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In psychoanalysis, as well as other social and behavioral sciences, aggression refers to behavior between members of the same species that is intended to cause pain of damage.

Predatory or defensive behavior between members of different species is not normally considered "aggression".

The assault led to a variety of forms among humans and can be physical, mental or verbal.

Aggression should not be confused with assertiveness, although the terms are often used interchangeably among the laity, for example, an investor in the stock market aggressively.

There are two broad categories of aggression.

1. Hostile aggression, affective or retaliation;

2. Instrumental aggression, predatory, or goal-oriented aggression.

Empirical research indicates that there is a fundamental difference between the two, both psychologically and physiologically.

Some research indicates that people with tendencies toward affective aggression have lower IQs than those with a tendency to predatory aggression.

In many different human cultures, men are more likely than women to express aggression through direct physical violence.

Women are more likely to express aggression, by indirect means or non-physical. One explanation for this difference is that, on average, women tend to be physically weaker than men, and thus need to resort to other means.

Evolution of aggression

Like most behaviors, aggression can be analyzed in terms of its ability to help an animal to reproduce and survive. Animals may use force to win and secure territories and other resources, including food, water and mating opportunities. The researchers theorized that aggression and the ability to murder are products of our evolutionary past.

Aggression against outsiders

The most apparent of aggression is observed in the interaction between a predator and its prey.

An animal to defend itself against a predator becomes aggressive to survive and to ensure the survival of their offspring.

Due to the aggression against an enemy much larger group of enemies or lead to the death of an animal, the animals developed a good sense when they are at a disadvantage. This ability to measure the strength of other animals gives a "fight or response" to escape predators, depending on how hard to evaluate, for the predator.

The need to survive and the viability of cooperative behavior as a survival strategy leads to a phenomenon known as altruism. An example of a selfless act is the cry of alarm is given when a predator approaches. Although this call will inform the community of the presence of a predator, but will also inform the predator of the whereabouts of the animal that gave the alarm. While this seems to sound the alarm of a caller evolutionary disadvantage, would facilitate the continuation of the genes of this animal, because their relatives and descendants would be able to avoid predators.

According to several researchers, predation is not aggression. Cats purr down and arch your back when in search of a mouse, and areas in their hypothalamus are more similar to those that reflect hunger than those that reflect aggression.

Aggression within a species

Aggression against conspecifics offers a variety of effects that has to do with reproduction. One of the most common of these effects is to establish a dominance hierarchy.

When certain types of animals are first placed in a common environment, the first thing they do is fight to assert its role in the dominance hierarchy. In general, the more dominant animals are more aggressive than their subordinates. There are many theories that attempt to explain how men and women developed these different aggressive tendencies. One theory states that in species where one sex makes a higher parental investment than the other, sex is the biggest investment of resources to the opposite sex it is in most species, women are the major investors in sex. Further maintains that reproductive success is cardinal to the perpetuation of the lineage of an organism and the hereditary characteristics.

For men, it is crucial to establish domination and exploitation of opportunities for reproduction in order to pass their genetics. Unlike females, whose reproductive success is limited by the long gestation and lactation periods, the male reproductive success is limited by the number of partners that could come across them. As a result, men use physical aggression more often than females, they take more risks in order to compete with other males and gain a high status.

Males can go so far as to kill one another, although this is rare. Males show less concern for their physical well-being in such competitions. In contrast, women compete for resources, which can be converted to offspring.

The establishment of a dominant position is more costly for females than for males and females have more to gain from the completion status.

The female presence is more critical to the survival of offspring and thus their reproductive success is greater than the father.

It is logical then that the health and well being of females is associated with less aggressive, low risk and indirect strategies to acquire resources. As a result, most women female conflict, rarely cause serious damage to one another over resources. When translated to human health, these facts suggest that women should be expected to show less evidence of dominance hierarchies and that of men.

In society, aggression among boys is becoming more motivated by social status and self-esteem, which are usually determined by varying degrees of aggressive reaction of personal challenge. The aggression in girls is mainly concentrated in the acquisition of resources rather than a state, and is more likely to be physically less dangerous and more covert form of indirect aggression. There are, however, ample criticism of the use of animal behavior to explain human behavior and the application of evolutionary explanations of human behavior contemporary.

Aggression in humans

Aggression in humans differs in almost all aspects of the non-humans (animals) in the complexity of their aggression because of factors such as culture, customs and social situations. A variety of studies have been done about these situations.

