Biological influences on aggression Flashcards
neural and hormonal, genetic, evolutionary, ethological, Raine et al study
Neural and hormonal
Neural influence
Certain areas of the brain play a key role in aggressive behaviour
- the limbic system and the amygdala
- the prefrontal cortex
Neural influence
Limbic system
The limbic system is part of the ‘old brain’ that we share with other animals.
It is also the brain’s emotion centre where our most basic urges (appetite, sleep, sex drive, fear) are regulated.
Neural influence
The amygdala
The amygdala is strongly associated with fear and aggression. It takes interpretated information as a threat or not.
Neural influence
Pre-frontal cortex
- responsible for planning, reasoning and more specifically, in relation to agression, impulse control and personality.
Pre-frontal damage
Phineas Gage
Cases such as Phineas Gage have shown patients with damage to this part of the brain become irritable, with inappropriate outbursts of anger and are more likley to respond aggressively in conflict situations.
Neural and hormonal
Hormonal influence
Typically, hormones are released by a gland and travels around the bloodstream, affecting organs or other parts of the body.
Neural and hormonal
Neurotransmitters
- a chemical released by neurons which carry information from one neuron to another
Neurotransmitters
Serotonin
A neurotransmitter linked to mood and sadness.
- makes us feel happy so treatment for depression often involves medicines that boost serotonin levels in the brain
Neurotransmitters
Low levels of serotonin
Low levels of serotonin are also associated with increased aggression. This is because serotonin seems to inhibit aggression so if you have low serotonin levels, you are more likely to act aggressively.
Serotonin Study
A rat study by Popova et al in 1991 found that rats selected for reduced aggression levels had higher serotonin levels than wild, more aggressive counterparts.
Hormonal influence
Testosterone
It is particulary associated with male sexual development - its levels greatly increase in boys when they approach puberty.
Testosterone is strongly associated with competition and aggression. Higher levels of testosterone is associated with increased fighting in many species.
Hormonal influence
Testosterone - Challenge hypothesis
suggets that the hormone’s main function is to help species seek and fight for mates, fight challengers and keep mates that they have already paired up with (mate guarding)
Testosterone research
Wagner et al (1979)
Over 19 sessions, it was discovered that the mouses aggression varied a lot, but after castration it clearly drops. When mice are injected with 150 micrograms of testosterone a day, their aggression creeps back up to the old levels.
Testosterone research
Mazur and Booth (1993)
Men with higher levels of testosterone are most likely to:
- divorce, or remain single
- be arrested (for offences other than traffic violations)
- to buy and sell stolen property
- use a weapon in fights
Genetics
Selective breeding
The role of genetics and selective breeding is most easily explained through canine behaviour. For centuries, dog breeders have selected particular traits by simply watching how a dog behaves. They have bred dogs for specific tasks by removing the dogs that perform less well from their breeding stock.
Genetics
Human aggression
A general principle of the evolutionary approach is that behaviours have evolved to serve a purpose that aids survival or reproduction.
It is of great social importance to know why people become mass murderers while others to go through life engaging in little or no aggression at all.
Genetics
MAO
MAO, or monamine oxidose, exists in each neuron in the brain, and it acts like a recycling factor for neutransmitters. In people who have the ‘warrior gene’, less MAO is produced, which means that less of the neurotransmitters serotonin, norepinephrine and dopamine are broken down.
Higher levels of these brain chemicals see to equal higher levels of aggression. These people feel less empathy for others, and are more willing to harm others on a whim.
Genetics
MAOA - the warrior gene
MAOA is regulated by the MAOA gene and humans have various forms of the gene, resulting in different levels of activity of the enzyme.
One variant of the gene is associated with high levels of MAOA (MAOA-H) and another variant is associated with low levels (MAOA-L). Several studies have now found a correlation between low-activity from the MAOA gene and aggression
Genetics
MAOA research
A study by Caspi et al (2002) looked at the role of MAOA-L in boys who had suffered abuse. They wanted to know why some men who have suffered abuse in their childhood grow up to be antisocial and violent while other do not. They believed that deficient MAOA activity caused by the MAOA-L version of the gene may lead to a person being hyper-reactive to threats, and this could be particularly problematic in early childhoods when resilience to threats has not fully developed.
Genetics
MAOA research - findings
They found that the presence of the gene interacted with child abuse, Of the men in the study who had experienced abusive childhoods, around 12% had the MAOA-L gene, but these participants were responsible for half of the convictions for violent crimes among the sample. This supports the idea that some people are gentically more predisposed to aggression but that adverse life events play a role too.
Genetics
MAOA - The warrior gene
Evidence
McDermott (2009) conducted an experiment in which she asked participants to cause physical pain to those they had believed had taken money from them by giving them various amounts of hot sauce. The resuts found that those with the MAOA gene were much more likely to administer higher levels of hot sauce.
Genetics
Twin Studies
In determining if a trait in a human’s behaviour is related to genetic factors or environmental factors twin studies are used. These studies examine correlations based on similarities of a trait and a person’s genetic factor that may be influencing the trait.
