[23] In the wild, they scratch at the soil to search for seeds, insects, and animals as large as lizards, small snakes,[24] and young mice.

[30] Chickens are capable of mobbing and killing a weak or inexperienced predator, such as a young fox.

Mating typically involves a sequence in which the male approaches the female and performs a waltzing display.

[35] Sperm transfer occurs by cloacal contact between the male and female, in an action called the 'cloacal kiss'.

[36] As with all birds, reproduction is controlled by a neuroendocrine system,[37] the Gonadotropin-Releasing Hormone-I neurons in the hypothalamus.

[40] Eggs of chickens from the high-altitude region of Tibet have special physiological adaptations that result in a higher hatching rate in low oxygen environments.

[53] In domesticating the chicken, humans took advantage of the red junglefowl's ability to reproduce prolifically when exposed to a surge in its food supply.

[48][55][56] A landmark 2020 Nature study that fully sequenced 863 chickens across the world suggests that all domestic chickens originate from a single domestication event of red junglefowl whose present-day distribution is predominantly in southwestern China, northern Thailand and Myanmar.

These domesticated chickens spread across Southeast and South Asia where they interbred with local wild species of junglefowl, forming genetically and geographically distinct groups.

[60][61][62][63] These chickens may have been introduced during pre-Columbian times to South America via Polynesian seafarers, but this is disputed.

A lack of data from Thailand, Russia, the Indian subcontinent, Southeast Asia and Sub-Saharan Africa makes it difficult to lay out a clear map of the spread of chickens in these areas; better description and genetic analysis of local breeds threatened by extinction may also help with research into this area.

[65] Chicken bones from the Arauco Peninsula in south-central Chile were radiocarbon dated as pre-Columbian, and DNA analysis suggested they were related to prehistoric populations in Polynesia.

Archaeological evidence is supplemented by mentions in historical texts from the last few centuries BC, and by depictions in prehistoric artworks, such as across Central Asia.

During the Hellenistic period (4th–2nd centuries BC), in the southern Levant, chickens began to be widely domesticated for food.

The earliest known remains are from Mali, Nubia, East Coast, and South Africa and date back to the middle of the first millennium AD.

[65] Chickens are susceptible both to parasites such as mites, and to diseases caused by pathogens such as bacteria and viruses.

The parasite Dermanyssus gallinae feeds on blood, causing irritation and reducing egg production, and acts as a vector for bacterial diseases such as salmonellosis and spirochaetosis.

[74] Chickens are common and widespread domestic animals, with a total population of 23.7 billion as of 2018[update].

Opponents of intensive farming argue that it harms the environment, creates human health risks and is inhumane towards sentient animals.

[80] Advocates of intensive farming say that their efficient systems save land and food resources owing to increased productivity, and that the animals are looked after in a controlled environment.

[92] Many people obtain chickens for their egg production but often name them and treat them as any other pet like cats or dogs.

While many do not cuddle much, they will eat from one's hand, jump onto one's lap, respond to and follow their handlers, as well as show affection.

[93][94] Chickens are social, inquisitive, intelligent[95] birds, and many people find their behaviour entertaining.

[96] Certain breeds, such as silkies and many bantam varieties, are generally docile and are often recommended as good pets around children with disabilities.

Equally important, embryologists can carry out experiments on such embryos, close the egg again and study the effects later in development.

The chicken is a sacred animal in many cultures and deeply embedded in belief systems and religious practices.

This involves the sacrifice of a sacred rooster, often during a ritual cockfight, used as a form of communication with the gods.

[110] The nursery rhyme "Cock a doodle doo", its chorus line imitating the cockerel's call, was published in Mother Goose's Melody in 1765.