Intelligence : individual differences, genetic factors, environmental factors and interaction between the genotype and the environment (author's transl)]

The authors undertook a review of published work on the sources of variation in individual differences in intelligence. They should : 1) that methods of quantitative genetics concerning intelligence are not applicable to human populations ; 2) that the results of studies on adoptions and on twins do not permit one to estimate the respective roles of environment and heredity ; 3) that this division of variance had no heuristic value in the study of human intelligence.