Bio Psy - Twin and Adoption Studies

• Twin Studies​

  MZ twins – 1 egg that splits into 2, genetically identical​

  DZ twins – 2 eggs 2 sperms, share 50% of genes​

  Higher MZ concordance rates = characteristics due to nature​

  Higher DZ concordance rates = characteristics due to nurture​
• Twin studies :) Generates large volume of data


  Bailey et al studied 4901 twin pairs on sexual orientation, larger sample sizes. T/f representative + can be generalized to twins
• Twin studies :) Supporting ev by Hettema


  Hettema et al found MZ more similar than DZ to be CC to stimuli like snakes, suggesting genetic components in psychological phenomena . T/f can explain predispositions to behaviours + used in therapy​
• Twin Studies :( MZ treated more similar than DZ

  Treated + dressed same, given similar opportunities + hobbies. T/f hard to distinguish nature/nurture​
• Twin Studies :( Pop validity

  majority of people don’t have twins, don’t share genes. T/f can only be generalised to twins, not wider population​
• Adoption Studies​

  Compare children's characteristics with their adoptive and biological parents​

  Higher concordance with bio – characteristics due to nature​

  Higher concordance w adoptive – characteristics due to nurture​
• Adoption :)  Most direct comparison of nature/nurture

  adopted child and bio parent share genes, but adoptive parents don’t, allows us to see influence of biology. If concordance rates....characteristics due to..... T/g adoption studies help explain origins of behaviours (either bio  or environmental)​
• Adoption :( Pop validity

  only look at characteristics of adopted ppl, not everyone's adopted. T/f samples used are unrepresentative + cant be generalised to the whole pop