Biologists Chris Klingenberg, of The University of Manchester, and Abby Drake, of the College of the Holy Cross in the U.S., looked at the extreme morphological variation to be found in the world of dogs.
The core findings, published in the peer-reviewed journal, The American Naturalist, are that:
When the skull shapes of domestic dogs are compared to those of entirely different species across the order Carnivora (which includes cats, bears, weasels, civets, seals, and walruses), the extremes of diversity were farther apart in domestic dogs than in the rest of the order. This means, for instance, that a Collie has a skull shape that is more different from that of a Pekingese than the skull shape of a cat is from that of a walrus.Almost all of the morphological variation in dogs has come through selective breeding in the last few hundred years, most of it since the rise of dog shows in 1859.What is going on with dogs is unprecedented in the history of the world in terms of the degree of selection for the unfit at the hand of man. As Dr. Klingenberg notes, "Domestic dogs don't live in the wild so they don't have to run after things and kill them -- their food comes out of a tin and the toughest thing they'll ever have to chew is their owner's slippers. So they can get away with a lot of variation that would affect functions such as breathing and chewing and would therefore lead to their extinction."Purely pet dogs are the most likely to be selected for maladaptive defect and deformity, while working dogs, such as hunting, herding, and guarding dogs are less likely to be saddled with extreme morphological variation. Notes Dr. Drake: "[Companion and pet] dogs are bred for their looks, not for doing a job, so there is more scope for outlandish variations, which are then able to survive and reproduce." In short, Kennel Club companion dogs are a product of unnatural selection and are often unfit when looked at in the most basic of Darwinian terms.
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