The above picture of this year’s best in show winner Hickory, a Scottish deerhound, is the result of years of selective breeding by dedicated breeders worldwide. The 2011 Westminster Kennel Club Dog Show, beyond providing plenty of cute pooches to ogle, is yet another opportunity to explore Darwin’s Theory of Natural Selection.
A study published in The American Naturalist by Chris Klingenberg and Abby Drake compared skull shapes of domestic dogs with those to other species belonging to the order Carnivora, such as cats, bears, weasels and walruses. They found that not only did the amount of variation among domestic dogs exceed the variation seen across the entire order, but that the shape differences between breeds of domestic dogs was larger than that seen between separate species. In other words, the difference in skull shape between a Collie and a Bulldog is greater than the difference in skull shape between a cat and a walrus! In addition, domestic dogs possess skull shapes not seen in any other wild species in the order Carnivora.
One thing interesting to note is that this variation has only arisen in the last 150 years or so, when breed standards for dogs had been established and their bloodlines and morphology had stabilized. When one contrasts this with the approximately 60 million year lifetime of the Carnivora order, it is astonishing to see the effects selective breeding can have on a species compared to the slow acting mechanism of Natural Selection. These results show that selection, whether natural or otherwise, can have a profound effect on evolution and the morphology of a species.
An explanation for the tremendous variation observed, and in particular the rise of skull shapes that are otherwise unheard of in the order Carnivora, is that the traits breeders select for are in many cases based on looks and not beneficial to wild species. Domestic dogs do not have to compete for food anymore, but rather for attention which leads to skull shapes that although not adept for hunting, are more visually appealing instead. One can think of this as a sort of “relaxed“ natural selection. Indeed Darwin himself studied domestic dogs for the purpose of observing long term natural selection.
The paper provides strong evidence for Darwin`s theory and shows its power. Selection whether natural or selective can have a large impact on the evolution of species and their morphology. The authors conclude that the example of head shapes in dogs proves just what can happen when you consistently apply a process of selection over time, as Darwin predicted.
Below is a link to the original article, as well as a requisite picture of my favourite puppy Kilo, relaxing on Christmas morning. I hope a Great Pyrenees or Icelandic Sheepdog wins next year!