Humans seem like they are wired from birth to be violent and aggressive. There have been wars fought for thousands of years, murders, rape, etc. and we still have not learned from our awful ways. What exactly is violence and aggression, and why does it prevail?
Defining aggression is not an easy task because it can vary depending on the culture, individual, or situation. What is aggressive to some might be normal to others. Aggressiveness can also be confused with assertiveness, which is a different thing altogether. Being assertive means standing up for oneself or taking the initiative to get things done. Aggression is an intentional behavior that is done to cause harm or pain to another person.  Aggression can come in many forms. It can be verbal, physical, successful or unsuccessful. No matter what, the action was intentionally made to try and cause harm, and that makes the action aggressive. Accidents cannot be classified as aggression because they were actions not intentionally made. Aggression can be broken down into two different types. 
- Hostile Aggression – When an act of aggression comes from feelings of anger and is intended to inflict pain, then it is called hostile aggression. An example of this would be someone stabbing a knife into another person’s leg. Obviously, this is an act that is made with the intention of causing pain.
- Instrumental Aggression – Any other act of aggression that isn’t intended to cause pain is called instrumental aggression. This might be an older brother wrestling with his younger sibling. The aggression is in good fun and not necessarily to inflict serious pain.
Where it Comes From
Aggression usually comes from anger, and the motives for violent acts of anger come from the feelings a person has. These feelings have been put into five different groups that Roy and Judy Eidelson believe explain acts of conflict and aggression. 
- Superiority – The belief that one is superior to another.
- Injustice – The belief that one has a legitimate reason to be aggressive against another.
- Vulnerability - The belief that one is one could be aggressively annihilated at the hands of another.
- Distrust – The belief that another will not honor their promises or commitments.
- Hopelessness – The belief that one cannot improve their condition.
The first four beliefs lead to aggression, while the last one leads to self-destruction.
There are a few different theories as to where aggression comes from. The classic debate about aggression is whether or not it is an inborn tendency that we are born with or something that is learned. Philosophers such as Thomas Hobbes argued that people are born selfish and self-interested, and will do anything for their own well-being, even if it means being aggressive.  Jean-Jacques Rousseau argued that people are born compassionate and loving but then molded by society to be aggressive.  Many years later, Sigmund Freud theorized that humans are born with two instincts. The instinct toward life is called Eros while the instinct toward death is called Thanatos.  Freud believed that humans work by way of a ‘hydraulic theory’, where pressure builds up inside and must be released as aggression. To Freud, aggressive energy could be seen in everything from art to architecture. He theorized that society helps people to sublimate the instinct to be violent by giving them the desire to be creative and work hard.  He called this theory sublimation.
Some psychologists argue that aggression is programmed into our genes. Buss and Duntley are two evolutionary psychologists who say that men are aggressive because it helps them to reproduce. If males are aggressive, then women will be attracted to them for their ability to produce strong offspring. Males will also show aggression if they believe that their mate is copulating with anyone other than them. This helps make sure that they are the ones who will be reproducing. Statistics show that men are indeed more aggressive then women. They are arrested for around 90% of all violent crimes, except for rape where they are arrested for 99% of the crimes.  Males commit most acts of violence and aggression when they are in their teens and 20′s, which also happens to be the time they are most fertile. 
Evolutionary psychologists speculate that in modern society men must be aggressive to attract females, as they have always been. But rather than be good at physical fighting, they must be able to excel socially and/or make a decent financial living. Scientists spend a lot of time researching animals such as bonobos or chimpanzees in hopes that their behavior will shed some insight on the causes of human aggression. Whereas bonobos are peaceful, loving animals, chimpanzees can be extremely violent.  Observation of the animal kingdom shows that most, but not all, species evolved to have aggressiveness. The determining factors are in an animal’s previous social experiences as well as the genes that have been passed down through time.
Aggressiveness and violent behavior has been linked to the following physical and biological causes  :
- Tumors and disruptions affecting the limbic system.
- Epileptic seizures.
- Endocrine abnormalities.
- Birth complications.
- Nervous system abnormalities like minimum brain dysfunction and extreme EKGs.
