The scientists believe their work will shed new light on when, where and under what conditions dogs were domesticated, and how dogs have adapted to human settlement, environmental stress and disease.
The first phase of the study included collecting samples from modern breeds, their mixed-breed relatives, breeds reputed to be from remote regions of the world and African village dogs. In 2009, they reported that African village dogs are a mosaic of indigenous dogs descended from more ancient dogs that migrated to Africa.2 Findings also indicated that their genome is being eroded at an alarmingly fast rate as they mate with recently introduced modern dogs. Researchers are now scrambling to find dogs in even more remote locations. In the summer of 2012, workers began collecting DNA samples in Liberia and the Democratic Republic of the Congo.
On a continuum, gray wolves, the progenitor of all dogs, have the most genetic diversity, and purebred dogs have the least. Village dogs’ diversity lies somewhere in between. Because purebred dogs are the result of strong selection for exaggerated traits, they have only a fraction of the genetic diversity displayed by village dogs. The genetic variant that underlies a desirable trait, whether it’s extreme size or intense behavior, has become fixed, wiping away not only competing variants but also variants associated with nearby genes.
Genes located close to each other on a chromosome are said to be linked, and tend to be inherited together or, conversely, wiped away at the same time. Thus, a trait that isn’t selected for can be wiped away simply as a result of being in the wrong place at the wrong time. If that trait happens to affect, for instance, immune response to disease, then that could be a problem.
By comparing the genome of village dogs to that of purebred dogs, scientists hope to be able to identify what’s been lost as a result of intense artificial selection. Dr. Boyko notes that “village dogs offer a chance to understand the mechanisms of certain genetic diseases. Knowing what those genetic variants are might be the first step towards invigorating genetic diversity in some modern breeds.”
The Significance of Canine Origin
The closer a village dog population is to the original canine domestication event, the closer it will be to the gray wolf and the more genetic diversity it will have. Will Dr. Boyko’s village dogs turn out to be close relatives of the first dogs? Not likely.
Previous studies suggest that dogs originated in places as varied as Eastern Europe, China’s Yangtze River Valley and the Middle East. In a 2002 study, researchers pinpointed East Asia as the place of origin. However, some scientists think these dogs are descendents of an even older population that developed in a different place. Dr. Boyko’s findings confirm this. African village dogs have about the same amount of genetic diversity as those in the East Asian study, suggesting that both groups are the same age. It’s possible that both populations originated together somewhere else and then migrated to East Asia and Africa at about the same time.
To thoroughly complicate matters, the Canidae family does not play by the same rules as most other mammalian families. Unlike, say, horses and donkeys, dogs, wolves, coyotes and golden jackals can interbreed and produce fertile offspring. Consequently, following the genetic trail from domestic dog to wolf leads to a lot of stops and starts and many dead ends as well as plenty of headaches for evolutionary biologists.
A Multi-Disciplinary Approach
Where to now? Some researchers think it’s time to go back to the road not taken. In a paper published in June 2012, Greger Larson, an evolutionary biologist in Durham University’s Department of Archaeology and the paper’s lead author, said that by putting genetic discoveries in the context of archaeology, history and biogeography, the study of the geographical distribution of species might help make better sense of what we already know.3