By comparing the layers with those at other archaeological sites in South Africa, the researchers concluded that the bone tools were used somewhat earlier than the Last Glacial, 60,000 to 70,000 years ago, when the ocean withdrew further from the current coastline.
Direct dating of the sediments and the materials they contain is now being done.
One of Many Indicators
Stone tools are regarded as a significant indicator of modern human behavior because of the skill and labor involved in producing them, and because they generally signify a shift toward more specialized toolmaking. "In Europe, prior to 35,000 years ago, people did not make formal bone tools," said Curtis W. Marean of the Institute of Human Origins at Arizona State University, a co-author of the study. "After that, bone and antler become favorite raw materials, and even stone tools become 'more formal' tools, with regular shapes and specialized uses."
The existence of bone and other "formal" tools is frequently included among a list of traits or archaeological details widely regarded as indicators that Stone Age and Upper Paleolithic populations practiced modern human behavior. Other indicators include the hunting of large fish, the use of decoration, and the production of artall of which offer evidence of symbolic thinking.
The excavations at Blombos Cave and other similar sites have also yielded substantial quantities of ochre, a mineral compound that aboriginal peoples frequently use for body decoration. "More than 8,000 pieces of ochre were brought to the site and were used almost certainly for symbolic purposes," said Henshilwood.
Extensive evidence from European sites, he explained, has pointed to an Upper Paleolithic "symbolic explosion" that archaeologists have considered the best recorded beginning of modern human behavior, about 35,000 years ago. "The evidence from [Blombos] cave, together with other evidence coming from other sites, is now starting to say to us that this is very questionable," said Henshilwood. "We're seeing evidence of a comparable change in Africa, but in the Middle Stone Agemore than twice as far back in time."
New Picture Emerging?
The scientists see the artifacts from Blombos Cave as only the first clues in what they say is likely to be an extensive body of evidence for early behavioral modernity in Africa. They expect further evidence to come from a number of digs that are still underway or from which the findings have not yet been published.
Europe has been extensively excavated in the last century, providing much information for archaeologists to draw on, Henshilwood pointed out. Yet, "right now we are only scraping the surface of information about pre-historic Africa," he said. "Africa is geographically enormous when compared to western Europe, but it has been excavated properly only for a very short period, and very few sites in Africa have really been well dug."
Marean said the rapidly growing evidence is beginning to put behavioral evolution in step with anatomical development. "I think that when we start to get a big sample," he said, "the picture of modern human evolution is going to look very different."
The other co-authors of the impending scientific paper on the bone tool discovery are Francesco d'Errico of the Institut de Prehistoire et de Geologie du Quaternaire, Richard G. Milo of Chicago State University, and Royden Yates of IzikoSouth African Museum.
The research was supported by grants from more than half a dozen cultural and scientific organizations, including the National Geographic Society.