Genetic Factors in Aggression: Twin Studies

Question 1

what have twin studies shown?

Answer 1

heritability accounts for about 50% of the variance in aggressive behaviour

Question 2

what did Coccaro et al do?

Answer 2

• studied men who were either monozygotic or dizygotic twins
• MZ twins share 100% of their genes whilst DZ twins only share 50% of their genes so we’d expect greater similarities in aggressive behaviour in MZ twins if aggression is influenced by genetic factors

Question 3

how did Coccaro explain why MZ twins would have greater similarities in aggressive behaviour?

Answer 3

• both MZ and DZ twins are raised together in the same environment, but MZ twins have a greater degree of genetic similarity than DZs

Question 4

how is aggressive behaviour defined as?

Answer 4

• direct physical assault

Question 5

what did Coccaro et al find about the concordance rates for aggressive behaviour?

Answer 5

• 50% for MZ twins
• 19% for DZ twins

Question 6

what did Coccaro et al find about the concordance rates for verbal aggression?

Answer 6

• 28% for MZ twins
• 7% for DZ twins