These occur in the behaviour of a wide range of organisms. The egg-rolling behaviour of the goose when it sees an egg next to its nest is typical. The stimulus of the egg starts a behavioural sequence in which the goose rolls the egg into the nest, moves it into a good position and then recommences its brooding activity. If the egg is shown and then removed immediately that the rolling sequence begins the goose will roll the now non-existent egg into the nest and reposition it and will do this again and again. Such behaviour patterns are common and are built into the system because they have improved survival of the species during countless years of natural selection.