- Body type (violent males are usually more muscular, athletic, and bony).
- Learning disorders.
- Personality disorders.
- Disconnect between the limbic and frontal cortex areas of the brain.
- Low blood sugar.
- Alcohol and drugs.
Aggression is linked most to an area of the brain called the amygdala. When the amygdala is stimulated it causes animals to become violent, and when activity to the amygdala is blocked animals will become calm and docile.  These reactions are more common in the ‘lower animals’ and not so much in humans, who are better able to control themselves.
Brain chemicals can influence aggression as well. Serotonin can have an inhibiting effect on impulsive aggression. If serotonin flow in the brain is disrupted it can cause violent behaviors. In fact, research shows that violent criminals have low levels of naturally occuring serotonin.  This helps to explain violent behavior in alcoholics because alcohol can decrease the level of serotonin in the brain, therefore increasing chances of aggressive behavior.
Another chemical that causes aggression is testosterone. When the brain has too much testosterone it can lead to violent behavior, as lab studies on rats injected with testosterone have shown.  Prisoners convicted of crime and rowdy, aggressive college students have shown high levels of testosterone.
It should be noted that these findings are correlational and that there may be other contributing factors besides decreased serotonin or increased testosterone in the cause of aggressive acts. These findings are also situational. For example, increased excitement can raise testosterone levels. Therefore, someone who engages in criminal activity could have a lot of testosterone because they commit crimes. They might not commit crimes because they have high testosterone levels.
Studies show that sociopathic violence in individuals can be caused by low levels of activity in the orbitofrontal cortex. In other words, these people lack the ability to feel.  In group violence, the opposite occurs as the orbitofrontal cortex is hyperaroused. This somehow numbs the feelings people normally have toward others, allowing for group-scale violence. 
We have already discussed how men are more likely to be aggressive than women, but this does not mean that women do not also commit acts of aggression and violence.  Whereas usually it does not take any external reason for a man to become aggressive, women are a different story. Women will react almost as aggressively as men when they are frustrated or insulted. In other words, it takes an external force to bring out the aggression in women. Women also tend to express their aggression more covertly than men. This explains why women gossip, spread rumors, or commit forgery while men punch, kick, and fire weapons. Men are usually arrested for violent crimes like murder while women are usually arrested for property crimes like fraud or larceny.
Though these gender differences might be explained biologically (i.e. men have more testosterone than women), it can’t all be based on one’s genes. Culture plays a role in molding the sexes; their attitudes and behavior. For instance, it is common for men to be ‘trained’ by society to be aggressive or violent while women are expected to be sweeter and more docile. Examples of this can be seen in the toys boys and girls play with or the movies they watch. A boy grows up watching Batman and playing with army trucks while a girl will grow up watching Mary Kate and Ashley Olsen movies and playing with Barbie dolls.
When people drink alcohol it often times lowers their inhibitions and causes them to do things they normally wouldn’t. This includes acting violent or aggressive.  By disrupting the way we process information, alcohol results in people responding to situations by doing the first thing that comes to mind. If someone were to bump into you while you were sober, you would be startled and might consider bumping back, but would stop yourself after some rationalization. While drunk in the same situation, rationalization would be lost and you might immediately respond by punching the person. Statistics show that most people prosecuted for murder, assault, and other violent crimes were drunk at the time of their arrest.
Recent research performed by Quartz and Sejnowski shows that aggression starts early in life and depends on the cultural influence of taming.  They cite the fact that a typical two year old does eight to nine acts of aggression every hour, and that we are most aggressive between the ages of two and two and a half years old. This aggression is instinctual and must be controlled through good parenting. If a child does not learn to inhibit their aggression then they will not learn social competence such as the ability to cooperate and make peace with others. Such research suggests that humans do have a natural tendency to be aggressive, but that society and culture can effect whether or not this aggression is allowed.
