When do animals become mutants?

Mutants - animals are said to be mutants when they show characteristics different from the rest of their species. Mutations are processes by which the hereditary properties of some of the reproductive cells in animals are altered. In nature these changes can take place spontaneously and unpredictably. But they are rare, and little is known about this cause, beyond the fact that the longer an animal takes to breed, the less likely it is to give birth to a mutant. Nowadays, the most common causes of animals producing mutants are chemical substances and radiation. Indeed, radiation is a rapidly increasing hazard. Animals born from parents who have suffered the effects of more than normal radiation are invariably mutants. Cows have been known to grow a fifth leg. In the Pacific Islands, where nuclear tests have been conducted, there are fish which have forgotten how to swim and have been found on land. Birds have lost the power to fly, and some may have only one wing. Turtle mutants are unable to find the sea and consequently die. Animal mutants have long intrigued and frightened people. In Greek mythology, mutants such as dogs and horses with two heads were believed to possess magical powers.