June 14, 2012 at 2:00 PM ET
When archaeologists tried out a new technique to determine the age of Spain's most famous Paleolithic cave paintings, they were surprised to discover that the paintings were thousands of years older than previously thought — so old that it's conceivable they were painted by Neanderthals.
The technique just might change the way we think about the paintings, and the way we think about our long-extinct, long-maligned Neanderthal cousins as well.
"Neanderthals, of course, have had this bad press for a long time," the University of Barcelona's Joao Zilhao, a member of the research team, told reporters. "But the research developments over the last decade have shown that this is probably not deserved."
The findings being reported today represent just an initial step in an "ongoing program" to date hundreds of European cave paintings more accurately, said the University of Bristol's Alistair Pike, lead author of a paper published in the journal Science. It's still too early to say conclusively whether Neanderthals were behind at least some of the artistry. However, Pike and his colleagues are confident that the earliest paintings go back at least 40,800 years. That time frame matches up with the earliest evidence of the presence of anatomically modern humans in Europe. It's also thousands of years earlier than the previously accepted maximum age, based on carbon dating.
"We were not expecting these results," Zilhao said. "When we put this project together, the idea was to improve the chronology of rock art, and particularly in the case of Spain."
Penn State archaeologist Dean Snow, who wasn't part of the research team but has worked on some of the same cave paintings that were recently put to the test, was impressed by the results. "The basic findings are the sorts of things you could take to the bank," he told me. But he also acknowledged that the latest findings produce "three or four new problems that we didn't have before."
"Now, with these older dates, we have to entertain the possibility that there might have been some Neanderthal involvement in some of these paintings," Snow said. "We've never really seriously considered that before."
How the tests were done
The tests were conducted on 50 Paleolithic paintings in 11 Spanish caves, including the famous pictures of horses and human hands at the Altamira and El Castillo caves. In the past, the paintings have been dated using radiocarbon tests, but Pike's team used a different technique that analyzed the proportions of uranium, thorium and related elements in the calcite deposits that formed above and below the paintings. Those proportions vary over time, due to radioactive decay, and can tell you how long it's been since the calcite was formed.
That's an interesting approach for several reasons: First, the scientists don't have to depend on getting a reading from the paint itself, which may be contaminated or may not even be amenable to carbon dating. Also, the calcite deposits are scraped away, using a knife or a drill, until the pigment just begins to appear beneath it. "That does two things," Pike explained. "It means we stop before we damage the painting, and secondly it proves to us and our audience that these things are directly above the art itself."
The scientists can thus be confident that the age they get will be the minimum age for the artwork. In some cases, the scientists could sample flowstone deposits beneath the layer of paint to get a maximum age as well.
The tests took advantage of the state of the art in mass spectrometry, which means the scientists didn't require much of a sample. The scrapings amounted to as little as 10 milligrams, which is about the weight of a grain of rice. "Perhaps 20 years ago, we would have needed a whole gram of material, and now we need one-hundredth of that size," Pike said.
That minimizes the impact on the caves, which is a sensitive topic for the officials in charge of the caves. "Getting permission to work in a cave is really difficult," Snow explained. "The bureaucratic and political difficulties of getting this work done are substantial."
Pike and his colleagues pioneered this process years ago, in a project aimed at verifying the dates for 12,800-year-old cave engravings in England's Creswell Crags, but the tests reported today represent the highest-profile application of what's known as uranium-series disequilibrium dating.
What the tests found
The uranium tests, like previous radiocarbon tests, showed that there was wide variation in the age of the paintings. The El Castillo paintings yielded a time frame stretching from 22,600 years ago all the way back to at least 40,800 years ago. That farthest-back age is particularly telling. Previously, archaeologists had thought the paintings went back to about 38,000 years. The new tests push the age back to near the time when modern humans were first thought to have inhabited the area, around 42,000 years ago.
Pike said that raises three scenarios: El Castillo's modern humans might have developed their cave-painting skills during their migration out of Africa, and put it to use when they arrived in Europe. After all, communities of Homo sapiens who lived in Africa and the Near East showed evidence of artistic behaviorgoing back as far as 75,000 to 100,000 years. Another possibility is that humans started painting cave walls soon after their arrival in Europe — perhaps as the result of cultural competition with the native Neanderthals, who are known to have inhabited the region as far back as 250,000 years ago. Or the Neanderthals themselves could have created the first paintings, and Homo sapiens picked up the artistic habit while Homo neanderthalensis faded away.
Zilhao said the Neanderthal vs. Homo sapiens debate could shed light on the roots of our own culture. "Cave painting is of course one of the most exquisite examples of human symbolic behavior," he said. "And that's what makes us human."
Although cave art has not previously been linked to the Neanderthals, Zilhao pointed out that the past few years have provided ample evidence that the species had an artistic bent. In 2010, he led a research team and fellow researchers suggested that Neanderthal cave-dwellers wore ornaments and painted their bodies with mineral-based pigments. Other researchers have found a perforated bear bone that may or may not have been shaped as a flute for Neanderthals, as well as bird feathers that may have been used as Neanderthal ritual objects or fashion statements.
