Why Dogs Vary Dramatically and Cats Don’t
Chihuahuas and Great Danes are both breeds of dog and everyone recognises them as such but their appearances are dramatically at variance. You would certainly never mistake one for the other! On the other hand, the physical traits of cats vary little across the many breeds. So, why are dogs so different when most cats look incredibly similar?
The differences between cat breeds are mere nuances compared to the staggering physical variations that are found in dogs. Both animals were domesticated thousands of years ago and both have been bred selectively to produce desirable traits. But whilst both cats and dogs have been living alongside humans for thousands of years, their roles have been very different.
Cats have always been either companions or pest controllers and nothing more. As hunters of vermin their physical appearance is of no importance and so hunting has never influenced selective breeding. Cats are difficult to train and so most of the selection that has produced the different feline breeds has taken place in the last 75 years and for aesthetic reasons. Cats have been bred to produce attractive coat colours and longer fur and not greater physical prowess.
The human-canine relationship has proved to be far more complex. This relationship developed and diversified quickly as it didn’t take long for people to realise that dogs could perform a variety of tasks and could be easily trained. People with widely differing lives began shaping dogs to meet their specific needs. Herding mountain goats required certain canine traits whilst herding sheep in the lowlands demanded others. Some dogs were primarily guard dogs and others were required to hunt.
In many environments speed and agility were desirable traits in dogs but elsewhere power or intelligence were all-important. Hence the incredible diversity that we see in dogs today. Dogs are different because they have needed to be in order to serve mankind.
The Downside of Selective Breeding
In both dogs and cats, selective breeding has its drawbacks, however. Selection often results in a reduction of diversity a population. In some cases, the mutations associated with specific traits also cause the animals to be prone to certain diseases and conditions. For instance, Persian cats are genetically predisposed to develop polycystic kidney disease. In dogs, a genetic variant that produces dark coats in standard poodles also predisposes them for squamous cell carcinoma – a form of cancer.
Diluting the Gene Pool
Exaggerated physical traits can also lead to health issues. Both cats and dogs with dramatically shortened skulls can suffer from serious breathing issues. Happily, many breeders are working to restrict some of the more extreme variations and are using genetic data to produce healthier animals. If we could avoid breeding carriers of conditions to other carriers, there will fewer problems in the future.
Selective breeding continues so who knows what cats and dogs will look like in the future!