While the researchers could definitively state the tools’ age and method of manufacture, a larger mystery looms: Who made them?
In the 1960s Leakey proposed that Homo was the first toolmaker, which remains the accepted view. The very name of the oldest known member of our genus, Homo habilis, translates to “handyman” in reference to tool making. Although the fossil record for the first members of the Homo genus is poor, the earliest definitive H. habilis specimen is about 2.4 million years old. The brain of H. habilis was considerably smaller than that of modern humans, but larger than that of Australopithecus, the family widely viewed as its ancestors.
Australopithecines proliferated in the rift valleys of eastern Africa about 2.6 million to 4 million years ago. The well-known Australopithecus afarensis fossil we call Lucy, for example, lived a little over 3 million years ago in Ethiopia’s Afar region, roughly 700 miles northeast of Lake Turkana. Earlier this year, researchers working at another site in the Afar region found the oldest known Homo fossils: Dated to 2.8 million years old, the fragmentary jaw and teeth, not yet formally assigned to H. habilis, suggest Homo emerged 400,000 years earlier than currently thought. But even with this revised timeline for our own genus, the Lomekwi 3 tools still predate any known species of Homo by more than half a million years.
The list of prime suspects features several species of australopithecine, but Harmand and Lewis also have their eye on Kenyanthropus platyops, a fossil discovered in 1998 very close to the Lomekwi 3 site. Kenyanthropus, at 3.3 million years old, is contemporaneous with the Lomekwi 3 toolmakers — probably not a coincidence. Lewis says the answer is still unclear and that there may be more fossils yet to be found. For now, the most tantalizing clue to the mystery may have come from a separate team of researchers working in a lab far from Lomekwi.
Inheriting a Toolbox of Traits
Enter Matt Skinner and Tracy Kivell of the University of Kent, who discovered an unexpected shared trait in humans and australopithecines. Using a high-resolution CT scan — think of it as a 3-D X-ray — their team documented that human hand bones show increased internal density in response to certain types of stress and repetitive motion, particularly that associated with the manufacture and use of stone tools. They detected these same modifications in a skeleton of A. africanus, another australopithecine that roamed South Africa between 2 million and 3 million years ago.