Sileshi Semaw felt as if he had stumbled onto a gold mine. And in the world of archaeology, where researchers count themselves fortunate to find a few scattered artifacts, he had. In the Gona region of Ethiopia in a small patch of desert about the size of a three-bedroom house, Semaw and his colleagues had dug up three thousand stone tools — and with them, clues to the early emergence of a human ancestor.
For these were not just any tools. The stones, which are 2.5 million years old, were evenly flaked to a sharp edge, as if they had been carefully carved into fine choppers. That kind of skilled manufacture, Semaw reported last year, had previously been seen only in tools that were about one million years younger — the work of early members of our own genus, Homo. Together with the discovery of a 2.3-million-year-old Homo jaw in a neighboring region of Ethiopia by another research team, the discovery pushes the first appearance of this important human ancestor back by about four hundred thousand years and fills in a major history gap.
“This is important,” says anthropologist Richard Klein of Stanford University in California. “You have the emergence of Homo, based on the fossil, and the appearance of stone tools at about the same time. The two reinforce each other.” Anthropologists had known that Homo predecessors, more apelike creatures such as the famed Lucy and her kin, lived about three million years ago. But Homo itself, they thought, didn’t show up until about two million years ago. So researchers had a million-year blank spot during which the apelike animals gave way to more humanlike creatures. The new tools help pin down the transition.
And the discovery does much more. “It shows that early hominids had surprisingly sophisticated control over their raw materials,” says Semaw, who works at Rutgers University in New Jersey, “We think they used the tools for chopping [tree limbs] to get fruit or sharpening digging sticks to get underground foods, like tubers.”
His Rutgers colleague, anthropologist Jack Harris, goes further, suggesting the tools had more elaborate uses forced on their owners by a changing climate. Ethiopia wasn’t always dry desert. Around three million years ago, the landscape was far more lush, with plants and forest providing fruits, nuts, and other food. Bit by bit, however, the dry season got longer and the forest got smaller. In its place, Harris says, was a more open landscape — complete with animal carcasses waiting to be eaten, if one only had the tools. Perhaps early people adapted, using the Gona tools as butcher’s knives. “I’d argue that the stone tools reflect a change in diet of some hominids as their food sources literally dried up,” Harris says.