Aggression and culture

Culture is a distinctly human factor, which plays a role in aggression. Kung Bushmen and people were described as "harmless" by Elizabeth Marshall Thomas (1958). Other researchers, however, have countered this view, calculating the rate of homicides among the Bushmen is actually higher than that of most modern industrial societies (Keeley, 1996). Lawrence Keeley argues that the savages "peaceful" is a myth that is not supported by most archaeological and anthropological evidence. Hunter Gatherers do not fight for possessions, but they can still get the conflict over the status and mating opportunities.

Research based on cultural experience has found differences in the level of aggression between cultures.

In one study, American men resorted to physical violence more easily than men Japanese or Spanish, while Japanese men preferred the direct conflict (verbal) more than their American counterparts and Spanish (Andreu et al. 1998).

Within American culture, Southerners were more excited and to respond more aggressively than the northerners when affronted (Bowdle et al. 1996).

There is also a higher rate of homicides among young people than among white men and Southern white men of the northern United States (Nisbett, 1993).

Changes in dominant behavior or social status cause changes in testosterone levels. Reports of changes in testosterone in young men during sporting events, involving face to face competition with a winner and a loser, show that testosterone increases just before their departure, as if in anticipation of the competition. In addition, one to two hours after the game competitive, testosterone levels of winners are high relative to levels of losers.

Aggression in the media

Behaviors such as aggression can be learned by observing and imitating the behavior of others. A considerable amount of evidence suggests that violence on television are assisted in the short term increases the likelihood of aggression in children (Aronson, Wilson & Akert, 2005), although at a different point of view, see Freedman (2002). Individuals may differ in how they respond to violence. The biggest impact is on those who are already prone to violent behavior.

Adults can be influenced by media violence as well.

Studies show increased aggressiveness or exposure to violence in the media and is associated with risk of short-term, and none of these studies provide definitive evidence of a causal mechanism. Instead, media violence may be one of many factors that may play a role in maintenance of such violent means which tend to be selected by people who are prone to violence.

Aggression and Situational Factors

* Alcoholic beverages

Alcohol impairs insight, making people much less cautious than they usually are (MacDonald et al. 1996). Alcohol also disrupts the way information is processed (Bushman 1993, 1997, Bushman & Cooper, 1990). A drunk person is far more likely to see an accidental event in a purposeful and therefore act more aggressively.

* The aggressiveness increases with the pain and discomfort.

Even the simple act of putting your hands in cold water can cause an aggressive response.

Temperatures have been implicated as a factor in a number of studies. A study completed in the middle of the civil rights movement found that riots were more likely in warmer weather than cooler (Carlsmith & Anderson 1979). Students, after the monthly test in the classroom hot became more aggressive, as well as drivers in cars without air conditioning used their horns more often (Anderson et al. 1996, Rule et al. 1987), (Kenrick & MacFarlane 1986).

* One of the main fuses of aggression and frustration.

Aggression is increased by the frustration when a person feels he or she is being prevented from achieving a goal (Aronson et al. 2005).

Frustration can be another unexpected factor.

There is some evidence to suggest that the presence of objects of violence, as a weapon can cause aggression. It is possible that a stimulus-related violence increases the likelihood of aggressive cognitions by activating the net.

Aggression and gender

Gender is a factor that plays a role both in human aggression and animal.

Males are historically more physically aggressive than females (Coie & Dodge 1997, Maccoby & Jacklin 1974), and men commit the majority of murders (Buss 2005). This is one of the most robust and reliable differences in sexual behavior, and has been found in many groups of different ages and cultures. There is evidence that males are quicker to express physical aggression than females (Frey et al. 2003), (Bjorkqvist et al. 1994). However, within the family, these old beliefs have been recently reassessed (Richardson, 2005). When considering indirect forms of aggression, such as the influence of power or a change in the environment that can change mood and relational aggression and social rejection, females and males are equally aggressive (Archer, 2004; Card, Stucky, Sawalani , & Little, 2008).

Although females are less likely to initiate physical violence, they can express aggression, using a variety of non-physical means to inflict damage on others.

The methods used by women to express aggression is something that varies from culture to culture.

On Bellona Island, a culture based on male dominance and physical violence, women tend to conflict with other women more often than men. When in conflict with men, instead of using physical means, they make up songs mocking the man, which spreads throughout the island to humiliate him.

If a woman wants to kill a man, she tries to convince her male relatives to kill him or hire an assassin. Although these two methods involve physical violence, both are indirect forms of aggression, as the aggressor would not be drawn directly or put yourself in immediate physical danger.

