They report in the journal Nature that two ancient animal bones from Ethiopia show signs of being butchered and smashed by stone tools about 3.4 million years ago. That's about 800,000 years earlier than the previous earliest evidence for tool use.
The researchers say the tools were used by the species best known from the skeleton known as "Lucy." No tools were found with the bones, and it's not clear whether our ancestors made the tools or simply used stones that they found.
Not all experts are convinced by the research. Some said they weren't sure the markings on the animal bones really came from tools.
