One major subject chapter 13 focuses on is aggression. The definition of aggression from the textbook is "behavior intend to harm others, either verbally or physically". Aggressive behavior can be accounted for on both large and small scales, and can be influenced either situationally or through disposition. Psychologist have pinpointed many situational influences on aggression in humans. The first situational influenced described is Interpersonal Provocation, which explains that people are more likely to show aggressive behavior towards those who provoke them. Another situational influence is Media Influences. Evidence has shown at watching media violence and playing violent video games boosts aggression in Western and Asian cultures. Alcohol and other drugs can disinhibit ones prefrontal cortex, lowering reservations toward behaving violently. However, alcohol is likely to trigger aggression only when the target of ones violence occupies the main focus of our attention. Arousal is another influence mentioned. When autonomic nervous systems are risen, people may unintentionally mistake that arousal for anger. The last situational Influence mentioned is Temperature. Warm temperatures increase irritability and warmer temperatures are associated with higher rates of violence.
Certain personality traits can also create aggression. People with high levels of irritability or mistrust tend to show higher rates of aggression. It has also been proven that males are show a higher rate of physical aggressiveness compared to females. Cultural differences also show a variety in levels of physical aggression. For example, Asian individuals have lower levels of physical aggression compared to American or European individuals.