Research called the Iowa adoption studies focused on studying children that had been taken at birth by parents who did not conceive them.  Since these children had different genes than their parents, it gave researchers an opportunity to see how much of a role nurture plays in raising people to be non-aggressive. The studies showed that the stability of the adoption parents did not matter as much as the stability of the child’s biological parents. If a child had unstable biological parents then they grew up to be unstable only if the house they were adopted into was unstable. If the house was stable, then the children from unstable parents were able to grow up well-adjusted. Children who came from biological parents that were mostly stable grew up to be stable whether or not their adopted homes provided them a stable environment.
Studies done on fraternal and identical twins have shown that violent behavior is normal for adolescents growing up in delinquency-filled neighborhoods, regardless of their genes.  The point is that one’s environment can be very influential to their behavior. An environment of violence is more likely to result in a person becoming violent themselves. Take the southern United States for example, where white men are much more likely to commit arugment-related homicide than white men in the northern United States.  Southerners have a culture which permits violence when it is for protection or in response to insults. This “culture of honor” is demonstrated through the emotions, cognitions, and behaviors of people living in the south and it is passed on to each generation.
Studies have tried to determine the global cultural differences in the aggression levels of men and women. The conclusion was that men were consistently more aggressive than women in all parts of the world.  This pretty much concludes that women have a biochemical difference which makes them, by nature, less violent than men. In some countries, however, women are given the freedom to be aggressive. When given the chance, woman will show more aggressiveness than women belonging to countries that oppress them.
A person’s peer group can also play a part in how aggressive or violent they are. The peer group can either enhance or dull a person’s biological tendency to be violent. Some groups might help to teach someone that violence does not pay. Such groups might be the Boy Scouts or good kids from school. Negative groups, like gangs, can cause someone to be violent.  Most peer groups work through a group contrast effect, where each one will attempt to be different from the other groups in the world. This results in rivalries between the groups, and explains why gangs or opposing ethnicities, schools, etc. will have the inclination to fight when they are put together.
Social Learning Theory
People are likely to copy the people they see around them. The idea that we learn social behavior by observing others and imiating them is called social learning theory.  Role models serve as a function for our own behavior. Children learn how to act by modeling the adults, peers, famous and fictional characters they admire most. The people children imitate most is their parents. Parents who abuse their children are usually people that grew up being abused themselves. Abuse is therefore handed down with each new generation in a neverending cycle.  If a child’s parents are well-rounded and non-violent, then the child will most likely grow up to be the same, though there are some exceptions.
A group of studies, often called the Bandura experiments, showcased the power of social learning. In these experiments a group of kids would watch an adult punch and knock around an air-filled “Bobo” doll.  After seeing the adult smacking, kicking, and yelling at the doll, the children were allowed to play. They imitated the adult they’d seen and abused the doll the exact same way. Some were even creative and did aggressive things that they hadn’t witnessed the adult do. Another group of children (control group) who had not seen the adult acted kindly toward the doll. This offers ample evidence that people learn social behavior by watching and imitating others.
The researchers Weiner and Wolfgang found these psychological causes for violence and aggression: 
- Prolonged frustration or disruption of goal seeking.
- Stress (inability to deliver what is demanded).
- Socially learned behavior.
- Combination of all environmental forces that invite violent response.
- Effect of rewards that come attached to violent behavior.
- Combination of all inhibitory forces, both internal and external.
- Strength of an immediate situation with respect to triggering the offender.
- Lack of alternative nonviolent responses available to the offender.
- Cultural inversion or reaction formula; i.e. “Since I can’t
be on the football team I will pick fights with the football players.”
Pain and Discomfort
Animals that are in pain will often times become irritable and attack anything around them. The same reaction occurs in human beings.  If someone accidentally hits their leg against something they will feel a rush of pain and immediately feel like lashing out or yelling. Experiments have shown that those who experience pain are more likely to act aggressively. Discomfort from things like heat, humidity, air pollution, and offensive odors can also cause irritability and result in violence or aggression.  Interpreting whether or not crimes were committed because of something such as the weather is not an easy task. By analyzing statistics we are able to see whether or not heat or humidity correlates to an increase in violence. We can also see the relationship by observing everyday situations like traffic jams and baseball games, comparing the attitudes and behavior of people on hot days versus cold days. Since heat increases aggression and violence, it is important that the police stay on high alert during days that the temperature is high.
