atement regarding the cat training school in the USA which advises owners to keep cats indoors:
Cats descend from the African Wildcat, which is a solitary hunter with a very large territory owing to the scarcity of prey. Therefore domestic cats are naturally territorial and may have large territories. They can become stressed if they have a small territory, especially if they have been used to going out. This stress can lead to negative behaviour – scratching, spraying indoors etc – all of which are perfectly normal and not an issue if done outdoors. Statistically, indoor cats get less exercise and are more prone to obesity and other diseases such as diabetes. They are also more likely to get bored and, without being able to fulfil their natural hunting behaviour, can become frustrated. However, it should be noted that cats can lead fulfilling lives indoors provided the owner makes sure the cat receives extra exercise and stimulation. Furthermore, some cats have to be confined indoors due to medical conditions or because they are simply not used to going outdoors.