In a report published Wednesday in the journal Nature, Russian scientists report using mitochondrial DNA (mtDNA) to identify a new species. While the identification is tentative, and awaits confirmation, it none-the-less represents an important new use of DNA technology.
The discovery occurred in the summer of 2008, when the scientists were digging in Denisova cave, in Siberia. They were looking for the remains and artifacts of Neanderthals, who occupied the cave between 30,000 and 48,000 years ago. During excavations, they found a small sliver of finger bone. According to the scientists, it was considered unremarkable at the time.
However, when they sent it to German scientists to have the DNA extracted and sequenced, they were in for a surprise. The results did not match Neanderthals. Nor did it match modern humans, who were also living in the area at the time.
The conclusion was that the bone represented a here-to-fore unknown human species. Based on the differences between the bone’s DNA and that of modern humans, it is estimated that the species diverged from human ancestors a million years ago, long before the split between modern humans and Neanderthals. By inference, this means that the proposed species left Africa in a previously unknown migration, sometime between that of Homo erectus about 1.9 million years ago and that of the Neanderthal ancestor Homo heidelbergensis, 300,000 to 500,000 years ago.
But, as yet, none of this is entirely certain. The use of mtDNA poses its own problems, and scientists also must examine the bone’s nuclear DNA to get a full picture. While mtDNA comes through the mother’s lineage, nuclear DNA comes from through the father’s. It is important to have both in order to make a proper assessment.
Researchers point out that it is possible that some modern humans or Neanderthals living in Siberia 40,000 years ago had unusual mtDNA. Only by also examining the nuclear DNA will a complete enough picture of the person it belonged to come out, allowing scientists to make a determination. Such a picture might also allow scientists to properly define this new relative’s position within the human family tree.
To read more about this find, please see the article in Nature News at the following URL: http://www.nature.com/news/2010/100324/full/464472a.html.