Statistics show that when a nation is at war, its people are more likely to commit aggressive acts against one another.  Crime rates since 1900 show that nations who have gone to war have had homicide rates rise much higher than other, peaceful nations. When a nation is at war, all of its citizens are affected in several ways:
- People’s inhibitions against aggression are weakened.
- Imitation of aggression increases.
- Aggressive responses become more acceptable.
- Senses are numbed to the horror of cruelty and destruction.
These phenomena will most likely increase now that technological advances have made it is easier to stay informed about wars.
Frustration stemming from social situations is a common cause of aggression. Imagine someone is talking negatively about someone you love very much, or that you are stuck in traffic and it is your first day to a new job. Both of these situations bring with them high levels of frustration and anger. The natural response is to try and verbally or physically attack something, even if deep down you know that it isn’t going to help the situation. This is summed up in the frustration-aggression theory, which states that frustration, or the perception of being prevented from attaining a goal, increases the probability of an aggressive response.
For a study from 1941 called “Frustration And Regression; An Experiment With children”, researchers performed an experiment with a group of kids to try and see how frustration would influence their behavior.  The group was led to a room full of attractive toys that was blocked by a wire screen. The kids could only stand there, frustrated that they could not play with the toys. When they were finally allowed into the room, the children threw, punched, stomped, and were altogether destructive. The researchers led a different group of children to the room and allowed them to immediately play with the toys. Without any previous feelings of frustration, the kids respected the toys and played very happily.
Another experiment involved college students and telephone calls. The students were told to call strangers and ask for a donation to charity. Some students were told to expect a high level of donations while others were told to keep low expectations. All of the ‘strangers’ being called were actually people told by the experimenters to never give any donations.  Students who had a high level of expectations were more likely to become frustrated and slam down their phones or become verbally abusive toward the people they called. Callers with low expectations were more relaxed.
Of course, frustration does not always lead to aggression, but it does seem to produce the anger and annoyance that makes a person more likely to snap and lose control of their temper. There are some factors that come into play when determining whether or not frustration will lead to aggression, such as the reasons behind the aggression and who is involved. If someone mentally disabled destroyed an art piece you had been working on for months, you might consider twice before throwing a punch or yelling an obscenity. If your son hid your shoes one morning and made you late for work, you could immediately become aggressive or realize that it was the day that you promised to take your son out on a walk and had not.
It is also important to understand that aggression is not the direct result of deprivation but rather a relative deprivation, where the perception that one is not getting what they deserve or expect will cause them to become aggressive or violent. Aggression is also the result of being provoked by someone else. For instance, if someone calls you a stupid moron for no reason, then you are being stimulated into aggression.
An aggressive stimulus is an object that is associated with aggressive responses and whose presence can increase the probability of aggression.  Studies show that when people are made angry or frustrated in areas where there is a gun or other weapon available, they will be more likely to show aggression than those in areas without such weapons. This helps explain why some cities that allow gun ownership have many more murders per year than cities that restrict gun ownership, as is the case with Seattle, Washington and Vancouver, British Columbia. Just the mere presence of a gun or weapon is enough to increase violence and aggression, and since America is a nation of gun admiring– this spells trouble. 
TV, Movies, and Video Games
Television, video games, and movies are still relatively new inventions and are becoming increasingly violent and realistic as technology advances and society changes. Just how does all the violence and sex found in the media and entertainment affect people’s behavior? Answering such a question is definitely not easy, and researchers are still struggling to find the answers.
As we know from the Bandura experiments, children who witness acts of aggression
will often mimic those acts. What is scary is that Leonard Eron, a
social psychologist, estimates that by the time the average American
child finishes elementary school, he or she will have seen 8,000
murders and more than 100,000 other acts of violence thanks in large
part to TV and movies. 
Obviously, not every American child mimics the acts they see on TV or in the movie theaters, but some might. Long-term studies have indicated that the more violence a child sees on TV while growing up, the more aggressiveness they will exhibit as adults. Many experiments have been conducted whose results support the same idea. Even children who are not naturally inclined toward aggression can become more aggressive by watching violent TV and movies. 
