The chicken (Gallus gallus) is a type of domesticated fowl, believed to be descended from the wild Indian and south-east Asian Red Junglefowl.The chicken is one of the most common and wide-spread domestic animals. With a population of more than 24 billion in 2003, there are more chickens in the world than any other bird. Humans keep chickens primarily as a source of food, from both their meat and their eggs.