Research with human studies has focused on twin studies that have looked at the incidence if aggression displayed by monozygotic (identical) and by dizygotic (non-identical) twins.
Genetics
Epigenetics
Genes and environment interact biologically, and genes can be switched on or off depending on life experiences and the environment.
Evolutionary
Aggression is seen in all animal species and is believed to be an innate behaviour. If behaviours is innate, evolutionary psychologists propose that the behaviour must be beneficial to the organism. Aggression as a behaviour can help survival, as aggression can protect resources such as land and food. Aggression establishes dominance hierarchies, and these are vital to allow access to resources
Evolutionary
Natural Selection
Natural Selection assumes that animals with the most successful traits for reproduction and survival will pass their genes on to offspring.
Evolutionary
Buss and Shachelford (1997)
Securing resources
Humans stockpile resources which are important for survival and reproduction
Evolutionary
Buss and Shachelford (1997)
Establishing status
Aggressions can enhance ones personal status within a group. In Western cultures aggression has been ritualised within sporting contexts and top performers can achieve very high status.
Evolutionary
Buss and Shachelford (1997)
Deterring attack
The presence of individuals who may attack you prompts groups or individuals to use aggression as a means of preventing ones resources from being taken.
Evolutionary
Buss and Shachelford (1997)
Sexual competition
Aggression or the threat of aggression may deter parent partners from sexual infidelity. There is much evidence to suggest that mate sexual jealousy is a key factor in spouse abuse.
Evolutionary
Evaluation of Buss
Gender and Ethics
Critics feel this theory could be used to justify violence against women
Evolutionary
Evaluation of Buss
Deterministic
Buss himself always points out that we are not controlled by our genes; we have inherited the ability to learn and to choose
Evolutionary
Evaluation of Buss
Reductionist
Is this an over-simplification? Are there other issues which promote aggression such as culture or individual differences in testosterone
Ethological
Ethology places more emphasises on the natural habitat It recognises that while behaviours have evolved and are caused by genes, most species also adapt to environmental circumstances and learn from experience.
Ethological
Two concept of ethology
A fixed action pattern - this is similar to an ‘instinct’, but ethologists are interested in how these actions can respond to circumstances and adapt to specific environemntal contexts
A releaser (or releasing mechanism) - this is a social action pattern
Ethological
How does Lorenz view aggression?
According to Lorenz, aggression builds up like a drive within the animal until it is released, in this way; the need to be aggressive is much like other psychological needs such as food, water and sex.
Ethological
Lorenz
The innate releasing mechanism is a set of inherited neural circuits in the brain that attempts to prevent the release of the aggression drive until there are cues in the environment. This is hardwired and part of the animal’s biology when born. Lorenz also suggested that most animals have innate releasers which bring an end to a fight.
Ethological
Lorenz - in relations with humans
Lorenz states that humans may have lost their releasers which leads to violence that doesn’t stop. It also argued that the long distance nature of violene with weapons means that we don’t get visual or auditory feedback about a victims suffering - cues which might put a stop to violence among other animals.
Ethological
Tinbergen (1952)
He was interested in how animals establish a territory, and show aggression when this is invaded by other individuals. His classic study of stickleback fish demonstrated how fixed action patterns relating to mating and aggression are promoted by releasers which experimenters were able to mimic.
Ethological
Tinbergen (1952)
Results
All males attacked only the unrealistic wooden models with the red bellies. This shows that the red patches act as a biological trigger to start an aggressive fixed action pattern, even when there was no threat.
Raine et al (1997)
Study of brain abnormalities in murderers
Aim
The study aimed to find out the role played by brain areas including the prefrontal cortex, the corpus callosum and the amygdala in predisposing people towards people who had controlled violent crimes.
Raine et al (1997)
Study of brain abnormalities in murderers
Method
This was a quasi-experiment. The experiment is considered quasi because the experimenters could not manipulate the independent variable as it was naturally occurring: a person was a murderer, or they were not a murderer.
Raine et al (1997)
Method - IV and DV
The IV was “whether the participant was a ‘normal’ non-murderer or a murderer who had plea ‘not-guilty by reason of insanity.’”
The DV was whether the participant showed evidence of brain dysfunction in their prefrontal cortex and other areas such as the amygdala and corpus callosum.
Raine et al (1997)
Study of brain abnomalities in murderers
Participants
41 participants (39 male, 2 female) who had been charged with murder and had pled not guilty on the grounds of insanity, the precise reasons varied from schizophrenia to head injuries. As part of their defense, the prisoners received brain imaging scans and Raine took the opportunity to compare the prisoners scans with a group of controls.
Raine et al (1997)
Study of brain abnormalities in murderers
Findings
Brain scans from these participants were compared with a control group of 41 participants with no convictions.
As expected, the scans showed less activity in the frontal lobe, especially the prefrontal cortex, which is associated with rational thinking and self-restraint. There was also less activity in the parietal lobe, which is associated with abstract thinking.
There was an imbalance of activity between the left and right hemispheres in the limbic system. There was less activity on the left and more on the right in the amygdala and on the right side of the thalamus.