Video games are likely to have the same priming effect as TV and movies. Studies so have shown that violent video game playing has a positive correlation with aggressive behavior and delinquency in children.  It is ultimately up to parents to govern and enforce rules related to the video games their children can play. Parents should also closely monitor the TV shows and movies that they allow their kids to watch.
Children are not the only ones that can be effected by violence and aggression in the media. Adults can also be swayed by the things they watch or play. A long-term study of more than 700 families over the span of 17 years showed that there is a strong link between the amount of time people watch TV during adolescence and adulthood and the likelihood that those people will commit violent acts against others.  Some people argue that adolescents and adults can get inspiration to bring violence from their entertainment out into the real world. With all the school shootings that have occured since the Columbine massacre, it is no wonder that parents, politicians, and people in general worry about the relationship between such atrocities and the violence in modern media. The Columbine shooters themselves were dressed a lot like characters in a 1999 movie, The Matrix, were dressed during a scene where many innocents are killed. 
With franchises like Grand Theft Auto continually pushing the boundaries of video game violence and sex, it is hard to predict exactly how behavior will change, if at all, as a result.
Studies have been performed and statistics have been heavily analyzed to decide whether or not pornography has a direct correlation with violence against women. Thanks in part to the internet, pornography has recently become more generally accepted by society. The amount of sexually explicit media and their availability have greatly increased. Pornography can contain extremely explicit scenes that demonstrate unrealistic sexual encounters. If a man is not able to understand that the porn he is watching is staged acting, then it might lead to unhealthy attitudes toward sex and women. Moreover, a man might believe that treating a woman as they are treated in pornography is perfectly acceptable.  Since porn is becoming increasingly violent and degrading toward women, such thinking on a man’s part can be very dangerous. It might even explain the coincidental correlation of rape crimes and porn availability, which might not be so coincidental at all.
Researchers have carefully been studying whether or not pornography increases the chances that men will commit violent crimes against women. One experiment conducted by Donnerstein and Berkowitz showed men who
had watched a violent pornography administered more intense shocks to
women than men who had not seen any violent pornography.  Another set of studies and experiments that has spanned over 25 years has shown that exposure to violent pornography promotes acceptance of violence toward women and is a factor associated with actual aggressive behavior toward women. 
While there have been many experiments and studies that do show a positive correlation between pornography and violence toward women, there have been many that do not. The only thing that seems to be clear right now is that there is a general trend for violent pornography to increase aggression toward women. Non-violent pornography does not show this same connection.
An interesting part about violence toward women in America is that half of all rapes or attempted rapes are instances of “date rape”.  Date rape is when a man is acquainted with or dating a woman and decides to force sex on her. Such acts may have a lot to do with the development of sexual scripts in young men.  Scripts are ways of behaving socially that we learn implicitly from our culture. The typical sexual scripts created in adolescents tell them that men are supposed to be persistent and even aggressive when trying to get sex and a women are supposed to resist the sexual advances of men. In one survey of high school students, 97% of the females believed that a man should stop sexual advances when a woman says “no”, but around half of those same students believed that when a woman doesn’t always mean it when she says “no”. 
Men and women are unsure about how they are supposed to act. A man might receive mixed messages from society; one person says to be aggressive to get the girls and another says to be sensitive and kind. Women are told to resist sex because they don’t want to be viewed as ‘sluts’ but are also told to embrace their femininity and natural sex drives. All of this conflict leaves teenagers confused about the role they should play in relationships.  This may or may not contribute to increased aggressiveness toward women.
Punishment is the most widely used tactic in trying to stop aggressive behavior, but how well does it work? The thing about punishment is that it can come off as an aggressive act itself. If aggression is used to fight aggression, then one might never learn why aggression is bad to begin with. Studies have focused on children who grow up with parents that use highly aggressive tactics as punishment. Such children will often become prone to violence when they grow up.  For this reason, severe punishment might not be the best route to take when one is trying to teach another person a lesson.
