Van Leeuwen Study

• Aim

  to research the hereditary nature of intelligence, and whether genetic factors and/or environmental factors affect intelligence
• Method


  twin study, including monozygotic (identical) and dizygotic (non identical) twins, their siblings and their parents
• Sample


  112 families, recruited from netherlands twin registry, mean age of twins 9 years, 48 monozygotic, 64 dizygotic, range of genders, also included siblings (mean age 11), and parents (mean age 42)
• Results- gender


  no significant differencesheritability of intelligence: intelligence is 67% genetics and 33% environment, but environment more important to children with 2 unintelligent parents
• Results - intelligence variation

  siblings scored higher but this may be because of age, IQ correlations higher in MZ twins, meaning they have less variance due to 100% genetic match
• Results - Spousal IQ

  significant correlation, parents had similar intelligence
• Conclusion


  individual differences in intelligence can be explained by genetics & environmental factors are much more important to kids with low IQ than high IQ