GoKawiilWhen he was a doctoral student at the University of Copenhagen, Eske Willerslev was a nobody. At least, that’s how it seemed to the budding evolutionary geneticist, who was unable to lay his hands on one of the few coveted fossils that might still contain traces of ancient DNA.
Who were the ancient Denisovans? Fossils reveal secrets about the mysterious humans
But frustration turned to inspiration one autumn day in 2000, when he saw a dog depositing its morning poo onto the ground. The droppings contain DNA, he thought, and perhaps, even after rain washes them away, some DNA might remain. And if it does stick around, the genetic material of long-dead animals might also persist in the environment. That would mean he could learn something about those creatures, even without getting access to priceless museum specimens.
Willerslev’s idea was ridiculed by his professors at the time. “I’ve never heard anything as stupid as this,” he recalls one of them remarking. But his hunch bore incredible fruit. In a 2003 paper in Science, he showed that plant and animal DNA could be recovered from a Siberian permafrost core that stretched back 400,000 years1.
Even in the warmer temperatures of a New Zealand cave, Willerslev identified DNA from the extinct emu-like moa (Euryapteryx curtus) in 600-year-old sediments. It was the first time that researchers had used sediment alone to identify long-dead complex organisms.
Two decades on, the study of ancient DNA from sediments has matured into one of the most exciting tools for studying the past, say researchers. Interest in soil DNA surged nearly ten years ago, when scientists found that human DNA could also be isolated from ancient sediments. Laboratories that had once focused on extracting genetic material from precious fossils are now turning their attention to dirt. Archaeologists, too, are re-examining soil collected decades ago, keen to discover more about the past using this modern technology.
The complex history archived in sediments is ripe for exploration, says Willerslev. And it is vast. In 2022, his team coaxed snippets of DNA from two-million-year-old permafrost sediments at the northern tip of Greenland, the oldest such genetic material so far2. “It is a huge new blue ocean” of possibilities, says Willerslev. “You have humans, you have animals, you have plants, you have the whole bloody ecosystem.”
“It’s really incredible how much molecular information you have in sediments,” says Matthias Meyer, a molecular biologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. “I think we’re really just sort of scratching the tip of the iceberg in terms of what’s possible,” he says.
According to Willerslev, whether a site has fossil remains could become irrelevant. “My expectation would be, we can almost drop the bones,” he says, “and just go to the dirt.”
Sediments in Denisova Cave have yielded fossil remains and DNA from ancient humans.Credit: Eddie Gerald/Alamy
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