First, heritability estimates apply to populations under quite specific conditions and not to individuals. For example, the statement that the heritability of Stanford-Binet IQ scores for U.S. school children is .70 does not mean that the IQ of a particular child is 70 per cent determined by heredity.
Second, even though intelligence has significant genetic component, environmental conditions can be crucially important individual’s mental abilities are a function of genetic potential in interaction with such prenatal postnatal environmental conditions as nutrition, health, enriched or impoverished stimulation, the ‘ climate of the home, and the type of feedback provided for behaviour.