It has been found that mild punishment is more effective in teaching a child to stop doing a certain behavior. Severe punishment does not cause a child to try and seek internal reasons to not do an immoral behavior, whereas mild punishment will. As long as the punishment threat is enough to cause a child to stop doing something long enough to think about why they would not want to do it, then it is often times enough to make the child never want to do the behavior again.  This phenomenon has to do with dissonance and is also called insufficient punishment.
Threat of Jail and Capital Punishment
Criminal justice systems are used to punish those that commit crimes such as murder or rape. Depending on the act committed, people are sentenced to a certain length of time in jail and/or death. Scientific studies mostly support the idea that such punishments help deter people from committing unlawful acts. One such study argues, however, that two ideal conditions must be met for this kind of punishment to work:
- the punishment must be prompt and certain.
- the punishment must follow quickly after the violence occurred and it must be unavoidable.
With as large a society we have now, and with the slow criminal justice systems in countries like the United States, it is almost impossible to meet these two conditions.  The probability of getting away with violent crimes in large American cities is actually rather high. Those that do get caught go through a very long process involving lawyers and jury dates before they finally get their verdict. For these reasons, punishment by the justice system probably does not deter violent crimes as much as we’d like to believe. Consistency and certainty of punishment are more effective deterrents than severe punishments that happen once in awhile. This might explain why there are 6 to 10 murders for every 100,000 persons in the U.S. every year, while countries like Germany, England, and France have homicide rates closer to 1 per every 100,000 persons. 
A common belief is that one can reduce feelings of aggression by doing something aggressive. Most of us will hear at least once about the importance of ‘letting of steam’ or ‘getting it out of your system’. To be rid of anger we must take out by yelling or punching something because if we hold it inside, it will eventually be expressed as something much worse. This belief is based on catharsis, or the idea that performing an aggressive act, watching others engage in aggressive behaviors, or engaging in a fantasy of aggression will relieve built-up aggressive energies and therefore reduce the likelihood of further aggressive behavior.  The idea of catharsis comes from Sigmund Freud, who believed that aggressive impulses have to be expressed in relatively harmless ways or they will become dammed up inside and eventually cause extreme violence or mental illness.
Unfortunately, catharsis actually increases rather than decreases anger and aggression.  Studies show that competitive games, long thought to help people vent their anger and frustrations, make participants and observers more aggressive.  Most all experimental findings offer little support for the catharsis hypothesis.
To help control anger, one can use a technique called actively enabling to try and make frustrations dissipate. To do this, a person does simple things like counting to ten, taking deep breaths, or engaging in a distracting activity.  These actions should help to calm someone down and prevent aggression and violence by giving them time to think things through.
Communication and Venting
It is important for someone in a relationship who feels angry to express their anger in a nonviolent and non demeaning way. This will help both members of the relationship gain insight into what could be improved in the relationship and how. To express this anger, one would usually make a clear and calm statement indicating what they feel and how their partner or friend caused those feelings.  This is also called effective communication.
If it is not possible to talk to the person who has caused the anger, another way one can release their inner anger or frustration is through writing.  By keeping a journal, inner thoughts can be clearly formulated and expressed, which is therapeutic for the mind.
Teaching Empathy and Problem-Solving Skills
To help lower violence and aggression everywhere, it is important that we teach people how to have empathy and effectively solve their problems. Empathy is the ability for someone to put themselves in another person’s shoes to imagine what or how they might be feeling. Doing this will usually help diminish feelings of anger, frustration, and misunderstanding.  Schools now more than ever try to teach children the value of empathy in diffusing anger and erasing hatred.
Training people how to problem-solve is also a good way to help lower aggression and violence. If people can think for themselves and successfully complete their goals and work through their problems, then they won’t have feelings of frustration and anger.  Without frustration and anger there is less violence or aggression. Of course, these are solutions that are easier said than done.
Violence and aggression are a part of being human. By understanding where our desire to inflict pain comes from we are given insights into controlling our aggressive and violent tendencies. Though we will never be able to rid the world of atrocities such as rape, murder, or racism — we can certainly try. Empathy and understanding are the key tools we have in the fight against unneeded violence.