Michael Greshko, National Geographic, July 11, 2018
Modern humans’ distant relatives left Africa earlier than previously thought — rewriting a key chapter in humankind’s epic prequel, according to a discovery unveiled on Wednesday in Nature.
Nearly a hundred stone tools found at the Shangchen site in central China may push back the spread of our ancient cousins — hominins — out of Africa by more than a quarter million years.
The toolmakers lived at Shangchen on and off for 800,000 years between 2.1 and 1.3 million years ago, leaving behind tools that are unprecedented outside of Africa. The site’s oldest tools are roughly 300,000 years older than Dmanisi, a 1.8-million-year-old site in the Republic of Georgia with the oldest known fossils of our extinct cousin Homo erectus.
“Finding artifacts that you knew were around two million years old — and therefore the oldest outside Africa — was for me, as a palaeoanthropologist, really exciting,” says study coauthor Robin Dennell, a professor at the University of Exeter.
“I’ve always said that once the Chinese researchers start looking for evidence on a similar scale as all the money spent in Africa, things will turn up!” exclaims Gerrit van den Bergh, a paleoanthropologist at the University of Wollongong who wasn’t involved with the study.
Today’s modern humans, Homo sapiens, trace back to a migratory pulse that left Africa some 60,000 years ago. But that migration was hardly the first to leave the continent — nor were modern humans the only hominins to make the trip. Remains of Homo erectus have been found from Georgia to Java. Neanderthals’ ancestors trekked to Europe roughly half a million years ago. At least 700,000 years ago, early hominins somehow swept through the South Pacific, giving rise to the “hobbit” Homo floresiensis and other island toolmakers.
Some sites have hinted at an even older hominin presence in Asia. In the 1980s, researchers suggested that stone tools in Pakistan could be as old as two million years old. In 2004, a Chinese team found 1.66-million-year-old stone tools in north China’s Nihewan basin. And in 2015, researchers made the case that a Homo erectus skull found less than three miles from Shangchen was more than 1.6 million years old.
Nestled on a hillside in China’s Shaanxi Province, this dig site exposed Shangchen’s oldest stone tools. Chinese Academy of Sciences geologist Zhaoyu Zhu and his colleagues excavated the area for 13 years.
But precisely when were the tools made? To find out, Zhu’s team measured the varying magnetic fields in the tool-bearing soil layers.
As each layer formed, minerals within the soil preserved the orientation of Earth’s magnetic field at the time. Because Earth’s magnetic field sometimes reverses polarity, some of the layers’ fields flipped in kind — as did the magnetic fields of similarly aged sediments all over Earth.
By comparing Shangchen’s sediments to well-dated African soils that preserved the same magnetic reversals, Zhu could accurately assign ages to each Shangchen layer. Six of the 96 tools discussed in the study were found in a layer dating back 2.12 million years.
Who Made the Tools?
Since there aren’t hominin fossils alongside Shangchen’s tools, nobody knows for sure who made them.
María Martinón-Torres, the director of Spain’s National Center of the Study of Human Evolution (CENIEH) and a world authority on Asian hominin fossils, says that even some Chinese hominin fossils once labeled as H. erectus are worth a second look.
“It is time to accept that not all hominins found in Asia fit in the Asian H. erectus taxon, a species that has been largely employed as a blanket term,” she says. “I think that the question about the first Asian hominin identity is not closed yet.”
Regardless, Shangchen’s toolmakers would have had brains about a third the size of our own. While brain size isn’t everything, experts say that it’s astounding that such early, small-brained humans made it from Africa to China some two million years ago.
“For a long time [the] scientific community has given a secondary role to Asia versus Africa in explaining relevant episodes of our evolution,” says Martinón-Torres. “With more fieldwork at Asia I am sure that more surprises are to come.”
[Editor’s Note: The original article concerning this find is in Nature and is available here.]