One morning in July 2011, while exploring arid badlands near the western shore of Lake Turkana in Kenya, a team of archaeologists took a wrong turn and made a big discovery about early human technology: Our hominin ancestors were making stone tools 3.3 million years ago, some 700,000 years earlier than previously thought.
The findings promise to extend knowledge of the first toolmakers even deeper in time, probably before the emergence of the genus Homo, once considered the first to gain an evolutionary edge through stone technology.
“Immediately, I knew that we had found something very special,” said Sonia Harmand, a research associate professor at Stony Brook University in New York, in a telephone interview from Nairobi. “I knew these were stone tools, and very old. It was very exciting.”
Within an hour, Dr. Harmand and Jason E. Lewis, co-leaders of the project, traced the source of the artifacts scattered in a dry riverbed to datable volcanic sediments at the top of a nearby hill. The stones showed that at least some ancient hominins — the group that include humans and their extinct ancestors — had started intentionally knapping stones, breaking off pieces with quick, hard strikes from another stone, to make sharp tools long before the practice had been recognized.
After further field research and laboratory analysis, the findings at the site known as Lomekwi 3 were described Wednesday in the journal Nature.
What the sharp blades were used for, whether butchering meat or cutting plants, is not yet known. Nor is the identity of the tool makers.
No bone fossils have been found at the discovery site. But in all likelihood, Dr. Harmand and Dr. Lewis said, the tools were produced by a more primitive member of the human family well before the appearance of the genus Homo. The earliest known Homo habilis, announced more than two months ago, lived 2.8 million years ago in what is now Ethiopia. The earliest previous evidence for toolmaking, also from Ethiopia, was dated 2.6 million years ago. Though even earlier Homo fossils may be identified, scientists say, it is unlikely they would be as old as the West Turkana discovery.
“These tools shed light on an unexpected and previously unknown period of hominin behavior, and can tell us a lot about cognitive development in our ancestors that we can’t understand from fossils alone,” said Dr. Harmand, who is also affiliated with France’s National Center for Scientific Research. “Our finding disproved the longstanding assumption that Homo habilis was the first tool maker.”
Alison Brooks, an anthropology professor at George Washington University and research associate at the Smithsonian Institution, who was independent of the discovery team, pronounced the finding “truly pathbreaking.” She said this “reaffirms the argument that the repeated and competent manufacture of useful sharp edges, on which we came to depend, may have been a driving factor in the evolution of our genus, both anatomically and cognitively.”
In one sense, the deeper record of stone technology was no surprise to paleoanthropologists. Previous examples, especially the 2.5-million-year-old artifacts collected at Olduvai Gorge in Tanzania, were thought to be too well made to have been a recent innovation. How far back the evidence for this stone technology extends is anyone’s guess, they say.
In a commentary in the journal, Erella Hovers, an archaeologist at The Hebrew University of Jerusalem, wrote that some form of tool making may have extended back to the last common ancestor of chimpanzees and hominins, as much as seven million years ago.
Dr. Hovers and other scientists not involved in the new research said the dating of the material appears to be solid and the objects are deliberately produced tools, not scraps of rock broken by accident or natural causes.
“Because the sediments in these layers are fine-grained, and a flake found by the authors could be fitted back onto the core from which it had been detached,” Dr. Hovers said, “it is unlikely that the tools accumulated through stream activity or that substantial disturbance of the sediments occurred after the tools had been discarded.”
Eric Delson, a paleoanthropologist at Lehman College of the City University of New York and a researcher at the American Museum of Natural History, noted that once in a generation, the age of humanity’s first known use of tools increases significantly. “Harmand’s find is the longest jump back in time, nearly three quarters of a million years, to a period when the only known hominin fossils belong to Australopithecus,” the genus most famously represented by the “Lucy” skeleton and found throughout East Africa.
Another possibility is a hominin known as Kenyanthropus platyops, whose fossils were found in the region of Lake Turkana. But Dr. Delson cautioned that fossils of this genus are “poorly known and still questionably distinct” as a separate hominin entity.
Dr. Delson said the discovery of what Dr. Harmand and her colleagues are calling the Lomekwian industry, raises several questions: namely, are these really tools, and what were these hominins, whoever they were, doing with implements far larger and heavier than the small and simple flakes and cores that characterized the more recent 2.6-million-year-old technologies?
Even now, researchers doubt that they have reached the earliest origins of stone tool technology. As Dr. Hovers of Hebrew University said, “Why not dig deeper in time?” The Lomekwi 3 site, she added, “may not be the final — or rather, the first — word on the roots of human technology.”
Dr. Harmand and Dr. Lewis will return to Lake Turkana this summer to search for more clues to the identities of the tool. “Now we have a better idea of what we should look for,” Dr. Harmand said.
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