In A Lost Baby Tooth, Scientists Find Ancient Denisovan DNA

Denisovans

More than 100,000 years ago in a Siberian cave there lived a child with a loose tooth. One day her molar fell out, and fossilized over many millenniums, keeping it safe from the elements and the tooth fairy.

But she wasn’t just any child. Scientists say she belonged to a species of extinct cousins of Neanderthals and modern humans known today as the Denisovans.

And in a paper published last Friday in the journal Science Advances, a team of paleoanthropologists reported that she is only the fourth individual of this species ever discovered.

“We only have relatively little data from this archaic group, so having any additional individuals is something we’re very excited about,” said Viviane Slon, a doctoral candidate at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and lead author of the study.

Denisovans cave

The scant fossil record for these ancient hominins previously included only two adult molars and a finger bone. The Denisovans were only correctly identified in 2010 by a team of researchers led by Svante Paabo.

Scientists exploring Denisova Cave in the Altai Mountains discovered the worn baby tooth in 1984 and labeled it ‘Denisova 2.’ At the time, its origins were a mystery.

But now, after performing DNA analysis on the deciduous, or baby tooth, researchers say it was one of the elusive Denisovans.

“We think based on the DNA sequences that ‘Denisova 2’ is at least 100,000 years, possibly 150,000 years old. Or a bit more,” said Ms. Slon. “So far it makes it the oldest Denisovan.”

Denisovans

To determine the origins of ‘Denisova 2’ the team first performed a CT scan of the tooth to preserve its structure for future studies.

After sequencing the DNA she compared genetic information from the sample with genetic data already collected from Denisovans, Neanderthals and modern humans.

“We saw it was most similar to Denisovan mitochondrial genomes,” she said. “That was exciting because that was a good indication that this was another Denisovan individual.”

Bence Viola, a paleoanthropologist from the University of Toronto and an author on the paper, said there was not too much to be learned from studying the tooth’s morphology or appearance.




The genetic analysis, on the other hand, provided the keys to learning more about the species. He said the genetic study was something the team most likely could not have done five years ago without destroying the tooth.

“For a long time we didn’t want to work on it because it’s such a small specimen,” he said.

But by drilling into the tooth and performing the genetic analysis the scientists were able to not only figure out who it belonged to, but also provide relative dates for when the Denisovan lived.

The study also suggests that the species had less genetic variability than modern humans, but more genetic diversity than seen in Neanderthal nuclear DNA.

Dr. Bernard A. Wood, a professor of human origins at the Center for the Advanced Study of Human Paleobiology at George Washington University, said the paper demonstrated the power of molecular biology as a tool for paleoanthropology.

“Talk about extracting blood from a stone,” he said, “this is extracting treasure from a tooth.”

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