Late last year, we learned that early humans and Neanderthals once shared Eurasia with a third hominin group, known as Denisovans. Now, the new discovery of a Denisovan toe bone might indicate that these three hominin groups were pretty much constantly interbreeding.
This new find is exciting scientists - so much so, in fact, that some researchers are discussing the find before the official publication of the DNA analysis. As a result, this is more speculative than normal, and we'll know more when the official DNA analysis of the find is released. Still, with those caveats in mind, let's take a walk on the scientific wild side and see what this new discovery might mean.
Here's what we do know. The existence of the Denisovans is known from a fossil tooth and finger bone found in a Siberian cave in 2000 and 2008 respectively. DNA analysis conducted last year indicated that these belonged to an otherwise unknown humanoid species that was contemporaneous with early humans and Neanderthals. Based on these two finds, the current hypothesis is that Denisovans split from Neanderthals about 300,000 years ago and came to occupy East Asia while first Neanderthals and then humans dominated Europe and Central Asia.
That said, two bones aren't enough to say with certainty that the Denisovans were their own species. That's why the new discovery of a toe bone is so exciting - it could greatly strengthen the case for the Denisovans being a separate species. Dating to about 40,000 years ago, the toe was found in the same cave but reportedly belongs to a different individual than the finger or tooth. Intriguingly, the toe bone's morphology is somewhere between that of a human and a Neanderthal.
What we're waiting on is DNA analysis from Svante Pääbo of the Max Planck Institute. Pääbo's analyses have previously provided the best evidence we have for interbreeding between humans and Neanderthals and between humans and Denisovans. And, as Maria Mednikova of the Russian Academy of Sciences seems to suggest, he might be about to complete the interbreeding triangle:
"The Neanderthals came to the Altai mountains [in Siberia] about 45,000 years ago and were probably assimilated by the native Denisovan population. It cannot be excluded that the individual was Denisovan, Neanderthal or even a hybrid - why not?"
Obviously, we have to read between the lines here, but the implication certainly seems to be that this might be a Neanderthal-Denisovan hybrid. If that's the case, then it suggests ancient humanoids didn't much bother with species distinctions when it came to breeding. Indeed, it might well force us to reconsider the assumption that humans, Neanderthals, and Denisovans really were separate species at all. In any event, depending on what the DNA analysis eventually reveals, the story of humanity's past looks like it's about to get a whole lot more complicated.