Genetic analysis of IQ in young adulthood: a Russian twin study

The present study is an investigation of 80 like-sex, Russian twin pairs aged 16–28 years undertaken to replicate and extend the existent research literature on the heritability of cognitive ability in young adults. Up to date, no study examining cognitive abilities in Russian population adult twins has been carried out. The main objective of the present investigation is to analyze the genetic and environmental contributions to individual differences in general cognitive ability in a sample of young adult Russian twins. The Russian adaptation of the Wechsler Adult Intelligence Scale (WAIS; Wechsler, 1972) was administered separately to members of twin pairs during the single visit at their home by two testers. The model-fitting showed that a simple genetic model, including additive genetic and nonshared environmental effects, provided the adequate and most parsimonious description of verbal, performance and full-scale IQ data. Additive genetic influences accounted for approximately the same amount of variance in verbal, performance and full-scale IQ data––86%, 84% and 89%, respectively. The results are consistent with the reports from the majority of studies, suggesting an increased heritability and decreased shared environmental influences on IQ variability in adulthood compared to childhood.