Researchers digging in Kenya say they've found the oldest stone tools ever discovered, at 3.3 million years old — pushing the record back by around 700,000 years. That places these tools before the birth of Homo, the genus that includes modern humans; as such, it calls into question the conventional belief that it was species within Homo that first learned how to work with stone tools. The findings are being published today in Nature.
Stone tools appear to have existed before the Homo genus
It's been the view for decades that the first stone tools were made by members of the Homo genus, says Sonia Harmand, a Stony Brook University researcher and the study's lead author. "The idea was that our lineage alone took the cognitive leap of hitting stones together to strike off sharp flakes, and that this was the foundation of our evolutionary success," she writes in an email to The Verge.
These new findings make it appear as though that may not be the case. The Homo genus only goes back — as far as we currently know — to 2.8 million years ago. The presence of stone tools half a million years before that either means that Homo's origins are even earlier than we believe, or that stone tools were developed by earlier ancestors. The latter option is "the most plausible," Jason Lewis, a Stony Brook researcher and co-author of the study, writes in an email to The Verge.
In fact, that possibility is one that researchers have been moving toward in recent years. Rather than stone tools appearing with the birth of Homo, it's possible that stone tools developed over a longer period of time. The tools discovered by Harmand and her team even suggest as much: they're cruder than the tools used by early members of Homo, and yet they're not entirely primitive either. The tools, Harmand says, are "sophisticated enough that they are likely not from the first time" that the creation of a stone tool was attempted.
Above: Anvils found at the Lomekwi 3 site.
The tools described in the study were largely used together with a common goal: creating flakes of stone with sharp edges, likely for cutting. Certain stones were used as hammers, and others were used as the "cores" that would be struck in the hope of knocking off sharp flakes. Other stones were used as anvils, upon which the cores were placed while striking. It appears that the tools' manufacturers held their hammers in two hands while striking down on the cores — a more rudimentary technique than what was used to create the stone tools we know of from 700,000 years later.
"It will force us [to rethink] what makes us humans."
"Maybe they needed sharp flakes to cut or otherwise process new food resources, whether animal or vegetal," Harmand says. Or "maybe they were using the cores to pound open nuts or bones." Either way, she says, it represents a species' development of the ability to modify its environment, imagine and create tools, and then "use those tools to solve problems and better survive."
The tools are distinct enough that the researchers have given them a name: Lomekwian, named after the Lomekwi 3 archeological site where they were found in West Turkana, Kenya. This name is meant, in particular, to distinguish these tools from the 2.6-million-year-old stone tools that researchers previously knew of, which went under the name Oldowan.
Above: Hammerstones found at the Lomekwi 3 site.
Paleoanthropologists who spoke with The Verge and were not involved in the study said that this is a major finding that changes how we view the Homo genus. One called it a "game changer." The other said it has "revolutionary implications."
"It will force us [to rethink] what makes us humans," Fernando Diez Martin, a University of Valladolid associate professor who was not involved in the study, tells The Verge in an email. He adds, "Increasing knowledge of our remote past is casting doubts on previous certainties and is showing that the process of becoming what we are now is far more gradual than what we previously thought."
It's not evident who actually made these tools
That said, this finding doesn't necessarily mean making large changes to how we view the genus. Early members of Homo are also seen as having a larger brain size, beginning to eat more meat, and possibly starting to use language. This finding only removes developing stone tools from the equation.
"If you're somewhat broader-minded as to what ought to characterize the genus Homo, then it shouldn't come as a big shock," William Kimbel, director of Arizona State University's Institute of Human Origins, tells The Verge. Kimbel, who was not involved in the study, says that it may turn out to be that Homo isn't defined by representing the first stone toolmakers, but by representing a "complete reliance on stone tools as part of its adaptive suite."
There's still so much uncertainty because researchers don't know which ancestor these tools actually belong to — they may well belong to a species that we don't know about yet. No bones from hominins, the broader group including humans and their ancestors, were discovered at the site.
"We think there are older, even more rudimentary stone tools out there to be found."
But it should be easier to find tools like these from here on out, which could bring new information that answers these unknowns. "All of us will be going out with fresh eyes, keeping our eye on the sediments for evidence of potential tools that are quite different" from the tools previously known about, Kimbel says. Now that researchers have a new understanding of what to look for, it should "absolutely" be easier to identify these early tools in the future.
Lewis, the co-author, says that looking for artifacts from between 3 million and 4 million years ago is now key to understanding the roots of the human genus, as well as what behaviors and characteristics come along with it. "We think there are older, even more rudimentary stone tools out there to be found," Harmand says, "and we will be looking for them over the coming field seasons.