The chicken is the most common and widespread domesticated animal on the planet with a population of more than 19 billion as of 2011.
Careful research has found chickens to be surprisingly intelligent and very sensitive. They have been found to communicate with each other using more than 24 distinct vocalizations. Each one has a distinct meaning such as the sighting of a predator.
It takes a fertilized egg about 21 days to incubate and hatch into a new chicken. Baby chickens are known as chicks, females are pullets until old enough to lay eggs and become hens, and males are called roosters, cocks or cockerels depending on the country you're in.
Chickens are a major source of food for humans, both for their eggs and their meat. Each year in the United States alone, we consume some 8 billion chickens, and house approximately 280 million laying hens that produce about 50 billion eggs. Today, more than 65.8 billion chickens are eaten each year by the world's growing human population.
Chickens are native to tropical rainforests where they evolved for millions of years. The first chickens to be domesticated were probably the red jungle fowl of Southeast Asia some 4,000 years ago. It is thought that early chickens of Indian origin were bred for the purpose of cockfighting in Asia, Africa and Europe.
Today, there are many varieties of chickens that have been bred for different purposes. For example, the Yokohama chicken, bred for its ornamental tail feathers which can be 20 feet long, is the most unusual. The most useful is the white leghorn which can lay an egg almost every day.
Research shows that over the last 2,000 years, chickens have gradually increased in size due to domestication. Around 1950, broiler chickens — those raised to provide meat rather than eggs — started to get very large. Today, they can be twice the weight of their Asian forebears.
Larrie Stone is a retired Dana College science professor.