DNA that sawped into an elk tooth pendant about 25,000 years ago has yielded clues about the ancient woman who wore it.
The tooth, worn as a necklace bead, probably absorbed DNA from the person’s sweat as it lay against her chest and neck. Marie Soressi at Leiden University in the Netherlands and her colleagues from her were able to extract that DNA without damaging the tooth through a new process that took eight years to develop. The technique might reveal unprecedented details about the social customs and gender roles of ancient populations, says Soressi.
“For the first time, we can link an object to individuals,” she says. “So, for example, were bone needles made and used by only women, or also men? Were those bone-tipped spears made and used only by men, or also by women? With this new technique, we can finally start talking about that and investigating the roles of individuals according to their biological sex or their genetic identity and family relationships.”
Scientists have often suspected that ancient tools, weapons, ornamental beads and other crafted artefacts contain DNA from the people who touched them. But getting DNA out of these objects typically means removing sections for analysis – causing permanent damage. “We absolutely didn’t want to do that,” says Soressi.
To see if DNA could be coaxed out of ancient artefacts without destroying them, Soressi and her colleagues tested numerous combinations of chemicals and heating regimes on 10 previously excavated artefacts from Palaeolithic caves in France. They found that placing them in a sodium phosphate solution and raising the temperature incrementally from 21°C to 90°C (70°F to 194°F) led to the release of relatively large amounts of human DNA with no damage to the specimens.
The team then tested the procedure on another 15 excavated bone specimens from one of the caves. Genetic sequencing revealed DNA from many different humans – probably the scientists and technicians who had worked with the artefacts across the years, says Soressi.
To avoid such modern DNA contamination, the researchers then tried their technique on four tooth pendants excavated by colleagues in Russia and Bulgaria who wore sterile gloves and face masks. Their analysis revealed mostly animal DNA that matched the species used to make the pendants.
One tooth pendant from Denisova cave in Russia, however, also contained human DNA fragments, primarily from a single individual. There was enough genetic material for the researchers to positively identify a female Homo sapiens, in addition to the elk (Cervus canadensis) that provided the tooth.
While the human might have rubbed her DNA into the pendant if she had crafted it, the large quantity of DNA recovered suggests she was the individual who wore it, says Soressi. “As a porous material, that tooth was likely soaking in sweat,” she says. “It worked like a sponge, pulling in that human DNA and trapping it there for 25,000 years.”
The DNA showed that the woman was closely related to an ancient tribe that, thus far, had only been found more than 1500 kilometers to the east.
Daniella Bar-Yosef Mayer at Tel-Aviv University, Israel, finds the paper “very exciting”, in part because it could help explain the purpose of ancient jewelery. For example, it might signal something about the identity of the wearer or their group her, or their marital status her, she says. “If we find them in different contexts on men, on women or children of this species or another species, or different age groups, that would give us some better clues about what they’re meant for.”
The technique might also help resolve long-running scientific debates about whether certain artefacts were made and worn by Homo sapiens or Neanderthals, she adds.
The study could open the door to DNA analyzes of museum artefacts across the globe, says David Frayer at the University of Kansas. “Curators are often hesitant to allow their specimens to be damaged for DNA analysis, however small the extraction,” he says. “The absolute strength of this paper is that [their] procedure gets around that. If it can be extended to specimens cleaned long ago, this would represent a great leap forward for ancient DNA work.”