Where are chickens from?
Wild chickens seem to have been common in India and East Asia (China, Thailand, and Vietnam) long ago, and that is where chickens were first domesticated (tamed), maybe around 7000 BC. Recent genetic evidence shows that people tamed chickens in two different places: in China and in India. Probably the people in each place didn't know that the other ones were also taming chickens. By about 5000 BC, people in China were certainly keeping chickens, and by 3000 BC people in India also had domesticated chickens.
From China, chickens spread to Japan. In Thailand and Vietnam, some people seem to have gotten their chickens from India and some from China, so that the chickens are a mixed breed.
A video of some chickens being fed
People really liked to keep chickens because they were
cheap to get started (you didn't have to be rich to buy a couple
of chickens) and they were pretty easy to take care of. You could just let
them run around the yard and eat old stale bread or leftover porridge.
Also, when you killed a chicken you could eat the whole thing up in one night - you didn't have to worry about the meat going bad, because there weren't any refrigerators.
Bibliography and further reading about chickens:
Chicks & Chickens, by Gail Gibbons (2003). Explains where chickens come from, and what they eat, and so on. For younger kids.
A Chicken in Every Pot: Global Recipes for the World's Most Popular Bird, by Kate Heyhoe (2003). Includes a brief history, and lots of recipes for chicken.
Much Depends on Dinner: The Extraordinary History and Mythology, Allure and Obsessions, Perils and Taboos, of an Ordinary Meal, by Margaret Visser (1999). Background on what you eat, including a chapter on chicken.
Food in Antiquity: A Survey of the Diet of Early Peoples, by Don and Patricia Brothwell (1998). Pretty specialized, but the book tells you where foods came from, and how they got to other places, and what people ate in antiquity. Not just Europe, either!