The National Academy of Sciences journal says that the archaeologists think that the skill could have been inherited from a common ancestor of chimps and humans or learnt from early humans by imitation, or even that humans and chimps may have developed the use of tools independently.
Julio Mercader, an archaeologist at Canada's University of Calgary, and his international team of scientists explored three sites about 200 yards apart in the Tai National Park, and it was there they discovered a total of 210 flaked and chipped stone hammers made from granite, quartz or quartzite.
