BIOLOGICAL EXPLANATION OF AGGRESSION

1
BIOLOGICAL EXPLANATION OF AGGRESSION

• THE ROLE OF GENETIC FACTORS

2
Learning objectives

• Understand how biological and physiological
  processes affect aggressive behaviour.
• Understand how biological explanations of
  behaviour are split into genetic, biochemical and
  neuro-anatomical explanations.
• Describe the various biological and physiological
  processes that lie behind aggressive behaviour.
• Evaluate the effectiveness of the various
  biological explanations of the cause of
  aggression.

3
The role of genes in aggression

• Genes do not directly cause aggression
• Genes affect muscle and bone development
  necessary for aggression.
• Genes influence neurochemical, hormonal and
  sensory systems.
• It is a combination of these that contribute to
  an animals aggressive behaviour.

4
Is aggression passed on?

• Nelson 2006
• Found selective breeding can lead to more
  aggressive behaviour in animals.

5
Selective breeding

• Choosing animals with desirable characteristics
  for breeding.

6
Selective breeding for aggression

• Spanish fighting bulls
• Chickens (cock fighting)
• Fish (Siamese fighting fish)
• Dogs (pit bull terriers)
• Compared to regular animals they are more
  developed for fighting.

7
Lagerspetz 1979

• Isolated mice after weaning
• Tended to be aggressive when put with other mice
  (attacking, biting, speed).

8
interbred

• These mice were interbred.
• By the 19th generation rates of aggressive biting
  in aggressive mice was 52
• Only 5 in ordinary mice.

9
Aggressive mice

• These mice also had
• Heavier testes
• Heavier forebrains
• Altered levels of neurochemical serotonin in the
  forebrain and noradrenaline in brain stem.

10
conclusions

• Supports the notions that genes influence both
• Structural and
• Functional aspects of an animals biology.

11

• Aggression can be passed from one generation to
  another.
• Animal studies such as Cairns and Nelson have
  shown this.
• But there are environmental influences as well
  such as upbringing and social influences (SLT,
  deindividuation, cue arousal, relative
  deprivation etc.)
• These are played down by the genetic explanation.

12
Lagerspetz 1981

• Genetic factors do not absolutely determine
  aggressive behaviour.
• Environmental factors are also important...
• The aggressive mice can be conditioned to be less
  aggressive

13

• In the same way, wild animals have been tamed for
  years to become pets.

14
TWIN STUDIES

• FINDINGS EXTREMELY VARIABLE
• Canter (1973)
• Correlation of 0.14 for MZs reared together.
• OConnor (1980) found 0.72

• Twins reared apart showed slightly less
  variability.

15
Indicates a genetic contribution

• Greater association with MZ twins than DZ twins
  whether reared together or apart.

MZ MZ DZ DZ
Reared together Reared apart Reared together Reared apart
0.72 0.64 0.42 0.34
0.39 0.46 0.42 0.06
0.14 0.53 0.30 0.39
16
Heritability

• Heritability varies according to assessment
  method
• Self report 39
• Reported by others 53

• Heritability
• the extent to which genetic individual
  differences contribute to individual differences
  in observed behaviour (or phenotypic individual
  differences).

17
Is aggression caused by genetics?

• Most individuals have 46 chromosomes (23 from
  each parent).
• It is possible for a male to have an extra Y
  chromosome

http//www.youtube.com/watch?v5CYdMspQzDw
18
Richard Speck

• July 13 1966
• Speck murdered 9 nurses
• He was later found to have the XYY chromosome
• Aha!!

• This was later found to be a mistake!
• Oh No!

19
Popular beliefs about 47 XYY males

• The media have encouraged belief that the XYY
  male is more aggressive than normal males.
• Popularised in TV series such as Doomwatch, XYY
  Man, Alien 3.

20
Evidence Theilgaard 1984

• About one in a thousand males
• Taller than usual
• But not necessarily more likely to show increased
  levels of aggression.

21
Evidence for XYY and aggression?

• Jacobs et al 1965

• 3 in a hundred

• Found XYY syndrome at the rate of 3 in prisoners
• Only 0.1 in normal population (One in a thousand)

22
Doh!

• XYY males

• less intelligent
• More likely to commit crimes but not generally
  violent ones.
• More likely to get caught

23
Thematic apperception testing

• Theilgaard found that XYY men tend to give more
  aggressive interpretations to the images used in
  these tests.
• But consider the validity and reliability of the
  test.

24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
Rorschach test
28
(No Transcript)
29
(No Transcript)
30
The effect of genes on neurotransmitters

• MAOA gene

• Studies have found a link with aggression.
• MAOA gene regulates an enzyme in the brain
  (Monoamine Oxidase A)
• This removes excess amounts of neurotransmitters.

31
Biochemistry and aggression

• plausible

• Build up of neurotransmitters is related to mood
• And can cause an aggressive reaction to a
  stressful situation.

32

• Brunner et al (1993)

• Discovered a mutation in the MAOA gene in a Dutch
  family.
• Family records showed history of violence in the
  males (often associated with aggressive events.

33

• Only affects men

• Evidence

• Men have only one X chromosome.
• Might inherit the gene but have a second X
  chromosome carrying a good copy of the gene.

• Cases et al (1995)
• Disabled the MAOA gene in X chromosome of mice
  and found males became highly aggressive.
• Females didnt.

34

• Males

• Females

• Lacked the monoamine oxidase A enzyme.
• Levels of dopamine and serotonin increased.

• Had the other functioning X chromosome to do the
  job.

35
Predisposes the male to anti-social and
aggressive behaviour.

• MAOA - L

• MAOA - H

• Less of monamine oxidase

• More of monoamine oxidase

36

• Evidence

• With MAOA-L

• Caspi et al (2002)
• Longitudinal study of 1,037 children over 25
  years
• Males severely maltreated as boys more likely to
  engage in violent behaviour as adults.

• More than twice as likely to have a conduct
  disorder as those with the MAOA-H gene.
• Three times more likely to be convicted of
  violent crime by 26 years.

37

• Furthermore,

• conclusion

• 12 of the sample had the MAOA-L gene and had
  been mistreated.
• They committed 44 of the crimes.

• The importance of interaction between genes and
  environmental influence.
• One alone not a predictor.
• Two together boom..

38
fMRI (functional magnetic resonance imaging)

• Brain scans

• Structural changes

• The MAOA-L variant may be linked to reductions of
  volume in areas of the brain.

39
Reduced volume of anterior cingulate cortex (Blue
/ yellow)

• MAOA-L

• Normal brain

40

• Meyer-Lindberg et al (2006)

• McDermort et al (2008)

• Significant reductions in volume in prefrontal
  cortex and amygdala in MAOA-L participants.
• Involved in emotion and are often impaired in
  anti-social individuals.

• MAOA-L gene displayed higher levels of aggression
  in response to provocation than MAOA-H.