- Chickens are largely descended from the Red junglefowl, a bird which none could say looks entirely dissimilar to the modern chicken. They are still scientifically classified as the same species, and can freely interbreed.
- Chickens share about 70-80% of their DNA with this still-surviving species, domesticated by humans in the Hellenistic period (4-2C BCE) after millennia of being used for cockfighting.
- Subsequently, interbreeding occurred with the grey, green, and Sri Lankan junglefowls, leading to the multifarious chicken breeds we have today.
Adapted reproductive patterns
- Chickens retain adapted characteristics of junglefowl which take advantage of the vast quantities of seed produced during the end of the multi-decade bamboo seeding cycle, causing it to breed prolifically when exposed to large amounts of food.
- In nature, junglefowl populations would balloon every few decades due to the abundant food produced by the simultaneous seeding of many bamboo plants, and slowly dwindle until the next seed cycle. This creates population graph which looks like an inverse Sawtooth wave.
- Humans took advantage of the junglefowl’s capacity for prolific reproduction when exposed to abundant food by feeding them all the time, leaving them in permanent state of hyperfertility.
- Chickens are one of few animals which show unihemispheric slow-wave sleep (USWS), a type of sleep where one half of the brain rests while the other half remains alert— this also means they sleep with one eye open, corresponding to the half of the brain which is not sleeping.
- No animal does not require sleep— this information is obscured by the varied forms of sleep that some animals exhibit, but animals like bullfrogs or bees, often said not to require sleep, actually do sleep. Bees do not require ‘recovery sleep’, meaning that after long periods of wakefulness they will be fully energised by a sleep of normal duration.