15.2.1 Twin Studies

• How is aggression defined in psychological terms?

  Intentional behavior to cause harm
• Hostile aggression is driven by emotions like anger
• Instrumental aggression aims to inflict harm impulsively

  False
• What is an example of instrumental aggression?

  Tackling in football
• The MAOA gene metabolizes neurotransmitters like serotonin and dopamine
• Low activity of the MAOA gene is associated with higher aggression
• What is the estimated heritability of aggression?

  30-50%
• Match the gene with its function and effect on aggression:

  MAOA ↔️ Metabolizes serotonin and dopamine; Low activity leads to higher aggression

  COMT ↔️ Metabolizes catecholamines; Variants influence aggressive behavior
• What type of twins share 100% of their DNA?

  Monozygotic
• Concordance rates in twin studies measure the likelihood that both twins share a trait
• Steps in estimating the heritability of aggression using twin studies:

  1️⃣ Compare MZ and DZ concordance rates

  2️⃣ Calculate the heritability using the formula

  3️⃣ Determine if genetics play a significant role
• If MZ twins have higher concordance rates than DZ twins, genetics are likely significant in aggression
• What is the estimated heritability of aggression in humans?

  $\text{30 - 50\%}$
• The MAOA gene metabolizes serotonin and dopamine, and low activity is associated with higher aggression
• What does the COMT gene metabolize?

  Catecholamines
• Twin studies compare identical and fraternal twins to understand genetic and environmental influences on traits like aggression.
• Monozygotic twins share 100% of their DNA.
• What percentage of DNA do dizygotic twins share?

  50%
• If MZ twins show higher concordance rates than DZ twins, genetics likely play a significant role in aggression.
• The heritability of aggression in twin studies is estimated using a specific formula.
• What do concordance rates in twin studies measure?

  Shared trait likelihood
• Twin studies suggest that genetic factors are the only contributors to aggression.

  False
• Heritability estimates from twin studies suggest that genetic factors account for 30-50% of the variation in aggression.
• Which researchers conducted meta-analyses to confirm the heritability of aggression across cultures?

  Miles & Carey
• Match the strength of twin studies with its explanation:

  Separating genetic and environmental influences ↔️ Estimates heritability by comparing MZ and DZ twins

  Natural experiments ↔️ Uses naturally occurring twin pairs

  High internal validity ↔️ Minimizes confounding variables
• The shared environments assumption in twin studies assumes that twins share equally similar environments.
• Researchers can estimate the heritability of traits by comparing MZ and DZ twins.
• Twin studies are considered natural experiments because twins occur naturally without artificial manipulation.
• Matched genetic similarity in twin studies minimizes confounding variables.
• Twin studies assume that twins share equally similar environments, which may not always be true.
• Twins may not be fully representative of the general population.
• Aggression is commonly defined as behavior intended to cause harm or pain.
• The psychological definition of aggression includes intentional physical or verbal behavior designed to cause harm.
• Match the type of aggression with its description:

  Hostile Aggression ↔️ Driven by anger and aimed at harm

  Instrumental Aggression ↔️ Used to achieve a goal
• Hostile aggression is often driven by emotions like anger.
• Instrumental aggression uses harm as a means to an end rather than the end itself.
• Key genes involved in aggression include MAOA and COMT.
• The heritability of aggression is estimated to be around 30-50%.
• Match the gene with its function and effect on aggression:

  MAOA ↔️ Metabolizes serotonin; low activity linked to higher aggression

  COMT ↔️ Metabolizes catecholamines; variants affect aggression
• Twin studies compare MZ and DZ twins to understand genetic and environmental influences on aggression.