Biological Explanation of Aggression

Biological Explanation of AggressionDescribe the Genetic Explanation of AggressionEvaluate Genetic Evaluation (A02)

Can anyone explain what these are? (class discussion hands up activity) Then go through and explain each. Then get them to link these to aggression, very basically e.g. Might be a gene that causes aggression, does anyone know any hormones that might explain it?2

The case of jeffrey landrigan29 years oldOn trial for murder of 42 year old male (Chester Dyer)Previous convictions: Stabbing childhood friend to death- 1982Date of trial: 9th Nov 1990

09 11 - 1990Arizona, USA

Chester Dean Dryer was a 42 year old man who worked in a health club and was known to pick up men and take them home. Dyer called friends to tell them he was having sex with a man named Jeff. He was later found strangled by an electrical cord and stabbed to death in his apartment. A deck of pornographic playing cards were strewn over the bed. Landrigan's shoes matched a footprint left in sugar in Dyer's apartment. He told police that he had beaten Dyer after Dyer made sexual advances, but that another man had done the killing.Landrigan was uncooperative and disruptive during his trial, and at sentencing told the Judge "If you want to give me the death penalty, bring it on, I'm ready."

The case of Jeffrey LandriganLandrigan was abandoned by his parents as an infant. He was adopted at 9months of age into a loving and stable home. He never met his biological family. Jeff stated that he felt loved but never really belonged. He had a drinking problem at age 10 and history of violence throughout his teens.During imprisonment, he was told by a guard that he looked similar to a man on Death row in Arkansas, Darrell Hill. Darrell Hill was Jeffreys biological father. They had never met but led parallel lives of drugs, alcoholism, violence and murderHe found out that his Grandfather had been shot dead by police whilst robbing a drug store. Jeffrey appealed his sentence with the claim that his destiny was bound by his DNA and requested a re-trial

The case of jeffrey landriganIf the defense is plausible, why dont more people use it?

1. If we accept it, well be forced to medicalize criminal behaviour and treat crime as a genetic disorder. 2. If genetic, there can be no cure or reformation. Capital punishment may be used in more cases

Genes and AggressionCan affect levels of testosterone

Can affect speed of testosterone circulating the body

Can determine severity of the Stress Response through neurotransmitter and hormone levels.

Can affect sensitivity of receptors to hormones and NT

Genetic ExplanationIs there a specific Gene for Aggression?

How could we test this theory to find out if there is an Aggression gene?

Twin studies are very useful in determining genetic influences of behaviour

Mz twins share 100% of their genesDz twins share 50% of their genes

Concordance rate = The probability that a pair of individuals will both have a certain trait given that one of the pair has that trait

Twin studiesIf aggression is caused by a particular gene

Mzs should have 100% concordance rate of aggressioni.e. if 1 Mz twin is aggressive, the other Mz twin will be too. Dzs should have a 50% concordance rate of aggression i.e. if 1 Dz twin is aggressive, there is a 50% chance the other will be too.

Aggression in twin studiesMcGuffin & Gottesman (1985)

Studied both Mz and Dz twins who had been brought up in the same environment for levels of juvenile delinquency and crime.

Concordance rate for delinquency in Mz twins was 87%Concordance rate for delinquency in Dz twins was 72%

Is this convincing evidence for the role of genetic factors in aggressive behaviour? Why?

What do the two findings show? And what does the 72% concordance rate in Dz twins suggest?

What basic problems are there with investigating aggression amongst twins?

Aggression in twin studiesMason & Frick (1994)

Meta-Analysis involving 3795 twin pairs from 12 twin studies and 3 adoption studies published since 1975.

Measured concordance rate of anti-social personality; aggression and criminality

Mason & Frick (1994)Results:

Concordance rate of aggressive behaviour calculated at 48%

Mason & Frick (1994)Results:

This effect was larger for more violent behaviour

Twin studies Twin studies provide evidence for a genetic vulnerability to aggression (concordance of approx. 50%) Mz twins have higher concordance rates than Dz twins suggesting heritability

However

Mz twins are often treated more similarily than Dz twins which may influence similarity in aggressive behaviour High concordance rate of aggression between twins may be due to their shared environment and upbringing

Problem with twin studies is that they usually share the same environment too so its difficult to accurately estimate the contribution of genetic factors on aggression.

