Sheep are ruminants typically kept as livestock and are descendants of the wild mouflon of Europe and Asia. They were among the earliest animals domesticated for agricultural purposes and are raised for fleece, meat, and milk. A sheep's wool is the most widely used animal fiber in the world. Domestic sheep may be polled, may have horns in both sexes, or may have horns only in males, and most horned breeds have a single pair of horns. Sheep have horizontal shaped pupils with excellent peripheral vision that enables them to see behind themselves without turning their heads. They graze on grass and other short roughage. Sheep are two to three and a half feet tall, weigh one hundred to three hundred fifty pounds, and live ten to twelve years.