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If you are wondering why dogs come in so many different shapes and sizes, you're likely surprised about the great variety of dog breeds out there ranging from the tiniest dogs like the Chihuahua to the tall and majestic breeds such as the great Dane or Irish wolfhound. 

Why is there such a bewildering kaleidoscope of different shapes and sizes in the canine world? If all dogs have the wolf as an ancestor, how can it be that they are so different? 

Your wonders are very justified as it turns out the dogs are the most varied animal species on the planet. 

Read on to learn why dogs come in so many different shapes and sizes.

A Glimpse Back in Time

Dogs are the most diverse land mammal, points out Elaine Ostrander, a geneticist who studies dogs at the National Institutes of Health in an article for the Inquirer.

 In order to better understand the process of how dogs ended up being the most varied land mammal on earth, it helps to gain a closer look into their history. 

In particular, it can be said that two phases have mostly contributed to molding our dogs into the animal we know today.

Phase 1: The Domestication Process 

If we look at the dog from a genetic standpoint, studies reveal that domesticated dogs are a close relative of the wolf.

 Initially classified as ''Canis familiaris '' by Linnaeus in 1758, domesticated dogs were later reclassified in 1993 as a subspecies of the gray wolf. 

This granted a further adjustment in classification so "canis familiaris" was re-named into ''Canis lupus familiaris'. 

Today, there are different theories as to how and when dogs evolved from wolves, but it certainly must have involved selection for characteristic necessary for co-living with humans (friendliness, docility).

However, one question remains: if all dogs have the wolf as an ancestor, a species that is pretty much uniform in appearance, how can it be that nowadays dogs boast so much variety? Phase two provides an explanation.

Did you know? As dogs were domesticated, several genetic mutations occurred, and an interesting one was the ability to digest starches, setting them apart from their wolf ancestors. 

Selective breeding has led to a vast array of shapes and sizes in dogs. 

Selective breeding has led to a vast array of shapes and sizes in dogs. 

Phase Two: Selective Breeding Process

Dogs are no longer wolves, and thousands of years separate them, sort of like chimps and humans.

As dogs were domesticated, the goal of humans was to utilize dogs as working partners. 

Humans therefore started selectively breeding dogs to make them more adept to carrying out specific tasks. 

Sighthounds were bred to be fast and chase down prey.  Terriers were bred to be small so they could dig into burrows and hunt down rodents.

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 Labs were bred to have a water resistant coat, an otter-like tail and webbed toes so they could jump in cold water to retrieve downed fowl.

Sled dogs were bred for stamina, insulating coats and strong pack drive, etc.

Several mutations allowed the development of different sizes, shapes of ears, snout and tails, coat type and color.

A Passion For "Dog Fancy"

As humans though started relying less and less on dogs for work, a new trend of creating breeds just based on appearance started.

 While the notion of breeding based on looks occurred long before, this trend was emphasized in 19th century, precisely during the Victorian Era when a passion for “dog fancy” put roots. 

As the wealth of people improved, dogs were being kept more and more as companions and as a status symbol of the new middle class. 

As the passion for breeding, showing and enrolling dogs in sports expanded, the 19th century saw the formation of breed clubs and the creation of hundreds of breeds.

Tinkering With Genetics

The answer to "how can dogs come in some many different shapes and sizes?" ultimately lies in the marvels of selective breeding. 

We must thank Charles Darwin and his studies in his book "On The Origins of Species" for this as he realized how, by carefully selecting animals with some desirable traits and purposely breeding them, these traits could be passed down to future generations.

 According to Scientific American, unlike natural selection which takes thousands of years for changes to occur, artificial selection speeds up the process greatly, often with changes occurring within a few generations. 

Scientists seem to agree that the process of selectively breeding wild plants and animals must have started about 10,000 years ago.

 An interesting study that helps explain how fast selective breeding produces changes, even as early as in 10 years, is Dmitry K. Belyaev's Farm Fox Experiment.

A Mixed Bag of Genes

A factor that contributed to the great variety of dogs we see today, is the dog's nature itself. Dogs are believed to have a vast array of physical and behavioral variations unlike any other mammal on earth. 

According to professor emeritus of biology, Raymond Coppinger, this is likely to be noticed the most when you cross two breeds.

He states: "Whenever you hybridize, instead of getting an average between the two types, you quite often get something that I call phylogenetically bizarre, which means you've never seen that form before in evolutionary terms." 

It is therefore thanks to this genetically malleability, that breeders can create those traits dog owners love so much in their favorite breeds.

Did you know? German, tax collector Louis Doberman, the "father of the the Doberman breed" took only about 35 years to create the Doberman breed by crossing shorthaired shepherd dogs with Rottweilers, black and tan terriers, and German pinschers.

 There are chances greyhounds, pointers and weimaraners might have been also included in his breeding program.

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