Chimpanzees may have been cracking nuts with primitive stone tools 4,000 years before anyone thought, according to findings from an international research team.

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SYDNEY: West African chimpanzees may have been using stone tools to crack nuts more than 4,000 years ago - thousands of years earlier than previously thought.

According to research performed by a team of Canadian, British and U.S. researchers, our closest relatives may have developed the behaviour on their own or inherited it from our common ancestor, rather than learning the use of tools from early humans.

The team, led by Julio Mercader, of Canada's University of Calgary, analysed stones found with chimpanzee remains in Taï National Park in Ivory Coast, near Ghana in West Africa.

Many of the excavated stones showed modifications suggestive of use as tools, reported the team. Some were formed by 'flaking', a hallmark of early human tool-making. Others, thought to be designed for cracking nuts, were created by 'bashing' - a technique that preceded systematic flaking.

The idea that these tools were created by chimps - and not early humans - stemmed from analysis of several types of starch grains found with the stones. According to the team, many of these grains were from nut species that today are consumed by chimpanzees but not humans.

The stones were dated at 4,300 years old. From the evidence, the researchers concluded that chimpanzees in the Taï forest have been cracking nuts with stone tools for some 200 generations.

Mercader and his collaborators are at the forefront of the burgeoning field of chimpanzee archaeology, which is the "application of archaeological techniques to the study of the chimpanzee past", Mercader explained.

With the help of these techniques, researchers hope to improve our understanding of the origins of human technological behaviour. Just as humans have passed down technology from one generation to the next, he explained, chimpanzees have transmitted theirs down through the ages. "Chimp material culture is ancient - the Chimpanzee Stone Age started thousands of years ago," he said.

The research expands the areas considered appropriate for the study of human and ape prehistory. According to the study, published today in the U.S. journal Proceedings of the National Academy of Sciences, much of what we know about the origins of humans comes from work in the savannah woodlands of east and southern Africa, but these findings show the importance of west African research.

Mercader also hopes that this work will pave the way for further explorations of the roots of chimp culture. "Archaeologists can now look for ancient chimp material culture elsewhere using similar research protocols, including the recovery and identification of food residue on tools."