If you frequent this site, you’ll know that I’m much more partial to cats than to dogs, but dogs do excel in one respect: they better demonstrate the power of artificial selection.
Every year I present to my students a much-tattered poster, made by the now-defunct Gaines dog food company, showing the various dog breeds recognized by the American Kennel Club. I use it to show the students how the lineage of the gray wolf (the ancestor of all domesticated dogs) contains ample genetic variation for almost any trait you choose: size, body shape, coat color and texture, and even behavior.
This, in turn, demonstrates that selection—artificial selection rather than natural selection in this case, but the principle is the same—has plenty of raw material to work with. As Darwin famously said in The Origin, “Breeders habitually speak of an animal’s organisation as something quite plastic, which they can model almost as they please.” And if that kind of genetic variation is present in one rather inbred lineage, then it is certainly present in nature. Remember that neither natural selection nor genetic drift could operate, nor selection produce complex adaptations, if genetic variation wasn’t ubiquitous. Demonstrating the pervasiveness of inherited variation was, then, an important task in verifying Darwin’s theory, and one reason he devoted so much space to artificial selection in The Origin.
The problems that afflict dog breeds, however, also demonstrate two other principles of genetics: inbreeding and pleiotropy. Inbreeding, because many breeds stem from only a few founders, and so bad recessive alleles can accumulate, causing genetic disease and malformations. (Breeders do attempt to eliminate this by outcrossing, but of course that dilutes the desired traits of the breed).
“Pleiotropy” is simply the observation that an allele (form of a gene) can affect several traits independently. Many eye-color mutations in flies, for example, reduce fertility independent of the mutant color. As an example in dogs, the short snouts of breeds like bulldogs can lead to respiratory problems.
Given that, here, from the website Pedigree Dogs Exposed, is a splenetic take on the evolution of the American cocker spaniel, one that sounds as if it were written by Andy Rooney. The change in this breed over 100 years shows not only the power of the breeder to change a lineage in only a few generations, but at least one pleiotropic effect of a change in the coat:
This breed needs to be re-classified as a Toy breed. Its retention in the Gundog Group does a disservice to those breeds that can and do still do the work for which they were bred. And, frankly, this amount of coat is a welfare issue – not perhaps directly (as long as it is groomed regularly), but because top show dogs can’t possibly get much of an opportunity to be dogs. There’s certainly no way they could do a day in the field – it would ruin that all-important coat.
And how on earth do the males pee without soaking their coat?
Here’s what the Americans have done to the Cocker… from sturdy sporting dog to dome-headed,over-coated, increasingly-brachycephalic hairdresser’s dog in 120 years. [JAC: I’ve chosen but a few pictures from their series.]
I make no claims for the veracity of this analysis, so if you own an American Cocker Spaniel, don’t complain to me!
The American Cocker spaniel, originally a sporting dog bred to find and bring back game to hunters, diverged from the English cocker spaniel in the late 19th century. One could, then, consider this divergence an example of incipient speciation, except that the breeds will almost certainly not become full species as they remain reproductively compatible. (My students often ask me whether dog breeds are separate species, and I say “no” because of this reproductive compatibility.)
As for the results of inbreeding and pleiotropy, one dog-breeds website reports this:
Some major concern in American Cocker Spaniels are cataracts, glaucoma and patellar luxation. Some minor concerns are hip dysplasia, ectropion, entropion, PRA, allergies, seborrhea, lip fold pyoderma, otitis externa, liver disease, urolithiasis, prolapse of nictitans gland, CHF, phosphofructokinase deficiency, and cardiomyopathy. Occasionally seen are gastric torsion and elbow dysplasia. Also IMHA (Immune Mediated Hemolytic Anemia) One owner stated, “Our cocker never had a sick day in her life until she suddenly became lethargic and urinated blood. Six days later, and $3000 in vet bills, she died. I know you can’t list every illness due to space limitations, but the internal medicine specialist that treated our dog said that IMHA is relatively common in cockers, and almost always fatal. It’s a fast-acting, silent killer.
This information all was inspired by a piece at the Manchester Evening News reporting a £ 500,000 grant given to researchers at Manchester University. These include our own Matthew Cobb, and the Evening News describes the study as follows:
The unique study will see zoologists and historians going back in time to see how far dogs have been transformed over the last century. Michael Worboys, an expert in the history of science, said breeding, training and socialising meant many of today’s breeds were barely recognisable from their 19th-century ancestors.
He said: “The dog was transformed in the 20th century by the application of science and medicine. No animal species has been more altered in size, shape, colour or temperament by human selection.
“No species has a closer relationship with humans. And no species has their health treated in a manner so close to what humans enjoy.
“We will study how changing ideas and practices with breeding, feeding, training and treating have essentially remade the modern dog – whether as pet, show dog or working animal.”
Here’s a picture of Professors Worboys (l.) and Cobb (r.) with Melsha the dog. I hasten to assure readers that Matthew is more partial to cats, and has two of them. I regard this grant, in fact, as a provisional act of treason.