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It suggested that Homo sapiens were in China at least 20,000 years earlier than early modern humans had been previously believed to have left Africa and spread around the world. It also tantalizingly hinted at the possibility that a different group of early humans could have evolved separately in Asia.
Not so fast, says the science in 2021. New research published Monday has suggested perhaps we shouldn't be so eager to rewrite the time line on human origins.
DNA analysis of two human teeth found in the same cave, called Fuyan, plus teeth and other fossilized remains from four other caves in the same region, suggested that it was unlikely early modern humans were in China so early.
"Our new research means it is very unlikely that Homo sapiens reached China before 50,000 years ago. It is always possible that our species reached the region more than 100,000 years ago, but we would have to say that there is no convincing evidence in favor of this at present," said Darren Curnoe, an associate professor at the Australian Museum Research Institute in Sydney and coauthor of the paper that published in the journal PNAS on Monday.
The researchers were able to extract DNA from 10 human teeth and establish the age of other materials in the caves, such as charcoal and animal teeth, using a range of different methods. The team found that the teeth were at least 16,000 years old, while the other materials were less than 40,000 years old.
"The 2015 study relied heavily on the results of a single dating method which determined the age of cave materials (flowstone) lying above and below the sediments containing the human teeth," he said via email. Flowstone is a sheetlike deposit of rock formed by flowing water.
"It is well understood that the most reliable dates come directly from the materials of interest to archaeologists, in this case, the human teeth. Our new (dates), including direct ages, are far younger than previously suggested."
The 2015 study measured the radioactive decay of uranium within cave deposits, not DNA.
Chris Stringer, research leader for human evolution at the Natural History Museum in London, said that the dates of Chinese fossilized teeth had always stood out and it was right to investigate them further using different methods.
However, he said the study, while interesting, didn't definitively rule out early modern humans in China before 50,000 years ago.
Complex family tree
Untangling human ancestry is a complicated business, and recent research has indicated the human family tree is much more bushy and less linear than the traditional "Out of Africa" narrative, which suggested modern humans originated in Africa and made their first successful migration to the rest of the world in a single wave between 50,000 and 70,000 years ago.
Many different ancient hominins existed and coexisted before Homo sapiens emerged as the lone survivor, and there was interbreeding between different groups of early humans.
Some of these groups -- like Neanderthals -- are easily identified through the fossil record and archaeological remains, but others -- like the Denisovans -- have been largely identified by their genetic legacy.
Maria Martinón-Torres, director of the National Research Center on Human Evolution in Spain and an author of the 2015 study, said she welcomed the new data on the early presence of modern humans in China.
However, she noted that the two teeth from Fuyan Cave were uncovered in 2019 and didn't belong to the original sample her team studied and published in 2015.
"The precise data about the location and morphology of the sample is crucial, but it is not provided in the paper," she said.
"I agree that we should be working in improving the dates of all sites of interest, especially with direct dating when possible. However, at the moment, there is an increasing number of samples that would support the presence of H. sapiens outside Africa before 50 ka (50,000 years ago)," she said via email.
She noted that there are other discoveries in Saudi Arabia, Israel, Sumatra and Laos, and another site in China where a jawbone has been found, that support the presence of Homo sapiens outside Africa before 50,000 years ago.
One of the main factors supporting the idea that early modern humans left Africa around 50,000 years ago is that there is a strong signal in the genes of present-day human populations.
"We would say that Out of Africa after 70,000 years ago seems to be the dominant picture. We can't preclude earlier dispersals in other regions, but certainly southern China seems to have been settled in this Out of Africa wave after 50,000 years ago," Curnoe said via email.
However, Martinón-Torres said this doesn't rule out the possibility that earlier groups of Homo sapiens wandered around Asia earlier -- just as groups of other early humans like Neanderthals and Denisovans did.
"We had no expectations about the dating of these fossils and sites and would have been pleased if we had confirmed an early dispersal. It would certainly have made the history of our species much older than generally believed, and perhaps more interesting," Curnoe said.
"Sadly, this seems not to be the case, at the least for southern China, according to our work."