Smeared on shells, piled in graves, stamped and stenciled on cave walls from South Africa to Australia, Germany to Peru, ochre has been a part of the human story since our very start — and perhaps even earlier.
For decades, researchers believed the iron-rich rocks used as pigment at prehistoric sites had symbolic value. But as archaeologists turn up evidence of functional uses for the material, they’re realizing early humans’ relationship with ochre is more complex.
Tammy Hodgskiss, an archaeologist at the University of Witwatersrand in South Africa, has studied sites in that country such as Rose Cottage Cave, where evidence of ochre use spans more than 60,000 years.
“People may say ochre is the earliest form of art and symbolism, but there’s more to it,” she says. “Ochre shows how our brains were developing, and that we were using our environment. It bridges the divide between art and science.”
Ochre is, in fact, one of the most important proxies researchers have for charting the evolution of human cognition. Hodgskiss adds, “We look at the action sequences to see what cognitive abilities were needed: Did it have to be heated? Did it need to be buried in the hearth?”
And recent finds in Africa have pushed back the start date for our species’ long love affair with the material, hinting that modern human cognition may have developed much earlier than we thought. Even more intriguing: A handful of researchers now suspect ochre may have actually fueled both brain development and our species’ expansion around the globe.
“The emergence of modern human behavior is one of the most important debates happening now,” says archaeologist Daniela Rosso of the University of Bordeaux and University of Barcelona. “And ochre plays a central role in that debate.”
Rock of Ages
“Ochre is not one thing,” says archaeological scientist Andrew Zipkin of the University of Illinois at Urbana-Champaign. “That’s one of the most annoying things about studying it.”
Ochre is most commonly defined by archaeologists as any iron-rich rock that can be used as a pigment. Most people associate the term with hematite, or red ochre, chemically known as Fe2O3. But a range of other rocks appear in the archaeological record, from the yellow ochre goethite to the often-dramatic specular hematite, sometimes called specularite.
Zipkin contrasts working with specular hematite — a heavy, glittery rock that’s deep purple-red and has a high iron content — with material much lighter in both color and iron content from Kenya’s volcanic Rift Valley: “They’re both ochre, but elementally and chemically they are radically different.”
To complicate matters even more, when heated to at least 480 degrees Fahrenheit, yellow ochre’s crystal structure changes and the goethite can transform into hematite, or red ochre.
Ochre use became widespread in the Middle Stone Age, a period of about 50,000 to 280,000 years ago, and during this time, Hodgskiss says, “there seems to be a preference for red — a larger percentage of the ochre used was red. But a lot of these sites have hearths one atop another. It’s possible some of the red ochre we find may have been yellow once.”
Confidently dated archaeological sites showing ochre worked by humans now go back more than 300,000 years, close to the emergence of Homo sapiens. And we’re not alone in the use of ochre. Numerous sites in Europe and western Asia show that our closest evolutionary kin, the Neanderthals, also used ochre beginning at least 250,000 years ago, although their applications of the material appear much more limited. Intentional ochre collection and use, however, may have begun much earlier in our family tree.
“I wouldn’t be surprised in the least if the last common ancestor of Homo sapiens and Neanderthals collected pigment,” Zipkin says. “Things like this don’t arise out of nowhere.”
Ochre use appears limited to the genus Homo, but the material’s attractiveness is likely rooted in an adaptation that occurred about 23 million years ago in an early primate ancestor: trichromatic vision. Old World monkeys, apes and hominins — the branch of the ape family tree that includes humans — inherited that ancestor’s ability to see red, particularly against a green background.
Detecting the color red likely helped our distant ancestors discern which fruits were ripe and ready to eat, and which leaves were young, tender and more easily digested. As our own hominin lineage became both more social and more exploratory, the ability to see red would have provided a particularly useful advantage.
“If you’re going to walk into someone else’s territory, you want to signal that you’re a friend, not a foe,” says George Washington University paleoanthropologist Alison Brooks. “Anything red is extremely visual.”
Brooks adds: “There are lots of rocks that come in powdery form that aren’t red and didn’t get used. Ochre has importance because it signals to others. … Its use is extremely widespread, even in the modern world. Why do we color our world when our world is colorful already? It could be a lot of reasons, but it’s a form of communication.”
