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Biology Articles » Psychobiology » African bone tool discovery has important implications for evolution of human behavior

African bone tool discovery has important implications for evolution of human behavior

An emerging set of archaeological evidence may answer a key question in the human origins debate by providing proof that not only did early Homo sapiens come "out of Africa," as Homo erectus did, but that they came out fully modern, with fully developed modern behaviors that had evolved much earlier than previously thought. The new evidence includes the recent discovery in a South African cave of a large set of specialized bone tools, all dated at more than 70,000 years old. The discovery conclusively proves that human use of formal bone tool technology is more than twice as old as the previously accepted dates. The advent of bone tools was a major development in human tool technology and is considered by many archaeologists to be a key indicator of "behavioral modernity" in humans.

An analysis of the find, forthcoming in the December issue of the Journal of Human Evolution, argues that this ancient use of bone tool technology, together with related discoveries, has strong implications that "behavioral modernity" first evolved in Africa and has a much longer history than most archaeologists believe.

"The real implications are that there was modern human behavior in Africa about 35,000 years before Europe," said lead author Christopher S. Henshilwood, affiliate archaeologist at Iziko - South African Museum in Cape Town , and adjunct associate professor of archaeology at the State University of New York at Stony Brook.

"What has been suggested up until now is that modern human behavior was a very late occurrence. The implication was that though people were anatomically modern in Africa from about 150,000 to 100,000 years ago, they remained behaviorally non-modern until about 40,000 or 50 000 years ago, when they suddenly changed and then moved into Europe and elsewhere."

The paper, authored by Henshilwood with archaeologists Francesco d’Errico of the Institut de Prehistoire et de Geologie du Quaternaire, Curtis W. Marean of the Institute of Human Origins at Arizona State University, Chicago State University anthropologist Richard G. Milo and archaeologist Royden Yates from Iziko - South African Museum, involves the detailed description of 28 bone tools and related artifacts recovered from Blombos Cave, a cave in a cliff overlooking the Indian Ocean at the extreme southern tip of South Africa. Though other bone tools of similar antiquity have been found previously at other sites in Africa, for example at Katanda in the Democratic Republic of the Congo, the Blombos discovery is the first indisputable evidence of an in situ Middle Stone Age bone tool industry. All other Middle Stone Age tools have either been singular finds, or the context has been disputed.

Bifacially flaked stone points, possibly used as spearheads, occur above and within the layers in which the bone tools were found. Archaeological sequences from other sites with bifacial points in the southern Cape date to about 65, 000 years ago, suggesting the bone tools at Blombos are at least as old.

Furthermore, a distinct sterile yellow sand horizon lies above the dark, anthropogenic (human produced) sediments that contain the bifacial points and bone tools, and below dark anthropogenic sediments of more recent age. The sand layer acts as a clear stratigraphic break because any penetration through this yellow sand by younger materials from above would be clearly visible and the sand layers are clearly undisturbed above where many of the bone tools occur.

At other archaeological sites in South Africa, such as at Die Kelders Cave 1, similar dune layers are found and they date to the Last Glacial (roughly 60,000-70,000 years ago) when the ocean withdrew further from the current coastline. On geological grounds, the sand layer at Blombos is almost certainly of similar age, making the bone tools somewhat older. Direct dating of these sterile yellow dune sediments and of burnt stone from the same layers as the bone tools using thermoluminescence methods is well advanced and the results are expected to be released shortly.

According to Marean, bone tools have been seen as one of a variety of significant indicators of modern human behavior because of the greater skill and labor involved in producing them and the shift to more specialized tool manufacture that generally accompanies them.

"In Europe, prior to 35,000 years ago, people did not make formal bone tools," said ASU’s Marean. "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 has been frequently cited as an important item on the "trait list" – a list of archaeological details traditionally seen as indicators of the presence modern human behavior in stone age and upper Paleolithic populations. Other items on the list include the hunting of large fish, the use of decoration, and the production of art – 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,” Henshilwood notes. Also found earlier at the site was a fragment of “deliberately engraved bone” (from a report published in Journal of Archaeological Science 28, Henshilwood et al. and a paper by d’Errico et al in Antiquity).

"Based on extensive evidence from European sites, what has been cited repeatedly is that there was an Upper Paleolithic ‘symbolic explosion’ that archaeologists have said indicates the best recorded beginning of modern human behavior at about 35,000 years ago," said Henshilwood. "The evidence from this cave, together with other evidence coming from other sites, is now starting to say to us that this is very questionable. We’re seeing evidence of a comparable change in Africa, but in the Middle Stone Age -- more than twice as far back in time." “The African record is starting to show evidence that is making it look fundamentally different from Eurasia at the time. We’re getting a lot of evidence for symboling behavior, and that is almost certainly related to language,” said Marean.

Henshilwood and Marean both point out that the Blombos Cave material is likely to be just the beginning of an extensive body of evidence for early behavioral modernity in Africa, as information from a number of current digs begins to be published.

“Right now we are only scraping the surface of information about pre-historic Africa,” said Henshilwood. “Europe, has been extensively excavated over the last 70 or 80 years and Europeans have an enormous amount of background information to draw on. 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.”

“I think that when we start to get a big sample, the picture of modern human evolution is going to look very different,” said Marean. “A clear picture is emerging. This puts the behavioral evolution in step with the anatomical evolution. “Once again, in terms of human evolution, we are seeing Africa as being precocious: Bipedal hominids evolved in Africa; the first real increase in brain size occurred in Africa; and now, we are beginning to see that the last great advance, the development of modern behavior, was made in Africa as well. Now the question becomes where in Africa did this first begin to happen, and why did it happen?” he said.

Arizona State University. November 2001.


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