The Domestic Dog

Nov 09, 2008 Features / Columnists, Interesting Creatures in Guyana

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The dog (Canis lupus familiaris) is a domesticated subspecies of the grey wolf which is a mammal of the Canidae family of the order Carnivora.

The term dog encompasses both feral and pet varieties and is also sometimes used to describe wild canids of other subspecies or species.

Based on DNA evidence, the wolf ancestors of modern dogs diverged from other wolves about 100,000 years ago, and dogs were domesticated from those wolf ancestors about 15,000 years ago. This date would make dogs the first species to be domesticated by humans.

Compared to equally sized wolves, dogs tend to have 20 per cent smaller skulls and 10 per cent smaller brains, as well as proportionately smaller teeth than other canid species.

Dogs require fewer calories to function than wolves and their diet of human refuse in antiquity made the large brains and jaw muscles needed for hunting unnecessary. It is thought by certain experts that the dog’s limp ears are a result of atrophy of the jaw muscles.

The skin of domestic dogs tends to be thicker than that of wolves, with some Inuit tribes favouring the former for use as clothing due to its greater resistance to wear and tear in harsh weather.

Unlike wolves, but like coyotes, domestic dogs have sweat glands on their paw pads. The paws of a dog are half the size of those of a wolf, and their tails tend to curl upwards, another trait not found in wolves.

Dogs display much greater tractability than tame wolves, and are generally much more responsive to coercive techniques involving fear, aversive stimuli and force than wolves, which are most responsive toward positive conditioning and rewards.

Also, unlike tame wolves, dogs tend to respond more to voice than hand signals and although they are less difficult to control than wolves, they can be comparatively more difficult to teach than a motivated wolf.

Evidence suggests that dogs were first domesticated in East Asia, and some of the people who entered North America took dogs with them from Asia.

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 working dogs and pets.

The domestic dog as a result is said to be one of the most widely kept working and companionate animals in human history as well as being a food source in some cultures and it has been estimated that there are about 400 million dogs in the world.

And according to researchers the dog has developed into hundreds of varied breeds with height measured to the withers ranges from a few inches in the Chihuahua to a few feet in the Irish Wolfhound.

Their colours can vary from white through grey to black and browns from light to dark in a wide variation of patterns.

Dog coats can be very short to many centimetres long and can be coarse to something akin to wool in straight, curly or smooth textures.

Notably though is that it is common for most breeds to shed their coat however non-shedding breeds are also quite popular.

A breed is a group of animals that possesses a set of inherited characteristics that distinguishes it from other animals within the same species.

Deliberately crossing two or more breeds is also a manner of establishing new breeds, but it is only a breed when offspring will reliably demonstrate that particular set of characteristics and qualities.

Like most mammals, dogs are dichromate and have colour vision equivalent to red-green colour blindness in humans. Different breeds of dogs have different eye shapes and dimensions, and they also have different retina.

It has also been ascertained that dogs with long noses have a “visual streak” which runs across the width of the retina and gives them a very wide field of excellent vision, while those with short noses have an “area centralis” which is a central patch with up to three times the density of nerve endings as the visual streak giving them detailed sight much more like a human’s.

Some breeds, particularly the sighthounds, have a field of vision up to 270 degrees compared to 180 degrees for humans, although broad-headed breeds with short noses have a much narrower field of vision, as low as 180 degrees.

According to hypertextbook.com, the frequency range of dog hearing is approximately 40 Hertz (Hz) to 60,000 Hertz. Dogs detect sounds as low as the 16 to 20 Hz frequency range which is compared to 20 to 70 Hz for humans and above 45 kHz compared to 13 to 20 kHz for humans.

In addition they have a degree of ear mobility that helps them to rapidly pinpoint the exact location of a sound.

Eighteen or more muscles can tilt, rotate and raise or lower a dog’s ear and reports are that a dog can identify a sound’s location much faster than a human can, as well as hear sounds up to four times the distance that humans are able to.

Those with more natural ear shapes, like those of wild canids like the fox, generally hear better than those with the floppier ears of many domesticated species.
(Source: Wikipedia the Free Online Encyclopaedia)

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