Inside of a Dog_ What Dogs See, Smell, and Know - Alexandra Horowitz [21]
The dog fanciers will be surprised to hear, perhaps, that the grouping of breeds based on genetic similarity does not result in the same groupings as the AKC. Cairn terriers are closer to hounds; shepherds and mastiffs share much of their genomes. The genome belies most people's assumptions about dogs' similarities to wolves, too: the long-haired, sickle-tailed huskies are closer to wolves than the long-bodied, skulking German Shepherd. Basenjis, who bear almost no physical resemblance to wolves, are closer still. This is yet another indication that, for most of their domestication, the dog's appearance was an accidental side effect of his breeding.
Dog breeds are relatively closed genetic populations, meaning that each breed's gene pool is not accepting new genomes from outside the pool. To be a member of a breed, a dog must have parents who are themselves members. Thus any physical changes in the offspring can only come from random genetic mutations, not from the mixing of different gene pools that usually occurs when animals (including humans) mate. Mutations, variation, and admixtures are generally good for populations, though, and help to prevent inherited disease: this is why purebred dogs, though they come from what is considered "good stock" in that the ancestry of the dogs is traceable through the breeding line, are more susceptible to many physical disorders than are mixed-breed dogs.
One boon of a closed gene pool is that the genome of a breed can be mapped, and in fact it recently has: a boxer's genome was the first, around nineteen thousand genes' worth. As a result, scientists are starting to make an accounting of where on the genome the genetic variations are that lead to characteristic traits and disorders, such as narcolepsy, the sudden and total fall into unconsciousness to which some dog breeds (particularly Dobermans) are susceptible.
Another advantage of a closed gene pool of a breed discussed by researchers is that it feels as though one is getting a relatively reliable animal when one selects from it. One can pick a "family-friendly" dog or one advertised as a skillful house guardian. But it is not so simple: dogs, like us, are more than their genome. No animal develops in a vacuum: genes interact with the environment to produce the dog you come to know. The exact formulation is difficult to specify: the genome shapes the dog's neural and physical development, which itself partially determines what will be noticed in the environment—and whatever is noticed itself further shapes continued neural and physical development. As a result, even with inherited genes, dogs aren't just carbon copies of their parents. On top of this, there is also great natural variability in the genome. Even a cloned dog, should you be tempted to replicate your beloved pet, will not be identical to the original: what a dog experiences and whom he meets will influence who he becomes in innumerable, untraceable ways.
So although we have tried to design dogs, the dogs we see today are partly creatures of serendipity. What breed is she? is a question I've been asked about Pump more than any other—and I in turn ask of other dogs. Her mongrelness encourages the great game of guessing her heritage: the resulting hunches are satisfying, even though none could ever be