It turns out the mysterious ancient Denisovans lived for for tens of thousands of years alongside both modern humans and Neanderthals in Eurasia. At least that’s what the genetic evidence from a Denisovan tooth found in a cave in Siberia suggests.
Tracking the genes of the Denisovan individual whose wisdom tooth was found in the cave strongly suggests that the direct ancestors of modern man shared the Eurasian continent with other hominid populations. It is already known that modern humans lived alongside Neanderthals (a sister species to humans that disappeared around 40,000 years ago), and now it appears that Denisovans also lived close by early modern humans for some tens of thousands of years.
The new research was published this week in the Proceedings of the National Academy of Sciences, and represents a huge step in our understanding of the place of Denisovans on the human family tree.
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The Denisovans were first discovered in 2010, when geneticists and anthropologists led by Svante Paabo of the Max Planck Institute announced the discovery of unknown DNA sequences from a finger bone and molar tooth found in Denisova cave in the Altai Mountains of Siberia.
The most recent discovery comes from a second, much older, Denisovan molar found at the back of the cave.
New information on ancient Denisovans
The genetic data from the initially found finger bone and tooth show that Denisovans were related to modern humans, and in fact contributed close to 5% of the genome of modern Melanesians who inhabit Papua New Guinea and other areas in the Pacific.
However, researchers found a second wisdom tooth in the back of the cave in 2010. The physical dental analysis was assigned to Bence Viola, from the University of Toronto, who was the anthropologist involved in the research with the first Denisovan wisdom tooth. Viola, in fact, initially thought it was a tooth from a cave bear, because of its large size and unusually long, splayed roots.
Although there is not enough evidence to accurately project what ancient Denisovans would have looked like, it is clear that “large teeth with massive roots would probably require massive jaws,” Viola points out.
Susanna Sawyer of the Max Planck Institute was appointed to lead the genetic effort to describe and date the new Densovan tooth.
The first step was to isolate the useful mitochondrial DNA. After she had a good sample of the new tooth’s mitochondrial DNA, Sawyer confirmed that the tooth was from a Denisovan. Even more importantly, Sawyer was able to reconstruct the mitochondrial genome of the common ancestor of the three individuals found in the Denisova cave.
This information offers a key baseline, as it enables the calibration a “genetic stopwatch” that can count mutations. The technique works because Denisovans who died closer to the common ancestor’s time would have fewer mutations in their genomes than their more recent ancestors. It turned out that the newer Denisovan tooth had just half the mutations of the other specimens, meaning it was much older.
When you do the math, it means that the Denisovan to whom the second tooth belonged lived close to 60,000 years earlier than those who left the finger bone and the other tooth. The researchers point out that this shows that the Denisovans were a “single biological group” that at least sporadically lived in this part of Asia at least as long as modern humans.
“The world at that time must have been far more complex than previously thought,” Sawyer noted. “Who knows what other hominids lived and what effects they had on us?”