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Cave floors might hold an important key to understanding long-extinct human ancestors. Scientists in Germany are analyzing dirt from cave floors in search of DNA. NPR's Joe Palca recently visited Leipzig where the research is taking place.
JOE PALCA, BYLINE: Most ancient DNA is extracted from bones or teeth. Matthias Meyer of the Max Planck Institute for Evolutionary Anthropology in Leipzig says you don't need very much of the bone. Just a thousandth of an ounce will do. But there's a problem - anthropologists hate to give away any of their precious bones.
MATTHIAS MEYER: We've been recently trying to explore new sources of potential archaic human DNA as the fossil record is very limited.
PALCA: So Meyer and his colleagues began to wonder, what if you don't need an intact bone at all? Many of these interesting bones come from caves. What if, over the millennia, some of the bones just degraded into a kind of dust and fell to the floor of the cave? It would be easy enough to get at.
MEYER: You just take a shovel with some dirt, and then you look for DNA. And it's actually been shown in the past that there's DNA from plenty of species can be preserved in caves - in sediments in general for long periods of time.
PALCA: Meyer has some of this DNA from cave floors, and he's been able to begin analyzing it. But there are problems to solve before he can make sense of it. You have to develop methods to be certain that it came from an ancient bone and not a more recent human cave explorer or some contaminating bacteria. And the DNA they'll get will be tiny snippets of all the DNA in an ancient human ancestor. Piecing together the big picture will be tricky. Meyer says they're making headway with those issues.
MEYER: Currently, there are some initial promising results that sort of make it very worthwhile to follow up on this.
PALCA: Now, let's say you can get lots of DNA that you know comes from an ancient human ancestor. What do you do with it? Janet Kelso says plenty. Kelso is Meyer's colleague at the Max Planck Institute.
JANET KELSO: We've initiated a project just this year to try and generate sequences from a large number of Neanderthals to try and understand something about the Neanderthal population histories.
PALCA: Even though they're gone now, Kelso says Neanderthals were on Earth for quite a while.
KELSO: We know Neanderthals lived in Europe and western Asia for 200,000, 300,000 years.
PALCA: And during that time, the climate in those areas changed dramatically. There were times when glaciers covered a large chunk of the landscape. Kelso says if they can get DNA samples from Neanderthals at various time points in their history...
KELSO: We can see - how were they adapting to the environment? How did they differ over time? Can we understand what happened to them in the end? That may not be something you can tell from the sequence, but it would be interesting to try.
PALCA: Another question is just how often Neanderthals and modern humans had sex with one another.
KELSO: Was this something that was happening relatively regularly over some time? Was it quite rare?
PALCA: Kelso says most modern human populations have at least some genetic connection to Neanderthals. But there are many questions about when and where Neanderthals made their contributions to the modern human gene pool. It would be pretty amazing if the answers came from the dirt on the floor of caves.
Joe Palca, NPR News.
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AUDIE CORNISH, HOST:
One more thing we want to note in our story yesterday about a study on gun violence - we incorrectly said the study was published in JAMA. It was published in JAMA Internal Medicine, a different medical journal.
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