The nature versus nurture topic has been an unremitting debate for various aspects of human behavior including aggressive behavior. Aggressive behavior is any behavior exhibited verbally or physically with the intention to destroy property or to injure or infuriate another person. There are studies supporting the source of aggression to be innate, indicating links between behavior and biochemical activities, while other studies have considered environmental and societal factors as influences on behavior.
The founder of behaviorism John B. Watson argued that the conditioned response was viewed as the smallest unit of behavior, from which more complicated behavior could be created. Evidence supporting aggression as a learned behavior comes from studies of behavior in experimental and natural settings, social learning theory and the effect of cultural and social variables.
Biological theories propose that aggression may have a chemical, hormonal or genetic component. Scientists have explored various possibilities of behavior. Some of the most compelling evidence comes from genetics, serotonin research and the influence of hormones on aggression.
The purpose of this paper is to present an overview of the existing theories and research findings that support both the nativist view and the empiricist view and to reveal the relationship between biology and the environment in determining behavior.
Aggression is learned
2.1 Studies of behavior.
Controlled studies of behavior in experimental settings have demonstrated that aggressive behavior is similar to other operant behavior because it is influenced by rewards and punishment. We can use the example of the rat in the “skinner box” to demonstrate the effect of operant conditioning in experimental settings. When the rat presses the bar, it is rewarded with a food pellet. The food is the reward which reinforces the action that leads to the rat pressing the bar again in order to obtain another reward. This concept can be applied in the natural setting. If you give a child a toy to stop him or her from exhibiting temper tantrums, the toy will reinforce that behavior. Children then learn that aggression can enable them to control resources such as toys and gain parental attention. If after behaving aggressively, a subject receives positive reinforcement, they are likely to repeat the behavior in order to gain more rewards. This is a form of operant conditioning where the positive reinforcement encourages further display of aggression, concluding that aggression is learned through reinforcement.
2.2 Social learning theory.
Bandura, (1977), pioneered the social learning theory which emphasized the role of learning by observation of behavior. Bandura disputed that social imitation rather than Skinner’s model of reinforcement was responsible for aggressive behavior, implying that aggression is imitated rather than learned through conditioning. Research such as the Bobo Doll study (Bandura) has shown that aggression can be learnt through imitation. Children learn aggression by imitating adult actions from live experiences or from viewing violence through the media. Bandura concluded that viewing aggression increases the likelihood of the viewer acting aggressively. By demonstrating aggression one can unknowingly encourage aggression in suggestible children. They can learn that aggressive behavior is common and acceptable and can be used to solve problems, attain needs, influence another person or even make them a hero. The media portray the violent model as a hero who is rewarded. Children by imitation learn how to be violent and this behavior is reinforced by learning the “rewards” of violence.
2.3 Aggression is influenced by cultural and social factors.
Cohen and Nisbett (1994) attributed the existence of regional subcultural differences in aggression in the United States to different local norms for aggressive behavior. Society plays a fundamental role in influencing behavior. Poverty and crime has become an intrinsic part of society; which unfortunately molds the behavior of people through imitation and reinforcement. The residents of a high crime area such as Laventille, Trinidad form a social order where their lifestyle reinforces criminal activity as a means for survival. Members of this society know who the criminals are and do not report them. When residents of these communities commit crimes or aggressive acts such as robberies, their actions are reinforced when they escape the law and obtain positive reinforcement such as material possessions. The children in these communities learn aggression through social imitation. They also become desensitized towards aggression and view it as common and acceptable behavior in their community.
Aggressive behavior can also be a function of national culture. Residents of some countries show a more pervasive tendency to think of violence as means of solving problems than persons living in other nations (Archer & McDaniel, 1995). In some cultures, ones religious view is expressed aggressively with the subject sacrificing his or her life (in some cases risking the lives of others) for the sake of their god. In other cultures, aggressive behavior is influenced by sports. American football, Wrestling, Ice Hockey and Boxing promotes behavior that is intended to physically injure another person. I am by no means diminishing the sport to a mere exhibition of rough play but simply stating that some sports disguise aggressive behavior as part of the art.
