Domestic animals are those whose behavior, life cycle, or physiology have been changed as a result of human interaction or the animals' being under human control for several generations. Domestic animals differ from tamed wild animals in that their genotypes have actually changed, and the evolutionary process of the animals has been altered so that the animals evolve to become accustomed to life with humans. Humans began domesticating animals thousands of years ago, and the domestication of animals has played a large part in human evolution and enormously benefited human society. Domestic animals include pets, livestock, companion animals, poultry, and working animals. Livestock is usually used to refer to animals raised for food, whereas pets are raised to provide companionship.
The domestic dog (Canis lupus familiaris) is believed to be the first animal domesticated by man; it is estimated that the domestication of the dog from the gray wolf began anywhere from 15,000 to 30,000 years ago. The domestic dog is an excellent example of how artificial selection can change an animal species. Artificial selection is how domestication is accomplished, and it occurs when humans breed animals to encourage certain traits to recur in the next generation of animals. Domestic dogs are all evolved from the grey wolf, and through selective breeding have evolved into a few hundred recognized and distinguishably different breeds, each with specific physical and personality traits.
Other animals which have been domesticated for thousands of years include sheep, pigs, goats, cattle, yaks, water buffalo, cats, chickens, donkeys, Guinea pigs, horses, rabbits, pigeons, honey bees and silk worms. Most of these were domesticated as livestock and work animals, or because they provide a certain product. Cats, like dogs, are now one of the world's most common household pets, but were initially domesticated for their pest-controlling abilities.
Of all of the millions of extant animal species on earth, man has been able to successfully domesticate relatively few. Man cannot domesticate all animals, and there are several characteristics which allow domestication and make domestication desirable. The animals must be relatively east to feed and must be willing to breed in the presence of humans. They must also have a relatively calm and friendly disposition; some animals are simply too skittish for captivity or too vicious for human interaction. Pack animals are the easiest to domesticate because they have, in the wild, adopted a social hierarchy. In fact, cats are one of the few if not the only domesticated animal which in the wild is solitary.