Denisovans are an ancient population of hominims known from Mitochondrial DNA extracted from one pinky bone found in Denisova cave in Siberia. Some of their genes are part of the modern human genome, primarily in Melanesia, Australia, and New Guinea.
I have seen the Denisovans referred to as Homo denisova, but no such determination has been made by paleoanthropologists. Remember, all we have is a juvenile pinky and an adult molar!
The find at Denisova is no longer being called X-woman, perhaps because two individuals are represented. Perhaps the name just wasn't very appealing. Either way, they are now the Denisovans, not X-woman.
It is also unlikely that the Denisovans will ever be classified as a separate species, since their DNA comprises up to 4% of some modern humans. Populations that can interbreed are generally considered the same species. These are archaic humans, not a separate species.
Such a definition is not set in stone. Scientists disagree over how a species should be defined.
The mitochondrial and nuclear DNA (yes, we now have both) extracted from the pinky bone is sufficient to determine that the owner of that pinky branched away from the line of modern humans between 250,000 and 500,000 years ago. The cave indicates that this individual lived in what is now Russia about 40,000 years ago.
Mitochondrial DNA has also been extracted from the molar. The DNA is very similar to the pinky, so these are likely two individuals from the same population.
The cave at Denisova is still being excavated.
With only this one find, there is no way to know when this population went extinct. We can only know that at least two of them were alive 40,000 years ago!
The modern humans with the most Denisova DNA are the Melanesians, a population which includes the islands of New Guinea and Fiji. Their DNA is also found in Australia.
Since humans outside of Africa average about 4% of their DNA from Neanderthals, this means 8% of the Melanesian genome has managed to come down from these ancient Pleistocene (previous to 11,700 years ago) populations.
I've leaned heavily on a blog by a paleoanthropologist named John Hawks. There's two reasons for this.
Since Dr. Hawks is very good about distinguishing between what is his opinion and what is consensus among anthropologists, he's turned out to be a terrific source for this article. Who could have imagined that one of the scientists working at the Denisova cave and on the Denisovan genome would be blogging about it??
Thus, if you're one of those people that wants to deeply research the Denisovans, the number one place to go is his Denisova Genome FAQ. It is going to be over the average reader's head, discussing HLA alleles, and the various ways that DNA can be merged with archeological information to determine population divergence, but he is the source for those that want to go deep. Further, he'll send you to all the other sources.
Sorry for going on about that. I was just so surprised to find such a great source!
Here's his comments on the issue of the amount of Neanderthal and Denisovan DNA in the Melanesian genome. They lead to fascinating new issues:
Well, the Denisovans didn't have to live in India when the ancestors of Melanesians ran across them and intermarried. But Denisova and the Neandertal genomes now make it very likely that the inhabitants of South Asia were one or the other.
In other words, there were hominins living in India around 40,000 years ago. We don't know what they were like, but Dr. Hawks is guessing that they were either Denisovan or Neandertal and they intermarried with Melanesian ancestors there.
It should be pointed out here that further research may well find that Australian and Polynesian peoples will have a significant amount of Denisovan ancestry as well.
I read some discussion about whether the Denisovans should be classified as Homo erectus, given their own species, or simply defined as archaic human, a branch of the Homo sapien species like Homo Heibelbergensis, Homo ergaster, and Cro-Magnon Man. There is no consensus, and any discussion I write here will be out of date in six months, so I will simply leave it up in the air, where it is anyway.
I will point out that Dr. Hawks argues that by definition the Denisovans ought to be Homo sapiens because we have proof they interbred with us.