That communication, or signaling, is what archaeologists and anthropologists call symbolic behavior, and it’s why ochre use is often cited as a proxy for the cognitive ability of the people who used it. Collecting ochre, turning it into a powder or paint, and then applying it to the body or surroundings to express something to others is a multistep process, done to convey something to another individual who possesses the ability to understand the signal.
In addition to being highly visible over long distances by our species, red is also the color of blood, charging it with even more symbolic significance.
It’s no coincidence, Brooks says, that “some languages have only two words for color: red and not-red. A language may not have a word for green or blue, but there is always a word for red.”
Humans have collected and used ochre since the dawn of our species, including at these key archaeological sites:
1. Olorgesailie, Kenya: Researchers recently discovered two pieces of ochre, intentionally shaped by humans, that were at least 307,000 years old. It’s the oldest such confidently dated find.
2. Blombos Cave, South Africa: Dated to about 100,000 years ago, ochre-processing “tool kits” and other artifacts found at the site — including an engraved piece of ochre, the oldest known art of its type — suggest early humans were capable of modern, complex behaviors much earlier than once thought.
3. Northern Cape, South Africa: Ochre fragments from a cluster of sites suggest the material was being collected as early as 500,000 years ago, though some researchers dispute the dates.
4. Twin Rivers, Zambia: Pieces of ochre up to 266,000 years old include a quartzite cobble stained with ochre that may be the earliest known ochre-processing tool.
5. Porc-Epic, Ethiopia: The largest collection of ochre pieces ever found, weighing nearly 90 pounds in total, includes a variety of tools to process and use the material 40,000 years ago.
6. Maastricht-Belvédère, the Netherlands: Fragments of ochre up to 250,000 years old, found among animal bones and stone artifacts, are the oldest evidence of the pigment’s use by Neanderthals.
7. Rose Cottage Cave, South Africa: Researchers have pieced together a story of ochre collection and processing that spans more than 60,000 years, from 30,000 to 96,000 years ago.
8. Madjedbebe, Australia: Various ochre pieces, found among thousands of stone tools, helped researchers establish in 2017 that humans were in Australia 65,000 years ago — 20,000 years earlier than researchers thought.
There’s An App For That
But some archaeologists have begun to challenge the idea that ochre was primarily symbolic for early humans. Instead, they believe ochre had a number of functional applications, some of which traditional societies, particularly in Africa and Australia, still employ.
In the arid environment of southern Ethiopia, for example, the Hamar people use ochre to clean their hair. “They use ochre for aesthetic as well as hygienic reasons,” says Rosso, who spent a few days among the Hamar. “There really isn’t this limit to functional or symbolic. They’re combined.”
And in South Africa, Hodgskiss says, ochre is widely used as sunscreen. “You can buy it at hardware stores and in traditional medicine shops,” says Hodgskiss, where the sunscreen is known as ibomvu, the Zulu word for red.
The archaeological record suggests ochre had some other practical uses, turning up on tools and weapons. Experimental archaeologists, who seek to understand how our ancestors used different materials by replicating the processes involved, concluded that ochre was mixed with other substances to create a hafting adhesive used to attach, for example, a stone arrow point to its wooden shaft.
Riaan Rifkin, an archaeologist at the University of Pretoria in South Africa, has been one of the leading proponents of a new, functional interpretation of ochre in the story of human evolution. For nearly a decade, his experiments, along with those of colleagues, have pointed to prehistoric use of the material not just as a sunscreen and adhesive but also an insect repellent and leather preservative.
Rifkin believes, in fact, that ochre’s functional applications may have contributed directly to H. sapiens’ greatest early achievement: spreading across the world. “The use of red ochre as a sunscreen must have enabled humans to traverse longer distances without getting excessively sunburnt. This was an amazing adaptive advantage. They could forage longer and explore further,” says Rifkin. He suspects ochre sunscreen evolved about the same time humans began using ostrich eggshells as containers for water and other provisions, about 65,000 years ago. “As soon as we could carry water with us, had a good [ochre-based] sunscreen and mosquito repellent, and warm [ochre-tanned] clothing, we were able to expand from Africa.”
