Evidence from a cave in eastern Ethiopia has revealed something extraordinary about the origins of symbolic thought among humans. Forty-thousand years ago, Porc-Epic Cave was surrounded by lush grassland full of lakes and rivers. It was home to a thriving community of people who devoted considerable time to processing ochre, a reddish powder used for variety of things including paint. Writing in PLoS One, anthropologists Daniela Eugenia Rosso, Africa Pitarch MartÃ, and Francesco d’Errico describe how they worked with the National Museum of Ethiopia to analyze these Middle Stone Age people's ochre-making tools. What they found was this workshop's artisans produced a far more complicated array of substances than anyone had understood before. Some were used for art and decoration, and others were used for engineering better weapons.
Anthropologists often use ochre processing as a proxy for the origins of human symbolic thought. That's partly because ochre is relatively difficult to make, requiring a few steps and at least two kinds of tools. As the researchers write, ochre comes from "rocks containing a high proportion of iron oxides, often mixed with silicates and other mineral substances, which are red or yellow in color, or are streaked with such shades." Ochre itself is made by pulverizing the rock with one kind of tool and then reducing it to a powder between two grindstones.
There are many aesthetic uses for ochre, including as fabric dye, paint for cave walls, or a stain for rocks and other materials. All these artistic or cosmetic uses imply symbolic thought. But early humans also used ochre for utilitarian purposes too. The powder was mixed with other adhesives to keep weapons snugly attached to their hafts. Put simply, ochre was a key ingredient in glue.
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