Heritability of IQ

Research on the heritability of intelligence quotient (IQ) inquires into the degree of variation in IQ within a population that is associated with genetic variation between individuals in that population. There has been significant controversy in the academic community about the heritability of IQ since research on the issue began in the late nineteenth century. Intelligence in the normal range is a polygenic trait, meaning that it is influenced by more than one gene, and in the case of intelligence at least 500 genes. Further, explaining the similarity in IQ of closely related persons requires careful study because environmental factors may be correlated with genetic factors. Outside the normal range, certain single gene genetic disorders, such as phenylketonuria, can negatively affect intelligence.

Estimates in the academic research of the heritability of IQ vary significantly by study and by study design. The general figure for heritability of IQ from behavioral genetic studies is about 0.5 across multiple studies in varying populations. The relationship between heritability and age is uncertain, though most researchers believe that there is an increase in heritability over the course of the lifespan and that this increase reflects the importance of gene-environment correlations. Recent genetic research has come to more equivocal results, with estimates of heritability lower than those derived from twin studies, causing what is known as the "missing heritability problem".

Although IQ differences between individuals have been shown to have a hereditary component, it does not follow that disparities in IQ between groups have a genetic basis. The scientific consensus is that genetics does not explain average differences in IQ test performance between racial groups.