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The findings, published in the journal Nature, may compel researchers to reconsider the current view of human migrations out of Africa — and could hint that Neanderthals may have been a much greater barrier to Europe than previously thought.
"I really think it’s opening a new period of understanding and more creative thinking about the other possibilities of long-established models," said paleoanthropologist María Martinón-Torres of University College London, who co-led the study with Wu Liu and Xiu-jie Wu of the Chinese Academy of Sciences.
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Scientists believe that Homo sapiens first emerged in East Africa somewhere between 190,000 and 160,000 years ago, spread into the eastern Mediterranean around 100,000 to 60,000 years ago but then were replaced by Neanderthals after that, according to Robin Dennell of the University of Exeter, who was not involved in the paper.
The successful dispersal westward into Europe would not have come until much later, around 40,000 years ago. And scientists think that our species didn’t trek eastward until around 60,000 years ago, an idea based on some genetic estimates as well as on the similarities between stone tools in South Africa dated to 60,000 years ago and some in South Asia from 36,000 to 30,000 years ago.
Paleoanthropologists have looked to the karst caves in southern China that are full of fossils, but it has been hard to pin down a date on the specimens gathered — or even to tell which hominid species the fossils belong to.
Fuyan Cave in Hunan province, where these teeth were found, has an ideal mix of features that allowed scientists to pin down the fossils’ age. (Teeth often are the best-preserved remains in an acidic environment like a karst cave because enamel is the hardest tissue in the human body, and dentin, while not quite as hard, is still harder than bone.)
For such fossils, understanding their context — where they were located, how deep they were buried — is vital because each layer of rock represents a different epoch in time. The deeper the objects were found, the older they are. So if those layers are disturbed in any way, it becomes very difficult for excavators to tell the true age of those fossils.
Luckily, in Fuyan Cave, a layer of flowstone had grown over the layer that held the human teeth, sealing them in and preventing them from being disturbed. Over the flowstone grew a stalagmite, which was dated to at least 80,100 years old — which means all the material below it, teeth included, must be older.
Beneath the flowstone, the scientists also found mammalian fossils from 38 species as well as five extinct large mammals, including Stegodon orientalis (a relative of mammoths and elephants) and Ailuropoda baconi (an ancestor of the giant panda). These animals must have come from a period of time known as the Upper Pleistocene, about 125,000 to 10,000 years ago.
Together, the stalagmite and the mammalian fossils allowed researchers to put an upper limit on the age of the human teeth. Their owners must have lived sometime between 80,000 and 120,000 years ago.
Taken together, these teeth look remarkably like those of contemporary humans; they’re smaller and smoother than those of earlier human species, such as Homo erectus.
“The fact that the teeth resemble those of Upper Pleistocene Europeans and modern humans implies that the population they came from were immigrants and not the outcome of local evolution from H. erectus,” Dennell wrote in a commentary on the study. “To place these finds in their continental context, the Fuyan teeth indicate that modern humans were present in southern China 30,000 to 60,000 years earlier than in the eastern Mediterranean and Europe.”
That’s a pretty big difference between the two populations, and it could hint that our relatives the Neanderthals could have been the reason that Homo sapiens failed to break into the continent on their apparent first try. Before this, many thought that modern humans fairly quickly led to the demise of Neanderthals as they moved through Europe; but perhaps Neanderthals were a bigger block than previously believed.
“We should not rule out the possibility that H. neanderthalensis was for a long time an additional barrier for modern humans’ expansion, who could only settle in Europe when Neanderthal populations started to fade,” the study authors wrote.
There could be other explanations for the delay in getting to Europe, others said.
“The predominantly colder winter conditions of the enormous landmass between Europe and northern China may better explain the earlier colonization of southern zones,” Dennell wrote.
Either way, it opens up a lot of questions about whether, and how, this migration into southern China relates to the human population today,” Martinón-Torres said. Did these humans die out before being replaced with a later migration? Did they somehow mix with other African homo sapiens who later spread to other continents?
“We really have a lot of new questions about the origin of current populations. ... I think it’s an exciting period, in that sense,” she said.
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