3.1 Electrical stimulations
Electrical stimulations and lesion in specific parts of the hypothalamus can influence one’s tendency to behave aggressively (Moyer, 1976). When a cat’s hypothalamus is stimulated using implanted electrodes, the animal hisses and would strike at any object that is placed in its cage. However, electrical stimulation of a different area of the hypothalamus causes the cat to act in a different way. Similarly, a laboratory rat bred in isolation from other rats and has never seen the aggressive behavior of a wild rat can live in harmony with a mouse. However, when the hypothalamus is electrically stimulated, the rat will attack and kill the mouse by using a similar technique that its untamed kin uses. By injecting the rat with a neurochemical blocker in the same area of the hypothalamus that was previously stimulated, the rat then becomes temporarily peaceful. These responses provide proof that animals have an innate aggressive drive that can become active or inactive with the right stimulus.
3.2 Neurotransmitters and behavior.
A neurotransmitter is a chemical that diffuses across the synaptic gap and stimulates the next neuron. Neurotransmitters such as serotonin, dopamine and norepinephrine are three of the most common chemicals found in the brain and are associated with aggressive behavior.
Serotonin, or 5-hydroxytryptamine (5-HT), is produced in the brain from an amino acid tryptophan and is involved in inhibiting impulsive responses to frustration such as aggression. Tryptophan hydroxylase (TPH) is an enzyme that controls the rate of synthesis of the neurotransmitter serotonin. It can limit the production of serotonin since it is the only catalyst in the reaction producing serotonin. Therefore, serotonergic activity is linked to the deficiency of TPH. Serotonergic activity can be determined by measuring the levels of 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid. Individuals who exhibit abnormal low levels of serotonin are said to suffer from serotonin depletion and were found to be more violent or impulsive than those who had normal serotonergic activity. Studies done by Linnoila and colleagues (1983) have found that men imprisoned for violent crimes have lower levels of serotonin than nonimpulsive violent offenders. Decreased serotonergic activity may produce some symptoms such as irrational behavior, anger, and obsessive worry; which can be treated by drugs such as Prozac. Prozac is a selective serotonin reuptake inhibitor that manipulates serotonin levels. It inhibits the reuptake of serotonin into the neurons, enabling serotonin to remain active in the synapse for a longer period of time and therefore controls impulsive behavior.
Dopamine is used to regulate emotion and is also converted to norepinephrine which is affected by stress and moods in the brain. The release of norepinephrine and dopamine can be stimulated by the drugs classified as amphetamine. Prolonged use of amphetamines can result in hallucinations, paranoia and violent behavior. Scientist suggests that schizophrenia results from excess dopamine activity in certain brain regions or as a result from an abnormal sensitivity to dopamine. Evidence supporting this claim comes from the antipsychotic drugs which reduce psychotic symptoms in schizophrenia by blocking brain receptors from dopamine.
3.3 The influence of hormones on aggression.
The male sex hormone testosterone is associated with aggressive behavior in both humans and animals. Testosterone contributes to antisocial behavior in some women especially during the premenstrual period. The imbalance of the estrogen-progesterone ratio during the premenstrual period triggers both physical and psychological impairments such as changes in mood, depression, irritability and aggression. These elevated levels of aggression and irritability is associated with the hormone testosterone. Research has found that a significant number of females imprisoned for aggressive criminal acts were found to have committed their crimes during the premenstrual phase, and female offenders were found to be more irritable and aggressive during this period. Reinisch (1981) found that girls whose mothers were treated with a hormone similar to testosterone while pregnant grow up to be more aggressive than comparable control subjects. Research done by Olweus (1988) has also shown that adolescent boys who have more testosterone behave more aggressively when provoked. To control aggressive behavior in stallions, horse owners usually remove the testes of males that will not be used for breeding. All these studies have provided a link between testosterone and aggressive behavior.
