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Modern human teeth that are at least 80,000 years old have been found in China. Museum human origins expert Professor Chris Stringer says the discovery is a 'game-changer'.
Researchers have dated 47 human teeth found in a cave in China to between 80,000 and 120,000 years ago - at least 20,000 years before modern humans were thought to have been present in southern Asia.
The discovery, published in the journal Nature, could force scientists to reconsider theories of how Homo sapiens spread around the world from Africa.
'This paper is a game-changer in the debate about the spread of modern humans across southern Asia,' says Prof Stringer.
'The ultimate origin would still be Africa, but attention will now focus on regions like Arabia and India as possibly important stopovers on the pre-80,000-year-old route to southern China.'
Visitors will be able to explore the fascinating history of the human lineage in the Museum's new Human Evolution gallery, opening later this year.
Until now, the earliest indisputable H. sapiens fossils found east of the Arabian Peninsula have been dated as roughly 40,000 to 50,000 years old.
Claims for older modern human fossils have been made - including a skeleton from Liujiang and a jawbone from Zhirendong, both in southern China - but these findings have remained controversial because of questions over the accuracy of dating and whether the specimens are truly modern humans.
This latest discovery, from Fuyan Cave in Daoxian County, Hunan Province, looks better-established, according to Prof Stringer.
'The teeth from Daoxian seem unquestionably modern in their size and morphology, and they look to be well-dated by uranium-thorium methods to at least 80,000 years ago,' he says.
The international team of scientists found the teeth in a layer of sandy clay 20 to 50 centimetres thick, which was capped by a thin layer of rock with a small stalagmite growing on top.
When dated, the stalagmite gave a minimum age of 80,000 years for the human teeth buried below, while an analysis of mammal fossils found alongside the teeth yielded an upper limit of around 120,000 years.
The teeth were compared to large samples of dental fossils from early humans, including Neanderthals, and were found to consistently match the features of H. sapiens samples from the last 100,000 years. In fact, the researchers concluded that the Daoxian teeth were generally smaller than other contemporary specimens from Asia and Africa, and were much closer to later European and even recent humans.
The scientists say their discovery could break the 'quarantine' that has constrained theories about H. sapiens in Asia to the last 40,000 to 50,000 years. If the findings are correct, our species may have successfully established itself in large parts of Asia 35,000 to 75,000 years earlier than in Europe.
Prof Stringer says that one of two competing theories could help to explain how H. sapiens spread from Africa into Asia earlier than previously thought.
The first relates to what has long been thought of as a 'failed dispersal' through north-east Africa and the Levant (an area east of the Mediterranean Sea that today contains Syria, Israel, Palestine, Lebanon and Jordan) about 100,000 to 120,000 years ago.
Fossils from two sites in modern-day Israel (discovered in the Qafzeh and Es Skhul caves) have been considered by some as close to the end-point of this earlier unsuccessful migration.
'Many researchers (often including me) have argued that the early dispersal of modern humans from Africa into the Levant recorded by the fossils from Skhul and Qafzeh about 120,000 years ago was essentially a failed dispersal that went little or no further than Israel,' Stringer says.
One option is that there was a successful dispersal along these lines, and that the populations evolved rapidly to the modern human stage evident in the Daoxian teeth once they reached Asia.
The other option, Stringer says, is that the Daoxian fossils are evidence of a 'hitherto-unsuspected, early and separate dispersal of more modern-looking humans'.
In this theory, some populations of H. sapiens left Africa through a different, perhaps more southerly route into Asia, possibly passing through southern Arabia and India.
The authors of the article in Nature point out that fossils found in more northern latitudes lack some of the modern human traits of the Daoxian teeth.
'This evidence could support different origins or routes of dispersal for modern humans across Asia,' they write.
The Museum's new Human Evolution gallery opens in December 2015. Journey through 6-7 million years of evolution, find out about our ancient relatives and encounter key specimens and research that are shedding light on our past.