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45,000 years ago, in an area that is now part of Ethiopia, humans found a roomy cave at the base of a limestone cliff and turned it into a special kind of workshop. Inside, they built up a cache of over 40 kilograms of reddish stones high in iron oxide. Using a variety of tools, they ground the stones into different colored powders: deep reds, glowing yellows, rose grays. Then they treated the powder by heating it or mixing it with other ingredients to create the world's first paint. For at least 4,500 years, people returned to this cave, known today as Porc-Epic, covering its walls in symbols and inking their bodies and clothes. Some anthropologists call it the first artist's workshop.

Now, a new study in PLoS One suggests that the cave offers us a new way to understand cultural continuity in the Middle Stone Age, when humans were first becoming sophisticated toolmakers and artisans. Paleoscientists Daniela Eugenia Rosso, Francesco d’Errico, and Alain Queffelec have sorted through the 4,213 pieces of ochre found in the cave, analyzing the layers of history they represent. They argue that Porc-Epic is a rare continuous record of how humans pass on knowledge and rituals across dozens of generations.

It's possible that humans used Porc-Epic to make conventional tools, as ochre can be used for adhesives and for tanning hides. But after analyzing the methods people used to powder the rocks, researchers are fairly certain that these techniques were optimized to produce small amounts of powder best suited for decoration and art. Over the centuries that people used the cave, they see many changes. Early artisans ground the ochre down with other rocks to produce powder, but later ones would reduce the rocks to flakes before crushing them.

Color choice also seemed to change over time. "Although red and dark red shades are dominant in all levels, they become proportionally less well represented in levels in which ochre is more abundant," write Rosso and her colleagues. "These levels are richer in grey, brown, orange, and yellow pieces and pieces of multiple colors. We also observe a decline in dark red, and red+yellow, and an increase in red, and red+grey."

At roughly the midpoint of the cave's use, perhaps about 43,000 to 42,000 years ago, there is a noticeable uptick in the amount of ochre being processed. That's when the researchers find that red is "less well represented," supplemented by a wide range of colors. Later in the life of the cave, when the grinding techniques had all but stopped, colors become less vibrant.

One of the great mysteries of Porc-Epic cave is what happened during that peak period when suddenly we see people working with a large number of different colors of ochre. The cave appears to have been bustling with activity. There's even evidence of what might have been apprentices, whose grinding and flaking work is far more irregular and imprecise than what we see typically. It seems obvious that a larger number of people were using the cave at this point, but why? The researchers believe there was no dramatic cultural shift taking place, simply because there are no changes in the other kinds of tools that people were using at the time. There may have been a change in the environment that made the area more hospitable for larger populations. Or perhaps the existing population was simply demanding more ochre powder.

But perhaps the most incredible part of the Porc-Epic cave is the lack of change. For more than four millennia, humans used this cave to produce paint out of the same kinds of reddish rocks. Their techniques and favored colors varied a little over time, but for the most part they stuck with what they had learned from generations of ancestors. We're left wondering what the ochre symbolized for these people. The researchers wonder whether they may actually have perceived colors differently than modern people do. They write:

Continuity in raw material choice through time supports the hypothesis that Porc-Epic late Middle Stone Age inhabitants provisioned themselves over a considerable duration with ochre types featuring different textures, hardness, density, coloring power, and shades. Although most of the color types fall within the broad category of "red," a small proportion of pieces show color features that appear to fall outside this category. This raises the question of whether different shades of "red" and other colors were perceived as distinct categories by Porc-Epic inhabitants.

Perhaps each shade of red, each tinge of yellow or gray, held its own significance. That might explain why Porc-Epic artisans always kept many different types of ochre on hand. These different types of ochre may have been elements of a culture whose traditions endured for many thousands of years, whether in rituals or fashions or something we can't imagine.

Looking into Porc-Epic cave, we're forced to acknowledge that ours is not the first society on Earth to boast millennia of ancient history. Back when Neanderthals still walked the Earth, our ancestors could look back on their distant past and touch the same stones that their forebears had, thousands of years before.

PLoS One, 2017. DOI: 10.1371/journal.pone.0177298