The Evolution of Dog Breeds
Dogs have been purposefully and selectively bred by humans for thousands of years, sometimes by inbreeding dogs from the same ancestral lines, sometimes by mixing dogs from very different lines. This process continues today, resulting in a wide variety of breeds and hybrid dogs. Centuries of selective breeding by humans has resulted in dogs being considerably more genetically diverse than any other land mammal on earth. This has resulted in dogs being the only animal with such a wide variation in appearance and behavior without speciation – ranging in size and appearance from the tiny Teacup Poodle to the massive Great Dane – with hundreds of variations in-between.
DNA evidence shows an evolutionary split between the modern dog’s lineage and the modern wolf’s lineage around 100,000 years ago. The oldest fossil specimens genetically linked to the modern dog’s lineage date to approximately 33,000–36,000 years ago. The dog’s value to early human hunter-gatherers led to them quickly becoming common across cultures worldwide. Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship, aiding handicapped individuals, and serving as a source of meat in some cultures.
As humans migrated around the planet, a variety of dog forms migrated with them. The agricultural revolution and subsequent urban revolution led to an increase in the dog population and a demand for specialization. These circumstances would provide the opportunity for selective breeding to create specialized types of working dogs and pets. Most breeds of dogs are at most a few hundred years old, having been specifically selected for particular physical characteristics and behaviors by people to fulfill specific functional roles.
This rapid evolution of dogs from wolves is an example of neoteny or paedomorphism, which are terms used to describe the rapid evolution of diverse dog breeds. As with many species, young wolves are more social and less dominant than adults; therefore, the selection for these characteristics, whether deliberate or inadvertent, is more likely to result in a simple retention of juvenile characteristics into adulthood than to generate a complex of independent new changes in behavior. (This is also true of many other domesticated animals.)
This paedomorphic selection naturally results in retention of juvenile physical characteristics as well. Compared to wolves, many adult dog breeds retain such juvenile characteristics as soft fuzzy fur, round torsos, large heads and eyes, ears that hang down rather than stand erect, etc.; characteristics which are shared by most juvenile mammals. These characteristics generally elicit some degree of protective and nurturing behavior across species from most adult mammals, including humans, who see these characteristics as “cute” or “appealing”. The example of canine neoteny goes even further, as various breeds are differently neotenized according to the type of behavior that was selected.
- Herding dogs exhibit the controlled characteristics of hunting dogs. Members of this group, such as Border Collies, Belgian Malinois and German Shepherds, use tactics of hunter and prey to intimidate and keep control of herds and flocks. Their natural instinct to bring down an animal under their charge is muted by their training. Other members of the group, including Welsh Corgis, Canaan dogs, and Cattle dogs, herd with a more aggressive demeanor (such as biting and nipping at the heels of the animals) and make use of body design to elude the defenses of their charges.
- Gun dog breeds used in hunting, such as pointers, setters, spaniels, and retrievers, have an intermediate degree of paedomorphism; they are at the point where they share in the pack’s hunting behavior, but are still in a junior role, not participating in the actual attack. They identify potential prey and freeze into immobility, but then refrain from stalking the prey as an adult predator would do; this results in the “pointing” behavior for which such dogs are bred. Similarly, they seize dead or wounded prey and bring it back to the “pack”, even though they did not attack it themselves. Their physical characteristics are closer to that of the mature wild canine than the sheepdog breeds, but they typically do not have erect ears, etc.
- Scenthounds maintain an intermediate body type and behavior pattern that causes them to actually pursue prey by tracking their scent, but tend to refrain from actual individual attacks in favor of vocally summoning the pack leaders (in this case, humans) to do the job. They often have a characteristic vocalization called a bay. Some examples are the Beagle, Bloodhound, Basset Hound, Coonhound, Dachshund, Fox Hound, Otter Hound, and Harrier.
