We can think of emotions as behavioral packets for social animals. They are a very quick and efficient way to respond to different circumstances in the environment. Such circumstances might include aversive conditions, such as danger or aggression, or rewarding conditions such as food, sex, safety, or social bonds. All emotional reactions involve coordination of several features. These include autonomic nervous system arousal, facial expression, muscular tension, and subjective experience. This packet of responses is almost like a computer macro that serves as preparation for a specific situation. For example, when people are angry their blood pumps faster, their face becomes flush, their brow furrows, their mouth purses, the large muscles in their arms and legs tense, and they have the distinct subjective experience of anger. In this way, their body is prepared not only for action, but for aggressive action in particular.

All emotions serve at least three purposes: they prepare the individual for appropriate action; they alert the individual of the salience (or significance) of the situation; they communicate to others how the individual is reacting. For example, in a situation of danger, the emotional response of fear alerts the individual to the danger of the situation, prepares the individual for physical flight, and communicates to other people via facial expression, vocalization, and physical posture that the individual senses danger.