Cave girl was half Neanderthal, half Denisovan
EXCITING DISCOVERY OF ANCIENT HUMAN BONE FRAGMENT REVEALS IT HAD A NEANDERTHAL FOR A MOTHER AND A DENISOVAN FOR A FATHER
Anthropologists have just hit the genomic jackpot: Discover ancient human bone fragment |
The discovery in 2010 of the first Denisovan fossil (called Denisova 3) spurred Russian researchers to carry out a more systematic exploration of the cave floor. It is littered with bone fragments.
Anthropologists have just hit the genomic jackpot.
In an ancient limestone cave in the Altai mountains in Siberia, scientists have discovered the fossil of an extraordinary human hybrid.
The 90,000-year-old bone fragment came from a female whose mother was Neanderthal, according to an analysis of DNA discovered inside it. But her father was not: He belonged to another branch of ancient humanity known as the Denisovans.
Neanderthals are our closest extinct human relatives and Denisovan a distinct species of primitive human.
Scientists have been recovering genomes from ancient human fossils for just over a decade. Now, with the discovery of a Neanderthal-Denisovan hybrid, the world as it was tens of thousands of years ago is coming into remarkable new focus: home to a marvellous range of human diversity.
An analysis of this bone, published on Wednesday in the scientific journal Nature, provides further evidence that the genetically distinct Neanderthals and Denisovans met and interacted with each other multiple times throughout their history.
“We are learning that human evolution is much more interesting and much more complicated than we used to think,” said Bence Viola, an anthropologist at the University of Toronto who worked on the study. “The vision of evolution that was very linear has now become this very bushy, interconnected thing.”
1 What did the bone fragment reveal?
The half-Denisovan/half-Neanderthal sample is small enough to fit in a matchbox, but scientists said it was once part of one of the longer bones in the body — perhaps a femur, an upper arm bone or a shin bone.
DNA analysis at Max Planck Institute for Evolutionary Biology in Leipzig, Germany, revealed two X chromosomes and no Y chromosomes, which is how scientists know the bone belonged to a female.
The thickness of the outside layer of the bone suggests that its owner was likely over 13 when she died. And marks on the exterior of the bone indicate that this bone fragment was probably brought into the cave by a carnivore like a cave hyena, or a wolf.
“You can see that it has been digested because the surface looks like it was affected by stomach acid,” Viola said. “Hyenas regurgitate and throw up bones.”
The bone fragment was found in Denisova Cave, just north of the Kazakhstan border. Previous work has shown that the cave had been used as a hunting stop by both Denisovans and Neanderthals going back as far as 282,000 years ago.
2 Who are the Denisovans?
In 2010, researchers working in this Siberian cave, called Denisova, announced they had found DNA from a scrap of bone representing an unknown group of humans. Subsequent discoveries in the cave confirmed that the Denisovans were a lineage distinct from modern humans.
The Denisovan is a distinct species of primitive human that roamed the Eurasian continent 50,000 years ago. Scientists cannot yet say what Denisovans looked like or how they behaved, but it is clear they were separated by Neanderthals and modern humans by hundreds of thousands of years of evolution. The hominid group was first discovered in 2010 and so far, all known Denisovan fossils were found in Denisova Cave. Scientists say it is possible that hominid remains in China and other places in Asia may also be Denisovans. Some people living today, especially those from Papua New Guinea and aboriginal Australians have as much as 5 per cent Denisovan DNA. East Asians have about 0.2 per cent Denisovan DNA.
The discovery in 2010 of the first Denisovan fossil
(called Denisova 3) spurred Russian researchers to carry out a more systematic exploration of the cave floor. It is littered with bone fragments, deposited in sedimentary layers.
Many of those fragments were sent to the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
3 A cave of treasures
The cave has turned out to be especially good at preserving DNA, and scientists at Max Planck have already sequenced the DNA of four other Denisovan bone fragments and teeth found at the site. This previous work showed that the ancestors of Denisovans and Neanderthals split from each other sometime between
400,000 and 500,000 years ago.
It also indicated that the two groups exchanged genetic material periodically throughout their histories. “The first Denisovan ever identified has small traces of Neanderthal ancestry,” said Viviane Slon, a research scientist at Max Planck who led the genetic testing.
4 Why the fossil is an extraordinary find
Just because scientists knew that Denisovan and Neanderthal hybrids must have existed sometime in the past didn’t mean they expected to find one. “The first question that came to mind was whether this could be a mistake — either a mix-up in the lab, or an error in data analysis,” Slon said.
It was only after she repeated the experiment several times on DNA samples from different parts of the bone that she was convinced the result was real. “This has been checked and rechecked,” Viola said. “We are unbelievably lucky to have found it.”
Further genetic analysis revealed that the Denisovan father of the hybrid individual had a little bit of Neanderthal ancestry himself as a result of his forebears mixing with Neanderthals at least 300 generations before he lived. “So from a single genome, we are able to detect multiple instances of interactions between Neanderthals and Denisovans,” Slon said. However, the genetic data does not indicate that Neanderthals and Denisovans were constantly interbreeding, she said. The two groups were more genetically different from each other than any two people living today.
“Their overlap may have been very restricted, both geographically and possibly also in time,” Sion said.