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History about Dogs
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ORIGIN AND EVOLUTION OF DOMESTIC DOGS |
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Written by T Vernon
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Tuesday, 03 June 2008 17:06 |
ORIGIN AND EVOLUTION OF DOMESTIC DOGS
Canis lupus familiaris refers to the origins of the domesticated dog.
The Eocene Miacids are the earliest fossil carnivores that can be connected to the canids with a particular amount of certainty around 56 to 38 million years ago. The dog-like (Canoidea) evolved from the miacids. The canoid line was most important in the descent of the dog, which lead from the coyote-sized Mesocyon of the Oligocene some 38 to 24 million years ago, to the fox-like Leptocyon and the wolf-like Tomarctus which wondered around North America 10 million years ago
There were several characteristics shared by both human hunter-gatherers and wolves due to them both being social species. They both shared the same territory and hunted the same prey. There are several different theories to explain the possible routes for domestication of the dog, including:
Studies have revealed that certain wolf pups that were taken at a young age and raised by humans were easily tamed and socialized. When these early adoptees began to breed amongst themselves, a new generation of tame wolf-like domestic animal was a result, which would become more dog-like over generations of time.
Bones and refuse dumps of human campsites would be a magnet for wolves as they were scavengers. It has been argued by Dr. Raymond Coppinger of Hampshire College, Massachusetts, that those particular wolves that were more successful in interacting with humans would pass on these traits to their offspring. This would eventually create wolves that possessed a greater tendency to be domesticated. Dr. Coppinger believes that âflight distanceâ, which is a behavioral characteristic representing how close an animal will permit humans to get before it runs away, was crucial to the transformation from wild wolf to the ancestors of the modern dog. It is the animals with a shorter flight distance that would linger and feed when humans were close by. This behavior would be passed on for generations and increase over time, so that an animal was created that would be more comfortable around humans.
The earliest known domestication has been placed, through archaeology, at approximately 12,000 BC to 10,000 BC, with an absolute certainty at 7,000 BC. Over time, the domestication of the wolf has produced a number of physical changes which are typical of all domesticated mammals. These changes include:
- An overall size reduction
- Changes in the coloration and markings of the coat
- The brain being reduced in size
- Intelligence being reduced
- The development of a pronounced âstopâ, or a vertical drop in front of the forehead
Tail wagging and barking are particular behaviors only found in wolf puppies, retained via neoteny throughout the dogâs life. Wolf-like behaviors such as regurgitating partially digested food for the young have also disappeared.
A Russian scientist by the name of Dmitry Belyaev carried out an experiment in the domestication of wolves called the âfarm foxâ experiment. This is whereby he attempted to recreate how domestication may have occurred. Researches that worked with selectively breeding wild silver-foxes over thirty-five generations and forty years for the solitary trait of friendliness towards humans, created more dog-like animals. However, the more friendly animals towards humans is the âdomestic eliteâ foxes, which in actual fact sought human attention, even though they also show new physical traits that parallel the selection for tameness, even though the physical traits were not selected for originally. These traits include, black and white or spotted coats, floppy ears, tails curling over the back, and earlier sexual maturity.
DNA evidence shows that a majority of domesticated dogs were found to be members of one of four groups. The groups which were the largest and most diverse contains sequences found in the most ancient dog breeds, including the Australian dingo, the New Guinea Singing Dog, and many modern breeds such as the collie and the retriever. Other groups such as the German shepherd showed to have a closer relation to wolf sequences than to those of the main dog group, which would suggest that these breeds were produced by crossing dogs with wild wolves.
A variety of dog forms migrated with humans as they moved around the planet. The agricultural revolution and urban revolution is what led to the increase in the dog population and a demand for specialization. It was these circumstances that provided the opportunity for selective breeding to take place in order to create specialized types of working dogs and pets.
An example of neoteny or paedomorphism is the fast evolution of dogs from wolves. Young wolves, as with many species, are more social and less dominant than adults. For this reason, the selection of characteristics, whether they are premeditated of unintentional, is more likely to result in a simple retention of juvenile characteristics into adulthood rather than generate a complex of independent new changes in behavior.
Juvenile physical characteristics are also retained due to this paedomorphic selection. In comparison to wolves, many adult dog breeds retain such juvenile characteristics such as:
- soft fuzzy fur,
- round torsos
- large heads and eyes
- ears that hang down rather than stand erect etc
Canine neoteny goes even further, in that various breeds are neotenized differently according to the type of behavior that was selected. Some of these examples include:
- Gun dogs used for hunting. These include pointers, setters, spaniels and retrievers that have an intermediate degree of paedomorphism. They are similar in that they share in the packâs hunting behavior, but do not participate in an actual attack. They identify potential prey and freeze, pointing to their prey. They also seize dead or injured prey and take it back to the pack.
- Livestock guardian dogs show controlled characteristics of hunting dogs. They include Border Collies, Belgian Malinois, and German Shepherds. These dogs use hunting tactics in order to frighten and keep control of herds and flocks. Other group members include Welsh Corgis, Canaan dogs, and Cattle dogs that herd with more aggressiveness whilst biting and nipping at the heels of the animals.
- Scenthounds pursue prey by tracking their scent, but tend to avoid undertaking individual attacks. Rather, they call the pack leaders to do the job. Some examples of this group are the Beagle, Basset Hound, Bloodhound, Coonhound, Dachshund, Fox Hound, Harrier, and Otter Hound.
- Sighthounds pursue and attack prey on sight, and maintain their mature canine size and some features, such as lean bodies and narrow chest. Some examples of this group are Afghan Hound, Azawakh, Borzoi, Greyhound, Pharaoh Hound, Saluki, Sloughi, and Whippet.
- Mastiffs are traditionally bred for war, protection, and guardian work. They are large dogs, both tall and massive with barrel-like chests, large bones and thick skulls.
- Bulldogs are medium in size and are bred for combat against both wild and domesticated animals. They have massive and square skulls with large bones and broad shoulders.
- Terriers have adult aggressive behavior that is famously coupled with a lack of juvenile submission. They have very often been selected for size and dwarfed legs in order to enable them to pursue prey in their burrows.
One breed, which most probably has the least paedomorphic behavior pattern, is that of the basenji. This dog is bred in Africa to hunt alongside humans. This breed is very often described as being highly independent, neither requiring nor appreciating a great deal of human attention or nurturing. It is often described as being catlike in its behavior.
Of course, dogs possess the ability to modify their behavior to experience. This includes adapting to the behavior of their pack leaders (humans). Because of the ability, they can be trained to behave in such a way that is not natural to their breed.
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Last Updated on Monday, 09 June 2008 18:33 |
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