Researchers at McMaster University have developed a new technique to tease ancient DNA from soil, pulling the genomes of hundreds of animals and thousands of plants—many of them long extinct—from less than a gram of sediment.
The DNA extraction method, outlined in the journal Quarternary Research, allows scientists to reconstruct the most advanced picture ever of environments that existed thousands of years ago.
The researchers analyzed permafrost samples from four sites in the Yukon, each representing different points in the Pleistocene-Halocene transition, which occurred approximately 11,000 years ago.
This transition featured the extinction of a large number of animal species such as mammoths, mastodons and ground sloths, and the new process has yielded some surprising new information about the way events unfolded, say the researchers. They suggest, for example, that the woolly mammoth survived far longer than originally believed.
In the Yukon samples, they found the genetic remnants of a vast array of animals, including mammoths, horses, bison, reindeer and thousands of varieties of plants, all from as little as 0.2 grams of sediment.
The scientists determined that woolly mammoths and horses were likely still present in the Yukon’s Klondike region as recently as 9,700 years ago, thousands of years later than previous research using fossilized remains had suggested.
The technique resolves a longstanding problem for scientists, who must separate DNA from other substances mixed in with sediment. The process has typically required harsh treatments that actually destroyed much of the usable DNA they were looking for. But by using the new combination of extraction strategies, the McMaster researchers have demonstrated it is possible to preserve much more DNA than ever.