Adaptive radiation on a smaller scale [i.e., smaller than what happened with mammals once reptiles (dinosaurs) had been eliminated as major rivals] seems to have taken place soon after the dog became domesticated. Within the various human societies, dogs found a whole new habitat. The dog, as one of the first domestic animals, was a remarkable social invention, both for protection and as an aid to hunting, and every tribe must have wanted to get hold of one. In this way dogs spread rapidly over the world, differentiating as they moved, and so produced the southern short-haired varieties like the dingo and, at the opposite extreme of their range, the northern Eskimo dogs which are almost like wolves. A further multiplication of habitats was provided when the herd animals were domesticated. Now dogs were needed to protect those herds against their own close relatives, the wolves, which found the domestic beasts easy prey.
Then there’s the following on the overbreeding of champions, an issue I’ve discussed here before:
The desirability of multiple standards makes the practice of breeding a champion to a large number of females within a breed a questionable one. Almost every animal carries some sort of injurious recessive genes, and this practice insures that they will be spread throughout the whole breed, with resulting disappointment as the descendants of these champions are eventually bred together and the recessive traits begin to show up in large numbers. The breed objectives should not be the development of a single, fixed type—something which is only possible by strict inbreeding—but rather for the development of a population varying within desirable limits and within which new and more valuable combinations of genes will always be possible.