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DNA Reveals Mysterious Human Cousin

denisovan-family-tree

The analysis of a fossil tooth from Siberia reveals that a mysterious people known as Denisovans, discovered a mere five years ago, persisted for tens of thousands of years alongside modern humans and Neanderthals.
In 2010, teams of geneticists and anthropologists led by Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology announced strange DNA sequences recovered from a finger bone and molar found in the remote Denisova cave, in Siberia’s Altai Mountains.
“This is the only place in the world where we know that three different groups of humans with very different histories all lived.”, says Pääbo.
The results also underscore the innovative genetics that anthropologists are increasingly using.
Sausanna Sawyer’s team at the Max Planck Institute for Evolutionary Anthropology analyzed the tooth’s mitochondrial DNA. This part of the genetic material is known to be better preserved in fossils over time.
But finding a clean piece of Denisovan DNA wasn’t easy. Sawyer and Pääbo had to identify and rule out contamination from modern humans, modern and ancient bacteria, and ancient hyenas, which seem to have long prowled the cave.
The DNA provided the team with a genetic stopwatch that accrues mutations with each tick. Denisovans who died closer to the common ancestor’s time would have fewer mutations in their genomes than more recent Denisovans would. Sawyer found that the recently discovered tooth had half the number of mutations of the other remains, suggesting it was older.
The discrepancy suggests that the Denisovan to whom the tooth belonged lived about 60,000 years before the individuals who left behind the finger bone and the other tooth.
When it comes to the actual branching of the human family tree, the recent findings seem to conflict with the 2010 studies, which analyzed DNA found in cells’ nuclei instead of mitochondrial DNA. The new study suggests that Denisovans are not as closely related to Neanderthals as the previous findings indicated.