At the end of the last ice age modern humans were migrating out of Africa, Neanderthals roamed Europe, and new research has shown that a previously unknown population of ancient humans lived in Asia. All that remains of this mysterious group is a section of finger bone and a wisdom tooth. The group has been named the Denisovans after Denisova Cave in Siberia where the tooth and bone segment were found. A few months ago researchers completed an analysis of mitochondrial DNA from the finger bone and concluded that it had belonged to a child who lived about 40,000 years ago and was genetically different from both modern humans and Neanderthals.
An analysis of Denisovan nuclear DNA extracted from the same finger bone was published today in Nature. Analysis of DNA extracted from the nuclei of cells offers a more detailed picture of genetic differences than analysis of mitochondrial DNA. The nuclear DNA confirmed that the Denisovans were more closely related to Neanderthals than to modern humans but were genetically different from both groups. The researchers suggested that the Denisovans were once a widespread population that occupied much of Asia. They suspect that other Denisovan remains may have already been uncovered in other parts of Asia but have not been identified as such because Denisovans were unknown at the time of discovery. Genetic tests on other ancient human remains would be needed to confirm this idea.
Most surprisingly, researchers found evidence of interbreeding between Denisovans and modern humans written in the DNA of present-day Melanesians – individuals who are native to New Guinea and other Melanesian islands share about five percent of their genome with the ancient Denisovan child. Strangely there is no evidence of Denisovan genes in present-day human populations from other parts of the world. This means that Melanesian ancestors must have come into contact and interbred with Denisovans sometime after separating from other groups of humans during their migration across Asia.
This evidence of modern human and Denisovan interbreeding follows the genetic confirmation earlier this year that modern humans also interbred with Neanderthals. The division of modern humans and Neanderthals into two separate species has become blurry because present-day non-Africans share genes with ancient Neanderthals. So were the Denisovans a separate species of human? The researchers have stopped short of making this claim, and given the evidence for interbreeding between modern humans and Neanderthals and Denisovans, it is difficult to draw distinct species lines between the three groups.
Despite wide differences in appearance there is very little genetic difference between present-day people from different parts of the world. In our ancient past, however, it seems that geographical separation over long periods of time gave rise to significant genetic differences among groups of humans such as Neanderthals, Denisovans, and anatomically modern humans. But as migration led to increased contact and interbreeding between these groups, these genetic differences may have been smoothed out. So, to quote T.S. Eliot, the Neanderthals and Denisovans may have ended “not with a bang but a whimper” as they simply faded into us.
Reich, D., Green, R., Kircher, M., Krause, J., Patterson, N., Durand, E., Viola, B., Briggs, A., Stenzel, U., Johnson, P., Maricic, T., Good, J., Marques-Bonet, T., Alkan, C., Fu, Q., Mallick, S., Li, H., Meyer, M., Eichler, E., Stoneking, M., Richards, M., Talamo, S., Shunkov, M., Derevianko, A., Hublin, J., Kelso, J., Slatkin, M., & Pääbo, S. (2010). Genetic history of an archaic hominin group from Denisova Cave in Siberia Nature, 468 (7327), 1053-1060 DOI: 10.1038/nature09710