Human teeth found in a cave in southern China show Homo sapiens could have arrived there 80,000 years ago, well before they moved into Europe or northern China, researchers say.
The finding puts the migration of our modern human species northward earlier by at least 20,000 years and may require a re-thinking of the accepted version of the "Out of Africa" story of the spread of modern humans, they suggest.
Current genetic and archeological evidence has mostly supported a later date for the start of that dispersal out of Africa.
"In this case, we are saying the H. sapiens is out of Africa much earlier," she says.
The teeth found in China suggest modern humans reached there long before they moved into Europe, as all available evidence points to their arrival in Europe no earlier than 45,000 years ago, the researchers say.
The teeth, unearthed from the clay of a cave close to the Chinese town of Doaxian, closely resemble those of modern-day humans, they say.
"It was very clear to us that these teeth belonged to modern humans [from their morphology]," says Martinon-Torres. "What was a surprise was the date."
Some researchers have previously proposed earlier dates for the dispersal from Africa, she points out. There may have been more than one Out of Africa migration, she acknowledges.
The finding may also help explain why it took Homo sapiens another 40,000 years to move into Europe, which was already inhabited by some early relations, the Neanderthals.
"Why is it that modern humans — who were already at the gates — didn't really get into Europe?" Martinon-Torres asks.
Neanderthals may have provided much more opposition to the move of modern humans into Europe than previously thought, she suggests, until they began to drop in numbers on the way to becoming extinct.
Also, experts suggest, Homo sapiens — who began in Africa — may have been less adaptable at first to the wintry climates of Europe than Neanderthals were.
"H. sapiens originated in or near the tropics, so it makes sense that the species' initial dispersal was eastwards rather than northwards, where winter temperatures rapidly fell below freezing," Robin Dennell of the University of Exeter in England writes in a commentary in Nature accompanying the published study.