The recent DNA analysis of a tooth found in Siberia has revealed that Homo sapiens’ cousins, the Denisovans—who were discovered only five years ago and only exist in a total of three tiny bone fragments—actually lived for tens of thousands of years among modern humans and Neanderthals.
Previously, we knew that modern humans spent hundreds of thousands of years alongside Neanderthals, but the fact that Denisovans joined the party for as long as they did was a bit of a surprise, and means scientists have come even closer to understanding where Denisovans fit into the human family tree.
The original discovery, according to National Geographic, was in 2010, when three bone fragments from three different Denisovans were discovered in the remote Denisova cave, in Siberia’s Altai Mountains.
“It’s an amazing place,” Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology told National Geographic, “because it’s actually the only place in the world where we know that three different groups of humans with very different histories all lived.”
After drawing DNA from these samples, researchers discovered that the Denisovans did more than just coexist with modern humans: They interbred with them too, contributing about five percent of the genome of a modern people known as the Melanesians in Papua New Guinea and other nearby islands.
What did they look like?
But while we know a lot about their genes, we knew very little about them. Even their appearance is an unknown. The bones found included two large wisdom teeth, which were initially confused with the teeth of a cave bear thanks to their size and splayed roots. From this, the researchers posited that these large teeth would have required large jaws to fit them, giving us the only true clue to their physical appearance.
But now new discoveries are coming in, thanks to a new study published in Proceedings of the National Academy of Sciences. Researchers focused in on the mitochondrial DNA of the samples—which tends to handle the ravages of time better than regular DNA. After isolating and sequencing this genetic material, the team reconstructed the mitochondrial genome for the common ancestor of the three Denisovans found in the cave.
From this, the team was able to date the age of each bone fragment. This is because the older the bone, the “purer” the DNA within is, as DNA accumulates mutations over the course of years. A younger sample has more mutations; a more ancient one has less.
After comparing the mutations in each sample, they discovered that one tooth had about half the number of DNA mutations as the others, thus suggesting it was far older. In fact, the researchers believe the tooth belonged to someone who died 60,000 years before the other two Denisovans, meaning they were around for far longer than previously known.
“The world at that time must have been far more complex than previously thought,” said co-author Susanna Sawyer of the Max Planck Institute for Evolutionary Anthropology. “Who knows what other hominids lived and what effects they had on us?”
Of course, we still don’t know how old any of these bone samples are—carbon dating can only guarantee that they’re more than 50,000 years old. And there are many other mysteries about them as well, like who they were, how they lived, and what they looked like.
Next step: Find more Denisovans
Finding more Denisovans, therefore, would be massively helpful in untangling these questions. And there is a good chance this could happen again sometime soon, as previous discoveries of ancient Homo sapiens remains may actually be misidentified Denisovans. Most promising are some recent finds of teeth in southern China.
“I would not be surprised if some of these were indeed Denisovans,” said María Martinón-Torres, an anthropologist at the University of College London.
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Feature Image: Bence Viola
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