Domestic Dog

 

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Classification:

Global Population

Description and Natural History

Physical Description
For years, the domestic dog was classified by scientists as a distinct species, Canis familiaris. However, recent DNA analysis that shows that dogs evolved from wolves, Canis lupus, has led scientists to reclassify the domestic dog as Canis lupus familiaris, a subspecies of the wolf rather than a separate species. It is difficult to generalize about the physical appearance of the domestic dog because extensive manipulation by humans has resulted in much variation in size, coat type and color, and overall morphology. Today, there are about 800 recognized breeds of dog around the world and although we often think of them as pets, most breeds arose from attempts to maximize certain physical, behavioral and temperamental characteristics. It was these characteristics that made them very good at specific jobs such as guarding, herding, and hunting. All dog breeds today are descended from mixed breed dogs.

Domestic dogs range in size from the very small chihuahua that can weigh as little as 1 kilograms (2 pounds), to the St. Bernard of Switzerland or the Tosa Inu of Japan that can weigh as much as 91 kilograms (200 pounds). Heights also differ dramatically, from the short-legged miniature dachshund that stands 13-23 centimeters (5-9 inches) at the shoulder, to the true long legged giant, the Irish wolfhound which tops out between 71-90 centimeters (28-35 inches). Through the years humans have had an unbelievable influence over their best friend, and the outcome includes different types of ears, tails, coat colors and types, conformation, temperament and function. Yet, regardless of what the dog looks like, all can interbreed with one another and with their wild relatives.

Natural History
Canids first appeared in the fossil record before other carnivores including bears and cats. The first group of dog, called hesperocyonines, looked similar to a cross between a weasel and a fox, and evolved in North America 40 million years ago. This animal became extinct about 15 million years ago. About 34 million years ago, the hyena-like borophagines evolved, only to become extinct about 2.5 million years ago. The third group, the canids, include extinct and extant species of canid including the domestic dog. This group evolved in North America but crossed a land bridge to Asia about 7 million years ago. DNA analysis suggests that dogs evolved from wolves about 130,000 years ago. Today, domestic dogs are found in association with humans worldwide.

The domestic dog is a member of the family Canidae which includes wolves, foxes and the coyote. This family also includes less familiar species such as the jackal, the maned wolf, the bush dog, the African wild dog, the Dhole and the racoon dog. Because of their close genetic relationship with wolves, coyotes and jackals, domestic dogs can interbreed with any of these species to produce fertile offspring. Dogs were the first animal to be domesticated by early humans, somewhere between 10,000 and 14,000 years ago. There are a number of theories as to how early dogs were domesticated but it seems now that initial domestication was not deliberate, but took place through natural selection. Wild dogs that were less likely to flee from humans, scavenged in areas near human settlements and flourished in this niche becoming increasingly tame over generations. And yet, after thousands of years of domestication dogs continue to exhibit the keen sense of smell, hearing and vision of their wolf ancestor and retain some level of prey drive.

Breeding occurs at any time throughout the year and females can give birth to two litters per year. Both males and females can reproduce between 6 and 12 months of age although this can depend on breed and status. Gestation lasts about 9 weeks followed by the birth of one or more puppies (average 3-9). Because eggs survive for about 4 days, it is possible for females to mate with numerous males and have pups from more than one father in the same litter. Pups are weaned between 4 and 10 weeks of age. Longevity varies between individuals and depends on breed, size, nutrition, and overall lifestyle. Small dogs tend to live longer than large dogs.

Dogs live and thrive in packs where they establish hierarchy and relate to one another based on this hierarchy. This dominant/submissive social order helps dogs to avoid conflict and also enforces social stability within the pack. Dogs most often fight when this hierarchy is not well-defined or when a new dog has been introduced and a new hierarchy must be established.

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Status of the Species

Status
Depending on the country, domestic animals, including dogs, may be protected under national, state, provincial, and local legislation. In some countries, no protective legislation exists. There are no internationally agreed upon humane standards, and existing legislation is often difficult to enforce. Fortunately, in most places around the world, however, dogs continue to enjoy an elevated place in society. Along with their loyalty and companionship, their contributions as service dogs, search and rescue, drug trafficking, and police dogs are well acknowledged. Their devotion and intelligence are highly recognized. Especially since dogs have been domesticated for thousands of years, it is our social and moral responsibility to provide them with care and protection.

Threats to the Species
Domestic cats and dogs are not threatened with extinction, although some rare breeds have very low numbers. Ironically, overpopulation of the species is the main threat. There are not enough homes available.

Cruelty is another problem. In many countries, dogs are farmed for commercial enterprise and human consumption. According to the International Aid for Korean Animals/Korean Animal Protection Society, more than 2.6 million dogs and cats are killed in South Korea each year for human consumption. Many dogs suffer a slow, inhumane death, as it is believed by some that torture before death makes the meat tastier. Also, dogs suffer from stress and disease while being farmed and transported in cramped conditions.

Neglect and abandonment are major issues. Poor care can be the result of either apathy, lack of awareness, limited resources, inaccessible and unaffordable veterinary services, or a combination of all. A lack of knowledge about how to take proper care of dogs and cats and limited understanding of their behavior adds to increased relinquishment and abandonment rates. These conditions contribute to the overpopulation problem, and the continuing cycle of problems. Mutilations such as tail docking, ear cropping, and declawing are also practiced around the world. These threats can be resolved by raising awareness, encouraging legislative changes and through humane education.

International Trade
Dogs and cats are farmed and traded in some countries for meat, fur, and tonics thought to be medicinal. Mass farming of puppies for sale as pets is an international, profitable enterprise that also subjects dogs to neglect and cruelty. At the time of purchase, hopeful pet owners are unaware of a puppy's health condition, which includes a wide range of disease and illness. Health certificates accompanying the dogs are often inaccurate. It is far more humane to adopt from a responsible shelter or rescue group to help ease dog and cat overpopulation.

Both dog and cat consumption and the puppy mill trade are driven by economic incentives which conflict with basic animal welfare considerations. Cats and dogs should not be treated as commodities to be massed produced for consumer markets.

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Authors and Sources

Sources
Anonymous. Dog. Wikipedia: the free encyclopedia (On-line). http://en.wikipedia.org

Anonymous.  Evolution:  from early canids to today’s dogs.  Natural History Museum of Los Angeles County.  http://www.nhm.org  

Bhagat, S. and T. Dewey.  2002.  Canis lupus familiaris (On-line), Animal Diversity Web.  http://animaldiversity.ummz.umich.edu
 
Lange, K. E.  Wolf to woof:  the evolution of dogs.  National Geographic.  http://magma.nationalgeographic.com

Vila, C. et al.  1997.  Multiple and ancient origins of the domestic dog.  Science.  Vol 276: 1687-1689.  13 June 1997.  www.sciencemag.org
 
Zgurski, J.  The origin of the domestic dog, Canis familiarus.   http://www.ualberta.ca/~jzgurski/dog.htm

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