Marks on the bones of two antelopes uncovered in Ethiopia may indicate that hominids were using sharp stones to butcher their meat 3.4 million years ago. If so, the discovery represents the earliest evidence of stone tool use by a human ancestor. "This find will definitely force us to revise our textbooks on human evolution, since it pushes the evidence for tool use and meat eating in our family back by nearly a million years," says paleoanthropologist Zeresenay Alemseged of the California Academy of Sciences in San Francisco.
The age of the cut marks pegs them as the handiwork of Australopithecus afarensis, a species made famous by the 3.2-million-year-old partial skeleton nicknamed Lucy, says Alemseged. That suggests our ancestors were already using sharp stones to cut meat when their brains and bodies were barely bigger than a chimpanzee’s. Although the earliest known stone tools don’t appear until 800,000 years later—also in Ethiopia—the marked bones may offer a glimpse of the first stage of tool use, when hominins were beginning to use sharp rocks but perhaps not yet making their own stone flakes.
In January 2009, Alemseged and other members of an international team of researchers—known as the Dikika Research Project—found the bones in the Afar Depression of Ethiopia. The researchers were using a new method to collect every scrap of bone from large mammals so they could reconstruct the ancient environment there. Archaeologist Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, says he picked up an unimpressive rib from a cow-sized ungulate and saw two "obvious, V-shaped cut marks." A few moments later, he found a thighbone shaft from a goat-sized antelope, with many marks on it. "In this case, they were incredibly obvious cut marks. But they were so old, we wanted to play it cautious," says McPherron.
Back at camp, the researchers examined the bones under a microscope and felt confident that the marks were made when a hominin cut flesh from the bones and pounded the bones open for marrow. Later, the bones were given to paleoanthropologist Curtis Marean of Arizona State University, Tempe, who showed that the marks were made by stone rather than by carnivore teeth. Other members of the team used secondary electron imaging and energy-dispersive x-ray spectrometry to show that the marks were created before the bones fossilized and also found a tiny piece of rock embedded in a cut mark, perhaps left during the butchering.
Radiometric dating of the sediments at the site shows the marked bones date to almost 3.4 million years ago—a time when the only known hominin in east Africa was A. afarensis. To butcher ungulates as large as a cow, the researchers say, A. afarensis must have ventured into dangerous terrain to compete with other carnivorous scavengers, such as hyenas. The team reports its findings in the 12 August issue of Nature.
"This is really a very exciting find," says archaeologist David Braun of the University of Cape Town in South Africa, who was not involved with the work. "This find emphasizes that tool use and carnivory have very deep roots in human ancestry." Others, though, say it will take stone tools—and marks on more than two bones—to prove that hominins, rather than crocodiles or other animals, made those cuts. "Extraordinary claims demand extraordinary evidence," says paleoanthropologist Tim White of the University of California, Berkeley.
Full coverage of this story will appear in the 13 August issue of Science.