Development of Aggression

Aggression is defined as the overt behavior of initiating hostilities or launching attacks. In psychology, aggression relates to many different types of behavior. Originally, aggressive behavior is defined as one person is intended to injure or irritate another people. However, it is difficult to know or to measure if a person's behavior is intentional, especially in children. Hence, when researchers carry out studies on aggression, the operational definition of aggression is often referred to the behavior that injures or irritates another person. Aggression behaviors are caused by many factors, such as social and environmental. People often associate aggression with the nature of human. There were two arguments on this nature; one defended that humans were fundamentally good (Rousseau, 1782) against children were originally wicked (Hobbes, 1651). In addition to these arguments, people are in favor of the view of blank slate by Aristotle. Blank slate states that human enter the world without having any built-in mental content; it is after the exposure of the environment of the outside world, they gain experiences and sensory perceptions which define their identity. Therefore, human are not born with aggression in the beginning and aggression is a learned behavior.

The frequency and duration of aggressive acts decline throughout early childhood. During childhood, aggression doesn't occur noticeably in children. However, children do present some traits of aggressive behavior. The most aggressive preschoolers tend to be the most aggressive school aged children. There is evidence to suggest that early aggressive behaviors in childhood can partly, although not fully, predict an increase aggression later in adolescence and early adulthood. This is the age trend in the development of aggression.

The purpose of this paper is to show how aggression is developed throughout lifespan and to explain the age trend in the development of aggression. The paper will be examining three stages of aggression across lifespan, from childhood to early adulthood. Besides, this paper will also be talking about how different factors contribute to aggression at each stage by different learning approaches. In childhood, aggression doesn't occur obviously in children. However, it does appear some aggressive behaviors. There is evidence to suggest that early aggressive behaviors in childhood can partly, although not fully, predict an increase aggression later in adolescence and early adulthood.

Childhood

Aggression develops early in life. Several longitudinal studies investigated aggression during the first five years of life. They examined the intra-individual change, and found out that "aggression first appears towards the end of the first year of life and peaks in humans between 2 and 3 years of age" (Tremblay et al., 72). Children's first aggressive behavior can be seen when they bite, kick, or cry, due to their limited language skill. Children are not able to express themselves clearly and hence they are not able to speak their needs. As a result, they act aggressively in order to catch attention and get what they want. However, children from age 3 to age 5 have shown a decrease in their physical aggression for they begin to use words to express needs and communicate with each other. At school age, children tend to act aggressively. Boys show higher levels of instrumental aggression, which means performing aggressive behaviors in order to achieve some goals, such as obtaining another child's plaything. Girls are more likely to practice relational aggression, which is not physical aggression, but they perform aggressive behaviors to hurt other's feelings, such as defaming and ostracizing others. However, most children at school age have self-control; thus, they learn to hold back their aggression. Even though children learn to inhibit aggressive behaviors, we can still notice some engage in aggression that is pervasive, frequent, and severe. A research has shown that children who are aggressive in 4th grade tend to continue to be aggressive thereafter.

There are several factors that contribute to the development of aggression during childhood. Although most people believe that aggression is a learnt behavior, some still argue that aggression is caused by some biological factors. Researchers argue that not only the physical characteristics of an individual determined by genetic information, but an individual's social roles, behaviors, and relationship are also determined by the biological factor (Keyley, 1996). Serotonin is the neurotransmitter in central nervous system; it plays an important role in regulating mood, sleep, and etc. Several researches have shown that people who have reduced in serotonin level will more likely to have reduced in the control of their aggressive impulses, hence perform aggressive behavior. In addition, a study (Nagin & Tremblay, 2001) has shown that if boys' mothers first gave birth before 20 years old, and didn't finish high school education, they are at highest risk of engaging in chronic physical aggression from the time they enter kindergarten through adolescence. These claims show that biological factor does indeed contribute to the development of aggression.

On the other hand, behaviorists believe that aggression is a learned behavior; hence the most important factor is the environment of children and the learning conditions to which the children are exposed. Eron (1987), suggested that there were four critical dimensions of a child's learning environment which were instigation, reinforcement, identification, and sociocultural norms.

Instigation refers to the frustration of children which triggers the aggressive behavior, this happens when children are in the conditions such as parental rejection. Shaw, Keenan, and Vondra (1994), showed that in the absence of parental responsiveness, children are likely to develop aggressive behavior at age 3. Bates et al. (1998), also showed that preschoolers with passive parents tended to have difficulty. By the late childhood, those difficult preschoolers with passive parents tended to perform aggressive behavior in school.

Reinforcement refers to the contingent response from parents towards children's aggression. Children who are rewarded for aggression tend to continue such aggressive behavior. On the other hand, children who are punished for aggression tend to stop such aggressive behavior. A study if the development and socialization of aggression done by Keenan (2002), revealed a gender differences on aggression. He demonstrated that rates of aggression were higher in boys than in girls at the end of the preschool period. Besides, Ross et al. (1990), reported that mothers of boys were likely to support (reward) their sons when the children