Australia: The Land Where Time Began

A biography of the Australian continent 

Denisova Cave Used by Denisovans for many thousands of Years

DNA sequencing of genetic material extracted from a finger of a young girl that had been found in Denisova Cave in the Altai Mountains of Siberia resulted in the discovery of a new type of hominin, Denisovans. A small number of Denisovan molars were found in the cave and together with new dates for the material show that the cave was being occupied by the Denisovans over a very long period. It is suggested by the data that the girl lived about 50,000 BP and 2 other Denisovan individuals died in the cave at least 110,000 years ago and possibly as long ago as 170,000 BP. The new dates have helped to improve the murky view of Denisovans, who left very little evidence of their presence, and provide more convincing evidence of their multiple occupations of the cave over a very long period, according to Fred Spooner, a paleoanthropologist.

Layer 11, a thick sandstone band, is where most of the key fossils in the cave have been found. The first attempt to date the animal bones and artefacts from the sandstone layer varied widely between 30,000 and 50,000 BP. When 20 samples of artefacts and animal bones that had cut marks indicating they had been butchered by the occupants of the cave gave ages on a second dating of likely older than 48,000-50,000 BP. The sediments at the base of the sandstone layer, where the finger bone was discovered, gave dates at the very limit of radiocarbon dating, so are probably older.

The dates that had been obtained were from bones with cut marks, and ornaments, and the dates were consistent across 3 caves, as well as fitting with genetic evidence.

Nuclear DNA sequencing was carried out on 3 molars recovered from layer 11 and the molar of a child recovered from a deeper layer, 22. Thermoluminescence, a dating method that is considered to be experimental in the case of cave dating, gave a date of 170,000 BP for layer 22.

A significant amount of nuclear DNA from 3 teeth that was analysed proved to be from Denisovans, and a 4th was Neanderthal. When key sites on the tooth DNA were compared with corresponding sites in the high quality genomes from the Denisovan girl, Neanderthal and modern humans, it was revealed that the Denisovan inhabitants of the cave were not closely related. The Denisovans displayed more genetic variation among them than the entire DNA that has been sequenced from all the Neanderthals tested to date, though Neanderthals are known to be genetically similar.

The entire mtDNA genomes of the Denisovans were sequenced to determine when the Denisovans were in the cave and they were placed on a family tree. The number of mtDNA differences between individuals was counted and the mutation rate of modern humans was used to estimate the length of time it would require for these mutations to appear. By this method it was concluded that the girl was in the cave about 65,000 after the oldest Denisovan, who was there at least 110,000 years ago, though possibly earlier.

Pääbo’s team has sequenced the DNA from a Neanderthal toe bone and a molar recovered from the cave. Also, modern humans were apparently in the cave, which was large and light-filled, as indicated by more recent artefacts. It appears from the interdigitisation of the Denisovans and the Neanderthals both groups were in and out of the cave.

A new technique, ZooMS, was used to scan 2,315 bones from the cave searching for proteins that were uniquely of human origin, which found a fragment of a human toe bone.

Sources & Further reading

  1. Gibbons, A. (2015). "Cave was lasting home to Denisovans." Science 349(6254): 1270-1271.

 

Author: M. H. Monroe
Email:  admin@austhrutime.com
Last updated  11/03/2016
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading