Chicken Evolution

The chicken or the egg causality dilemma is commonly stated as "which came first, the chicken or the egg?" To ancient philosophers, the question about the first chicken or egg also evoked the questions of how life and the universe in general began.
The chicken (Gallus gallus domesticus) is a domesticated fowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other bird. Humans keep chickens primarily as a source of food, consuming both their meat and their eggs.