SCIENTISTS HAVE discovered a previously unknown human ancestor. It has a genetic lineage separate to that of modern humans and also the Neanderthals, but some of its genes still persist today in the genetic material of western Pacific islanders.
The research shows how very much can be learned from so very little given the work is based on analysing a single fossilised finger bone. Its past owner was a young girl who lived about 30,000 years ago.
The bone and a tooth were dug out of the Denisova Cave in Siberia, hence the name for these extinct ancestors, the Denisovians.
David Reich of Harvard Medical School, Svante Pääbo of the Max Planck Institute and colleagues managed to extract ancient genetic material – DNA – from the bone and described their findings this week in the journal Nature.
This enabled a direct comparison with modern human DNA and also DNA taken from the bones of Neanderthals, an early human-like species who died out about 30,000 years ago.
The young girl and the adult responsible for the fossil tooth (who must also have been from this distinct lineage) were neither modern humans nor Neanderthals. The molar tooth reflected this difference given it varied from the normal shape of human and Neanderthal teeth. The researchers said that it was more like a tooth from much older ancestors such as Homo erectus.
The genetic analysis showed that the Denisovians did not contribute their genes by mixing with Eurasian humans or Neanderthals. Yet the scientists were surprised to see its genes have persisted in the people who live on island chains in the western Pacific north of Australia.
“The data suggest that it [the young Denisovian] contributed 4 to 6 per cent of its genetic material to the genomes of present-day Melanesians,” the authors write.
They believe that Denisovians and their ancestors “may have been widespread in Asia during the Late Pleistocene epoch” . Evidence for this comes via their genetic contribution to the Melanesians.
Yet the Denisovian line either died out or was driven to extinction by the spread of modern humans. There is no evidence to say which explanation might be correct.
The cave is located in the Altai Mountains in southern Siberia and has come under “systematic excavations over the past 25 years”, the authors say.
Occupation of the site by early humans started up to 280,000 years ago.
The researchers only have the finger bone and this can tell them very little about what the young girl might have looked like.
The molar does show however that there were physical differences between them and modern humans and Neanderthals at least on that level.
Usually fossils of that age do not readily yield up DNA from the nucleus or centre of cells. It is the DNA from the young girl’s finger bone that has provided such a wealth of comparative information.
The scientists now believe that both Neanderthals and Denisovians left Africa between 300,000 and 400,000 years ago, with the former mostly migrating west while the latter migrated east.
Meanwhile, modern humans remained in Africa until 70,000 to 80,000 years ago, when they started to migrate out of Africa, spreading in all directions.