BIOLOGICAL EXPLANATIONS OF AGGRESSION

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BIOLOGICAL EXPLANATIONS OF AGGRESSION

• BIOCHEMICAL FACTORS IN AGGRESSION

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Objectives

• Understand the effect of hormones on aggressive
  behaviour
• Understand how hormones and selected
  neurotransmitters can influence aggressive
  behaviour
• Evaluate the contribution of research into neural
  and hormonal influences on aggressive behaviour.

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Hormonal insanity !

• In the Uk
• Since the 1980s
• A series of high profile cases where hormonal
  fluctuations surrounding pre-menstrual tension
  have been used as grounds for claims of temporary
  insanity.
• A murder charge was reduced to manslaughter on
  account of PMT.

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Lawyers argument

• Their clients were automatons of their body.
• The aggressive act was caused by uncontrollable
  hormonal changes associated with the monthly
  cycle.

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Hormonal influences

• Androgens male hormones
• There is a positive correlation between the level
  of androgens and aggressive behaviour in female
  and male prisoners.

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Testosterone

• An androgen produced by Leydig cells in the male
  testes and adrenal cortex.
• The release of testosterone follows a natural
  circadian rhythm.

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• During puberty aggression increases when androgen
  levels are higher (especially in males)
• Testosterone has masculinising effects.

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Castration

• This technique has been used for making domestic
  and farm animals more manageable for many years.
• Lab studies established the involvement of
  testosterone in increased aggression at puberty.

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Wagner et al. 1979

• A castrated mouse showed less aggression.
• After testosterone treatment, aggression
  increases again.

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Changing levels of testosterone in mice
pre-castration and post-castration

• Blue pre-castration
• Pink post-castration
• Green 150 microgm testosterone per day.
• BEEMAN (1974)

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Commentary

• Aggression did not disappear after castration
• It cannot be stated that testosterone causes
  aggression.
• Subsequent studies found that aggressiveness in
  mice is only reduced if castration occurs before
  puberty.
• Therefore, testosterone contributes to the
  development of aggression and once it has
  accomplished this, its effects become relatively
  permanent and largely unaffected by the
  subsequent loss of testosterone.

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Testosterone in humans

• The role of testosterone is clear in lower
  animals, but androgens cant be given to humans
  to see if changes in aggression occur.
• Dabbs et al (1995) investigated the relationship
  between testosterone, crime and prison behaviour.
  
• They measured testosterone in saliva of 692 adult
  male prisoners.

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Findings

• Those who had committed crimes involving sex and
  violence had higher testosterone levels and
  violated more prison rules than those who had
  committed burglary and theft.

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Fraternity behaviour

• Dabbs et al (1996)
• Relationship between testosterone and fraternity
  behaviour.

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Fraternity testosterone

• They measured testosterone of 240 members of 12
  fraternities in 2 universities.
• Compared to descriptions of behaviour.
• Found less smiling and generosity and lower
  academic achievement in high testosterone
  fraternities.

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Further findings

• High testosterone - boisterous and macho
• Low testosterone attentive and helpful

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Problems with research

• Correlations

• Unreliable measurements

• Do not establish cause.
• There may be other factors causing aggression
  apart from testosterone.

• Behaviour is open to interpretation e.g. Lack of
  smiling may not be related to testosterone at
  all.

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Women and testosterone

• Dabbs et al 1988

• Testosterone high

• 84 female prison inmates
• Testosterone highest in cases of unprovoked
  violence
• Lowest in defensive aggression (abused wives who
  retaliated)

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Problem!

• Contradictory to Olweus 1983

• Operationalisation of aggression

• Testosterone was highest in defensive aggression

• Olweus referred to provoked aggression when
  participants were frustrated or restricted in
  some way.

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Pillay 2006

• Testosterone levels varied according to which
  sport different athletes played.
• Males and females in aggressive sports had the
  highest levels of testosterone.

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Kimura 1999

• Female spatial ability tends to improve with high
  levels of testosterone.

ttp//www.youtube.com/watch?vrn0e6xA5G
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Two models of testosterone

• Reciprocal model
• Aggression causes raised testosterone

• Basal model
• Testosterone is the cause of aggression

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The reciprocal model of testosterone

• The reverse of the basal model. It suggests that
  testosterone levels are influenced by changes in
  the level of dominance.

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The basal model of testosterone

• The level of testosterone influences dominance.
  The more testosterone, the more competitive and
  hence more dominant they become. Dominance is the
  effect of testosterone.
• The more testosterone a person has, the more
  competitive and dominant they become.
• It follows that..

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The more testosterone

• The greater the likelihood of anti-social
  behaviour, fighting, expressions of dominance
  etc.

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Mazur and Booth 1998

• Men with higher levels of testosterone were
• More likely to
• Divorce,
• Remain single,
• Be arrested for offences other than traffic
  violations
• Buy and sell stolen property
• Incur bad debts
• Use weapons in fights.

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Mazur and Booth 1998 cont.

• The reciprocal model of testosterone
• Levels vary with the persons dominance
• 2,100 air force veterans studied
• Over 10 years given 4 medical examinations
• Testosterone levels varied
• Reduced when married
• Increased when divorced.

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The role of serotonin

• Serotonin is a neurotransmitter
• Davidson, Putnam and Larson (2000)
• Serotonin may have inhibitory function
• i.e. Helps individuals to fight their aggressive
  urges.

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Research evidence

• Serotonin levels lower in violent criminals.
• Reducing serotonin levels in Vervet monkeys
  resulted in increased aggressive behaviour.

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Effects of low serotonin

• Also known as 5-hydroxytryptamine -5HT
• Affects whole body
• Impulsive behaviour
• aggression
• Overeating
• Depression
• Alcohol abuse
• Violent suicide

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Studies of domestic pets

• Bred for reduced aggression
• They seem to have higher levels of serotonin.

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Russian silver foxes

• Tamed for more than 30 years
• Higher levels of serotonin and lower levels of
  monoamine oxidase.

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Research evidence

• Various research suggests that low levels of
  serotonin are linked with aggression.
• While high levels of serotonin are linked with
  more peace-loving behaviours.

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Evidence for link with serotonin

• Tryptophan a precursor of serotonin (found in
  starchy foods)
• Tryptophan and other serotonergic drugs have been
  given to patients with unpredictable behaviour.
• The effectiveness of this treatment indicates a
  link with aggression and levels of serotonin.

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But

• While serotonergic drugs modify aggressive
  behaviour, this cannot be the only cause of
  activity in these regions of the brain.