HOW A BIT OF CAVE DIRT JUST CHANGED ARCHAEOLOGY

The study of humans has long relied on bones to reveal human DNA. The problem is that those bones are hard to come by. As the Atlantic points out, scientists have only a finger bone and two teeth belonging to the Denisovans, cousins of Neanderthals.

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It's no wonder then that a Harvard geneticist refers to a new technique of recovering human DNA without bones, described in a study published in Science Thursday, as a "real revolution in technology," per the New York Times.

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German researchers took dirt samples at seven cave sites in Europe and Asia where Neanderthals or Denisovans once lived. Four returned Neanderthal DNA, and one of the four sites contained Denisovan DNA, per a release, which notes many of the sediment samples were taken from archaeological layers or sites that hadn't previously yielded bones.

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"It's a bit like discovering that you can extract gold dust from the air," as one geneticist puts it. Researchers had previously taken animal DNA from sediment, but this study describes the first successful effort involving human DNA.

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It involved collecting samples at sites where human bones or tools had been found and using molecules that recognize mammalian mitochondrial DNA to "fish out" the material, which sticks to minerals in sediment.

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The implications are huge, say scientists, and one gives this potential use: probing the soil along the routes early Americans took to get here via Alaska.