Aggression: The Role of Nature
• Soundtrack
– Bohemian Rhapsody (Queen)
– Mack the Knife (Bobby Darin)
To what extent is aggression caused by
internal (innate, genetic, or biological)
Factors
For students who participated in the
survey earlier in the semester: 2nd part to be
handed out on Tues.
Study Guide for Exam 4 is now available
Is it aggression?
• Exercise
What is aggression?
• Aggression: Intentional behavior aimed at
causing either physical or psychological
pain.
• Key feature: Intention
• Not the same as “assertive” or “ambitious”
• Examples:
– Beer bottle at party
– Drunk driver
Why might people behave aggressively?
• Is aggression inborn?
– Instinct theorists
• Freud: Aggression innate, destructive
– Freud: Death instinct (Thanatos) = innate impulse for
self-destruction. Opposite of life instinct (Eros).
• Lorenz: Aggression innate, but adaptive.
– Ethologist. Emphasized that aggressive instinct
facilitates the individual’s survival, reproduction.
Instinct theories
• Instinct theories are NOT widely accepted.
• Problems with assuming that aggression is
innate
Problems w/Instinct Theories
•
Humans vary greatly in aggressiveness.
– Cross-cultural differences (groups in South
Seas vs. Yanomamo in South American;
Iroquois and social change)
Problems w/Instinct Theories
• Regional differences in aggressive
behavior
– Culture of honor: Homicide rates for males
are significantly higher than those for white
northern males, especially in rural areas. But
this is true only for "argument-related"
homicides.
Culture of honor experiments (Dov Cohen,
Richard Nisbett & colleagues)
• IV: A confederate “accidentally” bumped into the
participant, and called the P an insulting name
(or no incident in the control condition).
• DVs: P’s guess about evaluator’s ratings of his
masculinity; his physiological response to stress;
and his behavior
• Results: Southerners in insult condition were
than northerners to think they would be seen as
less masculine, experienced increased cortisol
and testosterone, and were slower to move out
of the confederate’s way in a very narrow
passageway.
Problems w/Instinct Theories
• If aggression is a human instinct, then it is
hard to account for this variability both
within and between cultures.
Problems w/Instinct Theories
• Circular reasoning:
– Why do sheep herd? Because they have a
herding instinct.
– Doesn’t explain the phenomenon, just names
it.
Biological influences on aggression
• Neural influences
– AMYGDALA -- associated with aggressive
behavior in humans and in lower animals.
• When electrically stimulated, docile animals
become violent; when neural activity in the
amygdala is blocked violent animals become
docile.
Neural influences: Interaction
w/environment
• Social factors can influence the impact of
these neural mechanisms.
– If a male monkey is in the presence of
other, less dominant monkeys, he will
attack the other monkeys when the
amydala is stimulated.
– But if the amygdala is stimulated while the
monkey is in the presence of more
dominant monkeys, he will not attack but
will run away instead.
Chemical/hormonal influences
• Testosterone
– Injection of testosterone will increase
aggression in animals (cause and effect
relationship in non-human animals)
Testosterone in humans
Dabbs and colleagues
• Naturally occurring testosterone levels are higher
among prisoners convicted of violent crimes than
those convicted of nonviolent crimes.
• Once incarcerated, prisoners with higher
testosterone levels violated more prison rules
• Compared fraternities within a given college: those
known to be more rambunctious, less socially
responsible, and more crude had the highest
average testosterone levels.
• Correlational: Questions about direction of causality
and third variables
• Behaving aggressively also can increase
testosterone
• 3rd variables: Violent prisoners may differ in
many ways from less nonviolent prisoners (e.g.,
in stress, family history, etc.)
• However, people opting for sex reassignment
show more aggression as testosterone is
increased. (Still correlational and not a random
sample – expectations may influence)
Genetic influences
• Are people who are more aggressive
genetically different from those who are
less aggressive?
• Can breed animals to be more or less
aggressive
Genetic influences
• Twin studies
• Identical (monozygotic) twins have
identical genetic makeup.
• Fraternal (Dizygotic) twins are no more
similar genetically than any other
siblings.
• Twin studies are based on the
assumption that identical twins should
show greater similarity on any trait that
is presumed to be inherited than
fraternal twins.
Genetic influences
• Identical twins twice as likely as fraternal twins to
be similar in degree of criminal activity.
• Christiansen: 7000 twins born in Denmark 18811910
– 35% identical vs. 13% fraternal showed similarity in
serious criminal activity
– Problems:
– 65% identical twins did not have similar records
– Identical twins may have more similar environments
than do fraternal twins.
Genetic/biological vs. environment
• Debate:
• Aggressive behavior results from an interaction
between genetic/biological factors and
environmental factors, but aggression is more
powerfully influenced by genetic and/or
biological factors.
• Aggressive behavior results from an interaction
between genetic/biological factors and
environmental factors, but aggression is more
powerfully influenced by environmental factors.
Heredity vs. environment
• Example: Serial killer, Joel Rifkin
• Researchers examine both environment
and possible genetic basis (look at brain
scans)
– Video clip & discussion
– To what extent do you think that Joel Rifkin’s
killing was caused by genetic/biological
factors or environmental factors?