Adoption studies look for correlations in aggressive behaviour between children raised by non-biological parents, and aggression in the biological parents.

Nature vs. Nurture

If more similar to adopted parents . Environment; if more similar to biological parents genes19

Hutchings & Mednick (1973)

14,000 adoptions in DenmarkMeasured number of convictions for criminal violence

Hutchings & Mednick (1973)

Results:Significant positive correlation found between adoptees and biological parents for criminal convictionsNo significant correlation between adoptee and adoptive parents.

Cadoret (1995)

Best predictor for Aggressive behaviour in children is when the biological family were aggressive AND the adoptive experience marital dispute or drug abuse.

XYY SyndromeSandberg (1971) First identified the XYY genotype

Xyy syndromePrevalance of approx. 1 in 1000

Affected men are usually very tall and thin

Symptoms include, learning disabilities (IQ 10-15 points lower than siblings) and anti social behavioural problems

Xyy syndrome

Out of a sample of 314 patients in a high security hospital, 9 were found to have XYY Sandberg concluded that those with XYY should be hospitalised due to an increased likelihood of aggressive behaviour

HoweverTheilgaard (1984)

Compared a sample of XYY men with XY and found fluctuating levels of aggression within the sample

Conflicting evidence for aggression XYY link

Media may have influenced peoples perception of Xyy causing aggressive behaviour

MAOAGene Monoamine Oxidase A (MAOA)

The gene controls an enzyme which breaks down the neurotransmitter Serotonin.

MAOASerotonin is a neurotransmitter

It modulates Vasoconstriction; Body temperature; Mood; Appetite; Anger and Aggression

MAOABrunner et al (1993)

Examined a Dutch family which had males displaying high levels of violenceThere were high levels of domestic violenceOne brother had tried to rape his sisterThe father had been convicted for violent crimes many times

Brunner et al (1993)All the aggressive males in the family had defected MAOA genes with very low activity from the gene

This results in increased serotonin levels as a result of a reduction of the enzyme.

MAOA Warrior geneLower-level activation of MAOA is associated with increased Aggression

Low Level MAOA (LL-MAOA) affects 1/3 of Western societiesLL-MAOA effects 2/3 in countries with a history of warfare

LL-MAOA causes a genetic prediposition to aggression

Increased aggressive behaviour occurs as a result of a combination between genes and environment

The most aggressive strains of a certain species can be interbred and the offspring can be measured for aggressive behaviour.

Lagerspetz (1979)

Mice classified as either aggressive or docile The 2 strains were then interbred and fosteredBy the 19th generation, 52% of the aggressive mices offspring showed biting behaviour compared to just 5% of the non-aggressive

Lagerspetz (1979)

Demonstrates a genetic basis for aggressive behaviour in mice

Concordance rate was not 100%... Must be environmental factors too

Exam PrepDiscuss Genetic factors involved in Aggressive Behaviour

4+16 marks

A01 Discuss genetic factors involved in aggression(4 marks)Aggression is the intent to verbally or physically harm others. Genetic explanations of aggression suggest that aggressive behaviour is as a result of a biological, genetic predisposition to aggression and ignores environmental explanations. The explanation assumes heritability of aggression amongst family members who share genetic make-up. Previous research into an inherited gene for aggression have found specific genetic mutations that may lead to increased aggressive behaviour in the males who carry the genotype XYY. The additional Y chromosome is associated with many symptoms including heightened levels of aggression. Other genes associated with aggression is Monoamine Oxidase A gene (MAOA) which is responsible for the breakdown of the neurotransmitter Serotonin. Lower activation of this gene and subsequent higher levels of serotonin (due to reduced enzyme activity from MAOA) have also been correlated with increased aggression in those who carry it. One third of people in Western countries carry the lowered activation variation of MAOA, compared with two thirds in countries with a history of warfare, leading the gene to be named the Warrior gene.