 Dear students, in this topic we shall discuss the fixed action patterns which are also known as instincts. They are a type of instinctive behavior which are relatively fixed within members of a species. They are essentially unchangeable behaviors. They consist of a sequence of unlearned acts. And once triggered, the full behavior inevitably runs to completion. Dear students, the fixed action patterns are triggered in response to some external cues or signals. These external cues are known as sine stimuli or key stimuli. They are also called releasers because they appear to release a pre-patterned behavioral response within an animal. This means that they are a pre-patterned response given by an animal and a sequence of acts. They are released once and then run to completion. Dear students, the best example of a fixed action pattern is seen in the male three-spined stichle-backed fish that have red bellies. These male stichle-backed fish with red bellies are seen as invaders, attackers, and dangerous. They show aggressive attacking behavior against them. However, their behavior is not limited to only the male members of their own species. Actually, red bellies are a sine stimulus for them, so they attack anything that moves to them and has a red underside, which may be a non-living object or unrealistic model. So red underside is a sine stimulus and the aggressive attacking behavior of the fish is an instinct that is fixed action pattern. Dear students, let us view some properties of fixed action patterns. The fixed action patterns are not simple reflexes. They are relatively complex motor acts. Each act consists of a specific temporal, i.e., timed sequence of events. These patterns are typically elicited by specific key stimuli. The fixed action patterns are all or none responses. That is, once initiated, they continue to completion even if the stimulus is removed. For example, if we want to exemplify this phenomenon, which is all or none, and reaches completion, even if the stimulus is finished, it means that if someone is pushed from a higher space, the push will be a stimulus. After that, the stimulus will be finished, but the process of falling down to earth will be completed. Such a process cannot be stopped in the environment. Fixed action patterns are also behavioral patterns in which an aggressive behavior has started, and it will be completed by removing the stimulus from the environment. Dear students, the threshold stimulus may vary with the physiological state of the animal. The response of these threshold stimulus will start. This depends on the physiological state of the animal. For example, an animal has copulated once as a result of an arousing stimulus. Now, that animal is physiologically not ready to copulate again. If it is given the same arousing stimulus again, it will not induce copulating behavior unless the intensity of the stimulation is very high. Dear students, another property of fixed action patterns is that all members of a species perform a given fixed action pattern identically. Because these patterns are inherited genetically and are exhibited perfectly without any prior experience.