Biological explanations of
aggression.
L/objectives
• ALL: Will be able to Describe how biological and
physiological processes affect aggressive behaviour
Grade/Level: E/D
• MOST: Will be able to Understand how biological
explanations are split into genetic, biochemical and
neuro-anatomical explanations
Grade/Level: C/D
• SOME: Will be able to elaborate & evaluate these
explanations (inc research for and against)
Grade/Level: B+
Types of Aggression
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Aggression
Evo explanations
Instrumental
Person orientated
Reactive Aggression
Proactive Aggression
• Initiated by an individual
to achieve a desired
outcome.
• Response to someone
else's aggression.
• Obtaining personal
reward
• Attempt to harm another
person.
• Adaptive/hunter gatherer
• Behaviour with intent to
harm.
‘Aggression is in our nature’
• Aggression in animals and humans is an
inherited, spontaneous tendency much the
same as the motivation to eat, drink and make
love.
According to who?
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A
T
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R
E
• Inheritance of behavioural
capacity for aggression.
Behavioural genetics
James Watson
• Control of aggression by
brain, blood and hormones.
Physiological psychology
Frank beach
• Interaction between genetic
and physiological factors.
Ethology - animal behaviour
Konrad lorenz
What do these two have in
common?
How can biology have a role in
aggression?
• The resulting aggressive behaviour can
be the result of imbalance of the four
main theories:
• Neurotransmitters.
• Genes.
• Hormones.
• Neuroanatomy
Genetics
• Biology has a role in aggression. Genetic
influences play a major part in some
aggression, as evidenced in animals
specifically bred to exhibit such
behaviour. Studies of identical twins
have frequently shown that if one twin
exhibits aggressive behaviour, the other
often does so as well.
Neuroanatomy
• Aggression may also have a neural basis;
aggressive behaviour has been produced
in animals through electrical stimulation
of parts of the brain.
Biological Aggression
• Konrad Lorenz, an ethologist, proposed
that aggression arises from instincts
and that such instincts help members of
a species maximize the use of food,
space, and other resources. Other
biologists have studied the aggression
produced by exposing the nervous
system to chemicals (drugs, such as
alcohol) or hormones (such as
testosterone).
Biological Aggression
• It is a common myth that testosterone causes
aggression but is there biological reason to back up
this assertion?
• Some say there is, while others are armed with
refuting information with which to contest this
argument.
• The bottom line is that we do not know for sure
whether or not testosterone causes aggression .
• So what do we know…well lets examine the evidence.
Aggression in the brain.
• The hypothalamus and
periaqueductal gray of
the midbrain are the
most critical areas
controlling aggression in
mammals, as shown in
studies on cats, rats, and
monkeys.
• (Can we extrapolate from
these findings?)
• They have direct
connections with both
the brainstem nuclei
controlling these
functions and areas such
as the amygdala and
prefrontal cortex.
Biology cont…
• According to the evolutionary biology theory
aggression serves an important function in
terms of both individual survival as well as
reproduction potential.
• Competition arises when resources are limited
and therefore animals/species must actively
compete in order to increase their own
fitness.
• Inferring that aggression is advantageous at
both the individual and genetic levels
Biology cont..
• In terms of aggression, there exists evidence that
there is a definite connection between the hormonal
effects of testosterone and the outward expression of
aggressive behaviour.
Empirical evidence #1
• Castration leads to a marked decrease in aggression as
shown by castration experimentation on various species.
Furthermore, when testosterone is replaced through
hormone therapy in these castrated animals, the amount
of aggression increases and is restored to its original
pre-castration level.
• Taken together, this seems to present a strong
argument for the role of testosterone in aggression.
• However, the story does not end here: if we are to
suppose that testosterone does in fact lead to
aggressive behaviour we must then necessarily ask how
and why it does.
Empirical Evidence #2
• Moffitt et al (1998) studied the blood serotonin
levels of 781 21-year-old men and women.
• The researchers report that "in this study, elevated
whole blood serotonin was characteristic of violent
men." (Low brain levels of serotonin, but high levels of
blood serotonin, are associated with behaviour
disorders-apparently because of serotonin's
different origin and function in blood and brain.)
• The violent men's mean serotonin level was .48
standard deviations (SD) above the norm for males as
a group, and .56 SD above the mean for non-violent
men. Among female subjects, no relationship between
serotonin levels and aggression was seen.
Biology cont…
• Maxon (1998), a leading theorist proposed a
theory that one's genes affect one or more
types of aggression in mice, which may be
applied to humans as a genetic explanation of
aggression.
• Childhood experiences appear to be especially
powerful, because a child's brain is more
malleable than that of an adult. A young brain is
extra vulnerable to hurt in the first years of
life. A child who suffers repeated abuse,
neglect as well as terror experiences physical
changes in his brain
Cont biological evidence..
1. The amygdala is also critically involved in aggression. Stimulation of the amygdala
results in augmented aggressive behaviour in hamsters (Decoster et al 2006)
2. Lesions of an evolutionarily homologous area in the lizard greatly reduce
competitive drive and aggression (Bauman et al. 2006).
3. In adulthood, several studies of the concentration of blood testosterone of
convicted male criminals who committed violent crimes compared to males
without a criminal record or who committed non-aggressive crimes revealed in
most cases that men who were judged aggressive/dominant had higher blood
concentrations of testosterone than controls.
4. Studies of testosterone levels of male athletes before and after a competition
revealed that testosterone levels rise shortly before their matches, and are
dependent on the outcome of the event: testosterone levels of winners are high
relative to those of losers.
5. Testosterone levels in female criminals versus females without a criminal record
mirror those of males: testosterone levels are higher in women who commit
aggressive crimes or are deemed aggressive by their peers than non-aggressive
females. However, no specific response of testosterone levels to competition was
observed in female athletes, although a mood difference was noted (Mazer et al
1998)
So what are we saying?
• Genetic and biological theories of aggression both
have strong points as well as weak points.
• Causation is not well established in genetic theories.
If it is found that one gene exists in aggressive
individuals and not in non-aggressive individuals it is
not determined if the genetic information causes
aggression or if aggression causes a change in genetic
information. Biological theories are strong in that the
choice of treatment is obvious and it has been shown
to be effective.
• Genetic theories' weakness is that it does not explain
every case of aggression. These theories also put the
responsibility within the individual.
Real Life examples of how aggression can be
affected by biology!
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In women, premenstrual tension syndrome is associated with a number
of aggressive behaviours, such as violent crime.
(That hormonal time of the month!!)
People with a serious physiological illness, such as cancer, may be
affected by negative mood states.
These mood states may indirectly affect the aggressive behaviour of
individuals.
Temperament may be indirectly related to aggressive behaviour. People
who are impulsive are more likely to be aggressive than people who have
a deliberate temperament.
The mind of a killer!!
• Read the located on the URL below and
be prepared to make a contribution to
the discussion of aggression being
largely a biological by product.
• http://archive.salon.com/books/int/200
1/07/27/killers/print.html
Aggression in real life.
• Columbine High school/The Littleton killers
• University of Texas massacre: Charles
Whitman.
• Hungerford massacre
• Dunblane massacre
• Virginia Tech massacre
• Could you use any of these real life cases
to illustrate the effects of biology on
aggression?