Bailey and Pillard (1991)

Genetic inheritance

• the transfer of genetic information from parents to offspring, influencing physical and behavioural traits

  concordance rate

• The likelihood that both individuals in a pair share a specific trait

  monozygotic (MZ) twins

• Twins that share 100% of there genes

  dizygotic (DZ) twins Twins

• Twins that share 50% of there genes

  CONTEXT

• genetic inheritance is a central focus on the biological approach which examines how genes influence behaviour

• Bailey’s and Pillards study explores the genetic basis of homosexuality, challenging societal assumptions and contributing to debates on the nature gs nurture debate

  THEORY

• genetic influence hypothesis ; predicts a correlations between genetic similarity and behavioural traits concordance rate

• Assumes that MZ twins, sharing 100% of there genes show a higher concordance rates for homosexuality than DZ

  EVIDENCE

• AIM - to investigate the role of genetics in male sexuality

  PROCEDURE

• recruited MZ, and DZ twins and adoptive brothers through gay publications

• Assessed the sexual orientation via self reports or reports from gay participant

• Used questionnaires to measure the Childhood Gender Non conformity

  FINDINGS

• 52% of concordance in MZ twins, 22% in DZ twins, 11% in adoptive brothers

• No correlation between CGN and homosexuality across groups

  EVALUATING

  strengths

• Provided early evidence supporting the biological basis of sexual orientation, challenging stigma and misconceptions

  limitations

• Sampling bias, recruitment through gay publications likely