Solving one of humanity’s oldest ‘missing person’ cases

Stones & Bones is back in your inbox with your biweekly dose of the latest paleontology and archaeology news. I’m Nicholas St. Fleur, a science editor at National Geographic, and today I’m bringing you up to speed on the search for ancient DNA in prehistoric cave art. 

We know many of you readers work in the world of Stones & Bones, so if you know of research that should be on our radar or interesting people we should be talking to, please reach out to me at Nicholas.St.Fleur@natgeo.com. 

Standing beneath the chandelier stalactites of Spain’s Nerja Cave in a white biohazard suit complete with face mask and gloves, National Geographic Explorer Genevieve von Petzinger looks more like a crime scene investigator than a paleoanthropologist.  

That’s because she is working on a missing person case—one that’s tens of thousands of years old. 

Earlier this week, von Petzinger ventured into the shadowy subterranean site to analyze its famous Ice Age art: crimson dots, hand stencils, and drawings of deer, horses, and other animals, some dating back more than 40,000 years. The expedition was part of a years-long, audacious mission to extract ancient DNA from cave art itself. 

If successful, the genetic signatures could illuminate a far better portrait of the prehistoric painters than what artifacts and skeletal remains can reveal. 

“We have the stones and the bones … but we’re trying to rebuild entire worlds from these little clues,” von Petzinger, a rock art specialist with the international FIRST-ART research team, told me when we chatted before her trip. “One of the things that would be really helpful for us is if we knew who the artists were.”  

Cave art DNA could provide direct answers to a range of questions: Where did the artists come from? Were they male or female? Did they belong to the same family? And, most tantalizing, were they Homo sapiens or Neanderthals?  

The answer to that last question could help redraw our preconceived notions of what Neanderthals were capable of creatively. 

“All of these things we can speculate; we can wonder,” she says. “But until you have it directly pulled off a wall, you don’t know for sure.”  

Von Petzinger admits her project, which is funded by the National Geographic Society, is “on the edge of possible.”  

Researchers have previously extracted ancient human DNA from cave dirt and even from a deer-tooth pendant worn around a woman’s neck 20,000 years ago. But no one, including von Petzinger, has successfully recovered ancient human DNA directly from cave art. Doing so would require the perfect set of conditions—and a paintbrush stroke of luck.  

To start, ancient artists would have had to leave DNA behind. Perhaps they shed skin cells while touching their limestone canvas. Or maybe they used a form of Paleolithic “spray paint” to create hand stencils: placing their hand on the cave wall, then blowing pigment from their mouth or through a hollow bird bone to make an outline of their hand—drenching the wall in saliva droplets. 

Next, the cave itself needed to have contributed to the masterpiece. Over the years, acidic water would need to seep through cracks in the rock, dissolving the limestone and ultimately leaving a layer of translucent calcite over the painting, sealing it like a time capsule. That protective layer would, in theory, shield the artists’ DNA from degradation and contamination over millennia.  

“It’s almost like Saran Wrapped—like a Ziploc baggie from the Ice Age,” von Petzinger says. 

Nerja Cave and other limestone caves in Spain may meet these conditions. 

I asked National Geographic Explorer Maxime Aubert what he makes of the feasibility of this research. He’s an archaeologist and geochemist at Griffith University in Australia who specializes in dating rock art and human remains. Earlier this year, he and his colleagues announced they had found the oldest known rock art in a cave in Indonesia, dated at 67,800 years old.  

Aubert told me that his team has also tried for a decade to extract DNA from Indonesian rock art. They’ve tested for flaking paint samples on cave walls, as well as pigment sealed beneath cave formations, all without success. 

“That said, I would not rule out the possibility entirely,” he told me over email. 

Southeast Asia is warm and humid, which is less than ideal for preserving ancient DNA. But the European caves that von Petzinger studies, with their cool, stable environments, may be more promising. 

Even then there are more hurdles that a researcher would need to cross. “The main question is not whether DNA extraction is theoretically possible,” Aubert says, but rather whether enough of it can survive to be distinguishable from contamination and environmental DNA. 

That’s why von Petzinger and her team are decked out in personal protective gear. “That way we don’t accidentally breathe on it, spit on it, put our hair in it, sweat in it,” she says.  

