"X-Woman" Discovered -Shared Ancestry with Neanderthals and Modern Humans
Scientists say a third hominin group may have co-existed with early Homo sapiens and Neanderthals. A DNA sample taken from an ancient pinky bone that belonged to a child who died between 48,000 and 30,000 years ago, suggests that a previously unknown group of human ancestors intermingled with Neanderthals and modern humans.
The finding, published in this week's issue of the journal Nature, emerged from a check of DNA samples from Denisova Cave in southern Siberia's Altai Mountains. Anthropologists know that the cave was occupied by human ancestors off and on for at least 125,000 years, based on the artifacts and bits of bone found there.
An unknown type of human, nicknamed "X-Woman," coexisted with Neanderthals and our own species between 30,000 to 50,000 years ago, according to a new study that suggests at least four, and possibly more, different forms of humans existed in Asia after Homo sapiens migrated out of Africa.
The finding has been described, not from the structure of its fossilized bones, but from the sequence of its DNA. Researchers focused on mitochondrial DNA (mtDNA), genes passed down from mothers to their children, hence the X-Woman nickname. The child's mtDNA shows X-Woman shared a common ancestor with Neanderthals (skull left) and modern humans (right skull) one million years ago, so X-Woman and her species likely migrated out of Africa 500,000 years before the ancestors of Neanderthals left Africa.
"So whoever carried this mtDNA out of Africa was a creature that was not on our radar screen before," co-author Svante Paabo, director of genetics at the renowned Max Planck Institute for Evolutionary Anthropology in Leipzig, told Discovery News.
Dr Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany said the DNA was different from the genetic code of Neanderthals and modern humans.
Almost nothing is known about the appearance or lifestyle of the new human species. It walked upright on two legs and was probably similar in appearance to the other ancient humans living at the time. They lived at a time when our ancestors were fishing and hunting, wearing jewellery, painting caves and making animal carvings.
Co-author Dr Johannes Krause said: 'We only have the little pinky bone and there are also isolated teeth found in the site but there is no other skeletal remains so far.'
The genetic sequence was then compared with those for 54 present-day modern humans, a Late Pleistocene early modern human from Russia, six complete Neanderthal mtDNA's, one bonobo and one chimpanzee. None of them matched with the new sequence, but they revealed the individual was a human that carried twice as many genetic differences as Neanderthals do with our species.
Since Neanderthals and modern humans were also living less than around 62 miles away in Siberia at the time, Paabo said, "At least three different forms of humans may have coexisted 30,000 to 40,000 years ago," making human history "a lot more complex and interesting" than previously thought for this period.
Conditions were often cold then in Siberia, as they are now, so everyone probably wore heavy, protective clothing. Ornaments dating to the period, such as bracelets, were also found in the cave.
Because the different humans appear to have lived within close proximity of each other, this "increases the potential for interaction," including inbreeding, Paabo said during a press conference yesterday in London with colleague Johannes Krause.
The apparently peaceful coexistence may not have lasted long, however, since only our species survived into modern times. As a result, Paabo believes the extinction of the other human groups may have been "early genocide" or due to environmental factors or competition for resources.