Aggression in children

It has been observed frequently assaults committed by children around 2-3 years of age. Then gradually decreases on average. These observations suggest that physical aggression is not primarily a learned behavior and that the development offers opportunities for learning self-regulation. However, a small group of children can not acquire the necessary self-regulation skills and tend to show atypical levels of physical aggression in development. These may be at risk for more violent behavior.

Children and assertiveness

Children need to prepare to enter the children to develop social skills, be assertive.

Examples of assertive: ask for information, start a conversation, or be able to respond to peer pressure.

However, some children use aggressive behavior, like hitting or biting, as a form of communication.

Aggressive behavior can impede learning as a skills gap, while assertive behavior can facilitate learning.

At school age, children should learn more socially appropriate ways to communicate, and express themselves through verbal or written, if they do not, this behavior can mean a disability or developmental delay.

* Generators of aggression in children

Physical fear of others, family difficulties, learning, neurological processes or behavior, behavioral disorders, emotional trauma, sexual assault.

Bandura found that children in contact with adults of aggressive behavior become much more aggressive than those in contact with adults

not aggressive.

Biology of aggression

The aggression is directed and often comes from external stimuli, but has a character very different procedure. Using various techniques and experiments, scientists were able to explore the relationships between the various body parts and aggression.

Aggression in the brain

Many researchers have focused on the brain to explain aggression.

The areas involved in aggression in mammals include the amygdala, hypothalamus, prefrontal cortex, cingulate cortex, hippocampus, septal nuclei, and midbrain periaqueductal gray.

Because of the difficulties in determining the intentions of animals, aggression is defined in neuroscience research as behavior directed toward an object or animal that results in harm or damage to the object or animal.

The hypothalamus and periaqueductal gray of the midbrain are the most critical areas to control aggression in mammals, as demonstrated by studies in cats, rats and monkeys. These areas of the brain that control the expression of all the behavioral and autonomic components of aggression in these species, including vocalization. They have direct links with the two nuclei in the brainstem and control these functions and areas such as the amygdala and prefrontal cortex.

Electrical stimulation of the hypothalamus causes aggressive behavior, the hypothalamus express receptors that help determine the levels of aggression based on their interactions with the neurotransmitters serotonin and vasopressin.

The prefrontal cortex (PFC) has been implicated in the psychopathology aggressive. Reduction of the activity of the prefrontal cortex, especially its medial and orbitofrontal cortex has been associated with violence / aggression antisocial. Specifically, regulation of levels of the neurotransmitter serotonin in the CPF has been linked with a specific type of pathological aggression, undergoing induced type mice genetically predisposed, aggressive, wild, to gain experience repeated, the male rats selected from aggressive lines had lower levels of serotonin in the tissue of the PFC low aggressive lines in this study.

The neurotransmitters and hormones

Several neurotransmitters and hormones have been shown to correlate with aggressive behavior. The most cited hormone is testosterone. In one source, it was found that the concentration of testosterone is more clearly correlated with aggressive responses involving provocation.

In adulthood, it is clear that testosterone is not related to the measurement methods consistent aggression in personality scales, but several studies on the concentration of testosterone in the blood of criminals convicted men who committed violent crimes than men, no criminal record or who has committed violent crime in most cases revealed that men who were deemed aggressive / dominant had higher concentrations of testosterone in their blood than those without criminal records. However, a correlation between testosterone levels and aggression does not prove a causal role for testosterone.

Studies of testosterone levels in male athletes before and after competition showed that testosterone levels rose just before their departure, as if in anticipation of competition, and are dependent on the outcome of the event: the testosterone levels of winners are high relative to the losers.

Interestingly, levels of testosterone in criminal female versus female, no criminal mirror of men testosterone levels are higher in women who commit crimes and are considered aggressive.

Studies indicate that the use of anabolic steroids causes increased aggression, coming then to anger.

Another line of research has focused more on the effects of testosterone circulating in the nervous system mediated by local metabolism within the brain. Testosterone can be metabolized to 17b-estradiol by aromatase, an enzyme or 5a-dihydrotestosterone by 5a-reductase. Aromatase is highly expressed in regions involved in the regulation of aggressive behavior, such as the amygdala and hypothalamus.

In studies using techniques of genetic knock out mice in inbred mice males who lacked a functional aromatase enzyme displayed a marked reduction of aggression. The long-term treatment of rats with estradiol partially restores aggressive behavior, suggesting that neural conversion of circulating testosterone to estradiol and its effect on estrogen receptors affects interagressão male. In addition, two types of estrogen receptors, ERA and ERb, have been identified as having the ability to exert different effects on aggression.