Also essential is the way they retrieve the DNA samples. Using a sterilized scalpel, von Petzinger slices through the calcite layer on the surface and collects tiny shavings from the rock art layer beneath. She then seals these samples in tubes to send to her colleagues at the Max Planck Institute for Evolutionary Anthropology in Germany for genetic sequencing.  

She says the DNA analysis techniques are sophisticated enough to differentiate between ancient DNA and contaminants from the crew. “If you’re the one who shed a hair, you’re going to be publicly shamed,” von Petzinger jokes. 

Nerja Cave is just one of the locations she and her colleagues are visiting on this expedition. Yesterday they sampled finger markings at Cueva de la Victoria, and today they were in Ardales Cave, which von Petzinger describes as a “winter wonderland” where quartz mixes with calcite to make the entire cave glitter. 

In addition to conducting ancient DNA research, another goal of this trip, she says, is to train other scientists on how to potentially extract DNA from cave art. There are about 400 known painted caves in Europe, many in Spain and France. Globally, there are hundreds more.  

Even if she and her colleagues aren’t successful today, she says collecting the samples is crucial because one day they might develop technology capable of decoding the identities of these anonymous Ice Age artists.  

Von Petzinger would like DNA sampling to become standard practice for scientists investigating cave art, one as common as radiocarbon dating. And this work, she adds, is also pressing. Caves can collapse and flood, endangering the artwork inside. 

“We may never get to go into this little time capsule of ancient humanity again,” she says. “If we’re taking samples out, even if we lose the cave, we still have stuff that’s preserved for future generations.” 

Getting unstuck

Mastodon tusks, dire wolf skulls, and saber-toothed cat fangs are among the more than 3.5 million fossils pulled from the La Brea Tar Pits that are going into storage this summer. The museum will close on July 7 for two years as it gets remodeled into the Samuel Oschin Global Center for Ice Age Research, a hub for studying the creatures that got stuck in the muck 50,000 to 11,000 years ago. 

Luckily for the moving crew, the fossils are much lighter than those of dinosaurs. That’s because when these animals fell into the bubbling asphalt, their remains were pickled in petroleum rather than lithified by minerals.  

“These are bones, not stones,” says Regan Dunn, a paleobotanist and a curator at the tar pits. That also makes them much more delicate, she tells me. In total, the crew expects to pack about 130,000 pounds of specimens, many in special archival foam, and ship them off-site until the museum reopens in time for the 2028 Summer Olympics. 

On the trail of the world’s best mummy sleuths

A mummy’s microbiome is mesmerizing. Among the tenants recently found in Ötzi the Iceman’s 5,300-year-old stomach was yeast that somehow survived the sub-zero temperatures that have preserved his body since its discovery in 1991. Researchers cultivated the yeast to make sourdough, and now they’re pondering if they can use it to ferment beer. 

In the July issue of National Geographic, we take a closer look at the mummy sleuths decoding our prehistoric guts and poop. As writer Nicola Twilley puts it, their discoveries “could offer a time machine of sorts, a way of glimpsing the ancient human microbiome in all its ancestral glory before it was decimated by the ravages of today’s ultra-processed diets.” 

A cocktail with a 66 million-year vintage

This week, I drank a dinosaur.  

National Geographic Explorer, paleontologist, and amateur “paleomixologist” Ryan Carney stopped by Base Camp on Monday for our annual Explorers Fest and mixed up a few of his dinosaur-inspired cocktails—including one made with a 66 million-year-old Triceratops bone.  

Carney had found the fossil, which was part of the three-horned beast’s frill, with fellow Explorer Tyler Lyson on a ranch in North Dakota. The bone was “nonscientifically important” and safe to ingest, he assured those of us at the tasting, as it was essentially iron oxide, which is also used as a food coloring.  

He calls his cocktail Triquilatops, and it features Chambord, blue curaçao, and Hornitos tequila topped with a sprinkle of bone powder, which Carney keeps in a tiny vial inside a 3D-printed Archaeopteryx skull he wears around his neck. Mine was a mocktail, but my colleagues said the drinks were delicious!  

READ MORE: The first known dinosaur feather inspired decades of dispute. Here’s why.