study

• aim


  How does intelligence depend on genetics?
• method


  Twin family design
• sample


  112 families from the Netherlands, twin registry

  23 monozygotic boy twins, 23 monozygotic girl twins, 12 Dz girls, 13 Dz boys, 20 Dz mixed gender twins
• procedure


  Parents in child completed the ravens, progressive matrices for adults or children
• results


  higher correlation for monozygotic twins than other family members

  Overall level of inheritance is 67%
• conclusions


  Biology influences intelligence
• AO2


  biological factors influence intelligence as they share genetic makeup

  Environment at home may have affected this but the correlation for Dz twins was not as strong

  They share genetics and biology, explaining why monozygotic twins correlation was higher

  Majority of influence comes from biology and genes when looking at IQ

  Siblings aged between 9 and 12 had similar results to their families

  It cannot be proven that this is due to biological factors as environment and upbringing also influence IQ.