Scientists uncovered genetic traces of Neandertals and Denisovans by screening cave dirt for DNA.
Fossilized skulls and skeletons found in European caves gave us our first glimpse of our ancient cousins, the Neandertals. And a finger bone, found in a Siberian cave, first indicated the existence of another relative—the Denisovans. But fossils are hard to come by. So here's another option: analyze cave floors to see if it contains any DNA.
"We find ancient hominins, we find Neandertal mitochondrial DNA, and Denisovan mitochondrial DNA."
Viviane Slon, a geneticist at the Max Planck Institute in Germany.
She and her team found that molecular evidence by testing teaspoonfuls of sediment from seven different caves. And they screened specifically for mitochondrial DNA—because there's a lot more copies of it in cells compared to nucleus DNA, which has just one set per cell.
The researchers uncovered genetic evidence of Denisovans where you might expect—at Denisova Cave in Siberia. Which showed that their strategy was sound. They found Neandertal DNA there too, and at three of the other seven caves—including a cave where no Neandertal fossils have ever been found, only artifacts and animal bones. And they found the DNA of some surprise guests, too: "The woolly mammoth, or the woolly rhino. We have cave hyenas and cave bears." The study is in the journalScience. [Viviane Slon et al., Neandertal and Denisovan DNA from Pleistocene sediments]
This preliminary success, Slon says, means the method could be a good complement to traditional surveys. "We're not trying to replace working on ancient DNA from fossils, but rather open all the archaeological sites where there are no hominid fossils for genetic analyses." Leading, hopefully, to a broader census of our ancient relatives. No bones about it.