3.4 The frustration-aggression hypothesis
Aggression, according to the drive theory, is created by some innate human need. The frustration-aggression hypothesis assumes that whenever a person is inhibited from reaching their goal an aggressive drive is induced that motivates behavior that causes the person to injure the person or object that is causing the frustration. This basic drive is like behavioral units of ability that are switched on or off as an appropriate challenge or task presents itself. In animals, this drive tells them when to migrate, when and how to court one another, when to feed their young, and so on. Animals like humans know what to do instinctively. For instance, if a person is being attacked by someone, their initial response may be to retaliate; frustration stimulates an inner drive that leads the victims to respond aggressively. This aggressive instinct or drive is what has allowed human beings to survive and protect their interest. Even though aggression is not a guaranteed response to frustration, it is certainly a frequent one. Laboratory studies have shown that animals behave aggressively in response to stressful situations. Caged animals respond aggressively to each other when they are shocked and the behavior then stops when the shocking has ended.
3.5 Psychoanalytic theory
Sigmund Freud, the father of psychoanalysis, asserts that human behavior is motivated by sexual and instinctive drives. When expressions of these instincts are repressed, these urges are displayed as aggression. Examples of expression of aggression are explained by Freud in his studies of childhood aggression and the Oedipal complex. A young boy begins to develop an intense sexual desire for his mother because she is the ultimate provider of love and food. The desire for his mother causes the boy to reject and display aggression toward his father because he views his father as a competitive rival for his mother’s affection. The boy later recognizes his father’s superiority and learns to reject his mother as a love object and eventually identifies with his father. The Oedipal complex relates to childhood aggression in girls. The theory is similar, in which the girl develops penis envy while trying to relate to her father and rejects her mother. The girl eventually realizes that her father is an inappropriate love object and identifies with her mother instead. These examples reveal the idea that aggression is an innate personality characteristic in all humans which is motivated by sexual drives.
3.6 Genetic contributions.
Behavior genetics combines the methods of genetics and psychology to study the inheritance of behavioral characteristics. Genes are the basic unit of heredity that determines the traits of human characteristics ranging from intelligence to height to emotionality. Selective breeding and twin and adoption studies have provided evidence for an association between genetic makeup and behavior. Selective breeding studies the inheritance of particular traits in animals. A study done on the inheritance of learning ability in rats provided evidence that intelligence is hereditary (Thompson, 1954). Rats that did poorly in learning to run the maze were mated with similar dull rats and those that did well (bright rats) were mated with other bright rats. After a few rodent generations, bright and dull strains of rats were produced. It is complicated to perform selective breeding studies on humans; however similarity in biological traits can be shown using twin and adoptive studies. In most studies of twins, the degree of consistency between the criminality of identical twins is approximately twice that of fraternal twins. In adoptive studies most cases reveal that criminality of the biological parent is a better predictor of the child’s criminal involvement than the criminality of the adoptive parents. Research has shown that there is a hereditary predisposition for schizophrenia, since the risk of developing the illness is higher if an individual is genetically related to a schizophrenic person. In all the above studies subjects shared the common characteristic of genes, showing the relationship between non typical traits and genetics.
Links between biological and environmental factors
4.1 The Link between the frustration-aggression hypothesis and social learning
According to the frustration-aggression hypothesis, frustration stimulates a drive that leads to aggression. However, frustration is not the only variable that causes aggression. The response to frustration may differ depending on the kind of responses a person has learned to use in coping with frustrating situations. If a person has learnt (through imitation or social learning) that aggression can elicit a desired result, then they would respond to frustration with aggressive behavior. For example, people in poorer communities become frustrated when their physiological needs cannot be met and some are motivated to acquire these needs through crime. This is where social learning plays a role. When a person becomes frustrated they are motivated to react in a way that they learnt would produce results. People can learn that crime pays. Therefore, while frustration and aggression seem to be closely linked, the mere presence of frustration does not seem to suggest aggression, social learning is also an instigating factor.
4.2 The Link between aggressive behavior and people in poor communities
People in poorer communities may exhibit more aggression; not only because of frustration but their monetary limitations may hamper their ability to have proper diets, particularly one high in protein. The link is serotonin. Serotonin is produced in the brain from the amino acid tryptophan which is derived from foods high in protein. Tryptophan hydroxylase enzyme is the only catalyst in the reaction producing serotonin and can therefore limit its production. Therefore a person’s diet may control the levels of serotonin that their body produces. People with low serotonin levels are more likely to act aggressively.