The researchers noted that the earliest paintings were not figurative works, but instead reflected simpler motifs such as dots, disks and lines. For example, the 40,800-year-old painting in the El Castillo cave was a large red disk, probably created by blowing pigment onto the rock surface. Nearby, there was the red outline of a hand, most likely made by placing the hand on the rock and blowing pigment over it. That stencil was found to be at least 37,300 years old.
"What's really exciting about the possibility that this is Neanderthal art is that anyone, because it's open to the public, can walk into El Castillo cave and they can see a Neanderthal hand on the wall," Pike said.
Just how possible is that?
"In probabilistic terms, I would say there is a strong chance that these results imply Neanderthal authorship," Zilhao said. "But I will not say we have proven it, because we haven't, and it cannot be proven at this time. It's just, you know, my gut feeling."
What lies ahead
Pike said further tests would show whether Zilhao's gut feeling was correct.
"I think it's a fairly straightforward thing to prove if they were painted by Neanderthals. ... All we have to do is go back and date more of these samples, and find a date that predates the arrival of modern humans in Europe," he told me.
The research team is currently concentrating on hand stencils and red disks, which appear to be the oldest types of cave paintings in Spain. If the minimum dates turn out to be significantly older than 42,000 years, that would be strong evidence that Neanderthals were involved, Pike said.
Snow said the big issue with uranium-series dating has to do with the accuracy of the process. "You've got to have measurement capabilities that are really, really precise," he said. "They can't tolerate anything like the kind of sloppiness and standard error that we had to tolerate in the past, using carbon dates."
He said it was a good sign that the research team ran multiple tests on succeeding layers of calcite and got back results that showed a consistent progression of dates. This suggests that uranium-series dating can go back to time frames where carbon dating becomes less reliable. "For the profession, part of the excitement is going to be that we've got some technologies that are going to be viable for sites in the 30,000- to 50,000-year range," Snow told me.
Zilhao said the research could eventually smash our stereotypical view of the Neanderthal tribe — which died out more than 20,000 years ago. Scientists suspect that the Neanderthals fell victim to competition with us Homo sapiens types, but they also have found that the species contributed to our genetic heritage through interbreeding.
"This evidence is, at least to my mind, sufficient for us to think about Neanderthals as fundamentally human beings that were simply, if you want, racially distinct. This is quite visible in aspects of their skeletons," Zilhao said. "What will change with the demonstration, if it comes, that Neanderthals were also the first cave artists? I guess [it would be] corroboration of the already-existing evidence, and perhaps if you want a catchphrase, the last nail in the coffin of the notion of Neanderthals as the archetypal 'dumb.'"
Update for 9:30 p.m. ET: University of Arizona geochemist Warren Beck got back to me with his outside perspective on the uranium-series test, and in a word, he thinks it's an "improvement" on previous methods when it comes to figuring out the age of rock art. It doesn't render radiocarbon dating totally obsolete: If you're trying to nail down the chronology of a charcoal drawing on a cave wall, carbon dating is what you want. But if you're trying to determine the age of a painting left behind in red ochre, or if you're working with paintings that go back further than, say, 40,000 to 45,000 years, "this is the way to do it," Beck told me.
Beck thought Pike and his team took "a very conservative approach here." Because the samples were taken from calcite deposits that formed over the paint in the Spanish caves, the team could be significantly underestimating the actual ages of the paintings themselves. "They could be substantially older," Beck said. That's one of the reasons behind Zilhao's gut feeling about Neanderthal involvement.
A few of today's reports about the research have included skeptical comments from Eric Delson, a paleoanthropologist at Lehman College and the American Museum of Natural History in New York. "There is no clear evidence of paintings associated with Neanderthal tools or fossils, so any such evidence would be surprising," Delson told The Associated Press' Seth Borenstein. He said his view was that Neanderthals were moving away from these caves around 41,000 years ago.
Delson told Reuters' Sharon Begley that the oldest Homo sapiens in Europe "may date from 45,000 to 42,000 years ago. ... There is no need to hypothesize that Neanderthals created these paintings." Could further tests by Pike and his team change Delson's mind? "The evidence will become very straightforward if we have these dates of 45,000 years or so," Pike said. Which is another way of saying, "Stay tuned."
More about ancient cave art:
In addition to Pike and Zilhao, the authors of "U-Series Dating of Paleolithic Art in 11 Caves in Spain" include D.L. Hoffmann, M. Garcia-Diez, P.B. Pettitt, J. Alcolea, R. De Balbin, C. Gonzalez-Sainz, C. de las Heras, J.A. Lasheras and R. Montes. The 11 caves that were sampled are Pedroses, Tito Bustillo, Las Aguas, Altamira, Santian, El Pendo, El Castillo, La Pasiega, Las Chimeneas, Covalanas and La Haza.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.