The Psychology of Aggressive Behavior

Inherited or Learned Behaviors

Research published in 2003 in Neuron suggests that there may indeed be a genetic link to aggressive outbursts. The study, conducted with mice, noted that the animals that lacked a specific gene were far more aggressive than those mice with the gene. Human beings also have this gene, so the research seems to support the idea of a genetic link to aggression. Learned behaviors, unlike inherited traits, are not linked to genetics but acquired through environmental influence. Much research exists supporting the learned behavior cause.

Medical Problems

Medical reasons corresponding to mental illness or medications are possible causes of aggressive behaviors. If a person has an underlying psychological disorder, it may be causing inappropriate aggressive reactions. Even if the mentally ill individual is aware of his or her condition, serious aggressions can sometimes occur. Medications also have the power to bring about hostile behaviors in people with or without a psychological illness. Prescribed pills or simple over-the-counter medications can cause irritability, nervousness or other aggression-causing feelings.


Inward aggression occurs when individuals direct the belligerent actions towards themselves. Punishment is one motivating factor for hurting oneself and many aggressive people regularly engage in this behavior. Rather than hurt another human being, people who cannot control the impulsive action let it out on their own body. Release is another catalyst for directing aggressions internally. Instead of allowing the aggression to build up inside, the individual releases it through self-mutilation or some other form of aggressive behavior. People who display inward aggressive behaviors should get medical attention, since these actions are often symptoms of an underlying emotional problem.


External aggression comes in many forms. From domestic violence and bullying to bar fights and schoolyard brawls, external aggressive behaviors occur when an individual directs the action towards another person. The causes of external aggressions vary and can include social pressure or a reaction to a previous abuse. Research published in 1998 in Psychological Science suggests that other factors, such as the presence of a gun, may also have an impact on aggressive behaviors. Each individual case will differ, and no single cause is linked as the reason behind external aggressive behaviors.

Hostility vs. Instrumental

Hostility is aggression that is rooted in anger. Anger-motivated aggressive behaviors can have serious consequences, especially when impulsive anger blinds the person, causing him or her to react in an extremely dangerous way. Most murders are committed in the heat of anger when a person does not have the time to think before reacting. Instrumental aggression, on the other hand, is aggression that is motivated with a purpose. A robbery is an example of external aggression when the person committing it strikes the victim. Calculated plans to act aggressively are less common than hostile acts that occur spontaneously in the heat of the moment. Aggressive behavior has many roots, from genetic causes inherited from a parent to learned acquisitions gained through a series of repetitive experiences. Medical considerations such as psychological disorders or reactions to medication can cause aggression to surface in people that are otherwise happy and compliant. Understanding the aggression also includes determining the intended direction of the behavior and the motivation behind it.