Deep African roots for toolmaking method

Stone-tool makers living in southern Africa 75,000 years ago pushed the cutting edge in more ways than one. These intrepid folk sharpened the thin tips of heated stone spearheads using a forceful technique previously dated to no more than 20,000 years ago, a new study finds.

This stone-tool making method, called pressure flaking, was invented and used sporadically in Africa before spreading to other continents, according to a team led by archaeologist Vincent Mourre of the University of Toulouse-Le Mirail in France. Having a flexible repertoire of tool-making methods aided the survival of modern humans who left Africa beginning around 60,000 years ago, the scientists propose in the Oct. 29 Science.

The finding fits with the idea that symbolic art, rituals and other forms of modern human behavior developed gradually over hundreds of thousands of years, not in a burst of cultural innovation marked by cave paintings and other creations that appeared after 50,000 years ago in Western Europe.

Excavations of sediment dated to 75,000 years ago in South Africa’s Blombos Cave produced stone artifacts displaying signs of pressure flaking, Mourre and his colleagues say.

“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.

Blombos Cave and nearby sites of comparable age previously yielded engraved pigment chunks (SN Online: 6/12/09), decorated ostrich egg shells (SN: 3/27/10, p. 10) and heat-treated stone artifacts (SN: 9/12/09, p. 15).

Southern Africans occasionally made items with symbolic meanings and used special forms of toolmaking beginning 100,000 years ago or more, Villa suspects. These practices flourished in and out of Africa starting about 40,000 years ago, in her view.

Pressure flaking consists of trimming the edges of a finished tool by pressing with a bone point hard enough to remove thin slices of rock. This process creates the narrow, evenly spaced grooves found on flint tools from Europe’s 20,000-year-old Solutrean culture and prehistoric Native American groups.

Wider, more irregular grooves characterize 36 pressure-flaked Blombos tools, which were made from silcrete, Villa says. This rock, a silica-rich material, is of lower quality than flint and requires heating to ready it for pressure flaking.

Villa and her colleagues identified glossy areas on silcrete tools at Blombos that, they surmise, formed when the stones were pre-heated for pressure flaking. Other marks on the artifacts indicated that they had been attached to handles, probably as spearheads.

By pressure flaking preheated replicas of the Blombos finds made from silcrete collected near the South African cave, Mourre was able to reproduce marks resembling those on the ancient artifacts.

Tool makers likely used pressure flaking by 100,000 years ago in East Africa, remarks archaeologist John Shea of Stony Brook University, New York. Several sites there contain stone artifacts, many made from obsidian, that deserve close analysis for pressure-flaking marks, Shea says.

Shea, an expert at making replicas of Stone Age tools, notes that pressure flaking can be taught in 30 minutes to a novice. “It is, literally, so easy a caveman can do it,” he says.

Pressure flaking doesn’t add much sharpness or strength to a cutting instrument, Shea adds. Blombos tool makers probably employed this technique to advertise their skill or to denote users’ social identity, he proposes.

Archaeologist Curtis Marean of Arizona State University in Tempe calls the evidence for pressure flaking at Blombos “suggestive but not completely convincing.” Further work needs to confirm that pressure flaking of replicated silcrete artifacts consistently produces marks like those on the Blombos finds, Marean asserts.

Knowledge of pressure flaking doesn’t imply any special mental or toolmaking abilities, he remarks. Like Shea, Marean regards pressure flaking as a simple way to finish shaping tools made from certain types of stone.

“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.”