils seem to show our species having left Africa over 100,000 years ago, while genetic evidence points to a migration around 40,000 years later.
Newly described fossils from Tam Pà Ling cave in Laos have now added more pieces to the puzzle. A fragment of a human leg bone was found in sediments believed to be as much as 86,000 years old. In combination with other fossils from the cave, it suggests Homo sapiens lived there for as long as 56,000 years.
Professor Fabrice Demeter, one of the co-authors of the study, says that research at the cave has only just scratched the surface so far. ‘Tam Pà Ling plays a key role in the story of modern human migration through Asia but its significance and value is only just being recognised,’ Fabrice adds.
The findings of the study were published in the journal Nature Communications.
The cave was discovered in 2009, with excavations over the past decade revealing animal and human fossils. Image © Vito Hernandez (Flinders University).
Early human migrations
While it’s tempting to think of human evolution as a straight line from our origins to now, it’s not that simple. After evolving over 300,000 years ago, some pioneering Homo sapiens made early migrations out of the continent, while others stayed behind.
Traces of these early migrations can be found across the world. Skull bones unearthed in Greece and Israel date to over 150,000 years old, while teeth found in China and the island of Sumatra are more than 70,000 years old.
This is much earlier than evidence from the genetics of humans alive today suggests.
Professor Chris Stringer, Research Leader in human evolution at the Museum, says, ‘Geneticists have reconstructed that there was one main dispersal of Homo sapiens from Africa, and that was about 60,000 years ago.’
‘This dispersal gave rise to current human populations outside of the ancestral homeland of Africa, and was the wave of Homo sapiens that successfully interbred with our ancient relatives like the Neanderthals and Denisovans.’
Trying to fit these two timelines together has proven challenging, with many different theories on how they can be explained. This has been complicated by the poor preservation of fossils in the humid regions of southeast Asia, which might have helped to resolve the mystery.
The discovery of Tam Pà Ling cave in Laos in 2009 offered a new source of evidence. A partial skull and jawbone dating to between 46-63,000 years old were identified as belonging to Homo sapiens.
However, questions over the site remained. It wasn’t known if the sediments containing the bones had been washed into the site, or whether they represented a gradual build up over time.
Following over a decade of research at the cave, the scientists behind the study are confident that Tam Pà Ling offers a window into tens of thousands of years of early human history.
PhD student and co-author Vito Hernandez says, ‘The results of our microarchaeological analyses have given us a better appreciation of the ground conditions in Tam Pà Ling in the past, allowing for a more precise interpretations of how and when these early modern human fossils were buried in this part of the cave.’
The environment of Tam Pà Ling cave protects fossils from the humidity of the surrounding rainforest, allowing them to survive for thousands of years. Image © Kira Westaway (Macquarie University).
What happened at Tam Pà Ling?
Studies of the sediment revealed that it had naturally built up over time, with heavy rains in the monsoon season washing it into the cave over thousands of years. There was little evidence that it had been disturbed after being put down, suggesting that it could be reliably dated.
To do this, the team used a mixture of techniques, including luminescence dating and U-series dating. The former allows scientists to work out when an object was last exposed to light, and therefore when it was buried.
U-series dating, meanwhile, looks at the decay of Uranium over time to give an estimate of age.
Together, these have allowed the team to create a timeline of the site. The earliest human fossil found at the site is a newly discovered leg bone around 77,000 years old, but could be even older. Meanwhile, the youngest fossil is at least 30,000 years old, suggesting that the cave was an important region for many generations of Homo sapiens.
While attempts to extract DNA from the fossils failed, their presence alone shows that humans were living around Tam Pà Ling for 10,000 years longer than previously thought. The task for scientists now is to explain what happened to these early pioneers.
‘If the growing picture of a pre-60,000-year-old dispersal to east Asia is confirmed, then this implies that the DNA of these earlier populations has not come through to the present day at detectable levels,’ Chris says. ‘This means that these older populations either died out, or they were replaced or swamped by a more substantial later spread of Homo sapiens into the region.’
Whatever happened to the first Homo sapiens at Tam Pà Ling, humans would continue to visit the region for thousands of years. The researchers suggest the cave might have been used by people gradually migrating across Asia and down towards Australia.
Along the way, it’s possible that Homo sapiens would have encountered its relatives which lived in the area, such as Homo floresiensis and Homo luzonensis. Finding more fossils in southeast Asia could help to reveal what relationship they might have had, as well as larger questions in human evolution, such as why we are now the only human species left on Earth.
