NEW YORK - Stone tools recovered from an excavation in China suggest that our evolutionary forerunners trekked out of Africa earlier than we had thought.
Until now, the oldest evidence of human-like creatures outside Africa came from 1.8-million-year-old artifacts and skulls found in the Georgian town of Dmanisi. The new find pushes that back by at least 250,000 years. There have been other claims of even older fossil discoveries, the study authors said, but those remain unproven.
“There may be older evidence in places like India and Pakistan, but so far … the evidence is not strong enough to convince most of the research community,” said study co-author Robin Dennell of Exeter University in England. “With this type of claim, for an early human presence in a region, the evidence has to be absolutely water-tight and bomb-proof.”
“It’s absolutely a new story,” said archaeologist Michael Petraglia of the Max Planck Institute for the Science of Human History in Jena, Germany, who did not participate in the study. “It means that early humans were getting out of Africa way earlier than we ever realized.”
That exit came long before our own species, Homo sapiens, even appeared. The researchers believe the tools were made by another member of the Homo evolutionary group. “Our discovery means that it is necessary now to reconsider the timing of when early humans left Africa,” Dennell said.
Hominins — humans and their extinct predecessors and relatives — are believed to have emerged in Africa more than 6 million years ago. They are thought to have left the continent in several migration waves starting about 2 million years ago.
The first migrants were likely members of the species Homo erectus (“upright man”) or Homo ergaster (“working man”) — extinct predecessors of Homo sapiens (“wise man”), which first emerged about 300,000 years ago in Africa.
The oldest known African fossil attributed to a member of the Homo family is a 2.8-million-year-old jawbone from Ethiopia.
The items found in China include several chipped rocks, fragments and hammer stones. The 96 artifacts — mainly flakes made with rudimentary hammers, and likely used for cutting meat and other food — were dug up from 17 layers of sediment in an area known as the Loess Plateau, north of the Qinling Mountains, which divide the north and south of China.
The youngest layer where tools were found was 1.26 million years old, and the oldest 2.12 million years, according to the study published in Wednesday’s journal Nature. The layers were used to date the tools, which are of a type known to have been manufactured by Homo species in Africa since at least 3.3 million years ago.
So far, no hominin bones have been found.
The team used paleomagnetism — minerals that show how the Earth’s magnetic field was oriented when they formed — to date the sediment layers, and so the artifacts found within them. The dates of geomagnetic reversals, when north and south flipped, are well known to scientists, and the movements of the magnetic poles and the continents can narrow down a date.
“We were very excited,” said Zhaoyu Zhu, a professor at the Guangzhou Institute of Geochemistry, who led the fieldwork. “One of my colleagues suddenly noticed a stone embedded in a steep outcrop. After a short while, more artifacts were found — one after another.”
The tools were distributed throughout layers of dirt, suggesting that our unidentified ancient relatives came back to the same site over and over, possibly following animals to hunt. Researchers also found bones of pigs and deer, but were not able to provide proof that the tools were used for hunting.
Some experts not involved in the research think that the findings need to be considered with caution. “I am skeptical,” said Geoffrey Pope, an anthropologist from William Paterson University in New Jersey. “I suspect this discovery will change very little.”
The problem, he said, is that sometimes nature can shape stones in a way that they look as if they were manufactured by hand. Scientists know, for example, that rocks smashed together in a stream can acquire sharp edges.
But Sonia Harmand, an archaeologist at Stony Brook University in New York who studies stone tools, disagreed.
“This could be, frankly, one of the most important (archaeological) sites in the world,” Harmand said.