Not everyone in the field is as enthusiastic about a functional interpretation of ochre. Notably, Brooks says, while ochre may have had practical applications, they were likely secondary to the material’s symbolic use.
“There are a whole lot of other things ochre is used for … but that doesn’t take away from the fact that it is extremely visible from a distance,” she says. Sure it works for gluing together arrowheads, “but quartz sand is found all over South Africa and is a better adhesive; it forms a better bond. If they’re making glue with red ochre, it’s because it’s red.”
Hodgskiss strikes a middle ground as she imagines how human ancestors might have begun using the material: “You’re walking through the landscape, and you see a beautiful red or yellow or purple stone, and you realize you can grind it and get a really nice powder from it. I think the initial attraction was the color. The awareness of its other uses came gradually, over time.”
And humans appear to have adapted those uses to their needs. At Middle Stone Age sites in South Africa, where ochre use was already complex about 100,000 years ago, different types of ochre were rubbed, ground or crumbled depending on the intended application and the individual rock’s hardness, which varies widely.
One of the obstacles to resolving how and why the rocks were used is in their very nature. “Ochre use by definition is destructive,” Zipkin says. “Generally what we find are the remnants. Whatever the application was is gone. The vast majority of ochre used is no longer part of the archaeological record.”
The remnants archaeologists are left with can still be impressive. In Ethiopia’s Porc-Epic Cave, for example, Rosso and her colleagues have studied the largest ochre assemblage ever collected: more than 4,000 pieces weighing nearly 90 pounds in total.
The material was excavated in the 1970s, but in 2016 Rosso and her team performed a high-tech analysis on the pieces, which are about 40,000 years old. “In Porc-Epic, we see the complexity of how the ochre was used by the different tools they needed to work with it,” says Rosso.
Among their findings: assorted tools for processing ochre, such as grindstones, and a limestone pebble with ochre residue on one side. The pebble appears to have been dipped into an ochre-based paint and used as a stamp on an unknown material.
A few thousand miles to the south and much earlier — about 100,000 years ago — people were using ochre in even more complex ways at Blombos Cave in South Africa. In addition to pieces of ochre that appear to have been engraved — the oldest such abstract art in the world — archaeologists have found tool kits that included abalone shells used as containers to mix ochre with crushed bone, charcoal, quartz and other material to make paint.
“The Blombos Cave ‘red ochre paint factory’ represents a milestone in human cognitive evolution,” Rifkin says.
But Blombos is not the only — or even the earliest — such landmark moment. New research points to humans in Kenya working ochre pieces more than 307,000 years ago at a site called Olorgesailie. Brooks, a senior researcher on the Olorgesailie project, describes two roughly finger-sized pieces of ochre that bear the marks of human alteration — and perseverance.
“One of the pieces has been chipped with some kind of sharp object,” Brooks says. “The other one has grinding striations and what seems to be attempted perforation. It looks like someone took something like a chisel and just dug and dug.”
Networking in the Paleolithic
In addition to its use as a stand-in for charting human evolution, ochre also serves as a proxy for human movement. Last July, for example, a Nature study pushed back the earliest human presence in Australia to at least 65,000 years ago, nearly 20,000 years earlier than previously thought. The new date is based on thousands of artifacts from the Northern Australia site of Madjedbebe, including numerous examples of ochre in ground, slab and “crayon” forms.
Thanks to a new technique called elemental fingerprinting, ochre can also provide information about a different kind of human movement: social and trade networks.
“Elemental fingerprinting sounds a little CSI, but it’s the idea that you can sort something back to its origin,” says Zipkin, a member of the Olorgesailie research team and a leader in the method, which involves collecting samples of different kinds of material from a number of sites. The samples are then analyzed to determine the unique geochemical signature of each site. These signatures are made of multiple elements, some of which may exist at one site but not another, requiring archaeologists such as Zipkin to take a shotgun approach in deciding what to look for.
“If you talk to a geologist or a chemist about measuring something in the lab, they’ll say, ‘No problem. How much, say, selenium is in this? OK, we can measure that,’ ” he says. “But archaeologists are not interested in measuring specific elements; we measure everything and figure out later what’s relevant.”
