Ancient bone tools and spear points found in cliff-side caves along South Africa's coast appear to be turning back the clock on the emergence of modern human behavior.
In research released here this week, an international team of archaeologists and anthropologists exploring a site called the Blombos Cave described finding tools and large amounts of ochre encased in sandy deposits at least 70,000 years old. Ochre is a mineral widely used as a pigment to adorn bodies and clothing.
An ability to craft and in some cases polish "formal" tools, and the use of symbols, implied by the presence of ochre, are among the behaviors that separate humans from their primate relatives, notes Curtis Marean, an Arizona State University anthropologist and a member of the team that made the discovery.
If the artifacts themselves match the age of the deposits that harbored them, as expected, it could begin to shift the center of gravity for studying the evolution of human behavior from Europe to Africa.
Until now, sites on the European continent dating back some 40,000 years have set the benchmark for tracking the evolution of "behavioral modernity" in humans, who are thought to have expanded out of Africa some 50,000 years ago.
"We are at the frontier of discovery," Dr. Marean said at a series of briefings at the Council for the Advancement of Science Writing in Phoenix. As more evidence emerges from the Blombos site and a growing number of other locations in the region, "I think we are going to find that the pattern is conclusive."
If such a pattern emerges, it could begin to quell a longstanding debate over whether modern human behavior evolved as humans did physically, or whether it began to take shape long afterward. Although physically, modern humans appeared some 100,000 to 150,000 years ago, many have held that modern human behavior only emerged within the past 40,000 years.
The debate has been fueled by the fossil record from this period. That record is rich in Europe, which boasts some 200 to 250 well-excavated sites, Marean says. Until now, the African record has been at best ambiguous. Thus, the timetable for the evolution of human behavior has been based largely on European evidence, he notes.
Europe has a wealth of limestone formations that have caves early people used for shelter. Those caves also helped protect and even fossilize the remains of early inhabitants. For scientists looking for sites, it's easier to ride over the hill than travel to another continent, says Erik Trinkaus, an anthropologist at Washington University in St. Louis. In the most accessible parts of Africa, by contrast, many remains are found on the surface, where it can be difficult to sort out their ages and make connections, he says.
Ancient clues to human behavior
At Blombos Cave, the artifacts came from an unbroken layer of ancient dune sand, capped with a layer of organic material. It was as though the sand layer had been topped with a safety seal to indicate the sample hadn't been contaminated by younger artifacts that drifted down into the lower layer. Thus, the artifacts move to the head of the class as "the best examples of symbolics for this time period," Dr. Trinkaus notes.
The research team, headed by Christopher Henshilwood, affiliate archaeologist at the South African Museum in Cape Town, has been working the Blombos Cave site since 1991. The findings reported this week emerged between 1997 and 2000.
In addition to tools, spear points, and ochre, the site also has yielded clues about the range of creatures the inhabitants hunted - from large fish, seals, and
dolphins to antelope and buffalo.
If the find argues for much earlier origins for modern human behavior than previously believed, it leaves open the question of how that behavior spread. Modern humans are believed to have expanded out of Africa and into Eurasia about 50,000 years ago, researchers say. Blombos Cave information would suggest that they may have headed north as modern humans in behavior as well as in physical appearance.
To Trinkaus, the find "reinforces the idea that modern human behavior emerged in a patchwork fashion over long periods of time."
But no matter how such behavior emerged, the trail for evidence documenting its rise seems to be heading toward southern Africa.
"We need to discard a Eurocentric approach," says Marean. "We can't characterize the African record by what we know from Eurasia. We need to generate an empirical record for Africa that allows us to define the pattern the way it really is."