Emotions Within Human Evolution
As a product of evolution, emotions have a particular purpose: They have helped humans become the most successful species on earth. Emotions bypass the need for deliberative thought by providing biases toward the behaviors with better chances of survival—short-circuiting time-wasting rationalization. Other kinds of mammals also exhibit emotional capabilities with very similar reactions to humans.
Psychoevolutionary scientist Robert Plutchik shares such theories [Plutchik80]. According to Plutchik, there are eight primary emotions—associated in complementary pairs: anticipation and surprise, joy and sorrow, acceptance and disgust, fear and anger. His theory states that it's not possible for humans to experience two complementary emotions at the same time; they balance out to provide diversity in the behaviors.
In psychoevolutionary terms, each emotion serves its purpose by triggering a reactive behavior that's appropriate for survival. For example:
According to Plutchik, these primary emotions can be observed in varied intensities (for instance, rage, anger, annoyance, terror, fear, apprehension). Primary emotions also combine together into complex moods; acceptance and joy can be understood as love, fear and acceptance lead to submission, sadness and surprise form disappointment, and so forth.
Psychoevolutionary theory succeeds at explaining the reasons for emotions and provides a basic understanding of their roles as evolutionary tricks to improve survival rates. However, Plutchik's approach fails to take into account the cognitive process associated with emotions.