A chicken is a domesticated version of the Jungle Fowl, a wild bird native to the jungles of India and Southeast Asia. Chickens are the most abundant domesticated fowl in the world; a population survey in 2003 estimated the global chicken population to be around 24 billion. Humans have a long relationship with the chicken, using these birds as a source of nutritious eggs and meat, and also utilizing chickens for their feathers and as companion animals.
Formally, a chicken is known as Gallus gallus domesticus, referencing the fact that it is a subspecies of Gallus gallus, the wild Jungle Fowl. It is estimated that chickens were domesticated by 2,000 BCE, and possibly much earlier, with most evidence suggesting that the domesticated chicken originated in India. From India, chickens reached Europe through Greece, with the Romans bringing chickens along on their conquest of Europe. During the Age of Exploration, chickens went along for the ride as a source of food, thereby reaching the New World.
Female chickens are known as hens, with young hens being called pullets. Male chickens are roosters or cocks; when castrated, a male chicken becomes a capon. Baby chickens of either gender are chicks. Chickens have a social lifestyle, with a single rooster overseeing a flock of hens; hens usually incubate or brood only their own eggs, and they are responsible for raising their young. Chickens are also sexually dimorphic, with roosters typically being larger and more colorful than hens.
Most domesticated chickens are kept either for their eggs or for their meat, and sometimes both. Some breeds like the Jersey Giant are specifically geared towards meat production, with very heavy, fleshy bodies and a rapid maturation rate. Others are intended to produce high volumes of eggs, as is the case with Araucanas, Rhode Island Reds, and Minorcas, among many others. Heritage chicken breeds ranging from the diminutive Bantam to the aristocratic Lakenvelder have historically been kept for eggs and meat, and as companion animals.
Although many people think of the chicken primarily as a source for food, in fact some chicken breeds have been developed as companion birds. Many heritage chicken breeds are ornamental, with very interesting plumage which is designed to strike the eye, and chickens also make very good pets, for people with room to keep them. Although chickens are often thought of as stupid, some of these birds are in fact quite intelligent, and some chickens become skilled problem solvers and well-loved members of the family.