Wednesday, December 28, 2011

The Mysterious Hominids From The Denisova Cave

Bence Viola from the Max Planck Institute for Evolutionary Anthropology in Leipzig discovered the tooth fragments together with Russian colleagues in the Denisova Cave in the Altai Mountains. Initially, he thought the inconspicuous-looking object was the molar of a cave bear.

Tooth from Denisova Cave
 © Max Planck Institute for Evolutionary Anthropology
© Max Planck Institute for Evolutionary Anthropology

But when the remaining fragments of the tooth turned up, it became obvious that the researchers had found the tooth of a hominid. It was too large, however, to be from a modern man or Neanderthal.

When the researchers finally succeeded in decoding the DNA of the tooth, their suspicion was confirmed: it hailed from a previously unknown early human species living in Asia at least 30,000 years ago.
Credit: © Max Planck Society

An international team of scientists from the Max Planck Institute for Evolutionary Anthropology in Leipzig has sequenced ancient mitochondrial DNA from a finger bone found in southern Siberia. The bone is from a previously unknown form of human that lived in the Altai Mountains of Central Asia around 48,000 to 30,000 years ago. This mitochondrial genetic material, passed down through the descendants in the maternal line, is a sign of a new wave of migration out of Africa, one that is distinct from that of Homo erectus, the ancestors of Neanderthals and Homo sapiens (Nature, 24 March 2010).

Archaeologists in the Denisova Cave in August 2005. This is where the tiny fragment of finger bone was discovered.
© MPI für evolutionäre Anthropologie / Krause

The first group of hominins to leave Africa some 1.9 million years ago was Homo erectus. Archaeological finds and genetic data indicate that at least two other groups left Africa at a later date: first, around 500,000 to 300,000 years ago, the ancestors of the Neanderthals migrated. Then, about 50,000 years ago, it was the turn of the forefathers of anatomically modern humans. Direct descendants of Homo erectus may have survived in Indonesia until less than 100,000 years ago. Older representatives of Homo erectus and Homo heidelbergensis also lived in more northerly climes, for instance in the Altai Mountains in southern Siberia more than 125,000 years ago. Neanderthals also lived in Siberia at that time.

The discovery by Russian archaeologists of the remains of an extinct prehistoric human during the excavation of Denisova Cave in Southern Siberia in 2008 was nothing short of a scientific sensation. The sequencing of the nuclear genome taken from an over 30,000-year-old finger bone revealed that Denisova man was neither a Neanderthal nor modern human, but a new form of hominin. Minute traces of the Denisova genome are still found in some individuals living today. The comparisons of the DNA of modern humans and prehistoric human species provide new indications of how human populations settled in Asia over 44,000 years ago.

3D rendering of the Denisova phalanx. The blue concave surface shows the articulation, the green color stands for the rest of the bone.
Bred in the bone. DNA from a Siberian finger bone showed mixing between Denisovans and Homo sapiens. Copyright: Max Planck Institute for Evolutionary Anthropology 
Credit: © MPI for Evolutionary Anthropology

Johannes Krause, Svante Pääbo and their colleagues from the Max Planck Institute for Evolutionary Anthropology in Leipzig have now sequenced mitochondrial DNA from a tiny fragment of a finger bone. The bone was found in the Denisova Cave in the Altai Mountains in southern Siberia in 2008. The scientists compared the ancient DNA from the mitochondria, the "powerhouses of the cell", with the mitochondrial DNA of Neanderthals and of humans alive today. They found that the mitochondrial DNA of this hominin from southern Siberia differed markedly from all other known hominins.

A detailed analysis of the mitochondrial genetic material showed that this hominin shared a descendant with modern humans and with Neanderthals about 1.0 million years ago. This common descendant is about twice as old as the shared descendant of anatomically modern humans and Neanderthals, as determined on the basis of their mitochondrial DNA. Furthermore, the age of the fossil indicates that this unknown form of human could have co-existed with Neanderthals and modern humans in southern Siberia.

Denisova hominins were spread across an extraordinarily large ecological and geographical area extending from Siberia to tropical Southeast Asia. “The fact that Denisovan DNA can be detected in some but not other original inhabitant populations living in Southeast Asia today shows that numerous populations with and without Denisovan DNA existed over 44,000 years ago,” says Mark Stoneking, professor at the Department of Evolutionary Genetics at the Max Planck Institute for Evolutionary Anthropology and leading author of the study. “The simplest explanation for the presence of Denisovan genetic material in some but not all groups is that Denisova people themselves lived in Southeast Asia.” In December 2010, Svante Pääbo from the Max Planck Institute for Evolutionary Anthropology reported in the journal Nature that Denisova hominins contributed genes to human populations living in New Guinea today.

Contacts and sources:
Bence Viola
Abt. für Humanevolution
Max Planck Institute for Evolutionary Anthropology, Leipzig

Mark Stoneking
Max Planck Institute for Evolutionary Anthropology, Leipzig 

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