30 January 2019
Archaic humans moved into Siberian cave 100,000 years earlier than thought
Over the course of five years, multi-disciplinary teams of scientists from the UK, Russia, Australia, Canada and Germany worked on a detailed investigation to date the archaeological site of Denisova cave. Situated in the foothills of Siberia's Altai Mountains, it is the only site in the world known to have been occupied by both archaic human groups (hominins) at various times.
Two new studies published in Nature now put a timeline on when Neanderthals and their enigmatic cousins, the Denisovans, were present at the site and the environmental conditions they faced before going extinct.
Denisova cave first came to worldwide attention in 2010, with the publication of the genome obtained from the fingerbone of a girl belonging to a group of humans not previously identified in the palaeoanthropological record; the Denisovans. Further revelations followed on the genetic history of Denisovans and Altai Neanderthals, based on analysis of the few and fragmentary hominin remains. Last year, a bone fragment yielded the genome of the daughter of Neanderthal and Denisovan parents - the first direct evidence of interbreeding between two archaic hominin groups. But reliable dates for the hominin fossils recovered from the cave have remained elusive, as have dates for the DNA, artefacts, and animal and plant remains retrieved from the sediments.
One of the teams obtained fifty radiocarbon ages from bone, tooth and charcoal fragments recovered from the upper layers of the site, as part of the ERC funded 'PalaeoChron' project. In addition to these, more than 100 optical ages were obtained for the cave sediments, most of which are too old for radiocarbon dating. A minimum age for the bone fragment of mixed Neanderthal/Denisovan ancestry was also obtained by uranium-series dating by another team.
To determine the most probable ages of the archaic hominin fossils, a novel Bayesian model was developed that combined several of these dates with information on the stratigraphy of the deposits and genetic ages for the Denisovan and Neanderthal fossils relative to each other. The improved age estimates show that the cave was occupied by Denisovans from at least 200,000 years ago, with stone tools in the deepest deposits suggesting human occupation may have begun as early as 300,000 years ago. Neanderthals visited the site between 200,000 and 100,000 years ago, with "Denny", the girl of mixed ancestry, revealing that the two groups of hominins met and interbred around 100,000 years ago.
Most of the evidence for Neanderthals at Denisova Cave falls within the last interglacial period around 120,000 years ago, when the climate was relatively warm, whereas Denisovans survived through much colder periods, too, before disappearing around 50,000 years ago. Modern humans were present in other parts of Asia by this time, but the nature of any encounters between them and Denisovans remains open to speculation in the absence of any fossil or genetic traces of modern humans at the site.
One team also identified the earliest evidence thus far in northern Eurasia for the appearance of bone points and pendants made of animal teeth that are usually associated with modern humans and signal the start of the Upper Palaeolithic. These date to between 43,000 and 49,000 years ago.
"It is an open question as to whether Denisovans or modern humans made these personal ornaments found in the cave. We hoping that in due course the application of sediment DNA analysis might enable us to identify the makers of these items, which are often associated with symbolic and more complex behaviour in the archaeological record", commented geochronologists Tom Higham of the Oxford University.
Edited from Science Magazine, PhysOrg (30 January 2019)