33,000 year old dog skull discovered in Siberian cave

This skull once belonged to somebody's pet, over 33,000 years ago. It's one of the earliest known examples of the domestication of dogs — and it might actually mean modern dogs aren't all related to each other after all.

The skull, recently discovered in a Siberian mountain, dates to roughly the same time period as a skull previously discovered in Belgium. And that's problematic for the idea that dogs were only ever domesticated once. Though not impossible, it's questionable whether humans could have domesticated dogs from wolves in some central location and then spread out to the far east and west edges of the Eurasian landmass, all by 30,000 years ago.

Instead, this find may point to multiple domestication events for dogs, which might mean modern dog breeds don't actually represent a single species, which in turn might disprove the old evolutionary canard that a chihuahua could theoretically breed with a Great Dane. As University of Arizona researcher Greg Hodgins explains, this Siberian dog almost certainly represents a domestication event distinct from the one — or ones — that produced modern dogs:

"Both the Belgian find and the Siberian find are domesticated species based on morphological characteristics. Essentially, wolves have long thin snouts and their teeth are not crowded, and domestication results in this shortening of the snout and widening of the jaws and crowding of the teeth. The argument that it is domesticated is pretty solid. What's interesting is that it doesn't appear to be an ancestor of modern dogs."

Both the Belgian and Siberian skulls predate the peak of the most recent Ice Age, known as the Last Glacial Maximum. This event, which lasted from 26,000 to 19,000 years ago, severely disrupted Earth's ecosystems and drove many species extinct. Both the Siberian and Belgian dogs were likely among the species that didn't make it. But the fact that these represent two previously unknown domestication events suggest the evolution of modern dogs might be more complicated than we had anticipated. And, as Hodgins points out, this also means that dogs have been humanity's best friend for a long, long time:

"In terms of human history, before the last glacial maximum people were living with wolves or canid species in widely separated geographical areas of Euro-Asia, and had been living with them long enough that they were actually changing evolutionarily. And then climate change happened, human habitation patterns changed and those relationships with those particular lineages of animals apparently didn't survive...The dogs are not necessarily providing products or meat. They are probably providing protection, companionship and perhaps helping on the hunt. And it's really interesting that this appears to have happened first out of all human relationships with animals."

Via PLoS ONE via the University of Arizona. Photo by Nikolai D. Ovodov.