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Dog Evolution

"Dog" is, at times, used to refer collectively to any mammal belonging to the family Canidae such as wolves, foxes, and coyotes.

The word dog refers to the domestic pet Canis lupus familiaris. The species was originally classified as Canis familiaris by Linnaeus in 1758. In 1993, dogs were reclassified as a subspecies of the gray wolf, Canis lupus, by the Smithsonian Institution and the American Society of Mammalogists.

To begin to understand the dogs’ evolution, we must go back 40 million years to the time of the carnivores’ ancestors. The Miacids were small, forest-dwelling animals. Fossil records show that their paws were adapted for climbing, so they probably spent most of their time in trees. Miacids had slender heads, short legs, and long bodies. Some species were tree dwellers, others lived on the ground. Some of their teeth were specialized for meat eating so they probably fed on invertebrates, lizards, birds and smaller mammals like shrews and opossums.

About 25 million years ago, the earth's weather changed. As the climate became drier, grasslands appeared along with a great array of grass-eating prey. The Miacids began to diversify. Bears, dogs, raccoons, weasels, civets, hyenas and cats appeared, each specializing to deal with different foods and different habits. Some of the original carnivores remained in the forest and became highly efficient meat-eaters. Others moved out to exploit the new food sources in the open areas. This produced an entirely new set of challenges. Prey species that lived in developing grasslands gradually acquired different behaviors to avoid being eaten. They ran swiftly, formed herds or burrowed into the ground. The carnivore group that took to this prey had to be lithe, be able to run and dig and survive on other foods during the lean times. These are the animals that became the dogs we know today. The first dogs were small. They maintained the dual-purpose teeth of their ancestors along with an omnivorous diet of both plants and animals. These early dogs spent more time on the ground in open areas and became runners and chasers. Over the course of countless generations, they relied more on running down and capturing prey animals.

The earliest remains of a domesticated dog that have been found are dated around 12,000 to 14,000 years ago. Recent studies of DNA changes in dogs and wolves have provided evidence that the dog may actually have been domesticated more than 100,000 years ago.

Most researchers believe that the dog was first domesticated by humans living in small tribal groups which hunted large mammals as one of their food sources. Living and hunting as a social group allowed humans to be successful in hunting prey species that were larger or faster than they were. At that time, another predatory species, the wolf, was also successfully surviving as a social hunter. Most likely, humans and wolves were competing for the same food sources within geographical areas and existed in close proximity to one another.

The first attempts at taming and domesticating the wolf were probably occurred in many areas of the world at the same time. Being opportunists, wolves possibly followed human tribes to scavenge food from their campsites. It is known that humans of the Pleistocene age were in the habit of taking young animals of many species from the wild and raising them in captivity as pets.

Once an individual wolf pup was raised and tamed, it could serve several purposes for tribal people. They were used primarily as a food source. However, as time went on, humans began to recognize other advantages to keeping this predatory species as a campsite companion. A wolf's alarm bark would have been beneficial to alert humans to the approach of other tribes or predators as well as a possible deterrent to these intruders. The social nature of the wolf and its ability to hunt cooperatively led to uses of the wolf/dog in the detection, tracking and killing of game.

During the Mesolithic period, human culture developed the use of weapons for hunting. This allowed greater distances between hunters and prey and created the need for canine partners as trackers and retrievers. As the climate changed and human populations increased, humans slowly evolved from hunter-gatherers to inhabitants of settled agrarian communities. Within communities, the need for dogs to act as sentinels to warn of approaching animals or other individuals increased. The age of agriculture and the keeping of domesticated livestock as a food supply resulted in a need for the dog as a guard or herder. As human lifestyles changed, so did the dog. Intentional breeding was undertaken to develop specific types of dogs for specific jobs. This process was repeated often in many parts of the world.

Recent mitochondrial DNA studies suggest that wolves and dogs split into different species around 100,000 years ago. A recent study suggests that the entire population of dogs today descended from three females near China about 15,000 years ago. A burial site in Germany called Bonn-Oberkassel has a joint human and dog interments dated to 14,000 years ago. The earliest domesticated dog found in China is at the early Neolithic (7000-5800 BC) Jiahu site in Henan Province. European Mesolithic sites (5250-3700 BC) in Sweden have dog burials and Utah is the earliest in the United States, at about 11,000 years ago.

Over time, the dog has slowly diversified to numerous body types, coat types, temperaments, and working abilities. Heights range from a few inches (such as the Chihuahua) to the size of small ponies, such as the Great Dane. Colors vary from white through to black, and every variation of browns and various patterns. Coats can range from very short to very long, with textures from coarse to ultra fine, curly or smooth. Dogs fill a variety of roles today. For dogs that do not have working jobs, a wide range of dog sports provide the opportunity to exhibit their natural talent. However, the most important role of dogs is as companions. Because of their loyalty they have truly earned the title "man's best friend".