- Sighthounds, who pursue and attack perceived prey on sight, maintain the mature canine size and some features, such as narrow chest and lean bodies, but have largely lost the erect ears of the wolf and thick double layered coats. Some examples are the Afghan Hound, Borzoi, Saluki, Slough, Pharaoh Hound, Azawakh, Whippet, and Greyhound.
- Terriers similarly have adult aggressive behavior, famously coupled with a lack of juvenile submission, and display correspondingly adult physical features such as erect ears, although many breeds have also been selected for size and sometimes dwarfed legs to enable them to pursue prey in their burrows.
The least paedomorphic behavior pattern may be that of the Basenji, which was bred in Africa to hunt alongside humans almost on a peer basis. This breed is often described as highly independent, neither needing nor appreciating a great deal of human attention or nurturing, and often described as “catlike” in its behavior. It too has the body of an adult canine predator.
While all dogs are genetically very similar, natural selection and selective breeding have reinforced specific characteristics in certain populations of dogs, giving rise to a wide variety of dog types and dog breeds. Modern dog types are broad categories based on function, genetics, or physical characteristics. Dog breeds are groups of animals that possess a set of inherited characteristics that distinguishes them from other animals within the same species. For the most part, modern dog breeds are non-scientific classifications of dogs that have been developed by modern kennel clubs. Purebred dogs of one breed are genetically distinguishable from purebred dogs of other breeds, but the means by which the kennel clubs classify dogs is traditionally based upon the dog’s purpose or function or upon its appearance or size.
So just how many breeds of dog exist today? This is a difficult question to answer since many varieties of dogs that might be classifiable as separate breeds are not uniformly recognized by the various international kennel clubs and breed registration groups. The American Kennel Club (AKC) currently recognizes around 150 different breeds. However, The World Canine Organization, also known as Fédération Cynologique Internationale (FCI), which is the largest internationally accepted registry of dog breeds, currently recognizes 339 breeds of dogs which it divides into following 10 groups:
- Sheepdogs and Cattle Dogs other than Swiss Cattle Dogs (this group includes most of the dogs found classified as “herding dogs” by other kennel clubs).
- Pinscher and Schnauzer – Molossoid Breeds – Swiss Mountain and Cattle Dogs and Other Breeds (the Molossian breeds include the dogs known as the mastiffs by most other kennel clubs).
- Spitz and Primitive Types
- Scenthounds and Related Breeds
- Pointers and Setters
- Retrievers – Flushing Dogs – Water Dogs
- Companion and Toy Dogs
A recent phenomenon that has had a huge impact on dog breeding world is the increased popularity of the hybrid dogs, which are also often referred to as “designer dogs” in the media. A hybrid dog, such as a Goldendoodle, is not a specific breed; it is a hybrid, which means it is a mix of more than one purebred dog. Scientifically speaking, the term “hybrid” is incorrect as all dogs are a sub-species of the wolf (Canis lupus familiaris). Therefore, it is impossible to have a hybrid as they are two of the same species. Although technically incorrect, the term “hybrid” is the name which is predominantly used when referring to these mixes.
So what is the difference between a hybrid dog and a mutt? Generally, a mutt is of uncertain and undocumented ancestry, while a hybrid dog has documented purebred ancestry. A purebred dog is one that has been bred over many generations to breed true, meaning each puppy that is born looks like and has the same temperament and characteristics as the others in its litter. In most cases a standard is written and breeders must follow this written standard, and only those dogs that conform to the written standard are used for breeding. When acquiring a purebred dogs you know what you are getting. Unlike purebred dogs, when you acquire a hybrid, you do not have the same certainty as to what the temperament, size of the dog, or exact look of the dog will be.
Human involvement in the evolution of dog breeds has not only brought us many formidable and beautiful breeds, but had also created and increased many inherent weaknesses and health problems in many modern breeds. So how does one choose the right dog for their lifestyle and family with this bewildering variety of breeds to choose form? That is a complex question and a process that I will address in future articles.