Biological Determinants of

Aggression

Overview of Biology/Physiology

• Evolution (we already talked about)• Genetic• Neurotransmitters• Hormonal • Structural

Biology/Physiology is probabilistic, not deterministic (so how to prevent aggression?)

Genetics• Behavioral genetic research has shown genes influences individual

differences in a wide range of human behaviors: cognition, academic achievement, personality, temperament, and so forth.

• What about aggression?

• How studied?• Heritability – proportion of variability attributable to genetic factors• Environmental – proportion of variability due to situation• Monozygotic twins – same egg• Dizygotic twins – different eggs• Adoption studies – Raised separately so test genes/situation separately• Adoptive siblings share environments but not genes• Biological siblings raised apart share genes but not environments• Confounded because imitations and co-offending in siblings

• Findings• Clear evidence of heritability of criminality• Mixed results of heritability of aggression • Possible indirect effect through personality (impulsivity, dominance)

Genetics• A chromosome is an organized structure of

DNA and protein that is found in cells.• Men – XY• Women – XX

• Y-Chromosome Hypothesis• XYY

• More criminals than non

• Not more aggressive

• More likely charged/convicted

• X-Chromosome Hypothesis• XXY

• Not more aggressive

Only have to know first line for Final

Neurotransmitters

• Dopamine• animal studies show large changes during

aggressive behavior but not conclusive and not replicated in humans

• Norepinephrine• Does control mood and arousal but no relationship

to aggression• Serotonin

• Lower levels of serotonin linked to aggression because lowers inhibitions so more impulsive

• GABA• while it can inhibit behaviors, the findings are

mixed in regard to aggression

Hormonal

• Testosterone• sex hormone and anabolic steroid that has

mixed evidence to producing aggression, more likely about status and dominance so indirect relationship to aggression

• Premenstrual Syndrome (PMS)• inconclusive evidence its associated with

aggression and criminality but see next slide for indirect relationship

Structural• Hypothalamus – located under the thalamus that

controls several body functions, including feeding, breathing, drinking, and temperature.

• Amygdala – an almond-shaped neural structure that regulates emotions.

• Prefrontal cortex – implicated in planning complex cognitive behaviors

• How to study?• Brain damage• Direct stimulation• Physiological

Reactivity