Heredity, Environment, and Class

The social-class, ethnic, and racial differences in performance on tests of intelligence and scholastic achievement are discussed. Significant deficiencies exist in the means of lower-class and certain racial groups for many measures of ability, motivation, and performance. Composite attempts to estimate the proportion of phenotypic variance in IQ which is genetic approximate 80%. These heritability indices have been interpreted to mean that most of the observed deficiencies in the mean IQ's for classes and races is biologically inevitable. However, evidences of plasticity suggest that the range of reaction in the IQ must be of the order of 75 points. Such evidence of plasticity becomes less puzzling when one recognizes that estimates of heritability indicate the loss of deviation from the mean of the population to be expected from parents to off-spring in experiments on selective breeding, that indices o