Dog

The dog (Canis lupus familiaris) is a domesticated type of wolf, a member of the family Canidae and order Carnivora. The term is used for both wild and domesticated variants. The dog is descended from the wolf family.

The dog soon became ubiquitous in the culture of all parts of the world, usually in early human settlements. It is believed that the successful emigration across the Bering Strait could not have been possible without dogs to pull the sled. Dogs perform many jobs for humans, such as hunting, protection, helping individuals with disabilities. Currently, it is estimated that there are 400 million dogs in the world. During 15,000 years the dog was domesticated, only in a small part of the earth not, groups of animals similar in appearance and behavior from which they were formed by environmental factors and functional roles. As modern understanding of genetics developed, humans began to purposefully crossbreed dogs for a wide spread of specific traits. Through this process, the dog has evolved into hundreds of different breeds, and exhibits more behaviors unlike any other mammal on earth. Viewing Edit Like larger mammals, dogs have color vision equivalent to color vision (red-green) in humans (deuteranopia). The visual system (visual) in the dog has evolved to help in hunting. Their visual difference for moving objects is very high; dogs have shown that they are able to distinguish between people their owner from a distance of up to a mile. As hunters dogs often rely on their vision in low light situations: they have large pupils, a high density, a large range of vision, and a lucidum tapetum. The tapetum is a reflective surface behind the retina that reflects light which is returned to give a second image to better see the living thing. The eyes of different dog breeds have different shapes, sizes, and retinal configurations. Many of them have an optic nerve - a wide circuit that runs the entire width of the retina and gives it a very wide field and excellent vision. Some time ago some of them had a field of vision of up to 270° (compared to 180° for humans). Some of them, which have a poor sense of smell, have areas of vision similar to that of humans. Most have good vision, but some show a genetic predisposition to myopia - such as Rottweilers, where one in two has been found to be myopic (short-sighted). Listening Edit The frequency range of dog hearing is approximately 40 Hz to 60,000 Hz, which means that dogs can detect sounds far beyond the human limit. In addition, dogs have movable ears that allow them to quickly locate the location of noise. Eighteen or more muscles can tilt, rotate, raise, or lower a dog's ears. A dog can identify the location of a sound much faster than a human can, as well as hear sounds over 4 times the distance... Sniffing Edit While the human brain is dominated by a large visual cortex, the dog's brain is defined by an olfactory cortex, approximately 40 times larger than the olfactory portion of humans, relative to total brain size, at 125 to 220 million receptors sensitive to smell. Police dogs exceed this standard with nearly 300 million receptors. Dogs can detect scent in concentrations nearly 100 million times greater than a human. The humidity of the nose is essential for determining the direction of the air which contains the scent. The cold receptors on the skin are sensitive to the cooling of the skin and the evaporation of moisture from air currents. The dog is a loyal animal to its owner.