The chicken is a type of domesticated fowl, a subspecies of the red junglefowl. It is one of the most common and widespread domestic animals, with a total population of more than 19 billion as of 2011. There are more chickens in the world than any other bird or domesticated fowl. Humans keep chickens primarily as a source of food and, less commonly, as pets. Originally raised for cockfighting or for special ceremonies, chickens were not kept for food until the Hellenistic period.