They remain one of the most elusive groups of people to walk the earth. Evidence from the DNA traces left by Denisovans shows that they lived on the Tibetan Plateau, probably traveled to the Philippines and Laos in South Asia, and may have come to northern China more than 100,000 years ago. They also interbred with modern humans.
However, what Denisovans looked like or how they lived remained a mystery. Only a jaw fragment, a few pieces of bone and one or two teeth provide any evidence of their physical characteristics.
Their DNA, which was first found in samples from Denisova Cave in Siberia in 2010, provide most of our information about their existence.
But recently scientists have identified a strong candidate for the species to which the Denisovans may have belonged. It is Homo longi – or “Dragon Man” – from Harbin in northeastern China. This key fossil consists of a nearly complete skull with a brain case the size of a modern human and a flat face with fine cheekbones. Dating suggests it is at least 150,000 years old.
“We now believe that the Denisovans are members of the Homo longi species,” Prof Xijun Ni of the Chinese Academy of Sciences in Beijing said last week. “The latter is characterized by a broad nose, thick eyebrow ridges over his eyes and large dentures.”
The possible Denisovan-Homo longi link is one of several recent developments by researchers working on these people with whom Homo sapiens shared the planet for hundreds of thousands of years. It is even thought that they may have played a key role in our own evolution.
Scientists in Tibet there discovered a Denisovan gene in local people, the result of interbreeding between the two species in the distant past. Importantly, this gene helps modern men and women survive at high altitudes.
In addition, evidence for the Denisovan-Homo longi link has also been traced to the Tibetan Plateau, where scientists began to study a jawbone initially found in a remote cave 3,000 meters (10,000 ft) above sea level by a Buddhist monk, who kept it as a relic.
The bone was found not to be from a modern human. But it wasn’t until researchers began studying the cave where the jawbone was originally discovered that they found its sediments were rich in Denisovan DNA. In addition, the fossil itself was found to contain proteins that indicate Denisovan origins.
“This was the first time a Denisovan fossil was found outside Siberia and it was very important,” said Janet Kelso of the Max Planck Institute of Evolutionary. Anthropology in Leipzig, Germany. “Equally interesting was the fact that the jaw has teeth that are similar to the teeth in Homo longi. So I think the evidence points to a connection between the skull and Denisovans.
This view was supported by Prof Chris Stringer of the Natural History Museum in London. “The evidence supports the idea that Denisovans were members Homo longi but we still lack absolute proof. Nevertheless, it will come in time, I believe.”
A big problem for researchers was the fact that there is still no DNA in Chinese fossils such as e.g Homo longi, Stringer added. “Their genes have not survived the passage of time. However, using the techniques of proteomics can provide important new data. This focuses on a fossil’s proteins, which survive much longer than its DNA and can tell us much more about the species.”
Recent research also suggests that these people may have played a key role in the evolution of our own species.
The impact of the Denisovan gene found in Tibetans today provides one example. But Denisovan DNA has also been found in other modern populations, including people in New Guinea, northern Australia and the Philippines, and appears to have helped them fight infections from diseases such as malaria.
Denisovans settled in areas covering a very diverse geography, Stringer said. “Some were warm and low-lying, others were cold and mountainous. They represented very diverse habitats, from the Tibetan Plateau to islands such as Sulawesi [in Indonesia].”
In contrast, the Neanderthalsthe third major group of humans that evolved over the past few hundred thousand years confined themselves to the cooler climates of a region that stretched east of Europe into southern Siberia.
They did not expand out of this relatively uniform environment. So is the rich variety of homelands adopted by the Denisovans a sign that they were capable of much more diverse and adaptive behavior than Neanderthals, scientists now ask?
Homo sapiens also appear to have interbred with Denisovans on more than one occasion. “There is indeed good evidence that some modern humans interbred with genetically different Denisovans on multiple occasions,” Kelso said. “This suggests that the two groups have coexisted for a long time, with some studies suggesting a last contact as recent as 25,000 years ago.”
Crucially, by this time Neanderthals were already extinct.
Research conducted by Ni and Stringer also suggests that of the three main groups of people that developed at this time, Homo sapiens and the Homo longi group were the last to diverge down different evolutionary paths, possibly a million years ago, with the Neanderthals branching off even earlier.
However, DNA analyzes suggested more recent divergence dates, with Homo sapiens secrete first, so this is a crucial question for future research, Stringer said.
“How often we crossed paths after those paths diverged is also now a subject of intense scientific interest,” he added. “We have so much to learn.”
