All of us love them. They are very loving, loyal, social and even our best friends. Their calm eyes, elegant colour pattern and innocent voice entice our mind towards them. They are none other than our caring dogs. Dogs are mammals and belong to the class Mammalia, order Carnivora and family. Their scientific name is Canis. Dogs are the domesticated forms of the gray wolf. Dogs have been kept as pets from time immemorial by humans. The term dog is used for the male members of the canine species and the term bitch is used for the female members.
The common members of the dog family are foxes, jackals, bush dogs, African wild dogs and coyotes. The English word Dog comes from the Middle English word dogge which means a powerful dog breed. The word bitch also comes from the Middle English word bicce. A group of dog offsprings is called as litter and the little dogs are called as puppies. The father of the litter is called as sire and the mother is called as dam. The dogs are believed to be the ancestors of wolves. They have well developed complex sets of behaviour. They way of communication with the members of their own species as well with other species is drastically well advanced. The power of communication and cognition in dogs has helped humans to train them for various tasks. The evolutionists as well as the archaeologists believe that dogs have descended from their wolf ancestors about 15,000 years ago.
Dogs have benefited humans in a number of ways like by providing safety, feeding on reliable food stuffs, requiring less caloric needs and ability to breed in captivity. They have visual ability in comparison to human beings. Dogs are also consumed as food in the South-Asian countries as food. Apart from its usefulness they are also not free from the disease causing agents. The feaces of dog also acts as a source of hookworms that causes cutaneous larva migrans in humans. The dog bite is also harmful to humans. The dog-human bond leads a beneficial effect on the physical health and psychological well being of man. In the company of dogs the owners experience lesser risks of cardiovascular, behavioural and psychological levels of anxiety as is indicated by a study.
Modern dogs show marked variations in size, shape, colour, appearance and behaviour in comparison to other domestic animal. The morphology of the dogs has descended from their gray wolf ancestors. They are predators and scavengers and have well developed muscles, fused wrist bones, strongly set cardiovascular system and powerful teeth for catching and tearing of the prey. Dogs also show variation in height and weight. The smallest known dog is the Yorkshire Terrier and the adults is only 6.3 cm in height through the shoulder and the tallest known dog is the Great Dane and it is 106.7 cm. The largest known dog is the English Mastiff and it is 155.6 kilograms in body weight. Like majority of mammals dogs have a dichromatic vision which is comparable to the red-green colour blindness in the humans. The visual system of dog aids in hunting. Their visual acuity is poor but they can very well demarcate humans from longer distances which may be up to a mile. They have large pupils and very high density of rods in fovea with increased flicker rate and tapetum lucidum. Tapetum lucidum is a highly reflective layer and aids in better vision.
The dogs of different breeds have different shapes of eyes, dimensions and retina configurations. Many long nosed breeds of dogs have a wide foveal region that gives them excellent sense of vision. The sighthounds have a vision up to 270°. Short nosed dogs also have a good vision in comparison to humans as there is a patch called the area centralis having a high nerve supply that aids in better visual ability. Most breeds have good sense of vision but some forms are myopic also.
The hearing ability of fogs is about 40Hz-60,000 Hz which means that they can detect sounds much better in comparison to humans. Their ears are very mobile and help them to detect the exact location of the sound. There are eighteen muscles in the ears of dog which perform the function of hearing. Dog can hear sound much faster than humans. The dog brain is dominated by olfactory cortex while human brain is dominated by visual cortex. The olfactory bulb of dogs is about times bigger as compared to that of humans and is supplied by 125-220 million smell sensitive receptors. The dogs can smell odours at concentrations 100 million times lower as compared to that of humans. The nose of the dog is always kept moist because it senses the direction of air current containing odour. Cold receptors help the skin to remain cool by evaporating the moisture from the air currents.
The domestic dogs have two types of coats. These include coarse guard hairs and soft down hairs. The coats also help in protection of the animal from the foes by showing camouflage. The tails may be straight, straight up, sickle, curled or screw shaped. In the hunting species the tail is docked to avoid injuries. In some species the puppies are born either with a very small tail or the tail is absent. Dogs are also prone to diseases, poisons which may also affect humans. They are also vaccinated to remain free from diseases. Some breeds of dogs are also prone to some genetic problems like blindness, elbow or hip dysplasia, deafness, pulmonic stenosis, cleft palate and trick knees. The dogs are also attacked by the parasites like the fleas, ticks and mites. Hookworm, tapeworm, roundworm and heartworm also parasitize dogs. Dogs are highly susceptible to theobromine poisoning. Theobromine is a chemical present in the chocolates especially the dark chocolate. This chemical is toxic to them and even small amounts may be fatal to them. They also suffer from heart disease, diabetes, epilepsy, cancer, hypothyroidism and arthritis.
The life span of the dogs varies amongst the breeds but on an average it is 10-13 years. The breed Dogue de Bordeaux is having the shortest life span of only 5.2 years. The other breeds like Miniature Bull Terriers, Bloodhounds, and Irish Wolfhounds live for about 6-7 years. The breeds like the Toy Poodles, Japanese Spitz, Border Terriers, and Tibetan Spaniels have longest life span of about 14-15 years. Records have also shown that some dogs have lived for about 24 years too. The wild dogs like the wolves are the apex predators. Dogs are easily captured and killed by the dogs. The diet of dogs is variable and they are able to digest vegetables, grains as well as meat. A number of human food products are toxic to dogs like the chocolate solids, garlic, raisins and grapes.
Dogs including both the sexes become sexually mature at the age of 6-12 months after their birth but in some larger breeds they may take 2 years to attain sexual maturity. After attaining sexual maturity the estrous cycle of the female dogs gets activated. The estrous cycle may occur biannually during which the body prepares the female for pregnancy. At the peak of the cycle the females become mentally and physically receptive for copulation. The ovum released by the ovary is able to survive only for a week after ovulation so it is better for a female to mate with at least more than one male. The pups are born after 56-72 days after fertilization but the period of gestation may vary with the breeds. The average number of litters born is six but it may vary with the breeds. Toy dogs produce about 1-4 pups at a time but the number of litters may reach up to 12 in the larger breeds. In some breeds selective breeding has interrupted the natural process of reproduction for example the males of French Bulldogs are unable to mount females. The females of this breed are artificially inseminated in order to continue their race.
The population of the dog species is kept under control in some countries by the process of neutering. Neutering is the process of sterilization of animals by the removal of testicles of males or ovaries or uterus in female sin order to reduce the sexual drive. Dogs are very intelligent and their intelligence is indispensable in the animal world. They bear good learning ability through reinforcement and observation. They undergo cognitive stages of development and a young dogs starts learning things at an early stage say about 8 weeks after birth. Puppies learn easily from the experienced dogs. Dogs also learn by the mimicking of humans. They also demonstrate social cognition. Dr. Cohen has done much work on the social cognitive behaviour of dogs. Dog’s behaviour varies both genetically as well as with the environmental conditions.
Dogs differ from their wolf ancestors in having 20% small skulls, 30% small brains and small teeth. They require only few calories in order to perform their activities in comparison to the wolves. The jaw muscles have also undergone reduction because of the changed feeding habits. The skin is much thicker and the paws are also reduced in size in comparison to that of wolves. Dogs are poorer in observational learning but are better responsive to instrumental learning than wolves.
It can be extracted that dogs are very well adapted in the nature and are able to defend them in a better and unique way.