Glucocorticoids also play an important role in the regulation of aggressive behavior. In adult rats, acute injections of corticosterone promote aggressive behavior and reduced acute corticosterone decreases aggressiveness, however, a chronic reduction in the levels of corticosterone can produce an abnormally aggressive behavior. In addition, glucocorticoids affect the development of aggression and the establishment of social hierarchies. Adult mice with low basal levels of corticosterone are more likely to become dominant than the rats with high baseline levels of corticosterone.

Dehydroepiandrosterone (DHEA) is the most abundant androgen in circulation and can be rapidly metabolized in the tissues clear potent androgens and estrogens.

Gonadal steroids generally regulate aggression during the breeding season, but non-gonadal steroids may regulate aggression during the non-breeding season.

Castration of various species during the breeding season has no effect on territorial aggression.

DHEA levels have also been studied in humans and may play a role in human aggression. Circulating DHEAS (sulfate esters) levels rise during adrenarche (~ 7 years old), while plasma testosterone levels are relatively low. This implies that aggression in prepubertal children with aggressive conduct disorder can be correlated with DHEAS plasma instead of plasma testosterone, suggesting an important link between DHEAS and human aggressive behavior.

Another chemical messenger, with implications for aggression is the neurotransmitter serotonin. In many experiments, the action of serotonin was correlated negatively with aggression (Delville it al. 1997). This correlation with aggression helps to explain the reduction of aggression and the effects of selective serotonin reuptake inhibitors such as fluoxetine (Delville et al. 1997), also known as Prozac (antidepressant medication).

The two (2) chemical messengers investigated further with respect to aggression were serotonin and testosterone, other neurotransmitters and hormones have been shown to relate to aggressive behavior as well. Vasopressin neurotransmitter that causes an increase in aggressive behavior when present in large amounts in the anterior hypothalamus (Delville et al. 1997). The effects of norepinephrine, cortisol and other neurotransmitters are still being studied.

Genetics and Aggression

The study was conducted by Terry Moffitt, the Institute of Psychiatry, University of London. He had access to data collected by the University of Dunedin, New Zealand, which since 1972 came from the birth, 1 037 persons, men and women. Violence among young people may be linked to the presence of an enzyme called MAO-A, which regulates the amount of serotonin in the brain, in turn connected to the control of aggression.

In addition to all the external environmental factors, genetics may be behind the aggressive youth. Research on the subject was done by Juergen Hennig and published in Behavioral Neuroscience. In it, pointed to the relationship of specific components of aggression related to a gene called TPH.

A study conducted by Juergen Hennig, PhD, contributes to increasing evidence that the type of aggressive behavior that we consider to psychopathic or sociopathic has some genetic basis that may involve abnormally low levels of the neurotransmitter serotonin. Again, gene polymorphisms appear to influence individual differences.

Specific components of aggression in 58 participants appeared related to the U allele (variation) of a gene called TPH, a marker that should be linked to another yet unknown gene. Henning says, "connection means that both genes are transmitted together, as they are close together on the same chromosome".

The researchers measured genotypes dubbed AA, AC and CC. The genotype AA was associated with higher rates of aggression, while the genotype "CC" was associated with lower rates.

Using another sample of 48 men, the authors also validated the distinction between "neurotic hostility" and "aggressive hostility", the latter more violent and without guilt. The authors say their findings emphasize the value of distinguishing between different aspects of aggression.

Finally, only men "aggressively hostile" released high levels of cortisol, a key stress hormone, after taking an antidepressant drug that makes serotonin more available in the brain.

The authors speculate that, after being deprived of serotonin, the neural receptors of these men were sensitive and responsive than normal, partly by producing extra cortisol.

Joining the three discoveries, Henning concludes that, "We found that gene polymorphisms contribute to the variation that can be found in neuro-endocrine and personality questionnaires in healthy subjects. This demonstrates that certain aspects of behavior relate to systems biological, such as the neurotransmitter systems".

A rare genetic variant that causes MAO-A deficiency has been associated with violent behavior in men.

In 2002, a study published by researchers from King's College London found a link between a genetic variant that causes low levels of MAO-A and increased levels of antisocial behavior of people who had been abused as children.

In 2004 an American studying monkeys have found the so-called MAO-A, a gene "warrior." A 2008 study found a similar result involving the variant of the MAO-A and the DAT1 and DRD2 genes.

In all three cases, the variants of these genes were associated with a high risk of violent behavior and criminal, but only in people who have experienced certain stresses during childhood.