What it is
The chicken (Gallus gallus domesticus) is the domestic form of the red junglefowl. It is the most abundant domestic livestock: more individual chickens are alive than any other farmed bird or mammal. People keep this bird for meat and eggs.
Range
Villages, barns, and industrial houses on every inhabited continent. The Food and Agriculture Organization of the United Nations maps the global distribution of chickens as livestock.
What happened
Domestication in Asia produced a bird people could move. Industrial breeding then made meat and egg lines that live short, dense lives. Village flocks still exist beside the industrial houses.
When / status
A living domesticate, and the most numerous farm animal.
Human role
We bred, housed, and counted them as a food system of meat and eggs.
Sources
Food and Agriculture Organization of the United Nations, Livestock Systems: chickens.