Early humans migrated across Asia earlier than thought, study finds

(CN) — Early humans didn’t just hug the coastline of the Indian Ocean as they spread out from Africa and migrated on their way to Asia and Australia. According to new research, they also used inland routes – traveling through forested regions, possibly following the flows of rivers – and they made that journey earlier than previously thought.  

In a study published in Nature Communications on Tuesday, researchers describe a series of excavations from 2010 to 2023 that revealed both human fossils and pieces of cattle teeth deep within sentiment laid down in layers over tens of thousands of years in a cave called Tam Pà Ling, more than 180 miles from the coast in the southeast Asian country of Laos. 

Through a broad range of scientific dating methods, the researchers determined that humans were in the area for more than 56,000 years, and they arrived sometime between 86,000 to 68,000 years ago, pushing back our understanding of human migration to the area by 40,000 years.  

“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,” study co-author Kira Westaway, a professor at Macquarie University in Sydney, Australia, said in a press release.

Westaway was a part of the team of American, Australian, French and Laotian researchers who discovered the cave, and an early human skull and mandible fossil inside, back in 2009.   

Because the cave and the fossils in it are protected as a UNESCO World Heritage site and by Laotian law, the fossils themselves couldn’t be directly dated. Without remains of any tools or cave art in the area, radiocarbon dating couldn’t be done either.

Instead, researchers used a variety of different techniques, like luminescence dating, which establishes the time at which pieces of sediment were last exposed to light, and uranium-series dating of a stalactite tip buried in the sediment, plus electron spin resonance dating of two pieces of cattle teeth in the sediment and micromorphology, a technique that examines sediment under a microscope to determine the times at which early humans passed through the area.    

People didn’t live in the cave, explained Fabrice Demeter, a study co-author and professor of paleoanthropology at the University of Copenhagen, in an email. He said their remains just ended up there over the years.   

“This cave played as a trap where remains of skeletons that were surrounding the cave outside got washed in slowly and regularly,” Demeter wrote in an email.  

Both Demeter and Westaway were quick to warn that although the fossils found in the cave are human, they don’t have any genetic connection to modern-day humans. 

“According to the genetic evidence Homo sapiens did not arrive in Southeast Asia until 60-50,000 years ago and then moved on to Australia by 50,000 years ago - thus for H. sapiens to be in Southeast Asia earlier than [60,000 years ago] means that the migrations must have been unsuccessful as they did not contribute to the gene pool,” Westaway wrote.

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

Demeter was also the lead author of a study published in Nature Communications last year on a nearby area called Tam Ngu Hao 2, or Cobra Cave, where researchers found a molar tooth from a Denisovan child, a subspecies of archaic humans that interbred with Homo sapiens. The discovery suggests that the area might have been used as a migration route long before Homo sapiens showed up.

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