If you are blindfolded and grab an elephant’s tail, absent other clues you might think you’re the proud owner of a hairy snake. The more evidence you accrue, the closer to the truth you may approach. That’s the story of human evolution. All new evidence must be parsimoniously fit into the puzzle and where it flouts previous assumptions, the discredited assumptions, however credible when made, must be junked.
Now, what were thought to be signs of modern humans from as much as 120,000 years ago were actually signs of modern humans from around 16,000 years ago or less, claims a new paper published Monday in the Proceedings of the National Academy of Sciences.
Its informational innovation was extracting and testing DNA from teeth identified as early modern human that had been found in five caves in southern China, combined with wider genetic analysis and multiple geological dating methods.
To be clear, it’s still possible that lines of early modern humans did trek to Eurasia, China and even Southeast Asia very early. But if they did, they went extinct. No evidence of such an early migration has been found to date in China, the authors conclude – given that the fossil teeth in the caves were not the smoking gun after all.
The way we were and where it was
When did anatomically modern humans begin to evolve? Based on the latest evidence, between 500,000 to 315,000 years ago. Where? Africa, possibly all over Africa. Who exactly did we evolve from? The truth is, we aren’t sure of our direct ancestry; we are surer at this point that whoever it was, our forefathers co-bred with Neanderthals and Denisovans, and other human species too. The mechanism of that mixing also remains a mystery.
And when did we join other species of early humans in leaving Africa?
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We know non-sapiens hominins began leaving Africa almost 2 million years ago, going by the discovery of small-brained erectus remains in Dmanisi, Georgia. Over a million years after that exit, the hominin ancestral to Neanderthals and Denisovans also drifted out of Africa to Eurasia. In Africa, no evidence of either line has been found.
Hundreds of thousands of years after the proto-Neanderthal exit, anatomically modern humans began leaving Africa too. Whispers of evidence found in Israel and Greece date to around 200,000 years ago, and though the evidence remains controversial (is it really sapiens?), it seems quite clear that early sapiens were out and about by then.
But genetic analysis has shown, so far at least, that all non-African people existing today arose from humans who expanded out of Africa 65,000 to 45,000 years ago. Ergo, the earlier modern human exiters went extinct; in Europe, they were evidently replaced, or never prevailed over Neanderthals.
But how far early modern humans got before their lines went extinct is another matter. In 2015, scientists startled with the announcement that modern human teeth found in southern China dated to 120,000 to 100,000 years of age. Now, though, the new paper says the teeth were misdated.
The family’s been in Myanmar a long time
The teeth revisited in the new paper had been found in Huanglong, a popular tourism site because of its geological features, including travertine pools and stalactites; the caves of Luna, Fuyan in Daoxian province and Yangjiapo. In Zhirendong, archaeologists had actually found a partial mandible, not just isolated teeth.
Researchers Xue-feng Sun, Shao-qing Wen, Darren Curnoe, Hui Li and colleagues explain how the initial, erroneous estimates had been reached and caution that multiple dating methods are necessary.
In one case, uranium-thorium dating of capping flowstones in the caves Fuyan and Yangjiapo produced dates between 168,000 to 70,000 years; analysis of sediments from the same layer bearing the human teeth produced estimates ranging from 302,000 to 90,000 years ago. But DNA analysis and direct carbon-14 dating of other teeth and charcoal produced dates in the Holocene – i.e., recent history.
Now: Mitochondrial DNA extractable from teeth found at Yangjiapo and Fuyan was compared with sequences from 53 of today’s humans of diverse geographical origin; 10 ancient anatomically modern humans, 10 Neanderthals, two Denisovans, an enigmatic hominin from Sima de los Huesos, and a chimpanzee.
The result? The teeth from the two Chinese caves fell within the variation of present-day Eurasian lineages.
Wondrously, the mitochondrial DNA found in one Fuyan sample has been detected in living Tibeto-Burman people. Yes, there may be a very long term family relationship.
The authors conclude, based on the accumulation of evidence, that anatomically modern humans settled southern China in keeping with the timeframe indicated by molecular data: less than around 50,000 to 45,000 years ago.
Now, broad genetic studies indicate that anatomically modern humans left Africa about 65,000 to 45,000 years ago, and this new study supports that theory. In any case, they don’t support the theory that humans left Africa earlier than the great exit that created non-Africans, and ranged farther than thought back then.
Story of a pig
There is something enticing about imagining that our intrepid ancestors left Africa tens of thousands of tens earlier than we thought and shared the Old World with other human species, interbreeding with at least some before they went extinct.
Southeast Asia has been quite the hotbed of intriguing information. Islands now in Indonesia and the Philippines were home to tiny ancient hominins – Homo floresiensis and Homo luzonensis, respectively. “Luzon man” and “the hobbit” may not have been in the sapiens line at all and only went extinct quite recently, around 50,000 to 70,000 years ago. Which is about the time modern humans may have reached the area.
By the way, Luzon and Flores hominins were different species from one another. Each had characteristics so bizarre that some even quietly suspect these lines didn’t descend from erectuses that became diminutive because of their island lifestyles, and reverted to climbing trees, but from roaming australopithecines.
Meanwhile, researchers recently announced finding the oldest picture in the world, at least identified to date. It was a pig and was dated to about 45,500 years ago – and evidently done by Homo sapiens. That supports the late-dispersal theory of modern humans perfectly well.
As for Australia, the earliest supportable date for modern human arrival may lie not in competently depicted swine or marsupials, but in an aboriginal legend about a giant who turned into the volcano called Budj Bim, aka Mount Eccles. The postulation has arisen that the story describes an actual eruption that shocked the inhabitants so badly, they’re still telling the tale 37,000 years later.
The life lesson to learn is that layers in subtropical caves are messy. They can have a “complex depositional history” as the archaeologists put it, which means they may be significantly disrupted. Multiple methodologies are advised when studying archaeological layers, when possible. As for this study: Modern humans may have reached China much earlier than is presently known, but these teeth don’t show it. The final lesson: Carbon date your layers with human remains. The end.