[Intellectual activities of twins. II. Heredity and environment].

A study was carried out of the relative role of the genotype and the environment on the variability of intellectual abilities in children of 7--16 years old. 118 twin pairs were studied by WISC method: 57 MZ and 61 DZ. It is established that every parameter of the intellectual activity is characterized by the definite component of phenotypic variance, i. e. by genetic and environmental components. With that the genetic variance of intellectual parameters is determined mainly by the additive interaction of genetic factors, and the environmental variance -- by intrafamily (random) factors. It is noted the essential role of genotype of the population variability of verbal intellectual parameters. Components of phenotypic variance intellectual parameters -- genetic (additive and dominant) and environmental (interfamily and intrafamily) are changing during the ontogenesis. The role of environmental factors is increased in variability of most intellectual characteristics in the age of 14--16 years, i. e. the intellectual behavior is becoming more supple in regard to the factors of environment.