Genetic and Environmental Factors in Individual Differences of Cognitive Abilities in Primary School Children

The study, based on a sample of Russian twins (34 pairs of monozygotic twins and 33 pairs of dizygotic twins aged 7-8 years), shows that genetic factors make a significant contribution to the development of individual differences in nonverbal intelligence. Eighty nine percents of phenotypic variance of nonverbal intelligence are explained by the genetic influences, while the contribution of non-shared environment explains the remaining 11%.