The family tree of the domestic hen begins in the dense tropical forests of Southeast Asia. Swedish botanist Carl Linnaeus first classified the domesticated chicken as Gallus domesticus in 1758. Later evolutionary biologists corrected the record: our backyard layers are a domesticated subspecies of the wild red junglefowl, Gallus gallus.
Genetic sequencing published over the past decade confirms that ancient agriculturalists in northern Southeast Asia and southern China domesticated the red junglefowl roughly 3,500 to 4,000 years ago. Domestication was not an isolated event. As early agricultural societies migrated, their birds crossed paths with other wild gamefowl. Whole-genome analyses show that the distinct yellow skin found in commercial broiler and layer lines came directly from hybridization with the grey junglefowl (Gallus sonneratii), a species native to the Indian subcontinent.
In pure biological taxonomy, the genus Gallus contains only four true, living wild species:
- Red Junglefowl (Gallus gallus): The primary direct ancestor of all domestic hens.
- Grey Junglefowl (Gallus sonneratii): Native to central and southern India, responsible for the yellow skin allele in domestic poultry.
- Sri Lankan Junglefowl (Gallus lafayettii): Endemic to Sri Lanka, exhibiting starkly different vocal patterns and down plumage.
- Green Junglefowl (Gallus varius): Native to Java and surrounding Indonesian islands, possessing an unserrated, single-colored comb.
When poultry keepers discuss "species of hens," they are almost always referring to breed variations inside the subspecies Gallus gallus domesticus.
