Scientists working at the Blombos Cave in South Africa believe they have found 75,000 year-old evidence of a sophisticated stone-trimming technique called pressure flaking. If they are correct, it will mean that a complex human behavior developed much earlier in Africa than was previously known. Until now, the oldest evidence for pressure flaking dated to 18,000 BCE. The same site and others located nearby of the same era have yielded engraved stones, decorated ostrich eggshells and heat-treated stone tools.
     Vincent Mourre from the University of Toulouse-Le Mirail (France) lead the team. He notes that the pressure flaking technique was invented and used in Africa and then spread to other continents. "The Blombos evidence for pressure flaking is the oldest we know," says anthropologist and study coauthor Paola Villa of the University of Colorado Museum of Natural History in Boulder. The work was published in the October 29 issue of Science. The findings seem to support the theory that the evolution of modern human behavior occured gradually over time. Elaborate cave art dates to approximately 50,000 BCE.
     The pressure flaking technique is used to finish the edges of a stone tool. Pressure is applied to the edge with a bone which forces off thin flakes from the surface. The process leaves the characteristic narrow, even grooves along the sharpened edge. Villa's team also found tools made from silcrete, which is a softer, silica-rich mineral. These tools appear to have been fire-hardeded before being subjected to the pressure flaking process. There is also evidence of attachment points for handles.
     The scientists attempted to duplicate the tool marks using pressure flaking on rocks found around the cave area. Unheated silicrete could not be pressure flaked. When the mineral was heated, they were able to recreate the edges found on the ancient tools.
     John Shea, an archaeologist from Stony Brook University in New York (U.S.), is known as an expert at making replicas of stone tools. He believes that pressure flaking of obsidian tools developed 100,000 years ago in East Africa. According to Shea, pressure flaking does not improve the sharpness or strength of tools, and may have been used to a communicate the toolmaker's skill or status.
     Not everyone in the scientific community is in agreement about the interprestation of the work of the Villa team. Curtis Marean from Arizona State University (U.S.) calls it, "suggestive but not completely convincing". He believes that pressure flaking tools does not necessarily indicate a leap in human evolution. "If the authors are correct that pressure flaking occurred at Blombos Cave, the result is important in that that it extends the time range of the technique," Marean says. "But it's not game-changing in our understanding of the origins of complex cognition."

Edited from ScienceNews, LiveScience (28 october 2010)