Neandertal/Denisovan Hybrid?

As J. Lawrence Angel once said: “When two groups of people meet, they may fight, but they will always mate.”  A story is now coming out of Russia describing more research at the Denisova Cave, in the Altai Mountain region that recounts exactly what Angel was talking about.  From Richard Coniff, at Scientific American:

In a remarkable twist in the story line of early human evolution, scientists have announced the discovery of “Denisova 11”—a female who was at least 13 years old, lived more than 50,000 years ago and was a child of mixed parentage. Her parents were not just of different races, but two different and now-extinct early human types. Their exact taxonomic designations—whether they were separate species or subspecies—is still a matter of scientific debate. But the bottom line for Denisova 11 is that mom was a Neandertal and dad a Denisovan.

This is a remarkable claim, similar to the one that Erik Trinkaus made about the Lagar Velho child discovered in Portugal that is thought to be a Neandertal/modern human offspring. What evidence has been marshalled to support this claim?  In a word: genetics.  The evidence is taken from another bone fragment from the site.  From the abstract:

The father, whose genome bears traces of Neanderthal ancestry, came from a population related to a later Denisovan found in the cave. The mother came from a population more closely related to Neanderthals who lived later in Europe than to an earlier Neanderthal found in Denisova Cave, suggesting that migrations of Neanderthals between eastern and western Eurasia occurred sometime after 120,000 years ago. The finding of a first-generation Neanderthal–Denisovan offspring among the small number of archaic specimens sequenced to date suggests that mixing between Late Pleistocene hominin groups was common when they met.

So, if they interbred regularly (or regularly enough, anyway), why aren't they just one species?  Svante Paabo argues that it is because they simply did not come together very often.  To this, I would argue that they probably also had fairly distinct cultures. 

If this kind of information had come out a few decades back, there would have been quite a few squawks and naysayers but as the evidence piles up for hybridization between many different groups throughout the Pleistocene, researchers have become more accepting of it.  It is pretty clear that the evolutionary picture was a whole lot more complex than we thought.