Neanderthals and Denisovans could live side by side for tens of thousands of years, scientists report in two parts in Nature1,2.
Long-awaited studies are based on the analysis of bones, artefacts and sediments from Denisova cave in the southern part of Siberia, which is packed with ancient human remains. They provide the first detailed history of the occupation of the 300,000-year-old site of different groups of ancient people.
"Now we can tell the whole story about the whole cave, and not just pieces," said Zenobia Jacobs, a geochronologist at the University of Wollongong, Australia, who led one of the studies.
Ancient human hotspot
Soviet archaeologists began to uncover the story of the Denisova cave at the foot of the Altai Mountains in the early 1980s. Since then, scientists have discovered fragmentary remains of almost a dozen ancient people on the site. The cave became world-renowned in 2010, after analyzing DNA from the small bone of the hominine finger revealed that the creature was different from modern humans and Neanderthals3. It belonged to a previously unknown hominine group, later named Denisovani.
Further sequencing of DNA into bones remains from the cave found that the Denisovans were a sister group of Neanderthals and could once have lived through Asia – where they intertwined with the ancestors of some people who now live there4.
Last year, the site produced another spectacular discovery: DNA analysis of a long bone fragment revealed the first "hybrid" of two antique-human groups, a woman – the nickname Denny – whose mother is Neanderthal and Father Denisovan5.
The hustle is dating
The vast majority of the remains of the cave are older than the 50,000-year-old limit of the radioactive carton technique used for organic materials, and efforts to use other methods for the date of the sediments in which the remains were buried were hampered by the lack of a good map from the geological layers of the cave. Many scientists worry that disturbances in the cave, such as animal pits, mocked its contents so that it remains and artifacts no longer sit in sediments with a similar age.
In order to overcome these challenges, Jacobson and Wollongong-based geochronologists, Richard Roberts, used a dating technology that determines when individual grains of soil were last exposed to light1. This allowed them to identify the regions of the cave in which the soil was disturbed, so that the adjacent grains returned very different dates. They could then emit those areas when dated sediments in the same geological layer as the hominine and tools remain.
The first signs that every ancient-human species occupied the cave are stone tools – excavated from the beginning in the 80s – which were dated to about 300,000 years ago. But the researchers could not determine whether they were made by the Denisovites or the Neanderthals. Denisovan's remains in the cave (including DNA that lay in the soil) date back 200,000 years ago and 55,000 years ago, while the oldest remains of the Neanderthals are about 190,000 years old, and the youngest dated about 100,000 years ago.
The researchers can not accurately find out when the groups lived together, or whether they once shared the cave. But the existence of a hybrid individual – who lived about 100,000 years ago – means that the groups had to live close enough to meet at that time. Additionally, Denny's father hid a slave of Neanderthal descent, suggesting that his ancestors had previously interwoven with the Neanderthals.
Who was here?
Homo sapiens could live in the cave, researchers say. Bone pendants and tools – similar to those created by early modern humans in Europe – from the younger layers of the cave date back between 49,000 and 43,000 years, writes a team led by archaeologists Katerina Duka at the Max Planck Institute for Human History in Jena, Germany and Tom Hajdam at the University of Oxford, UK, in the second Nature paper2.
The researchers gave a hominine bone about 46,000 to 50,000 years ago but could not get the DNA to investigate which species belonged to it.
There are no others H. sapiens remains from this period, known as the initial upper Paleolith, are in the Denisova cave or the wider Altai region. For this reason, Russian archaeologists who lead the excavation at the site claim that Denisovites made artifacts that are more sophisticated than older stone tools on this site. But Higham would like to see more evidence before associating artifacts with any group. "It is possible for the Denisovites to make the Upper Paleolithic. It is possible for the Russians to be right. At the moment, with the evidence we have, we can not be sure," he says.
Danny-like hybrids are another suspect, says Robin Denel, an archaeologist at the University of Exeter, UK, and the author of an accompanying essay on studies6.
It is also possible that the one who made the artifacts was influenced by contact with H. sapiens, he says. "I will be very surprised if the initial Upper Paleolith in Denisova was made by Denisovans or Neanderthals without entry from our species."
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