The results will be published online by the journal Science, in the 30 August 2012 edition of ScienceExpress. Science is the flagship journal of AAAS, the nonprofit science society.
Fossil evidence of the Denisovans is scanty; the existence of this group only came to light in 2010 when DNA from a piece of a finger bone and two molars that were excavated at Denisova Cave in the Altai Mountains of southern Siberia was studied.
Because they had only a tiny sample of material from the finger bone, Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany and his research team developed a treatment that unzipped the DNA so that each of its two strands can be used to generate molecules for sequencing. This method allowed the team to generate an extremely thorough genome sequence (30X), similar in quality to what researchers can obtain for the modern human genome.
The researchers compared the Denisovan genome with those of several modern humans from around the world. The Denisovans share more genes with populations from the islands of southeastern Asia, including Melanesia and Australian Aborigines, than with populations elsewhere in Asia. Analysis of the Denisovan genome further illuminates the relationships of Neandertals with individuals from East Asia, South America and Europe.
The study reports several other findings. For example, the researchers generated a list of recent changes in the human genome that occurred after the split from the Denisovans, i.e. changes unique to modern humans. This list will help scientists understand what sets modern humans apart from Denisovans and Neandertals.
They also show that the Denisovan individual whose genome was sequenced carried genetic variants that in present-day humans are associated with dark skin, brown hair and brown eyes, and that the genetic diversity of the Denisovans themselves was extremely low. Given the Denisovans’ wide geographic range over time, it is likely that their population was initially quite small but grew quickly, without time for genetic diversity to increase.
If further research shows that the Neandertal population size changed over time in a similar way, that may suggest that a single population expanding out of Africa gave rise to both the Denisovans and Neandertals, the study authors say.