4.3 The relationship between genetics and environment
Genetics may influence both development and behavior however, it fully determines neither. Genes are hereditable and are not affected by environment factors such as rearing conditions however rearing conditions can influence gene expression. A person’s genes may predispose them to mental illness, diabetes or aggressive behavior however environmental factors may cause the emergence of these conditions. Someone may carry the gene for diabetes and may never develop it however, obesity increases their risk. There is a hereditary predisposition for schizophrenia and the risk of developing it depends on how closely a person is related to someone with schizophrenia. Conversely, environmental stress can also trigger schizophrenia in a person that is predisposed to the mental illness. Although some children may be biologically inclined to behave aggressively, their behavior can be controlled by the environment. Instead of rearing an aggressive child in an environment that fosters more aggression, it is better to provide an environment that reduces the inclination for the child to act aggressively. Parents who promote hitting as a means of discipline and often quarrel in the presence of their children encourage their children to resolve conflict by using aggression. The probability of aggressive behavior transpiring depends on the situational factors. Sometimes the same stimulation that causes a person to react aggressively to one person may not trigger the same reaction towards someone else. These reactions are controlled by the cortex and are influenced by previous experiences and social influences. Aggressive behavior in monkeys can be induced by electrically stimulating certain areas of the brain. The final behavior depends on the monkey’s position in the hierarchical structure of the monkey colony. Dominant monkeys will exhibit aggres¬sive behavior when electrically stimulated in the presence of a submissive monkey but would suppress the aggressive behavior in the presence of another dominant monkey.
4.0 Freedom of choice
Unlike animals, humans are equipped with a large cerebral cortex that allows for reasoning, consideration, creativity and behavior control. Humans are not hard wired like computers, where given a fixed command or stimulus results in a fixed response. We have the ability to choose our course of action and our decisions are preceded by will and thought. This capability has enabled us to survive and stand greater than animals. Because of our ability to consciously choose the values we instill in our children, our species can influence the outcome of our children’s behavior. Choice is the ability to select from a number of alternatives. When frustrated an individual has the choice to react in a certain manner. They can think about something else, distance themselves, suppress their anger or even laugh it off. The magnificence of human complexity is our ability to choose from an infinite amount of possible reactions.
Is aggression biologically or environmentally based? The answer is simple. Aggression cannot be credited to just one origin. Biological and environmental factors are complementary in understanding the origin of aggression. The traditional phrase for the debate nature versus nurture should be re-phrased as nature being nurtured. A normal person must be provoked and aroused to act aggressively. A person may have a genetic predisposition to aggression but the act would not occur unless certain environmental influences are present. It is best to approach the nature nurture debate from a position that embraces both view points in order to truly understand the basis of aggression. Biology provides the instrument for aggression but environment teaches us how to use them.
1. MORE THAN TWO AUTHORS
Atkinson, Smith, Bem & Nolen-Hoeksema. Hilgard’s Introduction to Psychology (13th edition)
Taylor, Stout, & Green. Biological Science one and two (2nd edition)
2. NO AUTHOR / EDITOR GIVEN
Does media violence really influence human behavior?
Genes and aggression: Is the propensity for violence inherited?
3. INTERNET ARTICLES
D’Orban, P.T. & J. Dalton. Violent crime and the menstrual cycle
McCawley, S. The nature of aggression (or is it nurture?)
Silvis, D. Brain-behavior and nature-nurture: Two interacting scientific debates.
4. WORKS IN SEVERAL VOLUMES
Microsoft Encarta Encyclopedia 2003
5. DOCTORAL DISSERTATION (PUBLISHED)
Fishbein, D. Biological Perspectives in Criminology. Published Doctoral Dissertation, University of Baltimore, Baltimore.
Geen, R. The importance of learning in aggression. University of Missouri- Columbia
Rowell Huesmann, L. How biology influences human aggression. University of Michigan.