The chicken is one of the most common domesticated species on Earth, central to global agriculture due to its success as a source of meat and eggs. Its familiarity conceals a fascinating evolutionary history. Tracing the lineage of the modern chicken requires starting with a specific wild bird in Asia and going back to the age of the dinosaurs.
The Direct Ancestor
The immediate predecessor of the domestic chicken, Gallus gallus domesticus, is the Red Junglefowl, Gallus gallus. This wild bird is a member of the pheasant family native to the tropical and subtropical regions of South and Southeast Asia. Its natural range extends across India, Indochina, Southern China, and down through Malaysia and Indonesia.
The Red Junglefowl is physically distinct from its domesticated descendant, generally possessing a smaller body mass. Males display brilliant plumage, including glossy orange-red feathers, a prominent red comb, and a sweeping black tail. Females are far less conspicuous, covered in brown and buff feathers that provide camouflage in their forest and scrubland habitat. The domestic chicken is technically classified as a subspecies of this fowl, reflecting their close genetic relationship.
Tracing the Deep Evolutionary Past
The chicken’s ancestry extends far beyond the Asian jungle, placing it firmly within the lineage of the Theropod dinosaurs. This group of bipedal dinosaurs includes famous species like Tyrannosaurus rex and Velociraptor. The evolutionary transition from non-avian dinosaurs to modern birds (Aves) is supported by a wealth of anatomical evidence.
Skeletal similarities, such as the structure of the ankle, the wrist, and the wishbone, indicate a shared common ancestor between the chicken and its dinosaur relatives. Many theropods possessed features previously thought to be exclusive to birds, including hollow bones and feathers. Molecular research confirms this, showing that the collagen protein sequences of T. rex are more closely related to those of chickens than to any other living species.
The Timeline and Location of Domestication
The transformation of the Red Junglefowl into the domestic chicken resulted from specific human actions, with the earliest archaeological evidence pointing to the Southeast Asian peninsula. Domestication occurred relatively late in the Bronze Age, between 1650 and 1250 BCE. This process was initiated by the expansion of dry rice farming into the jungle fowl’s habitat.
The rice fields, especially those relying on seasonal rainfall, created an attractive food source that lured the wild birds into closer association with human settlements. Humans began selecting for traits that differentiated the birds from their wild ancestors. One significant change was the loss of seasonal reproduction, achieved through changes in the TSHR gene, allowing the birds to lay eggs year-round.
Selection also favored docility, as less fearful birds correlated with faster growth and higher adult body weight. The early purpose of the chicken was often not for food; in many Iron Age European societies, the birds were culturally revered and sometimes buried unbutchered alongside humans. Chickens and their eggs only became a widespread food source much later, with the spread of the Roman Empire.