Pet

A pet is an animal kept for companionship and enjoyment, as opposed to livestock, laboratory animals, working animals or sport animals, etc which are kept for economic reasons. The most popular pets are noted for their loyal or playful characteristics, for their attractive appearance, for their song. Pets generally seem to provide their owners with non-trivial health benefits; keeping pets has been shown to help remove stress. There is now a medically approved class of 'therapy animals', mostly dogs, who are brought to visit confined humans (some illnesses, age related disabilities, etc). Walking a dog can also provide its owner (as well as the dog) with exercise, fresh air, and social interaction.

Domestication
While in theory any animal might be a pet, in practice, only a small number of species of mammals, especially dogs and cats, and other small animals, such as birds, are practical for several reasons. Fish have joined them more recently. Aside from the obvious, such as large animals not being able to fit inside small dwellings, which species are suited for being pets is less easy to understand.

One answer seems to be that a pet must either be so small or easily controlled that its own behavioral tendencies are irrelevant, or the animal must be able to be domesticaed. Examples of the former are such things as fish (small ones; including carnivorous ones such as piranha), invertebrates or small reptiles.

A few animals are capable of adapting to human requirements sufficiently closely as to be said to be domesticated. Dogs are the classic example of domesticated animals normally suited to being pets. The domestic dog is quite similar to the wolf (from which they are descended, as established by genetic analysis), but their physical form and behavior are characteristically different than wild wolves, more than because of mere differences in size and coat and coloring. Typically, this involves a changes in head and eye shape, likely because this is more appealing to humans (an extreme example of this is the appearance of nearly all stuffed animals (eg, Teddy bears, or the fictional Ewoks of the Star Wars movies). On the behavioral side, characteristic domestic changes in dogs include what is, in effect, a prolonged infancy, and oddly, barking. Wolves are far less playful and don't bark, but a very long term Russian project bred foxes for a few generations from captive wild animals, and got barking foxes rather unexpectedly. Domestic cats appear to be less changed by their association with humans (again, aside from coloration and fur issues), in comparison.

On the other hand, common chimpanzees -- especially males -- are not willing to allow humans to 'take the lead' when adult, and they are poor pets as a result. Gorillas, at least female ones, are rather better, though considerably larger. Bonobos, being more social than common chimps may be more suited to being pets when adult, but exhibit overt sexual behavior which could not be accepted from pets in any human society.

Some horse-like animals are suitable for human companionship as pets or as work animals, while zebras, otherwise quite similar, are not. Zebras use biting as a conflict expression tool within the herd, and it seems quite unchangeable. It's incompatible with humans, as the biting is by human standards rather savage. No zebras have been known to have been domesticated. Horses and donkeys don't have so deep seated a biting behavior.

Among large marine animals, various species of dolphins and other cetaceans either don't have such behaviors or can restrain them. Since humans are just about the size of seals, a primary orca prey, this is somewhat extraordinary for orcas. It has been established recently, however, that orca communities often have a preferred food type, either fish or aquatic mammals, and use different hunting techniques in the wild. Only orcas from fish-eating groups are suitable for training.

Many animal species are difficult to handle and cannot be pets for the general populace. Raptors, such as eagles and falcons, must be handled very carefully to avoid attacks on their handlers; the sport of falconry is to a large extent ways of avoiding such outcomes, and so they are not really pets in the sense meant here. Large cats, with the exception of the cheetah, cannot become pets, as they do not reliably restrain their impulses. Nor do the large bears, for similar reasons. Small monkeys can be human companions, but they are notoriously unable to defer their curiosity which leads to much destruction. Several of the ferret and otter varieties can be human companions, though, perhaps especially for otters, while others, the curiosity and destruction issue is significant as well.

Animals such as reptiles are typically considered exotic pets. This may change in the future, as 'exotic' pet ownership is increasing rapidly, and they suit many lifestyles owing to being low maintenance and do not take up much space. Some are quite exotic by any definition. The glofish, a genetically modified zebrafish with a bright red fluorescent color, is the first genetically modified animal to be engineered as a pet.

