In 1998, Alan R. Templeton, a professor of biology at Washington University in St. Louis, Mo., combed the DNA of different global human populations for racial differences. That figure is two or three times below the threshold biologists use to define race in other animal populations. While there is plenty of genetic variation among humans, all humans share the same genome. The between-population variation is very, very minor. Man's best friend, the dog, is in a similar fix.
All canines belong to one species and share a common genome.
Genetically, there are insignificant differences between a timber wolf and a Scottish terrier. But Rover, with his high reproductive rate and short lifespan, has had his individual variation manipulated by being bred in closed populations. That's why researchers at the Fred Hutchinson Cancer Research Center in Seattle and Cornell University's College of Veterinary Medicine began making genetic maps of various breeds of pedigreed dogs in the mid-'90s. Inbred dogs share a host of genetic diseases, including cancer, epilepsy, retinal degeneration, bleeding disorders, and skeletal malformations, with humans. But finding a genetic basis for those diseases is dificult in the mix of human diversity.