Zipkin typically measures more than 40 elements per sample and could find up to 15 of them useful for the fingerprinting, which creates that site’s geochemical signature. The signatures are added to a database which, when large enough, can be used to determine the geographic origin of material found at an archaeological site.
The ability to discover, by cross-checking the database for a geochemical signature match, that an object found at Site A was actually collected from Site B can have huge significance, says Zipkin. “How far material was transported can be seen as evidence of trade or social networks.”
Elemental fingerprinting has proven particularly important for the Olorgesailie material. The worked pieces of ochre there, while not fingerprinted yet, are the oldest ochre found in the region, and were discovered with pieces of obsidian that came from about 60 miles away.
“The ochre at Olorgesailie appears in the same time period as a new behavior: the importing of obsidian from distant places,” Brooks says. “This is a radical shift in behavior.”
Modern hunter-gatherer societies typically have territories of 12 to 25 miles in diameter, and researchers believe early human groups had similar ranges. The presence of exotic objects from well beyond that range implies different groups were interacting in some way.
“Whether you got it by trade or got it yourself, you had to make contact with people from another group,” Brooks says. At more than 300,000 years old, Olorgesailie is significant because this kind of interaction is a hallmark of modern humans that researchers previously thought developed around 100,000 years ago.
“We see this as the first evidence of a social network,” says Brooks. “The picture of modern human behavior was being put together much earlier than we thought.”
Feed Your Head
Ochre reveals details about our ancestors’ behavior, but could it have played a more active role in our evolution? Marine ecologist Carlos Duarte of Saudi Arabia’s Abdullah University thinks so. The idea came to him when preparing to give a talk on the role of the ocean in our past and future.
“I was aware of research arguing that the use of the marine food web had played a significant role in brain evolution, and expansion, through the supply of omega-3 fatty acids,” Duarte says via email while traveling. “However, when I searched for new research on evidence of use of marine food by early humans, I noticed that over and over, the traces of it, shells, were accompanied by ochre. This link is so prevalent that it could not be a coincidence.”
Indeed, different types of shells have been found with ochre at numerous prehistoric sites around the world. Duarte dug deeper into the archaeological record, eventually publishing a provocative commentary in Trends in Ecology & Evolution. The ingestion of red ochre, suggests Duarte, combined with consumption of seafood, boosted early humans’ supply of docosahexaenoic acid (DHA) and iodine as well as, potentially, iron and other nutrients essential for brain development.
Duarte believes the advantage conferred was particularly valuable for pregnant women: Fortifying a diet with iron from ochre might stave off anemia, a common problem in pregnancy. Combined with seafood, it might also result in a healthier baby. A significant amount of brain development occurs prenatally, when the developing fetus would have received DHA, iodine and other essential nutrients.
The key, Duarte says, is the combination of nutrient-rich seafood and red ochre — the iron in other types of ochre, or in red ochre ingested without protein supplied by the seafood, cannot be absorbed by the body.
But Stanley Ambrose, a paleoanthropologist at the University of Illinois at Urbana-Champaign, dismisses Duarte’s idea. In addition to studying ochre use in the Middle Stone Age, Ambrose is a leading expert in reconstructing the diet of Paleolithic people through chemical analysis of their remains.
“There were plenty of big-brained hominins running around without any access to sea life,” Ambrose says. “Ochre gets smeared on a lot of things, but he’s made a false connection. … They’re good ideas, but you have to put them in context.”
Other researchers are keeping a more open mind. “It wasn’t necessary for them to eat ochre,” says Hodgskiss. “But it’s plausible.”
In fact, geophagy, or intentionally consuming dirt, has been documented in multiple historical and present-day cultures, many of which ingest specific soils medicinally to prevent diarrhea or increase iron intake.
“People certainly engage in geophagy all over the world, especially while pregnant,” Zipkin says. “But I think it’s very, very hard to demonstrate in any meaningful way consumption in the archaeological record.”
While Duarte’s idea has yet to gain traction in the paleoanthropological world, it’s just one of several new directions ochre research is taking. Together with elemental fingerprinting, experimental archaeology and the discovery of new sites, it’s likely the story of humans and ochre has many more chapters to go.
“Fifteen years ago, no one did this work,” Zipkin says. “There are more things now that you can do with ochre than we ever thought possible.”