Dogs and cats are the most common types of pets, both having very different character traits. The dog is seen as a loyal companion, who is more amenable to be trained, whereas a cat is more independent, and as such are not generally trained similarly to dogs (though both of these generalizations vary widely by breed). Both can be very intelligent and can form incredibly strong bonds with humans.

Koko the gorilla is one of few examples of a non-human animal which has had an explicit pet. Using sign language, she requested a cat; her first pet was a kitten named All Ball, to which she was reported to be quite attached and mourned for several days after the cat escaped and was killed by a car.

A pet can be acquired from a pet store, an animal shelter, a breeder, and from private transactions, typically due to the giving away of extra newborns after the birth of a litter. See also pet adoption. Because of scarcity (unavailability due to import restrictions or danger of extinction) and personal safety (e.g. large cats), some pets are illegal in many jurisdictions.

People sometimes treat their pets much like children, especially when they do not have children, or their own have left home. Persons living alone often obtain a pet to help prevent loneliness or boredom.

Terminology
Some animal welfare organizations suggest that the term "companion animal" be used instead of "pet".

In veterinary medicine, dogs and cats are often considered "household" pets, while all other animals are grouped into either "farm animals" (such as horses, cows, sheep) and "exotics" (including pocket pets, birds, reptiles).

Pets and allergies
Some people with allergies can have adverse reactions to animal dander and fur or feathers. Some people with athsma can have attacks triggered by these. However, research supports that people who have been exposed to dogs and cats as pets from an early age actually develop an immunoresistance to these allergens.

Objection to pets
Some animal rights activists object to the idea of holding a pet. They believe that holding an animal against its will is violating it as an individual being. They also claim that all pets are slaves, and that the domestic animal should be phased out.

Local Restrictions
Many cities and towns have local ordinances limiting the number of pets a person may have, and may also restrict or forbid certain pets (such as fowl or exotics). Most condominium associations and rental properties ban the ownership of pets.

The cities of Berkeley, California and Boulder, Colorado have passed laws stating that people who have pets do not "own" them, rather they are the pet's "guardian."

Overpopulation
Animal protection advocates try to call attention to the "pet overpopulation crisis" in the United States. According to the Humane Society of the United States, 3-4 million dogs and cats are euthanized each year in the country and many more are confined to cages in shelters. This crisis is created by non-spayed/neutered animals reproducing and people intentionally breeding animals. In an average year a fertile cat can produce three litters of kittens, with up to 4 to 6 kittens in each litter. Based on these numbers, one female cat and her offspring could produce up to 420,000 cats over a seven year period if not spayed or neutered. There are also major overpopulation problems with other pet species, such as birds and rabbits. Local humane societies, SPCA's and other animal protection organizations urge people to spay or neuter their pets and to adopt animals from shelters instead of purchasing them from breeders or pet stores.

Mammals

 * Horses
 * Dogs
 * Cats
 * Rodents, including hamsters, guinea pigs, fancy mice, gerbils, chinchillas, degus, southern flying squirrels and fancy rats
 * Rabbits
 * Ferrets
 * Fennecs
 * Hedgehogs
 * Monkeys
 * Skunks
 * Deers
 * Otters

Birds

 * Budgerigars (parakeets)
 * Cockatoos
 * Macaws
 * Other parrot or conure species
 * Canaries and other finch species
 * Doves
 * Cockatiels
 * Peafowls

Reptiles

 * Tortoises
 * Lizards
 * Iguanas
 * Snakes
 * Turtles
 * Crocodilians, including alligators, crocodiles, caimans, gharials (can usually be kept as pets only when they are young)

Amphibians

 * Frogs
 * Toads
 * Salamanders
 * Newts

Arthropods

 * Praying Mantises
 * Ants
 * Crickets
 * Tarantulas
 * Scorpions
 * Millipedes
 * Cockroaches
 * Vinegaroons (whip scorpions)
 * Sea Monkeys (a type of brine shrimp)
 * Hermit Crabs
 * Centipedes
 * Pill Bugs(giant)
 * Stick Insects

Mollusks

 * Octopi
 * Cuttlefish
 * Snails

Refernces

 * Study supports theory that pets cut allergy risk - Reuters (Source: Journal of Allergy and Clinical Immunology, September 2006.)