Habituation
Habituation is a form of learning that is quite common among animals. When an animal experiences a situation for the first time, particularly one it considers threatening, it may instinctively respond by running away or by warning other members of its community with alarm calls. Normally, it responds this way each time the situation occurs. However, if through continuous and prolonged exposure the animal learns that the situation is harmless the behavior gradually diminishes. Ultimately, it will stop responding to the situation altogether. Thus, through habituation a natural or instinctive behavior gradually changes.