A series of parallel lines engraved in an animal bone between 1.4 and 1.2 million years ago may be the earliest example of human symbolic behaviour.
By Paul Rincon
BBC News Online science staff
University of Bordeaux experts say no practical process, such as butchering a carcass, can explain the markings.
But many researchers believe the capacity for true symbolic thinking arose much later with the emergence of modern humans, Homo sapiens.
The 8cm-long bone was unearthed at the Kozarnika cave in north-west Bulgaria.
Another animal bone found at the site is incised with 27 marks along its edge.
"These lines were not from butchering; in this place (on the animal) there is nothing to cut. It can't be anything else than symbolism," Dr Jean-Luc Guadelli, of the University of Bordeaux, France, told BBC News Online.
When early humans butchered animal carcasses for meat, they left cut marks on the bones made by the stone tools they used to scrape away the flesh.
But the French and Bulgarian researchers who have been excavating at Kozarnika claim the parallel cuts on the bones are too precise to be the result of hacking at the animal to strip away meat.
"Now, what is the meaning of these symbols? It is impossible to know. But they put on this bone something they wanted to explain: 'I saw 16 animals in this place'. It could be something like language."
Many researchers see the capacity for symbolism in humans as something that only became widespread after about 50,000 years ago in our own species. Therefore, evidence of this capacity in an earlier species of human is highly controversial.
"There's no precedent for this at all - if in fact they are incised markings rather than butchery marks. This would be a very welcome thing if it's confirmed," Paul Bahn, an expert in ancient art, told BBC News Online.
"I see a very long evolution for art and I see absolutely no credence in the view whatsoever that it magically appears with our sub-species through a genetic mutation," he added.
Back and forth
Dr Guadelli and his colleagues have discovered a human molar tooth of a similar age to the incised bones. It belongs to a species of early Homo, but the researchers are unsure of the exact species.
A good candidate would be Homo erectus, a species of hominid that was spreading beyond its homeland in Africa at the time the bone markings were made.
HUMAN FAMILY TREE
Scientists are trying to piece together the species relationships
The incised bone seems to have belonged to an unknown bovid mammal, the group that includes sheep, cattle and antelope.
It comes from ground layers dated using palaeomagnetism, which determines age using past patterns of reversals in the Earth's magnetic field.
The project is a collaboration between the Centre National de la Recherche Scientifique (CNRS) in France and the Archaeological Institute and Museum of the Bulgarian Academy of Sciences.
Details of the excavations have been outlined at a symposium in Rennes, France. The findings are to be published soon in an English-language archaeological journal.
Picture courtesy of Aleta Guadelli