Man's best friend once upon a time
I have a fascination with the topic of human relationships with animals, especially with the kind of affective relationships captured by pet-keeping culture. I've gone so far as to claim
that the nature
of our connections with other animals is a defining part of what makes us human.
And while stories about cats draw more readers than those about dogs, dogs hold a special place because they are the earliest animals to join human society. Dog domestication raises a terribly poignant question:
When did we stop being alone?
The search to address this origins issue continues to produce information that offers tantalizing hints that go beyond simple chronology.
The latest example: researchers dating dog skulls from Siberia and Belgium-- opposite ends of the early distribution of the dog-- provide suggestions that dogs were domesticated multiple times, independently.
A UPI article on January 23 based on a press release from the University of Arizona quotes physicist Greg Hodgins describing dating of these dogs ca. 33,000 years ago. The distance between the two finds from such an early date is an implied argument for them representing different domesticated populations. But even if they represented a single population thinly distributed across all of Eurasia that has been under-sampled, these dog lineages appear to have died out before the later domestication events that led to modern dogs.
The study of the Siberian skull was actually published last July in PLoS ONE. The research team, led by Nikolai Ovodov of the Institute of Archaeology and Ethnography in Novosibirsk, included the University of Arizona as one of three labs conducting dating. Morphological study of the skull, from the Razboinichya Cave in the Altai Mountains, found it to be closest in shape to fully domesticated dogs from Greenland that date to 1000 years ago.
The PLoS ONE article notes that the radiocarbon dating of the Siberian skull compares well to a specimen from the Goyet cave in the area of modern Belgium. That was published in a 2009 article in the Journal of Archaeological Science. Ovodov and his colleagues note that the description of the Goyet skull suggest it, like the new Altai specimen, was "an incipient dog whose lineage did not survive".
The researchers describe the Siberian occupation (starting around 100,000 years ago) as made up of "relatively sedentary" hunting and gathering groups that stayed in one place for months at a time. This, they say, was conducive to the beginnings of domesticating dogs. When later peoples in the area adopted a more mobile pattern they wandered without dogs.
Think about that in more familiar terms: selection for early wolf-dogs took place in situations where people had established hearth and home. And at least some proto-dogs chose to join them.
As Ovodov and company write:
Traditional anthropological definitions of domestication consider the process to be a deliberate act of selection by humans. ...this view has been challenged in recent years by the hypothesis that animals colonized anthropogenic environments of their own volition and evolved into new ("domestic") species via natural evolutionary processes...
Wolves appear to have been especially attracted to permanent or semi-permanent human settlements....The fact that the Razboinichya canid is likely an early incipient dog rather than the oldest ancestor of modern dogs in no way detracts from its historical or biological importance.
If anything, it creates a more powerful image: wolves repeatedly drawn to human settlements, giving rise to new generations more dependent on and with destinies intertwined with those of their human companions.
Of course, by definition, if these early experiments died out, this research does not really answer the question of origins for the dogs that share their lives with humans today. But there is more news on that front this month as well.
On January 22, the journal Mammalian Genome published an article about results from genetic studies of present-day dogs. They conclude that recent claims placing the ancestors of modern dogs in East Asia, should be re-assessed. Both mitochondrial DNA and Y-chromosome DNA analyses have reached that conclusion.
The newer studies cited in the Mammalian Genome article use other methods. They conclude that these
clearly do not support an East Asian origin for dogs but suggest multiple centers of origin or ancient backcrossing, or indicate a bias in mitochondrial DNA variation reflecting a higher rate of trade or female biased dispersal.
So, modern dogs, they say, more likely originated in a broader area, already pinpointed through archaeological studies of skeletal remains: Europe, the Middle East, and Siberia.
Citing studies that compared genetics of different wolf populations with modern dogs, the Mammalian Genome team found the highest level of genetic sharing between modern dogs and Middle Eastern wolves. East Asian dog populations showed a higher level of sharing with Chinese wolves, suggesting continued crossing between early domesticated dogs and wolves in this area. Such back-crossing between domesticated dogs and wolves is also likely a factor in the high level of shared genetic material with Middle Eastern wolves.
It seems wolves not only repeatedly crept up to the edge of human camps, settling in for generations; early dogs continued to have the option of moving back into intimate relations with the wolves that had kept their distance from humans.
Domestication, as archaeologists know, is a matter of degree: and it is not only cats whose pact with humankind has been open to reconsideration.
So maybe when Altai humans stopped providing proto-dogs an attractive environment, they didn't die out, but faded back into the broader wolf populations from which their ancestors stepped aside, the same reservoir from which, ages later, other wolves would take their chance at cohabiting with our messy human ancestors, scavenging the scraps that they threw into the dark at the edge of the campfire.