As a species, the ancient humans known as the Denisovans are an enigma. Known only from a few fragments of bone discovered in 2008, no entire fossil remains of them exist. We know that they lived at least around 50,000 years ago, that they interacted with both modern humans and Neanderthals, and that’s about it. But the new discovery of more Denisovan remains – a single molar tooth – is shedding some more light on these mysterious peoples. Perhaps most notably, it turns out they were more genetically diverse than the wide-ranging Neanderthals.  

Found in the Denisova cave in the Altai Mountains of Siberia, previously all that we knew about these mysterious ancient humans was based on two bits of skeleton: one tooth and one fragment from the little finger of a girl. From these, scientists were able to gather enough DNA to recognize these people as a species separate from both Neanderthals and us, Homo sapiens. This in itself was extraordinary, that scientists were able to identify an entirely new species of human despite only having a tiny amount of fossil evidence.    

But recent excavations have unveiled a second tooth, and with it a whole host of new insights into the species, published in the Proceedings of the National Academy of Sciences. By comparing the genomes of the recent and older finds, the researchers were able to trace back when the owner of the new tooth was last alive. What they discovered was totally unexpected. The new tooth turned out to be around 60,000 years older than the 2008 finds, suggesting that either the Denisovans lived in the cave for thousands of generations, or that they came to the region at least twice.

This has completely changed the perceptions of what these ancient peoples were like. The environment in Siberia, especially during winter, is not particularly forgiving, and so the researchers suggest that in order to be able to live and thrive here, the Denisovans must have been fairly resilient. This adds more evidence to the theory that these mysterious peoples were far more successful and widespread than previously imagined, as modern day Australian aborigines, New Guineans and Polynesians all contain around one percent Denisovan DNA.

The comparison between the few fossil remains of the species has also thrown up another enigma. It turns out that these three individuals who lived in or around the same cave in Siberia over a period of 60,000 years show more genetic diversity than all Neanderthals who lived from Spain to the Altai Mountains. It also appears that the Denisovans were interbreeding not just with our own ancient ancestors, as recorded in modern day aborigine DNA, but also Neanderthals who were living on the edge of their own range.

But the mystery goes deeper still. In this new specimen, the researchers have found portions of DNA that matches neither the Denisovans, Homo sapiens nor Neanderthals. This, the researchers claim, hints at the possibility that there was yet another so far unidentified species of ancient human sharing the landscape with the others. If true, this would be an astounding find, and currently museums in China are now testing their human fossils to see if they actually have either Denisovan or potentially new ancient human remains.     

^{Main image: loronet/Flickr CC BY-NC-ND 2.0}