One of the most basic emotion of human being is aggression. Aggression not often result of more subtle emotional responses. Instead of the dichotomy scheme prevalent in the prior literature, four-constituent scheme of classification of aggression based on the analysis of ethological and psychological materials is also done. From this point of view, intraspecies intermale aggression can be classified as follows:
(1) Instrumental type of offensive aggression;
(2) Frustration-induced offensive aggression accompanied by anger;
(3) Aggression linked to pleasure.
(4)Stress- and fear-induced reactive and defensive aggression;
Under general circumstances, formation of this type of aggression is due to the development of both types of offensive aggression. Aggression is typically characterized by decreased serotonin levels in emotiogenic structures of the brain. But literature excludes the possibility of serotonin as a determinant of aggression. Instead, aggressive behavior correlates with low levels of serotonin, and it tends to rise during stressful situation.