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On October 19, 2015, the prestigious Proceedings of the National Academy of Sciences, commonly known as PNAS, published the latest installment in the dog origins sweepstakes, “Genetic structure in village dogs reveals Central Asian domestication origin,” online. [A subscription is required to view the article.] Previous entries for where dogs began to separate from wolves have included the Middle East, especially the area encompassed by the Levant; the Mammoth Steppe across Eurasia. and East Asia south of the Yangtze River.
A Mongolian village dog.
This time, the researchers involved in a multi-year project to gain DNA samples from the world’s village dog population—freely breeding dogs living largely in the developing world—announced that the most comprehensive genetic survey to date pointed to Central Asia—a swatch running roughly from Mongolia to Nepal—as the likely region of origin for dogs.
Writing for the group, Laura M. Shannon said their conclusions were based on analysis of genomic data from 549 village dogs from 38 nations and 4,676 purebred dogs representing 161 breeds. Previous surveys of ancestry have tended to focus on mitochondrial DNA—the genetic material involved in the cell’s energy system and inherited from the mother—because it was relatively easy to sequence and analyze for patterns of maternal inheritance. Others looked at the Y chromosome to study paternal inheritance. Often the two methods revealed quite different results.
But with the sequencing of the dog genome in 2005, researchers began to study nuclear DNA inherited from both parents. This material, found on the autosomes, the numbered, non-sex specific chromosomes found in a cell’s nucleus, provides the most powerful tool yet for comparing populations and individuals at the genetic level.
A Mongolian Village dog. The dogs are quite diverse.
Shannon reports that she and her colleagues looked at all three types of DNA. In the process, Shannon writes, they amassed “the largest canine diversity panel assembled to date, allowing efficient comparison of Y, Mt [mitochondrial], and autosomal loci to evaluate the forces patterning genetic variation in diverse dog populations.” In all they studied 185,805 markers—alleles, or variations in the genetic code—that accrue in populations over time, the result of genetic drift, mutations, natural and /or artificial selection, bottlenecks, genetic swamping by outside populations, and migration. The more variation a group or population has in their genetic code, the closer they are thought to be to the founding population.
Not surprisingly, the researchers, most of them associated with the Cornell University village dog genetic diversity project laboratory of Adam Boyko, an assistant professor, found that modern breeds lack diversity because they come from limited gene pools and have high levels of inbreeding; indeed, despite their sometimes profound differences in appearance, purebred dogs represent only a fraction of the genetic diversity found in the world’s dogs, Shannon says.
Those genetically limited European breeds travelled with their colonial masters and now are in demand among the growing urban middle and professional classes in many developing nations. In and around those cities European breeds have crossbred extensively with indigenous village dogs and thereby reduced their genetic diversity and uniqueness, Shannon writes.
Fortunately, that does not appear to be the case away from cities like Cairo and Beruit or even Mumbai and Katmandu, or in sparsely settled areas not frequented by Westerners and their dogs. Village dogs not showing significant admixture of genes were found in enough different parts of the world for Boyko’s team to perform their comprehensive statistical analysis of genetic diversity, the results of which point to Central Asia
The parsimonious explanation for what they see in the data, Shannon writes, is that dogs originated somewhere in Central Asia and then experienced a severe genetic bottleneck before moving out with their humans to other regions with nearly the full complement of genetic variability. East Asia was the most immediate destination, and there, early dogs became more numerous and diverse.
The most plausible alternative interpretation of their data, Shannon writes, is that dogs originated somewhere else and passed through a less severe genetic bottleneck before diversifying again in Central Asia. They then moved out with their people as the glaciers began to recede from their maximum advance. The founding population in that event might have died out or been swamped genetically by subsequent canine invaders, she says.
I found this research interesting not least because it reinforces and clarifies some of the suggestions I put forth in How the Dog Became the Dog about the crucial role of Central Asia in the early history of the dog. I posited that because of their many affinities, wolves and early modern humans, as they are now often called, formed some sort of union wherever and whenever they met on the trail of the prey they hunted, like reindeer, horses, and saiga antelope.
Some of these alliances were stronger than others and from those came dogwolves (doglike wolves) who began travelling with their wandering humans, mixing at various rendezvous points which grew up where migratory trails met. People traded goods, furs and dogwolves who would also take up with new groups on their own. In that way, they spread fast, mixing with local wolves, as they went. I identified a hub in the region of the Black and Caspian Seas and the Caucasus Mountains, with major migratory routes across the steppe through Central Asia to the Altai Mountains—not an impossible distance. There dogs and people gathered and as the ice melted dispersed for the Americas, Japan, Korea, East Asia, Southwest Asia, back to Europe and North Africa. I suspect the dog population at the time included big dogs, small dogs, and between or t’weener dogs—the fundamental divide.
The evidence described here points to one domestication event, but I wonder why there could not have been several with a subsequent mixing at those meeting points. We might begin to have a clearer view in the not-too-distant future.
In fact, everyone interested in this subject is waiting now for the international team of researchers headed by Greger Larson at Oxford to begin reporting on the results of their analysis of ancient DNA of dogs and wolves from around the world.
